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I. Pentari, H. Ginis, D. De Brouwere, D. Bouzoukis, I. Naoumidi, I. Pallikaris; Corneal Healing Response and Light Scatter After Photorefractive Keratectomy in Rabbits. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3909.
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© ARVO (1962-2015); The Authors (2016-present)
Corneal haze is an adverse effect after photorefractive keratectomy (PRK) and is associated with morphological changes in the cornea. The purpose of this study was to employ optical and image processing techniques to calculate the intensity and angular distribution of scattered light in a series of post-PRK rabbit corneas and to correlate these findings with clinical and histopathological observations.
Eight pigmented rabbits underwent PRK (-6D, 6mm OZ). All eyes received local antibiotic drops until their reepithelialization. The animals were treated in accordance to the Statement for the Use of Animals in Ophthalmic and Vision Research. A specialized physician assessed subjective haze of all eyes on a weekly basis, while central corneal thickness (CCT) was also recorded. Animals were sacrificed at the tenth postoperative week. The intensity (and angular distribution) of scattered light was measured for all corneas by means of a purposely-developed camera lens that incorporated excised rabbit corneas between its glass elements. This lens was used with a CCD camera to record images projected on a computer screen. The power ratio of scattered light (SR=Scatter Ratio) was calculated by measuring the intensity of a dark disk on a uniform bright background. Based on images of a bright semiplane, the angular distribution of scatter was calculated. After the scatter measurement, the corneas were prepared for histological examination.
All measured parameters exhibited symmetry between fellow eyes. Maximum subjective haze grade (2.18±0.99) was observed at week 4 and minimum (0.92±0.93) at week 10. CCT did not change significantly postoperatively. SR was increased in all eyes in respect to previously measured intact corneas while ten eyes exhibited no subjective haze. Histology revealed a characteristic subepithelial irregular layer similar to scar tissue. SR was correlated to the thickness of this layer. The angular distribution of scattered light was characterized by a narrow forward peak (1.5 degrees FWHM).
Forward scatter following PRK can be attributed mainly to the subepithelial irregular layer. The angular distribution of scatter is in accordance to the size of structures observed microscopically in this layer. The optical technique was more sensitive than the subjective. The presented methodology may prove useful for the evaluation of different treatment schemes in terms of postoperative corneal haze.
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