Recovery time of corneal epithelial proliferation in the rabbit following rigid gas-permeable extended contact-lens wear

Purpose. To determine recovery time needed for the corneal epithelium to return to a normal proliferation rate following 24-hour rigid gas-permeable (RGP) lens wear. Methods. An RGP lens (Dk/t = 10) was fitted at 9:00 AM on one randomly chosen eye of each rabbit (N = 16) and removed 24 hours later while the other eye served as a control. Following contact lens removal, the rabbits were injected at four different time intervals (1,2, 4, and 7 days) with 5-bromo-deoxyuridine (BrdU) at 9:00 AM to label dividing corneal epithelial cells. All animals were sacrificed 24 hours after BrdU injection, and corneas were stained for BrdU. A series of continuously adjacent digital images of the whole-mount epithelium was collected from superior limbus to central cornea, and all BrdU-labeled epithelial cell pairs on each digitized image were counted. Results. On day 1 following lens removal, the number of BrdU-labeled corneal epithelium cells was reduced by 50% centrally (C) and 36% peripherally (P) (P < 0.001) compared with control eyes. At day 2, there was no statistically significant difference between control and experimental corneas (P = 0.675). At day 4, a marked significant increase in BrdU-labeled cells was noted, averaging 83% (C) and 96% (P) (P < 0.001). At day 7, BrdU-labeling returned to control values, although it was still slightly elevated (14% [C] and 5% [P], P = 0.045). Conclusions. The corneal epithelium in the rabbit required at least 1 full week to recover to its stable baseline proliferation rate following only 24 hours of RGP lens wear. Interestingly, hyperproliferation was noted within the limbal, peripheral, and mid-peripheral corneal epithelium 4 days after lens removal.