Quantitative histological studies of primate corneas after excimer laser photorefractive keratectomy
R. W. Beuerman, M. B. McDonald, R. S. Shofner, C. R. Munnerlyn, T. N. Clapham, B. Salmeron and H. E. Kaufman
LSU Eye Center, Louisiana State University Medical Center School of Medicine, New Orleans.
OBJECTIVE: To evaluate histological changes in the primate cornea after
excimer laser photorefractive keratectomy (PRK) and to correlate them with
clinical observations. METHODS: Sixteen African green monkey (Cercopithecus
aethiops sabaeus) corneas were examined by light and transmission electron
microscopy 6 weeks to 18 months after 1.5- or 3-diopter PRK. RESULTS: All
specimens had a smooth stromal surface surrounded by a smooth, centrally
tapered Bowman's layer. Epithelial thickness appeared to peak 12 months
after PRK. The trend was for the epithelium to be thickest in the
central-treated area; this phenomenon was more obvious in the
3-diopter-treated corneas. The numbers of activated keratocytes beneath the
treated zone peaked at 4 months and decreased thereafter, while the numbers
in the untreated areas decreased in the first 2 months after surgery,
increased by 4 months, and did not change thereafter. Regenerated basal
lamina averaged 86% intact over ablated areas; thickness was normal and no
duplications were seen. Overall, the density of hemidesmosomes was
significantly less in ablated areas compared with unablated areas.
CONCLUSIONS: These findings support the relationship between clinical
observations of corneal haze after PRK, reestablishment of the epithelial
cell layer, and the potential for stromal remodeling by active fibroblastic
keratocytes beneath the ablation zone. Overall, quantification of several
morphological parameters indicated that the values for the treated zone
tended, with time, to approach those of the untreated cornea after PRK.
