EPITHELIAL WOUND-HEALING OF THE RAT CORNEA AFTER EXCIMER-LASER ABLATION

Rats with excimer corneal ablations (ArF 193 nm, 228 pulses, diameter 3,5 mm, 17.3 mJ per pulse, depth about 1/2 of corneal thickness) in on e eye were killed 1, 2, 4, 6 and 13 days after treatment, The other ey e served as control, The cell number per microscopic vision field, the labelling index (LI) and the mitotic rate (MR) were calculated for th e peripheral, midperipheral and central areas of the corneal epitheliu m. The cell number showed a uniform depression in the remaining cornea l epithelium at Day 1, normalizing from the centre to the periphery, T he LI was only significantly increased at Day 1, while the MR was stat istically significantly increased peripherally at Day 2 and in all are as at Day 6. However, when the corneal epithelium was evaluated as a w hole, the MR was significantly increased at days 1, 2 and 6, The proli ferative response of the epithelium was very homogenous irregardless o f the distance to the original lesion. Both the migratory and the prol iferative phases of the healing process seemed to be delayed when comp ared to the healing of pure epithelial wounds. However, the initiation of an increase in DNA synthesis seems not to be delayed, indicating t hat it is primarily the G2 phase that has been prolonged with this abl ation procedure. The stromal thickness was increased from about one ha lf of the normal values immediately after the treatment to above norma l values at Day 4, thereafter decreasing to normal values at Day 13, T hus, the regenerative ability of the stroma is more pronounced in rats than in humans, but also in humans regeneration of the stroma can pos sibly explain the regression of the myopic shift seen some time after excimer laser treatment.