The effect of rigid gas permeable contact lens wear on proliferation of rabbit corneal and conjunctival epithelial cells.

PURPOSE: To study the effect of rigid contact lens oxygen transmissibility on cell proliferation of the corneal, limbal, and conjunctival epithelium in vivo following 2 days of extended wear in the rabbit model. METHODS: Fourteen adult New Zealand White rabbits were divided equally into two groups. Each group was assigned to one of two test rigid gas permeable (RGP) contact lenses (Dk/Ltotal = 10 and 97) with uniform thickness (0.15 mm) and diameter (14.0 mm). One eye of each rabbit randomly received a contact lens for two days (48 hrs) extended wear, and the fellow eye was used as a control. Rabbits were injected intravenously with 5-bromo-2-deoxyuridine (200 mg/kg) in sterile phosphate buffered saline (pH 7.4) 24 hours before being killed. Corneas with a limbal rim of episclera and overlying conjunctiva were fixed in situ and excised. Nuclei labeled with BrdU were detected with a monoclonal anti-BrdU antibody and an FITC-conjugated secondary antibody. Digital images were collected and BrdU-labeled nuclei of whole-mount corneas were counted from superior limbus to inferior limbus using epifluorescence microscopy. RESULTS: Twenty-four hours after intravenous injection of BrdU, labeled nuclei were confined to and appeared as pairs in the basal epithelial layer. The density of BrdU-labeled nuclei were found to be 258 +/- 42, 167 +/- 43, 372 +/- 64, and 310 +/- 46 (pairs/mm2, mean +/- SD, n = 14) in normal controls for adjacent conjunctiva, limbus, peripheral cornea, and central cornea, respectively. By contrast,there was significant 81.35% (low Dk)and 22.46% (ultra-high Dk) suppression of cell proliferation in the central cornea after two days lens wear (n = 7). In addition, significant increases in the labeling of limbal and conjunctival epithelium were also noted. CONCLUSIONS: Significantly less BrdU labeling of epithelial cells at the normal rabbit limbus was noted as compared to the peripheral and central cornea (P < 0.05) and is consistent with the presence of slow-cycling limbal basal cells and the limbal stem cell theory; however, this is the first report of up-regulation of limbal cell proliferation induced by contact lens wear. This study also revealed, for the first time, that short-term extended wear of RGP lenses inhibits central corneal epithelial cell proliferation. This effect was significantly more pronounced for a low-oxygen vs. a hyper-oxygen transmissible test lens. This data also suggests that corneal epithelial layer thinning seen following extended contact lens wear may be explained, in part, by suppression of basal epithelial cell proliferation. Further study is clearly necessary to validate and extend these preliminary findings.