Differences In Vulnerability To Desiccating Stress Between Corneal And Conjunctival Epithelium In Rabbit Models Of Short-Term Ocular Surface Exposure

We evaluate the difference in vulnerability to desiccating stress (DS) between the corneal and conjunctival epithelia to understand different ocular surface staining patterns in dry eye patients.

We generated a rabbit model of short-term exposure keratopathy. 

The interpalpebral fissures were kept wide-open for 30 min to ensure the exposure of the central cornea, limbus, and perilimbal conjunctiva, with blinking performed manually once every minute. Eyes were evaluated at each time point: 3 min, 10 min, 20 min, and 30 min. The cornea and conjunctiva of rabbits were examined under a portable slit-lamp microscope. Tear samples were collected from the rabbit eyes baseline and after 3, 10, 20, and 30 min of exposure. Tissue cell extracts from corneal impression cytology were subjected to western blot analysis to measure protein levels of AQP5. Those from conjunctival impression cytology were subjected to western blot analysis to measure protein levels of AQP5, MUC5AC, and CFTR.

Corneal staining scores increased from 3-min post-DS exposure, while conjunctival staining increased from 20-min post-DS. At 20 min, the tear MUC5AC level doubled as compared to pre-DS (p = 0.007). In Western blot analysis, conjunctival AQP5, MUC5AC, and CFTR expression increased significantly in response to DS, compared to control (p = 0.039, 0.002, 0.039, respectively). Immunohistochemistry for CD31 and LYVE-1 were performed. CD31-positive cells and lymphatic space surrounded by LYVE-1-positive cells increased significantly in conjunctival tissue post-DS, compared to control (p = 0.0006, p < 0.0001, respectively). Surface damage was worse in the corneal than in the conjunctival epithelium after DS, by scanning electron microscopy. 

This study showed that the cornea and conjunctival epithelium show differences in vulnerability to DS. Increased blood vessels and dilated lymphatics, accompanied by increased conjunctival epithelial AQP5, MUC5AC, and CFTR expression, underlie the protective mechanism of the conjunctiva to desiccating stress.