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Presents a study which investigated by Mössbauer spectroscopy two distinct microstructural phases produced in the same batch of melt-spun iron[sub 60]aluminum[sub 28]boron[sub 12]. Information on melt spinning; Results and discussion; Conclusion.

Presents a study which fabricated amorphous alloys Fe[subx]P[sub100] by radio frequency sputtering in a specific composition range. Reason that the studies of the amorphous iron-phosphorus system over a wide range of concentrations are desirable; Curie temperatures of the alloys; Magnetic hyperfine-field distributions.

Presents a study which examined the local atomic structure in amorphous iron-phosphorus alloys. Measurement of isomer yield information on the charge distribution; Experimental methods; Results and discussion.

Purpose: To evaluate the effect of intraoperative mitomycin C (MMC) on corneal light scattering after excimer laser keratectomy., Methods: Phototherapeutic keratectomy (PTK) was performed in 24 rabbit eyes. After 40-microm epithelial ablation, animals were divided into three groups. In group 1, filter paper discs soaked with MMC (group 1A, 0.5 mg/mL; group 1B, 0.25 mg/ml) were applied for 1 minute. In group 2, annular filter papers soaked with MMC (group 2A, 0.5 mg/mL; group 2B, 0.25 mg/mL) were applied for 1 minute. Controls received vehicle only (group 3). Six-millimeter diameter 100-microm deep PTK was performed. Corneal light scattering was measured weekly from 1 to 6 weeks, at 10 weeks, and at 8 and 13 months using a scatterometer. A corneal light scattering index (SI) ranging from 0 to 10 was calculated; SI of 1 represents normal scattering., Results: A statistically significant decrease in mean SI was noted in group 2A (annular MMC 0.5 mg/mL; p<0.05) as compared with the control group at 2 weeks. At 10 weeks, SI approached baseline levels in group 2 and the control group but showed significant increase in group 1 (MMC disc; p < 0.05). At 8 and 13 months, SI showed no statistical differences between groups., Conclusions: Controlled application of 0.5 mg/mL MMC in the corneal midperiphery transiently reduces corneal light scattering after excimer keratectomy in this rabbit model.

Corneal epithelial damage thresholds for exposures to 80 ns pulses of 10.6 microm infrared radiation produced by a CO2-TEA laser were investigated. Thresholds were determined for sequences of 1, 2, 8, 32, 128, and 1,024 pulses at pulse repetition frequencies of 10 and 16 Hz. Threshold damage is correlated by an empirical power law of the form EDth = CN(-alpha) in which EDth, is the threshold radiant exposure per pulse, and N is the number of pulses. The constants C and alpha are similar for the two pulse repetition frequencies. For the combined data set, C = 2,955 J m(-2) pulse(-1) (295.5 mJ cm(-2) pulse(-1) and alpha = 0.178. This value of the constant C is within 5% of the measured damage threshold for a single 80 ns pulse exposure. Temperature calculations reveal that the maximum temperature increase on the beam axis, 10 microm beneath the anterior tear surface, resulting from the different threshold exposures is constant to within +/-10% of the mean values. This result is consistent with a critical temperature damage model. Damage threshold measurements on cooled corneas indicate that the damage mechanism indeed has a substantial thermal component.

The purpose of this study was to develop an in vivo, noninvasive method to assess the velocities of normal and sickle red blood cells (RBCs) in the retinal and choroidal vasculatures of rats. Human and rat RBCs were isolated from whole blood, labeled with fluorescein isothiocyanate (FITC), and administered intravenously to anesthetized rats. A Rodenstock scanning laser ophthalmoscope (SLO) was used to image the FITC-labeled RBCs as an NTSC video signal. Video sequences of RBC transit in the retinal (pigmented rats) and choroidal (albino rats) vessels were captured directly to digital format. Following in vivo angiography, the animals were sacrificed, the eyes enucleated, and retinas prepared by our adenosine diphosphatase vascular labeling technique for viewing by conventional optical microscopy. Although rat and normal human RBCs differ slightly in size, their velocities were similar in the retinal arteries and capillaries (within 4%). Velocities of RBCs from sickle cell patients (sRBCs) were slower by 12 and 9% in arteries and by 38 and 25% in capillaries, compared to rat and normal human RBCs, respectively. Compared to velocities in retinal capillaries, the velocities in choroidal capillaries were much slower for rat RBCs (77%), normal human RBCs (79%), and sRBCs (67%). In contrast to normal human RBCs, sRBCs were often retained transiently in retinal capillaries at preferred sites, but in choroidal capillaries large numbers of cells were retained for extended periods. SLO imaging of FITC-labeled RBCs in rat retina and choroid provided a reliable method for evaluating normal and abnormal hemodynamics., (Copyright 2000 Academic Press.)

Purpose: Techniques employing polarized light propagation and scattering are useful in examining the cornea's lamellar structure. Recent advances in theoretical methods have significantly increased the ability to relate features of lamellar arrangements to measurements of transmitted polarized light. The chick cornea, because of its hypothesized structure of a gradual helical rotation of lamellar pairs, presents an interesting model for further development of this methodology., Methods: Small-angle light scattering (SALS) and polarized transmission measurements were made on 7-week-old chick corneas under conditions that closely approximate the physiological state. Birefringence properties were determined from the transmission measurements and compared to the results of model calculations of polarized light propagating through lamellae organized according to the hypothesized structure for chick cornea., Results: The I+ small-angle light scattering pattern had 4 cloverleaf lobes aligned with the crossed polarizer and analyzer axes. The lobes disappeared when the transcorneal pressure was increased from zero to 18 mmHg. Retardation measured at 18 mmHg was very small (approximately 0.01 microm)., Conclusion: The disappearance of the I+ small-angle light scattering pattern when IOP is increased suggests that the lamellae undulate in their relaxed state and the undulations straighten when IOP is increased. Measured birefringence properties are consistent with the hypothesized lamellar structure.

The propagation of polarized light through the cornea is affected by the orientations of the corneal lamellae and by the refractive imbalance between the collagen fibrils and the ground substance. Thus, well-designed measurements and analyses of polarized light propagation through the cornea can be used to obtain information regarding the cornea's lamellar and fibrillar structures. This paper shows that, for the rabbit, measured values of the optical parameters strongly suggest that the distribution of lamellae orientations is not random, but has one (or two) preferred orientation directions. Also, there is considerable evidence that collagen is intrinsically anisotropic. The Weiner formula gives the effective birefringence of an assembly of parallel isotropic fibrils and its generalization to the case of anisotropic fibrils is presented. Finally, calculations based on preferred orientation models having lamellae composed of anisotropic fibrils show that comparison with experimental values can yield structural information.

In this paper polarized light transmission measurements are made under conditions that closely approximate the physiological state in order to probe lamellar structure in the central cornea of New Zealand white rabbits. The results are interpreted with the aid of a newly developed theory (published elsewhere) in which the cornea is modeled as stacked birefringent layers corresponding to the lamellae. The theory enables predictions of the statistical properties of lamellar ordering based on characteristics of the transmission of polarized light. The experimental results are consistent with a structure in which a number of lamellae have a fixed azimuthal orientation (i.e. about an axis normal to the corneal surface), whereas the remainder are essentially randomly oriented. Comparisons with the theoretical predictions are consistent with a model in which the preferred direction in the apical region of the cornea does not vary significantly among rabbits; and the preferred lamellar orientation direction determined for the population measured here is very close to that suggested in previous experiments on a smaller number of rabbits. Mapping experiments using a new goniometric holder showed that the preferential order at the apical region is closely preserved throughout the central approximately 4 mm diameter optical zone in individual corneas.

Purpose: To obtain objective measurements of corneal light scattering after excimer laser keratectomy, and to evaluate the relation of light scattering to clinical haze grading and visual acuity., Methods: The authors measured best-corrected visual acuity, subjective clinical haze grade, and corneal light-scattering index in patients undergoing photorefractive keratectomy (PRK) (n=26), and phototherapeutic keratectomy (n=8), preoperatively and postoperatively at 1,3,6,9, and 12 months or later. Corneal light scattering was correlated with visual acuity and clinical haze grade., Results: Corneal light scattering increased after PRK and was reduced after phototherapeutic keratectomy. Corneal light scattering index showed a stronger positive correlation with logMAR visual acuity (r=0.57) than clinical haze grading (r=0.34). Corneal light-scattering index (P<0.05 at 1 and 3 months) and clinical haze grading (P<0.05 at 6, 9, and 12 months) were significantly higher in eyes undergoing PRK with ablation depths of more than 80 microns., Conclusions: Excimer laser surgery affects corneal light scattering. Ablations with depths greater than 80 microns produce significantly higher levels of haze than those less than 80 microns. Objective measurement of corneal light scattering may be useful in monitoring the outcome of excimer keratectomy.

Purpose: The authors sought to discover whether there are differences in the degree of spatial order in the fibrillar ultrastructure between anterior and posterior stroma., Methods: Human corneas were obtained from eye bank eyes. Although they had been classified as normal, some swelling remained after 3 hours of deturgescence. Freshly excised, unswollen rabbit corneas also were used. Image analysis methods were applied to transmission electron micrographs of the anterior, middle, and posterior stroma of these corneas to determine the positions and radii of fibrils, the fraction of total area occupied by fibrils, and the fibril number density. Results were used to calculate the interference factor that appears in the direct summation of the fields for light scattering theory and to estimate the total scattering cross-section per fibril. The interference factor is a measure of the spatial order in the positions and sizes of the fibrils., Results: Electron micrographs showed anterior-posterior variations in size and number density of fibrils. The interference factor at wavelengths of visible light was lower in posterior stroma than in anterior stroma for humans and rabbits. In some instances in humans, the anterior interference factor was characteristic of mildly swollen cornea. When averaged for the electron micrographs analyzed, the anterior stroma was predicted to scatter approximately twice as much light per unit depth as the posterior stroma in humans (at any given wavelength) and approximately three times as much in rabbits., Conclusions: Calculations of the interference factor showed that there were differences in the anterior-posterior spatial ordering of fibrils. In human corneas, the differences could have been caused by intrinsic in vivo differences between anterior and posterior stroma; however, possible anterior-posterior variations in swelling between the two regions in vitro also could have affected the results.

In recent studies other investigatiors have presented traces of "light scattering" versus depth into the cornea. The present investigation demonstrates that these traces do not measure the actual light scatter intensity and that a proper interpretation of such traces shows that most of the scattering is from within the stroma.

Threshold damage to the cornea from CO2 lasers is confined to the epithelium. Exposures well above the threshold for epithelial damage produce bowl-shaped stromal wounds. Light and electron microscopy and slit-lamp photographs all show a sharp demarcation between the damaged and undamaged regions 48 hr after exposure. The micrographs also show that the damaged region is accellular. Calculations of the expected temperature increases combined with analyses of slit lamp photographs show that the wound boundary corresponds to a surface of equal peak temperature increase. Comparisons with epithelial and endothelial damage conditions suggest that stromal, endothelial and epithelial cells have essentially the same thermal damage mechanism.