Study of corneal surface in sheep that habit in an Argentine region with high prevalence of Climatic Droplet Keratopathy

CAFARO T A,; TORREALDAY JI; CRESPO MG; MALDONADO, C; ORTIZ S,; E. A. URRETS-ZAVALIA,; J. A. URRETS-ZAVALIA; H. M. SERRA,

Miami

Congreso; ARVO; 2010

Climatic droplet keratopathy (CDK) is a human acquired degenerative disease of the cornea characterized by slowly progressive opacity.  In a rural northwest Patagonia region of Argentine the prevalence of CDK is 10.8%, with males over 40 years old predominantly affected. The diet of these patients has been poor in ascorbic acid (AA) along its life. We investigate if CDK or another corneal surface alteration affects sheep that they live in this region of Argentina with high prevalence of CDK.  Ninety nine (87 females and 3 males) Merino Argentinean sheep, aged 2 to 6 years old, were examined. A slit-lamp biomicroscopy was used to evaluate corneal appearance and transparency, epithelium erosions and tear film break-up time (BUT) in all animals. After biomicroscopy examination, the corneal sensitivity was studied with Cochet Bonnet aesthesiometer. In some animals we quantified AA levels in serum and aqueous humor by HPLC and them we carried out histological studies by optic and transmission electronic microscopy.  The sheep cornea was a thick structure (515.9+/-25.6µm) and had five different sheets: the epithelium (96.36+/-13.64 µm), that lies on the basement membrane, the very thin Bowman´s layer, the stroma (397+/-13.24 µm), the thick Descemet´s membrane (16.46+ / - 3.49µm), and the innermost is the monolayer the endothelium (4.18+/-2.14µm). The epithelium has 5 superficial cell layers, 5-6 intermediate and 1-2 basal. Below there is a marked basement membrane and, contrary to human, a thin layer of Bowman.  Combining results from all eyes mean and SD from corneal BUT values was 8.09±1.87 seconds and corneal sensitivity central and peripheral region was 4.23±0.53 and 4.42±0.44 respectively. Corneas very often showed discrete superficial erosions being the FS positive in both eyes from all the animals. The values of AA in serum and aqueous humor were 0.44 + / -0.11mg/dl and 27.35 +/-4.02mg/dl, respectively.  These results demonstrate that in sheep corneas is structural and functionally similar to the human one. The difference is that these animals can synthesize AA from glucose and to concentrate it on aqueous humor and cornea, contrary to the humans that should ingest it with the diet. We did not observe any corneal alteration, similar to CDK in these exposed animals to the same environmental conditions that the patients, it would indicate that the sheep have efficient protective’s cornea mechanisms, one of those which would be the AA.