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Purpose: The aim of this study was to correlate different biometric dimensions of the eye as measured from ocular magnetic resonance imaging (MRI) scans to predict the lens diameter., Methods: High-resolution ocular MRI scans of 100 eyes of 100 patients were reviewed. Various anatomical variables of the eye such as the axial length, the globe diameter, and the lens dimensions were measured. Also, the distances between the ciliary sulcus and angle-to-angle were measured. A partial least square (PLS) regression model was built to analyze which variables influence the model regarding the lens dimensions., Results: Sixty-two eyes of 62 patients were included in the final analysis. The lens diameter ratio (horizontal to vertical) was 0.93 (SD: 0.04; 0.83-1.00). The partial least square regression showed a significant connection (P < 0.001) between the horizontal and vertical diameter. The partial least square regression model that included the globe diameter and the axis length resulted in the best prediction for the horizontal lens diameter. Similar to the horizontal lens diameter, globe diameter was the best predictor for the vertical lens diameter followed by the distance of the ciliary sulcus. White-to-white distance, distance of the ciliary sulcus, and axial eye length were found to have a high influence on the angle-to-angle distance., Conclusions: The introduced models may serve as tools to predict the capsular bag biometry in a preoperative setting for cataract surgery or lens refilling procedures.

Purpose: To develop three-surface paraxial schematic eyes with different ages and sexes based on data for 7- and 14-year-old Chinese children from the Anyang Childhood Eye Study., Methods: Six sets of paraxial schematic eyes, including 7-year-old eyes, 7-year-old male eyes, 7-year-old female eyes, 14-year-old eyes, 14-year-old male eyes, and 14-year-old female eyes, were developed. Both refraction-dependent and emmetropic eye models were developed, with the former using linear dependence of ocular parameters on refraction., Results: A total of 2059 grade 1 children (boys 58%) and 1536 grade 8 children (boys 49%) were included, with mean age of 7.1 ± 0.4 and 13.7 ± 0.5 years, respectively. Changes in these schematic eyes with aging are increased anterior chamber depth, decreased lens thickness, increased vitreous chamber depth, increased axial length, and decreased lens equivalent power. Male schematic eyes have deeper anterior chamber depth, longer vitreous chamber depth, longer axial length, and lower lens equivalent power than female schematic eyes. Changes in the schematic eyes with positive increase in refraction are decreased anterior chamber depth, increased lens thickness, decreased vitreous chamber depth, decreased axial length, increased corneal radius of curvature, and increased lens power. In general, the emmetropic schematic eyes have biometric parameters similar to those arising from regression fits for the refraction-dependent schematic eyes., Conclusions: The paraxial schematic eyes of Chinese children may be useful for myopia research and for facilitating comparison with other children with the same or different racial backgrounds and living in different places.

Purpose: To determine the prevalence of myopia and ocular biometry in population-based samples of ethnic Yi and Han people living in an inland rural community in China., Methods: A random cluster sampling strategy was used to select ethnic Han and Yi adults aged 50 years or older living in Yunnan. Refractive error was determined by subjective refraction and ocular biometric parameters, including axial length (AL), anterior chamber depth (ACD), vitreous chamber depth (VCD), and lens thickness (LT), which were measured using an Echoscan., Results: Adults of Yi ethnicity had lower prevalence of myopia (10.3% vs. 8.1%; P = 0.02) and high myopia (2.3% vs. 1.6%; P = 0.10) than their counterparts of Han ethnicity. The prevalence of myopia increased with age (P for trend < 0.05), whereas the mean AL did not differ significantly among age groups in both ethnic groups (both P for trend > 0.05). In multivariate analysis, time spent outdoors was associated with myopia (P = 0.003) and AL (P < 0.001) but not high myopia (P = 0.33). No interaction effect was detected between ethnicity and other risk factors on myopia (all P > 0.05). Adjustment for lens nuclear opacity score reduced the excess prevalence of myopia in Han ethnicity by 37.5%., Conclusions: There was little evidence showing that ethnic disparities existed in the prevalence and risk factors between the major and minor ethnic groups living in the same communities in rural China. The "cohort effect" on myopia observed in many other populations was not seen in this study.

Purpose: To determine the eye size and shape obtained by magnetic resonance imaging (MRI), and to determine associations with antenatal factors in newborn children., Methods: A subset of 173 full-term newborn children from the Growing Up in Singapore Towards Healthy Outcomes (GUSTO) birth cohort underwent MRI. Eye volume and surface area were measured. Eye shape was assessed qualitatively from three-dimensional models, and quantitatively by measurement of longitudinal axial length (AL, the length from the posterior corneal surface to the retinal surface), and horizontal width and vertical height of the internal eye along the cardinal axes. Oblateness was calculated as 1-(AL/width) or 1-(AL/height). Oblate eyes had oblateness>+0.01, spherical eyes had oblateness between +0.01 and -0.01, and prolate eyes had oblateness<-0.01., Results: A total of 346 eyes of 173 children were included. Mean oblateness using width was -0.06±0.05 (range, -0.23 to +0.08), and mean oblateness using height was -0.01±0.04 (range, -0.19 to +0.13). Using width, most eyes were prolate (294 eyes, 85%); and using height, the largest proportion of eyes was prolate (163 eyes, 47%). Eyes with longer ALs had greater widths, heights, volumes, and surface areas than eyes with shorter ALs (P<0.001 for all). With increasing AL, eyes became increasingly prolate. Children of less educated mothers had longer ALs (P=0.02). Malay children had larger eye volumes and surface areas than Chinese or Indian children., Conclusions: Most newborn Singaporean Asian children are born with prolate eyes. A longitudinal study is required to determine if globe shape at birth influences subsequent refractive changes.

Purpose: Previous studies have shown a negative correlation between axial length (AL) and pulsatile ocular blood flow (POBF). This relation has been questioned because of the possible confounding effect of ocular volume on ocular rigidity (OR). The purpose of this study was to investigate the relation between AL, as a surrogate parameter for ocular volume, and OR, ocular pulse amplitude (OPA), and POBF., Methods: Eighty-eight cataract patients were enrolled in this study. A computer-controlled device comprising a microdosimetric pump and a pressure sensor was used intraoperatively. The system was connected to the anterior chamber and used to raise the intraocular pressure (IOP) from 15 to 40 mm Hg, by infusing the eye with a saline solution. After each infusion step, the IOP was continuously recorded for 2 seconds. Blood pressure and pulse rate were measured during the procedure. The OR coefficient was calculated from the pressure volume data. OPA and POBF were measured from pressure recordings., Results: Median AL was 23.69 (interquartile range 3.53) mm. OR coefficient was 0.0218 (0.0053) μL(-1). A negative correlation between the OR coefficient and AL (ρ = -0.641, P < 0.001) was documented. Increasing AL was associated with decreased OPA (ρ = -0.637, P < 0.001 and ρ = -0.690, P < 0.001) and POBF (ρ = -0.207, P = 0.053 and ρ = -0.238, P = 0.028) at baseline and elevated IOP, respectively., Conclusions: Based on manometric data, increasing AL is associated with decreased OR, OPA, and POBF. These results suggest decreased pulsatility in high myopia and may have implications on ocular pulse studies and the pathophysiology of myopia.

Purpose: The purpose of the study was to investigate the changes in axial length occurring with shifts in gaze direction., Methods: Axial length measurements were obtained from the left eye of 30 young adults (10 emmetropes, 10 low myopes, and 10 moderate myopes) through a rotating prism with 15° deviation, along the foveal axis, using a noncontact optical biometer in each of the nine different cardinal directions of gaze over 5 minutes. The subject's fellow eye fixated on an external distance (6 m) target to control accommodation, also with 15° deviation. Axial length measurements were also performed in 15° and 25° downward gaze with the biometer inclined on a tilting table, allowing gaze shifts to be achieved with either full head turn but no eye turn, or full eye turn with no head turn., Results: There was a significant influence of gaze angle and time on axial length (both P < 0.001), with the greatest axial elongation (+18 ± 8 μm) occurring with inferonasal gaze (P < 0.001) and a slight decrease in axial length in superior gaze (-12 ± 17 μm) compared with primary gaze (P < 0.001). In downward gaze, a significant axial elongation occurred when eye turn was used (P < 0.001), but not when head turn was used to shift gaze (P > 0.05)., Conclusions: The angle of gaze has a small but significant short-term effect on axial length, with greatest elongation occurring in inferonasal gaze. The elongation of the eye appears to be due to the influence of the extraocular muscles, in particular the oblique muscles.

As the eye changes focus, the resulting changes in cone contrast are associated with changes in color and luminance. Color fluctuations should simulate the eye being hyperopic and make the eye grow in the myopic direction, while luminance fluctuations should simulate myopia and make the eye grow in the hyperopic direction. Chicks without lenses were exposed daily (9 a.m. to 5 p.m.) for three days on two consecutive weeks to 2 Hz sinusoidally modulated illumination (mean illuminance of 680 lux) to one of the following: in-phase modulated luminance flicker (LUM), counterphase-modulated red/green (R/G Color) or blue/yellow flicker (B/Y Color), combined color and luminance flicker (Color + LUM), reduced amplitude luminance flicker (Low LUM), or no flicker. After the three-day exposure to flicker, chicks were kept in a brooder under normal diurnal lighting for four days. Changes in the ocular components were measured with ultrasound and with a Hartinger Coincidence Refractometer (aus Jena, Jena, East Germany. After the first three-day exposure, luminance flicker produced more hyperopic refractions (LUM: 2.27 D) than did color flicker (R/G Color: 0.09 D; B/Y Color: -0.25 D). Changes in refraction were mainly due to changes in eye length, with color flicker producing much greater changes in eye length than luminance flicker (R/G Color: 102 μm; B/Y Color: 98 μm; LUM: 66 μm). Our results support the hypothesis that the eye can differentiate between hyperopic and myopic defocus on the basis of the effects of change in luminance or color contrast.

Purpose: The primary aim of this study was to evaluate the efficiency of air-gas exchange techniques and the factors that influence the final concentration of an intraocular gas tamponade. Parameters were varied to find the optimum method of performing an air-gas exchange in ideal circumstances., Methods: A computer model of the eye was designed using 3D software with fluid flow analysis capabilities. Factors such as angular distance between ports, gas infusion gauge, exhaust vent gauge and depth were varied in the model. Flow rate and axial length were also modulated to simulate faster injections and more myopic eyes, respectively. The flush volume of gas required to achieve a 97% intraocular gas fraction concentration were compared., Results: Modulating individual factors did not reveal any clinically significant difference in the angular distance between ports, exhaust vent size, and depth or rate of gas injection. In combination, however, there was a 28% increase in air-gas exchange efficiency comparing the most efficient with the least efficient studied parameters in this model. The gas flush volume required to achieve a 97% gas fill also increased proportionately at a ratio of 5.5 to 6.2 times the volume of the eye., Conclusions: A 35-mL flush is adequate for eyes up to 25 mm in axial length; however, eyes longer than this would require a much greater flush volume, and surgeons should consider using two separate 50-mL gas syringes to ensure optimal gas concentration for eyes greater than 25 mm in axial length.

Purpose: Because interphotoreceptor retinoid-binding protein (IRBP) is expressed before being needed in its presumptive role in the visual cycle, we tested whether it controls eye growth during development., Methods: The eyes of congenic IRBP knockout (KO) and C57BL/6J wild-type (WT) mice ranging in age from postnatal day (P)2 to P440 were compared by histology, laser micrometry, cycloplegic photorefractions, and partial coherence interferometry., Results: The size and weight of IRBP KO mouse eyes were greater than those of the WT mouse, even before eye-opening. Excessive ocular enlargement started between P7 and P10, with KO retinal arc lengths becoming greater compared with WT from P10 through P30 (18%; P < 0.01). The outer nuclear layer (ONL) of KO retinas became 20% thinner between P12 to P25, and progressed to 38% thinner at P30. At P30, there were 30% fewer cones per vertical section in KO than in WT retinas. Bromodeoxyuridine (BrdU) labeling indicated the same number of retinal cells were born in KO and WT mice. A spike in apoptosis was observed in KO outer nuclear layer at P25. These changes in size were accompanied by a large decrease in hyperopic refractive error, which reached -4.56 ± 0.70 diopters (D) versus +9.98 ± 0.993 D (mean ± SD) in WT, by postnatal day 60 (P60). CONCLUSIONS; In addition to its role in the visual cycle, IRBP is needed for normal eye development. How IRBP mediates ocular development is unknown.

Purpose: To compare the distributional parameters for a series of ocular biometric traits between twins and their singleton siblings, to evaluate the generalizability of twin data, as used in heritability analyses to the general population., Methods: A series of birth, anthropometric, and 13 ocular biometric traits were selected for analysis: interpupillary distance (IPD), visual acuity (logMAR), spherical equivalent refractive error, corneal curvature, axial length, anterior chamber depth (ACD), central corneal thickness (CCT), intraocular pressure (IOP), optic disc, cup and rim areas, and measures of retinal vessel caliber; central retinal arteriolar equivalent (CRAE), and central retinal venular equivalent (CRVE). Structural equation modeling was used to test the assumption that the means and variances for each trait did not differ between twins and their siblings., Results: Significant differences in log-likelihood for birth weight and gestational age were observed between twins and siblings, with the latter being both heavier and closer to full-term at birth. Siblings were also found to have larger IPD and axial length, and better visual acuity compared with their twin counterparts. Refractive error, corneal curvature, ACD, CCT, optic disc parameters, and retinal vascular calibers did not differ significantly between the two groups., Conclusions: Twins are representative of the general population for some but not all measures of ocular biometry. Consequently, care should be taken when extrapolating twin data for these traits in heritability and other genetic studies. Birth weight differences between twins and siblings do not appear to account for the differences in ocular biometry observed in this study.

Purpose: To image the conventional aqueous outflow pathway and adjacent structures within the intact enucleated mouse eye using a noninvasive microscopy technique., Methods: Two-photon microscopy (2PM) techniques, including two-photon autofluorescence (2PAF) and second harmonic generation (SHG), were used to obtain images of the trabecular meshwork (TM) region within an intact mouse eye. Cardiac perfusion of fluorescein-conjugated dextran was used to label blood vessels within the eye to serve as an anatomic reference. Eyes were subsequently fixed, paraffin embedded, sectioned, and stained for comparison to the 2PM images., Results: Three-dimensional analyses of multiple 2PM images revealed a well-defined region adjacent to the iris and cornea that is free of SHG signal and consistent with the location of Schlemm's canal. This open region is continuous with smaller tube structures consistent with collector channels. These structures do not label in mice perfused with the vascular probe dextran, supporting the hypothesis that the enclosed spaces are filled with aqueous humor rather than circulating blood. The TM region in the mouse eye was also visible, with a clear SHG signal representing collagen fibers., Conclusions: These results support the hypothesis that 2PM may be useful for noninvasively imaging the conventional aqueous outflow pathway in mouse models of glaucoma. Studies are ongoing to validate our methodology in live animals.

Purpose. To investigate the extent to which shared genetic variants control (1) multiple ocular component dimensions and (2) both normal eye length and susceptibility to visually induced myopic eye growth. Methods. Two laboratory-reared populations of chicks were examined. The first was a three-generation pedigree of White Leghorn (WL) birds used in a selective breeding experiment testing susceptibility to monocular deprivation of sharp vision (DSV). The chicks were assessed before (age, 4 days) and after 4 days of treatment with diffusers. The second was the 10th generation of an advanced intercross line (AIL) derived from a broiler-layer cross (age, 3 weeks). Variance components analysis was used to estimate heritability and to assess the evidence for shared genetic determination. Results. All measured ocular components were moderately or highly heritable (range, 0.36-0.61; all P < 0.001) in both chick populations, and there were strong genetic correlations across the traits, corneal curvature, vitreous chamber depth, and axial length. The genetic correlations between eye size and myopia susceptibility traits were not significantly different from 0. Conclusions. The genetic variants controlling ocular component dimensions in chicks are shared across some ocular traits (corneal curvature, vitreous chamber depth, and axial length) but distinct for others (lens thickness and corneal thickness). The genetic variants controlling susceptibility to visually induced myopia in chicks are different from those controlling normal eye size.

Purpose: Adaptive optics scanning laser ophthalmoscopy (AOSLO) under optimized wavefront correction allows for routine imaging of foveal cone photoreceptors. The intersubject variability of foveal cone density was measured and its relation to eye length evaluated., Methods: AOSLO was used to image 18 healthy eyes with axial lengths from 22.86 to 28.31 mm. Ocular biometry and an eye model were used to estimate the retinal magnification factor. Individual cones in the AOSLO images were labeled, and the locations were used to generate topographic maps representing the spatial distribution of density. Representative retinal (cones/mm(2)) and angular (cones/deg(2)) cone densities at specific eccentricities were calculated from these maps., Results: The entire foveal cone mosaic was resolved in four eyes, whereas the cones within 0.03 mm eccentricity remained unresolved in most eyes. The preferred retinal locus deviated significantly (P < 0.001) from the point of peak cone density for all except one individual. A significant decrease in retinal density (P < 0.05) with increasing axial length was observed at 0.30 mm eccentricity but not closer. Longer, more myopic eyes generally had higher angular density near the foveal center than the shorter eyes, but by 1°, this difference was nullified by retinal expansion, and so angular densities across all eyes were similar., Conclusions: The AOSLO can resolve the smallest foveal cones in certain eyes. Although myopia causes retinal stretching in the fovea, its effect within the foveola is confounded by factors other than cone density that have high levels of intersubject variability.

Purpose: To measure eye and orbit anthropometric variation within the normal population by using CT images and to determine the effects of age and sex on eye and orbit anthropometry. Quantification of eye and orbit anthropometric variation within the normal population and between persons of different age and sex is important in the prediction and prevention of eye injury., Methods: A systematic method was developed to align head CT images three dimensionally and to measure ocular and orbital parameters in 39 subjects. Twenty-four measurements were collected along the orbital rim, to quantify the orbital aperture. Protrusions of the brow and the eye were measured, along with relative distances, to describe location of the eye within the orbit., Results: The orbit widened with age, and significant relations were identified between orbital aperture and eye location measurements, both of which varied significantly between the sexes., Conclusions: The comprehensive set of measurements collected in this study provides three-dimensional information on orbit geometry, as well as placement of the eye within the orbit. These measurements and the methodology used will contribute to the development of finite element models of the orbit and eye for computational modeling purposes and may be useful in the design of eye protection equipment.

Purpose: To examine whether the relationship of axial length (AL) to retinal nerve fiber layer (RNFL) and macular parameters measured by optical coherence tomography (OCT) differs according to ethnicity., Methods: As part of the Sydney Myopia Study, 2353 children from grade 7 (age range, 11.1-14.4 years) completed detailed ocular examinations in the 2004-2005 school year. AL was measured with noncontact interferometry and Stratus OCT was performed (Carl Zeiss Meditec, Jena, Germany)., Results: East Asian children displayed larger AL correlations with average RNFL, inferior RNFL, nasal RNFL, outer macula, and macular volume (r = -0.25, -0.36, -0.31, -0.35, and -0.31 respectively; P < 0.001) than did Caucasian children (r = -0.14, -0.20, -0.12, -0.17, and -0.13 respectively; P < 0.001). Positive correlations between the temporal RNFL and AL were found only among East Asian and South Asian children (r = 0.28, P < 0.001; and r = 0.27, P = 0.03, respectively). In Caucasian children, the foveal minimum and central macula correlated significantly with AL (r = 0.11 and r = 0.13, respectively, P ≤ 0.001)., Conclusions: Retinal parameters measured by OCT correlated with AL, and the extent of this correlation varied by ethnicity. It may therefore be that ethnicity should be considered when interpreting OCT scans on individuals with AL outside the usual range.

Purpose: To assess the relationship between macular retinal thickness and volume and age, sex, and refractive error/axial length with spectral domain-optical coherence tomography (SD-OCT)., Methods: One randomly selected eye of 198 consecutive ophthalmically normal subjects (104 men, 94 women) between July 2008 and January 2009, with corrected visual acuities better than 20/30 were included in this cross-sectional study. Complete ophthalmic examination, axial length measurement with a laser interferometer, and macular cube 512 x 128 scan by SD-OCT were performed., Results: The mean age was 55.6 +/- 16.4 years (range, 17-83), average refractive error was -2.17 +/- 4.82 (range, -23.50-3.75), and average axial length was 24.73 +/- 1.98 mm (range, 21.52-32.51). The central subfield thickness, average inner macular thickness, and overall macular volume were significantly lower in the female subjects (partial correlation: P = 0.009, P = 0.027, and P = 0.042, respectively). As age increased, average inner macular thickness, average outer macular thickness, overall average macular thickness, and macular volume decreased significantly (partial correlation: P = 0.002, P = 0.002, P = 0.002, and P = 0.000, respectively). Refractive error had no significant influence in partial correlation analysis. Axial length correlated negatively with average outer macular thickness, overall average macular thickness, and macular volume (partial correlation: P = 0.006, P = 0.044, and P = 0.003, respectively)., Conclusions: In normal subjects, SD-OCT showed that retinal thickness is related to age, sex, and axial length, with regional variations.

PURPOSE. To determine the anatomic variations in the peripapillary retinal nerve fiber layer (RNFL) thickness distribution and the relationship between these anatomic variations and other ocular variables. METHODS. A complete ophthalmic examination, including measurement of visual acuity, refraction, and axial length, was performed on 269 subjects with no ophthalmic abnormalities. Further, fundus photographs and optic disc cube scans of the subjects' eyes were obtained with a fundus camera and spectral domain OCT (Cirrus HD-OCT; Carl Zeiss Meditec, Inc., Dubin, CA), respectively. The distance between the foveola and the center of the optic nerve head was measured. The correlations of the angles of the peaks in the RNFL thickness profile with the axial length, spherical equivalent of refractive error (SE), and distance between the foveola and optic disc center were analyzed by simple linear regression. RESULTS. Considerable interindividual variations were found in the angles of the peaks in the RNFL thickness profile. Further, the angles in the eyes in each individual showed significant differences. The angles of the superior and inferior first peak correlated significantly with the SE, axial length, and distance between the foveola and optic disc center. CONCLUSIONS. Subjects with increased distance between the foveola and optic disc center are likely to have a temporal shift in peak RNFL thickness. RNFL profiles with horizontally deviated peak RNFL thickness differ considerably from the normative data provided with the HD-OCT system. The variations in RNFL thickness profiles should be taken into account.

Purpose: To determine the dependency of straylight on ocular biometry., Methods: This prospective study included 518 eyes of 277 volunteers of diverse ethnic backgrounds with healthy eyes of various iris colors. The eyes had retinal straylight tested using a commercial psychophysical device. Ocular axial length and refraction were also measured with an ocular biometer and an autorefractometer, respectively., Results: The measured retinal straylight was validated by comparing data with the age model described in the literature as log(s) = P(1) + log[1 + (age/65)(4)], where P(1) is the logarithm of the average straylight for the eyes of a newborn. The data agreed well with this model, although P(1) was slightly higher (0.931 vs. 0.87). When this model was subtracted from the measured straylight values, a quadratic increase was found in the function of axial length, L: log(s) = 0.931 + log[1 + (age/65)(4)] + (0.01089L(2) - 0.4820L + 5.330). A similar model was defined for the spherical equivalent refraction SE. This corresponds to an increasing amount of straylight for increasing degrees of myopia. No correlation was found with keratometry and corneal astigmatism or with iris color., Conclusions: Retinal straylight increases not only with age, but also with axial length. Further study is needed to identify the cause of this dependency.

Purpose: To assess the effects of body stature and years of education, in addition to age and sex, on six oculometric traits and to estimate the heritabilities of these quantitative traits in two Croatian cross-population studies., Methods: Adult subjects living on the two Croatian islands of Vis and Korcula were recruited for a large epidemiologic and genetic study that included eye biometry, keratometry, and autorefraction. Effects and heritabilities were estimated by using general linear mixed models for axial length (AL), anterior chamber depth (ACD), corneal curvature (CC), corneal thickness (CT), lens thickness (LT), and spherical equivalent refraction (SER). Both cohorts were genotyped with dense SNP arrays, allowing the use of kinship coefficients derived from genotypic data (realized kinship) rather than from pedigree information (expected kinship)., Results: Across cohorts, body mass index (BMI) did not consistently influence any of the ocular traits adjusted for age and/or sex, whereas height and years in education (YrEd) did, explaining up to an additional 5% of the variance (in CC). CT was the trait least influenced by covariates. Estimated heritabilities in Vis and Korcula, respectively, were 84% and 52% for CC, 75% and 71% for CT, 37% and 32% for LT, 59% and 45% for ACD, 37% and 74% for AL, and 0% and 17% for SER., Conclusions: While heritabilities of CT and CC seemed uniformly high across studies of Caucasian datasets, estimates for SER varied widely and were at the lower end of the spectrum of published observations in our study.

Purpose: To demonstrate the three-dimensional macular thickness distribution in normal subjects by spectral domain optical coherence tomography (SD-OCT) and evaluate its association with sex, age, and axial length., Methods: Mean regional retinal thickness measurements on the Early Treatment Diabetic Retinopathy Study (ETDRS) layout were obtained by three-dimensional raster scanning (6 x 6 mm) using SD-OCT in 248 normal eyes of 248 Japanese subjects., Results: Mean foveal thickness was 222 +/- 19 microm; it was significantly greater in men (226 +/- 19 microm) than in women (218 +/- 18 microm; P = 0.002) and did not correlate with age in either sex. Mean sectoral retinal thickness was also significantly greater in the men than in the women in all the quadrants of the inner ring (1-3 mm; P < 0.001 and P = 0.001-0.007) and in the temporal quadrant of the outer ring (3-6 mm; P < 0.001). The retinal thicknesses of each of the ETDRS sectors did not correlate significantly with axial length after adjustment for age in either sex. Retinal thickness in six of the eight sectors in the inner and outer rings showed a negative correlation with age after adjustment for axial length in the men (P < 0.001 and P = 0.001-0.018), whereas no correlation with age was observed in the women., Conclusions: SD-OCT demonstrated the three-dimensional macular thickness distribution in normal eyes. Macular thickness varied significantly with sex and age. These variables should be considered while evaluating macular thickness.

Purpose: To examine the distribution and systemic determinants of ocular biometry as measured using partial laser interferometry in an adult Asian population., Methods: A population-based, cross-sectional study of 3280 persons (78.7% participation rate) ages 40 to 80 years, of Malay ethnicity residing in Singapore, was conducted. Axial ocular dimensions, including axial length (AL), anterior chamber depth (ACD), and corneal curvature (CC), were determined with partial laser interferometry. Participants had a comprehensive interview and a standardized examination., Results: After 492 persons were excluded who had undergone cataract surgery, data on 2788 subjects were available. The mean AL, ACD, and CC were 23.55, 3.10, and 7.65 mm, respectively. AL and ACD decreased with increasing age. In multivariate models that adjusted for age, sex, education, height, weight, number of reading hours, diabetes, and current smoking, longer AL was associated with being male, height, increasing weight, higher education levels, and total reading hours. Increasing CC was associated with greater age and greater height and weight after multivariable adjustment., Conclusions: Age, sex, and stature were the most consistent predictors of the results of ocular biometry in the Singapore Malay adult population.

It is proposed that with the possible exception of owls, binocularity in birds does not have a higher order function that results in the perception of solidity and relative depth. Rather, binocularity is a consequence of the requirement of having a portion of the visual field that looks in the direction of travel; hence, each eye must have a contralateral projection that gives rise to binocularity. This contralateral projection is necessary to gain a symmetrically expanding optic flow-field about the bill. This specifies direction of travel and time to contact a target during feeding or when provisioning chicks. In birds that do not need such control of their bill, binocular field widths are very small, suggesting that binocular vision plays only a minor role in the control of locomotion. In the majority of birds, the function of binocularity would seem to lie in what each eye does independently rather than in what the two eyes might be able to do together. The wider binocular fields of owls may be the product of an interaction between enlarged eyes and enlarged outer ears, which may simply prevent more lateral placement of the eyes.

Purpose: To measure laminar and peripapillary scleral architecture in normal and glaucomatous Chinese eyes with normal and those with elongated axial length., Methods: The histomorphometric investigation included a normal group (nonaxially elongated eyes) of 40 human globes (40 patients; mean age, 41.3 +/- 13.4 years; range,15-68) enucleated because of malignant choroidal melanoma, a glaucomatous group (non-axially elongated eyes) of 55 eyes (55 patients; age, 43.3 +/- 20.3 years; range, 12-88) enucleated because of painful secondary angle-closure glaucoma, and a group of 26 glaucomatous globes (glaucomatous elongated axial length group; 26 patients; age, 29.0 +/- 14.4 years; range, 12-60) with an axial length > 27.5 mm. Anterior-posterior histologic sections were morphometrically evaluated., Results: The lamina cribrosa was significantly (P < 0.001) thicker in the normal group than in the glaucomatous group, in which it was significantly (P < 0.001) thicker than in the glaucomatous elongated-length group. Lamina cribrosa thickness decreased significantly with increasing axial length (P < 0.001) and presence of glaucoma (P < 0.001). Peripapillary scleral thickness close to the optic nerve scleral canal and just outside of the optic nerve meninges decreased significantly with increasing axial length (P = 0.04 and P = 0.02, respectively). Peripapillary scleral thickness did not vary significantly between the glaucomatous group and the normal group. The distance between the intraocular space and cerebrospinal fluid space was (P < 0.001) shorter in the two glaucomatous groups than in the normal group., Conclusions: Lamina cribrosa thickness and peripapillary sclera thickness decreased significantly with axial length, in addition to a glaucoma-related thinning of the lamina cribrosa. In non-axially elongated eyes, the peripapillary sclera thickness did not vary significantly between glaucomatous eyes and normal eyes.

Purpose: To investigate the diurnal variation in axial length and anterior eye biometrics, while simultaneously measuring intraocular pressure (IOP) with dynamic contour tonometry in human subjects., Methods: Fifteen young adult near-emmetropic subjects had axial length, anterior eye biometrics (central corneal thickness and anterior chamber dimensions), and IOP measured at six different times across a 24-hour measurement period. Repeated-measures ANOVA and sine curve fitting were used to analyze the diurnal rhythms in each measured parameter., Results: Axial length was found to undergo significant diurnal variation (P = 0.0006). The mean amplitude of axial length change was 0.046 +/- 0.022 mm. The mean peak in axial length was found to occur at 1113. Intraocular pressure and ocular pulse amplitude were also found to undergo significant diurnal change (P < 0.0001 and 0.0006, respectively). The variation in axial length exhibited a significant association with the change in IOP (r = 0.37, P = 0.001). No significant difference was found between the mean peak times of axial length and IOP. Anterior eye biometric measures of central corneal thickness and anterior chamber depth were also found to undergo significant diurnal changes (P < 0.0001 and 0.0368, respectively)., Conclusions: Axial length undergoes significant variation over a 24-hour period. Associations exist between the change in axial length and the change in IOP, as measured by dynamic contour tonometry. These results may have significant implications for the role of ocular diurnal rhythms in emmetropization.

Purpose: To compare the distribution of spherical equivalent refraction (SER) and other ocular parameters and to assess the contribution from oculometric parameters to SER in two age-specific, cross-sectional samples of children, and in two ethnic groups (European Caucasian and East Asian)., Methods: A random-cluster design was used to recruit predominantly 6-year-old (1765 participants, 78.9% response) and 12-year-old children (2353 participants, 75.3% response) from schools across Sydney, Australia. Data collection included questionnaires and eye examination (keratometry, biometry, and cycloplegic autorefraction). Results of three analytical methods (Pearson correlation, partial correlation coefficient, and linear regression analyses) are reported for 6- and 12-year-old children., Results: Kurtosis for SER and axial length (AL) in the 12-year-old children (14.3 and 2.1, respectively) was similar to that previously reported for the 6-year-old children (11.3 and 0.5). AL showed high correlation (r) with SER in the 6- (r = -0.44) and 12-year-old (r = -0.61) children. Lower correlations for SER with corneal radius (r

This study investigates the changes in aberrations with monocular accommodation as a function of age. Second-order and higher order wavefront aberrations and pupil size were measured as a function of accommodation demand over the range of 0-4 D in the right eyes of 47 normal subjects with ages between 17 and 56 years. Higher order ocular Zernike aberrations were analyzed for the natural pupil size in terms of their equivalent defocus and were also determined for fixed pupil diameters of 4.5 mm in the unaccommodated eyes and 2.5 mm in the accommodating eyes. With relaxed accommodation (0 D accommodation stimulus), the major change with age was in the value of C4(0), which increased in positive value over the age range studied, although the total higher order RMS wavefront aberration did not increase. When the data were analyzed for natural pupils, spherical aberration was again found to change systematically in the positive direction with age. The equivalent defocus of total higher order RMS error for natural pupils showed no significant correlation with age (p > .05). With active accommodation, spherical aberration was found to decrease and become negative as the accommodative response increased in the younger subjects (<40 years). Near-zero spherical aberration was found at accommodation levels of about 0.50 D in the youngest subjects (<20 years) and at around 2-3 D in subjects between 20 and 39 years. In the older subjects (>40 years), the spherical aberration showed only small changes, some of which were positive, within the limited amplitude of accommodation available. Other higher order aberrations and the RMS of higher order aberrations did not appear to change systematically with accommodation, except in the oldest subjects. The change with age in the relationship between aberration and accommodation is interpreted in terms of the changing gradients of refractive index and surface curvatures of the crystalline lens.

Purpose: The present study investigated retinal integrity in high myopia using spatial psychophysical tasks., Methods: Ten axial high myopes (-8.5 to -11.5 D) and 10 age-matched control subjects (+/-1.0 D) were recruited. All participants underwent clinical examination and ocular biometry and demonstrated no visible macular disease with visual acuities better than 6/12. Foveal summation thresholds were determined for white and S-cone-isolating spots of various diameters up to 5.4 degrees and spatial contrast sensitivity to luminance sine wave gratings (0.5-9.7 cyc/deg). Data were analyzed after correction for the magnification induced by eye size and correcting lens power., Results: Spatial summation for both white and S-cone-isolating spots showed a generalized loss of sensitivity at all spot sizes in myopes relative to control subjects (P = 0.01). Critical areas at maximum summation were significantly larger in myopes, for S-cone isolating spots only, after image size correction (P = 0.048). Sensitivity at maximum summation correlated negatively with vitreous chamber depth for both targets (P = 0.005). Sensitivities for S-cone and luminance spots also correlated (P < 0.001), indicating widespread dysfunction. Myopes displayed contrast sensitivity losses at high spatial frequencies (P

Purpose: The purpose of this study was to document the incidence rates of anisometropia, year-by-year prevalences, changes in the intereye difference in spherical equivalent (SE), and its association with myopia progression and axial length changes in a cohort of Singaporean school children., Methods: This is a prospective cohort study of Singaporean school children (n = 1979) aged 7 to 9 years who were examined annually with cycloplegic refraction and ultrasonography over a 3-year period., Results: In the 1908 children without anisometropia at commencement, the 3-year cumulative incidence rate of anisometropia (difference in SE at least 1.0 D) was 144 (7.55%; 95% CI: 6.42-8.85). The mean intereye difference in SE in all children at baseline was 0.29 +/- 0.46 D (SD: 0.46) and increased to 0.44 D (0.59) on the last examination. On the initial examination, 3.6% (95% CI: 2.8-4.4) or 71 children had anisometropia. Of the 59 of 71 children who completed all examinations, only 3 (5.1%) had an increase in the intereye difference in SE by at least 0.5 D, whereas 2 (3.4%) had a decrease of at least 0.5D. The mean intereye difference in SE was stable between visits. The change in intereye difference in SE correlated with the change in intereye axial length (r = 0.43). Compared with the isometropic children, each eye of the anisometropic children had a higher rate of progression of myopia., Conclusions: The 3-year incidence of anisometropia was 7.55% in these young Singaporean children. Although the frequency of anisometropia increased with time, the difference in SE between eyes tended to remain stable.

Purpose: A methodology for noninvasively characterizing the three-dimensional (3-D) shape of the complete human eye is not currently available for research into ocular diseases that have a structural substrate, such as myopia. A novel application of a magnetic resonance imaging (MRI) acquisition and analysis technique is presented that, for the first time, allows the 3-D shape of the eye to be investigated fully., Methods: The technique involves the acquisition of a T2-weighted MRI, which is optimized to reveal the fluid-filled chambers of the eye. Automatic segmentation and meshing algorithms generate a 3-D surface model, which can be shaded with morphologic parameters such as distance from the posterior corneal pole and deviation from sphericity. Full details of the method are illustrated with data from 14 eyes of seven individuals. The spatial accuracy of the calculated models is demonstrated by comparing the MRI-derived axial lengths with values measured in the same eyes using interferometry., Results: The color-coded eye models showed substantial variation in the absolute size of the 14 eyes. Variations in the sphericity of the eyes were also evident, with some appearing approximately spherical whereas others were clearly oblate and one was slightly prolate. Nasal-temporal asymmetries were noted in some subjects., Conclusions: The MRI acquisition and analysis technique allows a novel way of examining 3-D ocular shape. The ability to stratify and analyze eye shape, ocular volume, and sphericity will further extend the understanding of which specific biometric parameters predispose emmetropic children subsequently to develop myopia.

Purpose: To determine in human eyes whether diurnal fluctuations in axial length are related to fluctuations in intraocular pressure (IOP) by studying these fluctuations in both eyes of individual subjects and by assessing the regularity of both rhythms on two separate study days., Methods: Ten subjects, ages 18 to 24 years, underwent serial axial length and IOP measurements using highly precise, noncontact partial coherence interferometry and Goldmann applanation tonometry, respectively. Both eyes were measured at six 3-hour intervals during each of two study days, and significant fluctuations were modeled by sine curves., Results: Of the 40 data sets, 29 had significant axial length high-low differences and 32 had significant IOP high-low differences (ANOVA, P < 0.05 for each). The magnitude of the significant high-low differences were 38 +/- 22 microm for axial length and 6.0 +/- 1.9 mm Hg for IOP (mean +/- SD). Neither axial length nor IOP fluctuations necessarily occurred bilaterally on the same day, and neither rhythm was regularly observed on two separate days in individual eyes. In eyes in which both parameters fluctuated on the same day, there were no correlations in the amplitude, period or phase of the two rhythms., Conclusions: Both axial length and IOP fluctuate during the day much of the time in most subjects. However, diurnal IOP fluctuations do not appear to cause diurnal axial length fluctuations.

Purpose: Magnetic resonance imaging (MRI) was used to determine the effect of recessions and resections on horizontal extraocular muscle (EOM) paths and globe position., Methods: Four adults with horizontal strabismus underwent contrast-enhanced, surface-coil MRI in central, secondary, and tertiary gazes, before and after horizontal EOM recessions and/or resections. EOM paths were determined from 2-mm thickness, quasicoronal MRI by analysis of cross-sectional area centroids in a normalized, oculocentric coordinate system. Globe displacement was determined by measuring the apparent shift of the bony orbit in eccentric gaze., Results: In all subjects, the anteroposterior positions of the horizontal rectus pulleys shifted by less than 2 mm after surgery, indistinguishable from zero within measurement precision. In three subjects who underwent medial rectus (MR) recession or resection, postoperative globe position was similar in central gaze, but globe translation during vertical gaze shift changed markedly. There was no effect on globe translation in the subject who underwent only lateral rectus (LR) resection., Conclusions: Recessions and resections of horizontal EOMs have minimal effect on anteroposterior EOM pulley positions. Because the pulley does not shift appreciably despite large alterations in the EOM insertion, the proximity of a recessed EOM to its pulley would be expected to introduce torsional and vertical actions in tertiary gazes. Connective tissue dissection during MR surgery may destabilize the globe's vertical translational stability within the orbit, potentially changing the effective pulling directions of the rectus EOMs in vertical gazes. These changes may mimic oblique muscle dysfunction. LR surgery may avoid globe destabilization.

Purpose: To determine the effect of anthropometric parameters on refraction and ocular biometry., Methods: Noncontact methods were used to examine ocular dimensions and cycloplegic refraction in a stratified random cluster sample of year-1 Sydney school students (mean age, 6 years; n = 1765). Height, body weight, and waist circumference were measured according to a standardized protocol. Body mass index (BMI) was subsequently calculated. The percentage of body fat was measured with leg-leg bioelectrical impedance analysis. Associations between parameters were analyzed by multiple linear regression., Results: After adjustment for age in weeks, height was found to be strongly associated with axial length and corneal radius. Children in the 1st quintile for height had axial length of 22.39 +/- 0.04 mm compared with 22.76 +/- 0.04 mm in children in the 5th quintile. Other anthropometric parameters were not associated with axial length or corneal radius. Height was not associated with anterior chamber depth after adjustment for weight. Increases in weight, BMI, and waist circumference were associated with a deeper anterior chamber after adjustment for height. No associations were found between the measured anthropometric parameters and refraction or axial length-corneal radius ratio., Conclusions: This study found a strong association between height and axial length and corneal radius, but not spherical equivalent refraction. The findings may demonstrate the effectiveness of emmetropization in the presence of normal physiological influences.

Purpose: To study the distribution of spherical equivalent refraction and ocular biometric parameters in a young Australian population., Methods: Noncontact methods were used to examine ocular dimensions and cycloplegic autorefraction in a stratified random cluster sample of year 1 Sydney school students (n = 1765), mean age 6.7 years (range, 5.5-8.4 years). Repeated measures of axial length, anterior chamber depth, and greatest and least corneal radius of curvature (CR1, CR2, respectively) were taken in each eye. Refraction was measured as the spherical equivalent., Results: Mean spherical equivalent refraction in right eyes was +1.26 +/- 0.03 D (SEM; range, -4.88 to +8.58). The distribution was peaked (kurtosis 14.4) and slightly skewed to the right (skewness, 1.7). Prevalence of myopia, defined as spherical equivalent refraction < or = -0.5 D, was 1.43% (95% CI, 0.94-2.18) in the overall population. Axial length, anterior chamber depth, and corneal radii of curvature were normally distributed. The mean axial length in right eyes was 22.61 +/- 0.02 mm (SEM; range, 19.64-25.35). The mean anterior chamber depth was 3.34 +/- 0.01 mm (SEM; range, 2.14-4.06). Mean CR1 was 7.85 +/- 0.01 mm (SEM) and mean CR2 was 7.71 +/- 0.01 mm (SEM). The distribution of axial length/mean corneal radius ratio was peaked (leptokurtic) with a mean of 2.906. Mean axial length was longer, anterior chambers were deeper, and corneas were flatter in the boys., Conclusions: A peaked (leptokurtic) distribution of spherical equivalent refraction was present in this predominantly hyperopic 6-year-old population. The results also showed that ocular biometric measures were normally distributed, with statistically significant gender differences found in measurements.

Purpose: The contour of the human cornea is closely modeled by a conic section, which is fully described by asphericity (Q) and apical radius of curvature (r(o)). The relationship between corneal shape and other ocular dimensions in children, including anterior and vitreous chamber depths, axial length, and spherical equivalent refractive error, was investigated., Methods: Corneal asphericity and r(o) were calculated by using corneal topography data on 643 children (72 myopes, 370 emmetropes, and 201 hyperopes), ages 6 to 15 years, who participated in the Orinda Longitudinal Study of Myopia (OLSM) during 1991. Measurements from a younger subset of these children, including 8 myopes, 92 emmetropes, and 75 hyperopes, ages 6 to 9 years in 1991, were compared to 1996 data for longitudinal analysis., Results: Mean +/- SD Q of the 1991 study sample was -0.346 +/- 0.101, representing a prolate corneal shape. Almost all (99.7%) of the corneas examined were prolate. Corneal asphericity was less prolate among myopes than in emmetropes and hyperopes (P = 0.010). Less prolate corneas were related to deeper anterior chamber depths among emmetropes (r = 0.324, P < 0.0001) and hyperopes (r = 0.275, P < 0.0001), but not among myopes (r = 0.230, P = 0.0515). Flatter values of r(o) were related to longer vitreous chamber depth (r = 0.607, P < 0.0001) and axial length (r = 0.606, P < 0.0001) in all refractive error groups. Initial corneal shape was unrelated to change in refractive error over a 5-year period., Conclusions: Most corneas examined in this study were prolate in contour. Deeper anterior chamber depths were related to less prolate corneas among emmetropes and hyperopes, which is probably the result of mechanical influences on the peripheral cornea as the anterior chamber elongates during ocular growth. Longitudinal results suggest initial corneal shape is of little or no value in predicting refractive error progression.

Purpose: Since central corneal thickness may inversely influence the amount and rate of progression of glaucomatous optic nerve damage and because lamina cribrosa thickness may be of importance in susceptibility to glaucoma, it was the purpose of the present study to evaluate whether central corneal thickness is related to lamina cribrosa thickness., Methods: The histomorphometric study included 111 enucleated nonglaucomatous eyes of 111 white subjects. On anterior-posterior histologic sections through the pupil and the central optic disc region, the thickness of the cornea, lamina cribrosa, and peripapillary sclera and the shortest distance between the intraocular space and the cerebrospinal fluid space were measured. Axial length ranged between 20 and 32 mm., Results: Mean central corneal thickness (mean +/- SD: 616.6 +/- 108.3 microm) and mean central lamina cribrosa thickness (378.1 +/- 117.8 microm) were statistically independent of each other (P = 0.15; correlation coefficient, r = 0.14). In a similar manner, lamina cribrosa thickness at the optic disc border was statistically independent of central corneal thickness (P = 0.51; r = 0.06) and peripheral corneal thickness (P = 0.34; r = 0.09). In a parallel way, peripapillary scleral thickness (P = 0.84) and the shortest distance between the prelaminar space and cerebrospinal fluid space (P = 0.10) were statistically independent of central corneal thickness., Conclusions: In nonglaucomatous human globes, central corneal thickness may not correlate significantly with lamina cribrosa thickness, peripapillary scleral thickness, and shortest distance between intraocular space and cerebrospinal fluid space. Histologic artifact and sectioning methods could partially account for the lack of an association. The study results may suggest clinically that an assumed relationship between central corneal thickness and susceptibility to glaucoma cannot be explained by an anatomic correspondence between corneal thickness and histomorphometry of the optic nerve head.

Purpose: Ultrahigh-resolution, full-field optical coherence tomography (OCT), which uses a white light source, allows bidimensional, noninvasive tomographic imaging without scanning. The goal of the present study was to apply full-field OCT to ocular tissue imaging in an attempt to explore the capabilities of the technique., Methods: This full-field OCT system uses a Linnik-type interferometer with a tungsten-halogen source. The spatial resolution is 0.9 x 0.7 microm (transverse x axial). Unstained tissue samples (cornea, lens, retina, choroid, and sclera) and whole, unfixed eyes of rat, mouse, and pig were examined under immersion. A charge-coupled device (CCD) camera recorded a pair of interferometric images that were combined to display en face (i.e., in the x-y plane) tomographic images in real time. The acquisition time per tomographic image, which includes summation of 10 raw images, was on the order of 1 s. Postprocessing allows volumetric navigation through the image stack as well as three-dimensional (3D) imaging., Results: Cellular-level resolution was achieved in isolated tissue samples. En face (x-y) images revealed corneal epithelial and stromal cells, lens fibers, nerve fibers, major vessels, and retinal pigment epithelial cells. In x-z reconstructions, cellular layers within the cornea and retina and arterioles and venules were clearly defined. Transscleral retinal imaging was achieved in albino animals., Conclusions: Ultrahigh-resolution, full-field OCT allows cellular-level imaging of unstained ocular tissues with high penetration depth. Although the current system is unsuitable for clinical use, this simple technique has potential for in vivo ocular examination, for which a new system is currently under development.

This study investigated differences in geometrical properties and optical aberrations between a group of hyperopes and myopes (age-matched 30.3+/-5.2 and 30.5+/-3.8 years old, respectively, and with similar absolute refractive error 3.0+/-2.0 and -3.3+/-2.0, respectively). Axial length (AL) was measured by means of optical biometry, and corneal apical radius of curvature (CR) and asphericity (Q) were measured by fitting corneal topography data to biconic surfaces. Corneal aberrations were estimated from corneal topography by means of virtual ray tracing, and total aberrations were measured using a laser ray tracing technique. Internal aberrations were estimated by subtracting corneal from total aberrations. AL was significantly higher in myopes than in hyperopes and AL/CR was highly correlated with spherical equivalent. Hyperopic eyes tended to have higher (less negative) Q and higher total and corneal spherical aberration than myopic eyes. RMS for third-order aberrations was also significantly higher for the hyperopic eyes. Internal aberrations were not significantly different between the myopic and hyperopic groups, although internal spherical aberration showed a significant age-related shift toward less negative values in the hyperopic group. For these age and refraction ranges, our cross-sectional results do not support evidence of relationships between emmetropization and ocular aberrations. Our results may be indicative of presbyopic changes occurring earlier in hyperopes than in myopes.

Objective: To describe the variation in ocular biometry and its association with refraction in adult Mongolians., Methods: The study included 1800 subjects, aged 40 years or more, who were selected in two Mongolian provinces-Hövsgöl and Omnögobi-to participate in this population survey. Axial length (AL) and its components, as well as noncycloplegic autorefraction and corneal power (CP), were measured., Results: Of those selected, 1617 subjects (90.0%) were examined. Mean +/- SD of AL was 23.13 +/- 1.15 mm. There was a very small but significant increase in mean AL with age (0.05 mm per decade, P = 0.03). Autorefraction was performed on 620 of 675 subjects of those examined in Omnögobi. The age and gender standardized prevalences of myopia (< -0.5 D), emmetropia, hyperopia (> +0.5 D), astigmatism (< -0.5 D of cylinder) and anisometropia (>1.0 D difference between eyes) were 17.2%, 49.9%, 32.9%, 40.9%, and 10.7%, respectively. Prevalence of myopia showed no clear trend with increasing age, whereas hyperopia, astigmatism, and anisometropia all increased monotonically. Multiple regression models revealed that AL (P < 0.001) and VCD (P < 0.001) were the strongest determinants of refractive error., Conclusions: In this cross-sectional study of adult Mongolians, a much lower prevalence of myopia was found than in other East Asian populations studied to date. The mean AL differed little between age groups, in marked contrast to data on Chinese people.

Purpose: This study sought diurnal variations of eye length in human subjects, analogous to those reported in laboratory animals., Methods: Seventeen subjects, ages 7 to 53 (median 16) years and mean spherical equivalent refractive error -0.68 D (range, -3.00 to +1.00 D), underwent axial length measurements at multiple times during the day between 7 AM and 1 AM the following day, using partial coherence interferometry (PCI), a highly precise, noncontact method. Diurnal axial length measurements were obtained on two or more days in 10 of these subjects., Results: During at least 1 day, 15 subjects showed a statistically significant (ANOVA, P < 0.05) diurnal fluctuation of axial length, with a magnitude generally between 15 and 40 microm. From the diurnal tracings that fit a sine curve using statistical criteria, the mean period of fluctuation was 21.6 +/- 4.33 hours (SD), the mean amplitude was 27.1 +/- 11.9 microm (SD; range, 12.8-41.4 microm), and the maximum axial length tended to occur at midday. Each of the subjects with multiple daily measurements showed axial length fluctuations on at least 1 day, but there were day-to-day differences in the diurnal variations: most notably, four subjects showed axial length fluctuations on each day; in others, the fluctuations were not observed on each testing day., Conclusions: The human eye undergoes diurnal fluctuations in axial length, with a pattern suggesting maximum axial length at midday. Based on repeated measurements, these daily fluctuations may not appear regularly in all subjects, suggesting the possibility of physiologic influences that must be defined.

Purpose: To examine the relationship of ocular components to refraction throughout the adult life span of the rhesus monkey (Macaca mulatta)., Methods: Cycloplegic retinoscopy, A-scan ultrasonography, slit lamp examination, indirect ophthalmoscopy, and keratometry were performed in a cross-sectional study of 111 monkeys, aged 5 to 31 years. Lens thickness and anterior and vitreous chamber depths were measured from the echograms. The intercorrelations of these variables were analyzed, as well as their association with age and sex., Results: In monkeys aged 5 to 15 years, the mean refractive value of +1.5 D with an SD of 1.7 D was maintained near the previously established developmental asymptote of +2 D. In monkeys older than 15 years, there was greater interindividual variation (SD = 4.5 D), including extreme myopia and hyperopia. The cornea became steeper with age. The axial length of the eyes increased up to 12 years of age and began to shorten after 20 years. Changes also occurred in the other individual components that constitute eye length. These age-related changes were decreased vitreous chamber depth, decreased anterior chamber depth, and increased lens thickness. In general, males had longer eyes than females. The eyes of old monkeys were more likely to exhibit cataract and drusen, but age-related changes in focal atrophy of the retinal pigment epithelium did not achieve statistical significance., Conclusions: The components of the monkey eye change with age in a pattern similar to that reported in humans. Age-related changes in individual ocular components that could be detrimental to refraction appear to be compensated for by changes in other components.

Purpose: To describe the relationship of refractive errors and axial ocular dimensions and age-related cataract., Methods: Population-based, cross-sectional survey of ocular diseases among Chinese men and women aged 40 to 81 years (n = 1232) living in the Tanjong Pagar district in Singapore. As part of the examination, refraction and corneal curvature were determined with an autorefractor, with refraction further refined subjectively. Ocular dimensions, including axial length, anterior chamber depth, lens thickness, and vitreous chamber depth, were measured with an A-mode ultrasound device. Lens opacity was graded clinically according to the Lens Opacity Classification System (LOCS) III system. Refraction, biometry, and cataract data on right (n = 989) and left (n = 995) eyes were analyzed separately., Results: In analyses controlling for age, gender, education, diabetes, and cigarette smoking, nuclear cataract was associated with myopia (-1.35 D vs. -0.11 D, P < 0.001, comparing right eyes with and without nuclear cataract), but not with any specific biometric component. Cortical cataract was associated with thinner lenses (4.67 mm vs. 4.79 mm, P = 0.001, comparing right eyes with and without cortical cataract), but not with refraction and other biometric components. Posterior subcapsular cataract was associated with myopia (-1.80 D vs. -0.39 D, P < 0.001, comparing right eyes with and without posterior subcapsular cataract), deeper anterior chamber (3.00 mm vs. 2.89 mm, P = 0.02), thinner lens (4.62 mm vs. 4.77 mm, P = 0.001), and longer vitreous chamber (15.78 mm vs. 15.57 mm, P = 0.09), but not with overall axial length and corneal curvature. Adjustment for vitreous chamber depth attenuated the association between posterior subcapsular cataract and myopia by 65.5%, but did not substantially change the association between nuclear cataract and myopia., Conclusions: These population-based data support the associations between nuclear and posterior subcapsular cataracts and myopia reported in previous studies. Posterior subcapsular cataract is also associated with deeper anterior chamber, thinner lens, and longer vitreous chamber, with vitreous chamber depth explaining most of the association between posterior subcapsular cataract and myopia.

Purpose: In chickens, there are circadian rhythms in axial length, choroidal thickness, and intraocular pressure (IOP), the phases of which differ, depending on visual manipulations that alter ocular growth rate. In this study, these same rhythms were sought in the common marmoset, a primate model of eye growth, to establish whether these may play a role in ocular growth regulation across species., Methods: IOP was measured by applanation tonometry in 14 untreated marmosets ranging in age from 24 to 259 days. High-frequency A-scan ultrasonography was used to measure ocular dimensions (axial length and choroidal thickness) in 12 marmosets ranging in age from 24 to 572 days. Four monkeys were measured when they were juveniles (<110 days of age) and again later, when they were adolescents. Measurements were typically made at 12-hour intervals, although three animals were measured at 6-hour intervals. Nine monkeys had both IOP and axial dimensions measured in the same experiment., Results: There was a diurnal rhythm in IOP in the marmosets: IOP was higher during the dark period and lower during the light period (mean change, 3.6 mm Hg; P < 0.005). There were also rhythms in axial length and choroidal thickness. The rhythm in axial length was dependent on age, with faster-growing eyes of juveniles increasing in length during the day and decreasing at night (+25 microm vs. -22 microm; P < 0.001) and slower-growing eyes of adolescents showing the opposite pattern (-27 microm vs. +46 microm; P < 0.0001). The choroid thickened during the night and thinned during the day, at all ages measured (+19 microm vs. -16 microm; P < 0.0001)., Conclusions: Diurnal rhythms in IOP, axial length, and choroidal thickness exist in primates. Age-related differences in the phase relationships of these rhythms may be associated with differences in the rates of ocular growth.

Purpose: To examine the association between the anthropometric measurements of height, weight, body mass index (BMI) and refraction and other ocular parameters in Singapore Chinese children., Methods: In a cross-sectional study of 1449 Chinese schoolchildren, aged 7 to 9 years, from three Singapore schools, height and weight were measured according to standard protocol, and BMI was calculated. Refractive error and corneal curvature measures were determined by autorefraction in eyes under cycloplegia. Axial length, vitreous chamber depth, lens thickness, and anterior chamber depth were measured using A-scan biometry ultrasonography., Results: In comparison with the children with height in the first quartile for a given age and gender, the eyeball length in children in the fourth quartile was 0.46 mm longer, the vitreous chamber depth 0.46 mm deeper, the corneal radius of curvature 0.10 mm greater (i.e., flatter), refraction more negative by 0.47 D (-0.76 D versus -0.29 D), and axial length-to-corneal curvature radius (AL-CR) ratio higher, after analyses controlling for age, gender, parental myopia, reading, school, and weight. The associations of height with refractive error and AL-CR ratio were significant in girls but not in boys. Heavier and more obese children had refractions that were more hyperopic (P = 0.01, P = 0.08), after analyses controlling for age, gender, parental myopia, reading, and school (height was also controlled for if weight was evaluated). This association was present in boys but not in girls., Conclusions: Controlling for age, gender, parental myopia, reading, school, and weight showed that taller Singapore Chinese children had eyes with longer axial lengths, deeper vitreous chambers, flatter corneas, and refractions that tended toward myopia. In multivariate analysis, eyes in children who were heavier or who had a higher BMI tended to have refractions that were more hyperopic, and eyes in heavier children had shorter vitreous chambers. Differences between the present results and a recent report in Singapore adults suggest either a cohort effect or a potential influence of systemic endocrine or metabolic factors during childhood on refractive development.

The tuning properties of the ensemble of cone photoreceptors is due to the tuning properties of individual cones convolved with the disarray in pointing direction between the cones. We used direct imaging with the Rochester adaptive optics ophthalmoscope to directly image these properties in individual cones in living human eyes. We found that cone disarray is very small, accounting for less than 1% of the breadth of the tuning function of an ensemble of cones. The implication is that the optical fiber properties of an ensemble of cones mimic the tuning properties of a single cone.

Purpose: To determine the effect of continuous light exposure on ocular growth and emmetropization in infant monkeys., Methods: Nine infant rhesus monkeys were reared with the normal vivarium lights on continuously. The 24-hour light cycle was initiated between 1 and 4 weeks of age and maintained for 6 months. The ocular effects of continuous light were assessed by cycloplegic retinoscopy, keratometry, and A-scan ultrasonography. Longitudinal control data were obtained from 23 normal infants that were reared with an illumination cycle that included defined light and dark phases (either 12-hour light:12-hour dark or 8.5-hour light:15.5 hour dark)., Results: In contrast to previous studies involving light-reared chickens, no monkeys exhibited exaggerated ocular growth. There were no significant differences between treated and control monkeys in corneal radius, overall eye size, or the axial dimensions of individual ocular components. At the end of the treatment period, eight of the nine experimental monkeys also exhibited the moderate hyperopic errors (range, +1.5 to +3.4 D) that are typically found in normal animals. Aspects of emmetropization were, however, unusual for three monkeys. One monkey manifested a -0.50 D myopic error that was associated with an abnormally steep cornea but had normal axial lengths. Two additional monkeys developed persistent axial anisometropias., Conclusions: In infant primates constant light exposure does not promote the constellation of ocular changes (in particular corneal flattening, a decrease in anterior chamber depth, and an increase in vitreous chamber depth) that has been observed in light-reared chickens. The slight variations from the expected developmental sequence observed in three infants may reflect individual differences. However, it is also possible that aspects of the emmetropization process may not operate as effectively under constant light as they do under an ordinary light/dark cycle.

Purpose: To describe the association of ocular dimensions and refraction with adult stature., Methods: This was a population-based cross-sectional survey of adult Chinese aged 40 to 81 years residing in the Tanjong Pagar district in SINGAPORE: As part of the examination, ocular dimensions, including axial length, anterior chamber depth, lens thickness, and vitreous chamber depth, were measured using an A-mode ultrasound device. Corneal radius and refraction were determined with an autorefractor, with refraction further refined subjectively. Height (in meters) and weight (in kilograms) were measured using a standardized protocol, and body mass index (BMI) was calculated as weight divided by the square of the height (kilograms per square meter)., Results: Data on ocular biometry, refraction, height, and weight were available on 951 (55.4%) participants with phakic eyes. After controlling for age, sex, education, occupation, housing type, income, and weight, it was found that taller persons were more likely to have longer axial lengths (+0.23 mm longer axial length, for every 0.10 m difference in height), deeper anterior chambers (+0.07 mm), thinner lenses (-0.09 mm), longer vitreous chambers (+0.26 mm), and flatter corneas (+0.09 mm longer corneal radius), although refractions were similar. In contrast, heavier persons tended to have more hyperopic refractions (+0.22 D for every 10 kg difference in weight, +0.56 D for every 10 kg/m(2) difference in BMI) but similar ocular dimensions., Conclusions: Adult height is independently related to ocular dimensions, but does not appear to influence refraction. Thus, although taller persons are more likely to have longer globes, they also tend to have deeper anterior chambers, thinner lenses, and flatter corneas. Conversely, weight is independently related to refraction, although the exact biometric component responsible for this association is not apparent.

Purpose: Orbital and global layers of rectus extraocular muscles (EOMs) are believed to serve different functions. This study sought anatomic and functional evidence of differing blood flow in the two layers of rectus EOMs., Methods: Four human orbits ranging in age from 17 months to 93 years were serially sectioned and stained for muscle fibers with Masson's trichrome and for vascular smooth muscle with monoclonal antibody to smooth muscle alpha-actin. Digitally assisted microscopy was used to obtain measurements of luminal cross sections and counts of muscular blood vessels, as well as measurements of muscle fiber number and cross-sectional areas of the two layers. Findings were correlated with first-pass gadodiamide contrast magnetic resonance imaging (MRI) in two living humans to demonstrate relative perfusion of EOMs., Results: In all rectus EOMs, the orbital layer had significantly more vessels per unit area, more vessels per fiber, and more total vascular luminal area, than the global layer (P: < 0.05). Vascularity of EOMs was greatest in the youngest specimen. First-pass contrast MRI was consistent with perfusion of the orbital layer earlier than the global layer of living human rectus EOMs., Conclusions: Orbital layers of human rectus EOMs have significantly more muscular vessels than the global layers and stain earlier after intravenous bolus injection of paramagnetic MRI contrast. These findings suggest higher and even more rapid blood flow in the orbital layers that may correlate with greater metabolic activity. Greater blood flow is consistent with more sustained mechanical loading of the orbital than the global layer.

Purpose: Rectus extraocular muscles (EOMs) consist of orbital (OL) and global (GL) layers. This study enumerated the fibers in both layers along the length of each EOM., Methods: Four human (ages 17 months-93 years) and three monkey (ages 5-7 years) orbits were serially sectioned in the coronal plane and stained with Masson's trichrome. All fibers of the rectus EOMs were counted using light microscopy at midorbit in all specimens and regular intervals throughout the orbits for one human and one monkey., Results: In the GL, human EOMs in midorbit contained 8000 to 16,400 fibers, and monkey EOMs contained 3600 to 6600 fibers, varying little among the four rectus EOMs. In humans and monkeys, the number of OL fibers in midorbit varied widely according to specific EOM, being most numerous for the medial rectus (human: 7400-14,600; monkey: 3700-7000). The GL existed over the entire extent of each EOM from origin in the orbital apex into continuity with the tendon inserting on the globe. The OL was absent in the most anterior portion of each EOM, because OL fibers inserted on the respective EOM pulley., Conclusions: Primate EOMs contain substantial numbers of OL fibers. Numerical similarity of GL fibers is consistent with similar mechanical loading on each of the four rectus EOMs, as required to rotate the globe. Numerical dissimilarity of OL fibers correlates with varying mechanical loading because of varying elasticities of connective tissues onto which these fibers insert.