A preliminary study of changes in tear film proteins in the feline eye following nictitating membrane removal

Objective To investigate the influence of nictitating membrane (third eyelid) removal on selected proteins in feline tears. Animal studied Domestic short-haired cats (7-17months; 2.6-5.2kg) were used. Procedures Eye-flush tears were collected periodically for up to 18weeks from both eyes of animals with nictitating membranes removed, but nictitating gland left intact, (n=4) or with nictitating membranes intact (n=4). Tear comparisons were based on total protein content (TPC) using micro bicinchoninic acid assay, immunoglobulin A (IgA), and matrix-metalloproteinase (MMP)-9 measurements using sandwich enzyme-linked immunosorbent assay (ELISA) and tear gelatinase activity using gelatin zymography. Expression of MMP-2 and -9 in nictitating membranes removed at baseline (week 0) and eyes collected at 18weeks were also investigated in histological sections using immunoperoxidase for visualization. Results Nictitating membrane removal did not significantly change TPC and MMP-9 in tears within the first 4weeks. MMP-9 was not detected by ELISA in tears from eyes without nictitating membranes from week 5 onwards. IgA (%IgA of TPC) data varied between animals. Gelatin zymography showed increased MMP-2 and -9 activity in tears from eyes without nictitating membranes at week1 and a decrease following week 2 post-surgery. MMP-2 and -9 were immunolocalised to conjunctival goblet cells of removed nictitating membranes and to the conjunctival epithelium, respectively. After 18weeks, the distribution of MMPs in tissue was comparable between eyes with and without nictitating membranes. Conclusions Based on this preliminary study, nictitating membrane removal appeared to cause long-term changes in expression of tear proteins, including reduced MMP-9 expression.