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RL McCally, JA Bonney-Ray; Light Scattering From Healed Penetrating Corneal Wounds . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1710.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:To investigate the light scattering properties of aged (semi) transparent scars resulting from penetrating wounds in rabbit cornea. Methods:2 mm diameter penetrating wounds were made in the central cornea of rabbits by C. L. Kublin in the laboratory of Dr. Charles Cintron at the Schepens Eye Research Institute. The wounds were allowed to heal for periods of 3.5 to 4.5 years at which time the rabbits were sacrificed. The scar and cornea thicknesses outside the scar were measured using ultrasonic pachymetry. Corneas were excised immediately and their transmissivity, T, measured. The total scattering cross-section was derived from the transmission data. The tissue was prepared for TEM immediately following the transmission measurements. Results:The scarred regions were flat on all corneas and quite thin. Scar thickness averaged 0.25±0.05 mm and the cornea thickness outside the scar averaged 0.40±0.04 mm. Three of the scars were moderately transparent (T varying from 0.41 at 400 nm to 0. 70 at 700 nm), five were somewhat less transparent (T varying from 0.21 at 400 nm to 0. 58 at 700 nm), and one was much less transparent (T varying from 0.10 at 400 nm to 0. 27 at 700 nm). The transmissivity was independent of healing time. Analysis of the transmissivity data showed that the total scattering cross-section for each group contains a term that varies as the inverse square of the light wavelength. Conclusion:Despite the long healing time these scars remained highly scattering. The presence of a term in the total scattering cross-section that varies as the inverse square of wavelength is indicative of the presence of voids in the collagen fibril distribution. [Farrell, McCally, and Tatham, "Wavelength Dependencies of Light Scattering in Normal and Cold Swollen Rabbit Corneas and their Structural Implications," J. Physiol. (Lond.) 233, 589-612 (1973)] Such voids could be "lakes" or other regions that are devoid of fibrils, but which have a different average refractive index. Confirmation of the presence of voids will require completing the microscopy.
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