Sixteen eyes of eight rabbits were randomised to either mitomycin C or Balanced Salt Solution (BSS) application after photorefractive keratectomy (PRK). Regular examinations of wound healing and haze were performed with the slit lamp. The animals were killed between 1 and 26 weeks after treatment, and the corneas examined by light and electron microscopy. While the grade of haze showed no relevant differences between the two groups, scar tissue was found histologically in the mitomycin group in only 1 of 8 corneas compared with 5 of 8 in the BSS group. A marked reduction in keratocytes in all mitomycin-treated corneas and a normal density of keratocytes in the BSS group was observed. Mitomycin reduced the number of keratocytes in the treated corneas, leading to less scar formation but not to a reduction in haze. Since no morphological correlate has been found, haze remains unexplained in the mitomycin-treated corneas.
Transverse keratectomies with the Excimer laser were performed on seven eyes of 4 patients with a mean, naturally occurring astigmatism of 5.32D (SD l.O), range 4.25 to 7.OD. One month later mean astigmatism was 3.46D (SD 1.35), 3 months later 3.8D (SD 1.35), rising to 4.3D (SD 1.6) after 6 months, and to 4.68 (SD 1.4) after 1 year. The refractive cylinder was reduced from a mean of 5.8D to 4.5D and the mean uncorrected visual acuity rose from 0.16 to 0.3. No serious complications occurred, and uncorrected visual acuity could be improved slightly. Excimer laser transverse keratectomy cannot be recommended as a good method to treat high degrees of naturally occurring astigmatism.
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