Dry eye and blink rate simulation with a pig eye model.

Purpose: To simulate medium level "dry eye" and investigate the effect of "blink" rates in "dry eye" condition using a novel porcine dry eye model (pDEM).

Methods: In the first experiment, a 40 s "lacrimation/blink" interval (lacrimation occurring in conjunction with blink) was set in the pDEM to simulate a medium level of "dry eye" condition. In the second experiment, "lacrimation" interval was set at 60 s and three different "inter-blink" intervals of 6, 12, and 20 s were set in groups A, B, and C, respectively. The integrity of each cornea was assessed before and after experiments by slit-lamp microscopy with sodium fluorescein solution. The viability of corneal epithelial cells was assessed by the Trypan blue exclusion test after the experiment.

Results: The amount of sodium fluorescein staining was significantly (p < 0.05) lower at the end of the experiment, when the "inter-blink" interval was set at 12 s. The medians of the final fluorescein grades of corneas in the pDEM were grade 1.5, 1.0, and 2.0 when the "inter-blink" intervals were set at 6, 12, and 20 s, respectively. There was no significant difference in the number of damaged cells between the central and peripheral corneas with different "inter-blink" intervals. Although in each case the peripheral area had a lower number of non-viable cells than the central area of the cornea, there was no significant change in the number of Trypan blue stained cells in either area with different "inter-blink" intervals.

Conclusion: Different severity levels of "dry eye" can be simulated using the newly developed pDEM. Increased blink rate may protect the cornea against desiccation-induced damage; however, increased blink rate may also increase shear force between the cornea and conjunctiva and result in mechanical damage because of increased frictional force.