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T. A. Cafaro, J. I. Torrealday, M. Crespo, C. Maldonado, S. G. Ortiz, J. A. Urrets-Zavalía, H. M. Serra; Study of Corneal Surface in Sheep That Inhabit in an Argentine Region With High Prevalence of Climatic Droplet Keratopathy. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5648.
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© ARVO (1962-2015); The Authors (2016-present)
Climatic droplet keratopathy (CDK) is a degenerative disease of the cornea characterized by its slowly progressive opacity with a high prevalence in Argentinean Patagonia region. Patients have had a very restricted diet with very low intake of ascorbic acid (AA). In this study we investigated if CDK affects sheep that have been grazing in this region.
99 sheep were examined. A slit-lamp biomicroscopy was used to evaluate corneal transparency, epithelium erosions and tear film break-up time (BUT). The corneal sensitivity was studied with Cochet-Bonnet aesthesiometer. In some animals we quantified AA levels in serum and aqueous humor by HPLC and then in vitro histological studies were carried out.
Combining results from all eyes, mean and SD corneal BUT values were 8.09±1.87 seconds and corneal sensitivity in central and peripheral regions were 4.23±0.53 and 4.42±0.44, respectively. Corneas very often showed discrete superficial erosions in both eyes. The values of AA in serum and aqueous humor were 0.44±0.11mg/dl and 27.35±4.02mg/dl, respectively. Histological studies showed that the cornea of this animal is a thick structure (515.9±25.6µm) composed of an epithelium of 10-12 cell layers (96.36±13.64 µm), that lies on the basement membrane, a very thin Bowman's layer, the stroma (397±13.24 µm), a thick Descemet's membrane (16.46±3.49µm), and the endothelium (4.18±2.14µm).
These results demonstrated that the cornea of this animal is structurally similar to the human cornea. In contrast to humans sheep are capable of synthesizing AA from carbohydrates present in the pasture using the enzyme gulanolactone oxidase. The absence of significant corneal surface alterations in these animals exposed to the same environmental conditions as CDK patients could be attributed to the very efficient protective mechanisms provided by the AA accumulated in their corneas.
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