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.