Search

Purpose Assess feasibility and interexaminer reliability of a new test of contrast sensitivity (CS) for pediatric populations. Methods The Double Happy (DH) measures CS using a method similar to the Teller Acuity Cards. The schematic DH face is 16 degrees in diameter with features of 0.3 c/d and a channel frequency of 0.8 c/d. DH log10 CS is in 0.15 log unit steps, 0.05 to 2.1. Participants were 43 unselected patients, ages 2 to 18 years: 23 were diagnosed with ocular disorders only; 20 were diagnosed with cerebral visual impairment (CVI). Two examiners measured DH log10 CS. Visual acuity (VA) was also measured. Results All 43 participants were tested for binocular DH log10CS. Cohen's kappa values for interexaminer reliability were fair. The between examiner ICC was +0.92 (P < 0.001). The mean difference between examiners was near zero, and the 95% CI was -0.44 to 0.45 log10CS. DH log10CS was near normal in the ocular disorder group and reduced in the CVI group. VA was reduced in both groups. DH log10 CS and VA were correlated (r = -0.65). DH log10 CS was a marginally better predictor of diagnosis than VA. Conclusions DH log10CS test was successful in a diverse pediatric population diagnosed with ocular disorders or CVI. Interexaminer reliability was comparable to that of adults tested previously using the same stimuli and methods. Both CS and VA are reduced in CVI. Translational Relevance CS and VA both should be tested in pediatric clinical populations, especially in those at risk of CVI.

As a result of longitudinal chromatic aberration (LCA), longer wavelengths are blurred when shorter wavelengths are in focus, and vice versa. As a result, LCA affects the color and temporal aspects of the retinal image with hyperopic defocus. In this experiment, we investigated how the sensitivity to temporal color contrast affects emmetropization. Ten-day-old chicks were exposed for three days to sinusoidal color modulation. The modulation was either blue/yellow flicker (BY) (n = 57) or red/green flicker (RG) (n = 60) simulating hyperopic defocus with and without a blue light component. The color contrasts tested were 0.1, 0.2, 0.3, 0.4, 0.6, and 0.8 Michelson contrast. The mean illuminance of all stimuli was 680 lux. Temporal modulation was either of a high (10 Hz) or low (0.2 Hz) temporal frequency. To test the role of short- and double-cone stimulation, an additional condition silenced these cones in RG_0.4 (D-) and was compared with RG_0.4 (D+) (n = 14). Changes in ocular components and refractive error were measured using Lenstar and a photorefractometer. With high temporal frequency BY representing an in-focus condition for shorter-wavelengths, we found that high temporal frequency BY contrast was positively correlated with vitreous expansion (R2 = 0.87, p

A previous experiment showed that blue light (as a component of white light) protected against low temporal frequency dependent eye growth. This experiment investigated the role of temporal contrast. White leghorn chicks were exposed to white (with blue) or yellow (without blue) LED lighting modulated at either low (0.2 Hz) or high (10 Hz) temporal frequencies. Four cone contrast conditions were used: low (16%), medium (32%), medium-high (60%) and very-high (80%). Chicks were exposed to the lighting condition for 3 days (mean 680 lux). Exposure to high temporal frequencies, with very high temporal contrast, reduced eye growth, regardless of spectral content. However, at low temporal frequencies, eye growth was dependent on the illuminant. At lower temporal contrast levels, eye growth increased regardless of temporal or spectral characteristics. To conclude, very high temporal contrast, white light, provides a “stop” signal for eye growth that overrides temporal cues for growth that manifest in yellow light.

Purpose Longitudinal chromatic aberration can provide luminance and chromatic signals for emmetropization. A previous experiment examined the role of temporal sensitivity to luminance flicker in the emmetropization response. In the current experiment, we investigate the role of temporal sensitivity to color flicker. Methods Five-day-old chicks were exposed to sinusoidal color modulation of blue/yellow (N = 73) or red/green LEDs (N = 84) at 80% contrast for 3 days. The modulation frequencies used were as follows: 0, 0.2, 1, 2, 5, and 10 Hz. There were 5 to 16 chicks per condition. Mean illumination was 680 lux. Changes in ocular components were measured using Lenstar, and refraction was measured with a Hartinger refractometer. Results Eyes grew less when exposed to high temporal frequencies and more at low temporal frequencies. With blue/yellow modulation, the temporal variation was small; eyes grew 268 ± 15 μm at 0 Hz and 224 ± 12 μm at 10 Hz, representing a 16.4% growth reduction. With red/green modulation, eyes grew 336 ± 31 μm at 0 Hz and 218 ± 20 μm at 10 Hz, representing a 35% growth reduction. Choroidal and anterior chamber changes compensated for eye growth, reducing refractive effects; blue/yellow refraction changes ranged from -0.63 to 1.04 diopters. Conclusions At high temporal frequencies, color is not a factor, but at low temporal frequencies, red/green modulation produced maximal growth. The pattern of changes observed in each ocular component with changes in the temporal frequency and/or the color of the stimulus was consistent with the idea that the natural sunlight spectrum may be optimal for emmetropization.

Chicks respond to two signals from longitudinal chromatic aberration (LCA): a wavelength defocus signal and a chromatic signal. Wavelength defocus predicts reduced axial eye growth in monochromatic short-wavelength light, compared to monochromatic long-wavelength light. Wavelength defocus may also influence growth in broadband light. In contrast, a chromatic signal predicts increased growth when short-wavelength contrast > long-wavelength contrast, but only when light is broadband. We aimed to investigate the influence of blue light, temporal frequency and contrast on these signals under broadband conditions. Starting at 12 to 13 days-old, 587 chicks were exposed to the experimental illumination conditions for three days for 8h/day and spent the remainder of their day in the dark. The stimuli were flickering lights, with a temporal frequency of 0.2 or 10 Hz, low (30%) or high contrast (80%), and a variety of ratios of cone contrast simulating the effects of defocus with LCA. There were two color conditions, with blue contrast (bPlus) and without (bMinus). Stimuli in the “bPlus” condition varied the amounts of long- (L-), middle- (M-) and double- (D-) cone contrast, relative to short- (S-) and ultraviolet (UV-) cone contrast, to simulate defocus. Stimuli in the “bMinus” condition only varied the relative modulations of the L+D vs. M cones. In all cases, the average of the stimuli was white, with an illuminance of 777 lux, with cone contrast created through temporal modulation. A Lenstar LS 900 and a Hartinger refractometer were used to measure ocular components and refraction. Wavelength defocus signals with relatively high S-cone contrast resulted in reduced axial growth, and more hyperopic refractions, under low-frequency conditions (p = 0.002), in response to the myopic defocus of blue light. Chromatic signals with relatively high S-cone contrast resulted in increased axial growth and more myopic refractions, under high frequency, low contrast, conditions (p < 0.001). We conclude that the chromatic signals from LCA are dependent on the temporal frequency, phase, and relative contrast of S-cone temporal modulation, and recommend broadband spectral and temporal environments, such as the outdoor environment, to optimize the signals-for-defocus in chick.

In broadband light, longitudinal chromatic aberration (LCA) provides emmetropization signals from both wavelength defocus and the resulting chromatic cues. Indoor illuminants vary in their spectral output, potentially limiting the signals from LCA. Our aim is to investigate the effect that artificial illuminants with different spectral outputs have on chick emmetropization with and without low temporal frequency modulation. In Experiment 1, two-week-old chicks were exposed to 0.2 Hz, square-wave luminance modulation for 3 days. There were 4 spectral conditions: LED strips that simulated General Electric (GE) LED "Soft" (n = 13), GE LED "Daylight" (n = 12), a novel "Equal" condition (n = 12), and a novel "High S" condition (n = 10). These conditions were all tested at a mean level of 985 lux. In Experiment 2, the effect of intensity on the "Equal" condition was tested at two other light levels (70 lux: n = 10; 680 lux: n = 7). In Experiment 3, the effect of temporal modulation on the "Equal" condition was tested by comparing the 0.2 Hz condition with 0 Hz (steady). Significant differences were found in axial growth across lighting conditions. At 985 lux, birds exposed to the "Equal" condition showed a greater reduction in axial growth (both p 0.01) and a greater hyperopic shift compared to "Soft" and "Daylight" (both p 0.01). The "High S" birds experienced more axial growth compared to "Equal" (p 0.01) but less than in "Soft" and "Daylight" (p 0.01). Axial changes in "Equal" were only observed at 985 lux with 0.2 Hz temporal modulation, and not with lower light levels or steady light. We conclude that axial growth and refraction were dependent on the lighting condition in a manner predicted by wavelength defocus signals arising from LCA.

Purpose Longitudinal chromatic aberration (LCA) is a color signal available to the emmetropization process that causes greater myopic defocus of short wavelengths than long wavelengths. We measured individual differences in chromatic sensitivity to explore the role LCA may play in the development of refractive error. Methods Forty-four observers were tested psychophysically after passing color screening tests and a questionnaire for visual defects. Refraction was measured and only subjects with myopia or hyperopia without severe astigmatism participated. Psychophysical detection thresholds for 3 cyc/deg achromatic, L-, M-, and S-cone-isolating Gabor patches and low-frequency S-cone increment (S+) and decrement (S-) blobs were measured. Parametric Pearson correlations for refractive error versus threshold were calculated and nonparametric bootstrap 95% percentage confidence intervals (BCIs) for r were computed. Results S-cone Gabor detection thresholds were higher than achromatic, L-, and M-cone Gabors. S-cone Gabor thresholds were higher than either S+ or S- blobs. These results are consistent with studies using smaller samples of practiced observers. None of the thresholds for the Gabor stimuli were correlated with refractive error (RE). A negative correlation with RE was observed for both S+ (r = -0.28; P = 0.06; BCI: r = -0.5, -0.04) and S- (r = -0.23; P = 0.13; BCI = -0.46, 0.01) blobs, although this relationship did not reach conventional statistical significance. Conclusions Thresholds for S+ and S- stimuli were negatively related to RE, indicating that myopes may have reduced sensitivity to low spatial frequency S-cone stimuli. This reduced S-cone sensitivity might have played a role in their failure to emmetropize normally.

To evaluate the Spot Vision Screener in detecting targeted vision disorders compared to cycloplegic retinoscopy in children3 years of age.Children, ages 6 months to 36 months underwent vision screening using the Spot Vision Screener. Results were compared to results of comprehensive eye examinations. Validity of the Spot was evaluated by calculating the area under the curve (AUC); the receiver operating characteristics (ROC) were used to determine optimal sensitivity and specificity for detection of targeted vision disorders.A total of 249 children were included. The AUC for detecting targeted vision disorders as defined by the study specific criteria using the Spot was 0.790. Compared to cycloplegic retinoscopy, the Spot underestimated hyperopia by 1.02 D (95% CI, 0.86-1.17 D). For hyperopia ≥4.5 D spherical equivalent (n = 10), the mean difference between the Spot and cycloplegic retinoscopy was 3.46 D (95% CI, 1.95-4.98 D). In contrast, the Spot overestimated astigmatism compared to cycloplegic retinoscopy (-1.00 D vs -0.48 D; P 0.001) by -0.52 D (95% CI, 0.43-0.62 D).The Spot Vision Screener showed good overall validity in detecting targeted vision disorders. It was within 0.5 D and 1 D of cycloplegic retinoscopy with regard to low hyperopia and astigmatism. Higher hyperopic spherical equivalent refractive errors showed larger differences in mean values between the Spot and cycloplegic retinoscopy.

Leventhal et al. (Science, 2003, 300(5620), 812-815) reported that orientation selectivity of V1 neurons was significantly reduced in older macaque monkeys, which suggests that mechanisms that encode orientation in humans may become more broadly tuned in old age. We examined this hypothesis in two experiments that used sine-wave masking and notched-noise masking to estimate the bandwidth of orientation-selective mechanisms in younger (age approximately 23 years) and older (age approximately 68 years) human adults. In both experiments, the orientation selectivity of masking was essentially identical in younger and older subjects.

SummaryDiscriminating the direction of motion of a low-contrast pattern becomes easier with increasing stimulus area. However, increasing the size of a high-contrast pattern makes it more difficult for observers to discriminate motion. This surprising result, termed spatial suppression, is thought to be mediated by a form of center-surround suppression found throughout the visual pathway. Here, we examine the counterintuitive hypothesis that aging alters such center-surround interactions in ways that improve performance in some tasks. We found that older observers required briefer stimulus durations than did younger observers to extract information about stimulus direction in conditions using large, high-contrast patterns. We suggest that this age-related improvement in motion discrimination may be linked to reduced GABAergic functioning in the senescent brain, which reduces center-surround suppression in motion-selective neurons.

Changes in the physiological properties of senescent V1 neurons suggest that the mechanisms encoding spatial frequency in primate cortex may become more broadly tuned in old age (Zhang et al., European Journal of Neuroscience, 2008, 28, 201-207). We examined this possibility in two psychophysical experiments that used masking to estimate the bandwidth of spatial frequency-selective mechanisms in younger (age approximately 22years) and older (age approximately 65years) human adults. Contrary to predictions from physiological studies, in both experiments, the spatial frequency selectivity of masking was essentially identical in younger and older subjects.