Haze Development After Photorefractive Keratectomy: Mechanical vs. Chemical Epithelial Removal

Abstract

Purpose:: To compare mechanical epithelial debridement and ethanol-assisted epithelial removal with respect to myofibroblast development and haze formation after photorefractive keratectomy.

Methods:: Twelve rabbits had either mechanical or chemical debridement. The opposite eye of each rabbit served as a control. With the animal under anesthesia, an 8 mm optical zone marker was used to delineate the area for epithelial removal. In the mechanical group, the epithelium was scrapped with a blade. In the alcohol group, the barrel of 8 mm optical zone marker was filled with two drops of 20% ethanol. After 30 seconds the ethanol was absorbed using a dry cellulose sponge. The epithelium was removed with a spatula and discarded. A -9.00D PRK (6.5 mm-diameter optical zone) was performed in each eye and the eyelids were closed with a temporary tarsorrhaphy for one week after surgery. The level of haze in each cornea was recorded at four weeks at the slit lamp. The degree of opacification for each cornea was graded 0 through 4+, according to the Fantes scale. Then, rabbits were euthanized and corneoscleral rims removed. Myofibroblast generation was detected with immunocytochemistry for alpha-smooth muscle actin. The number of myofibroblasts per 400X field were counted in 6 random field bisected by the epithelial basement membrane, and the counts averaged for each cornea.

Results:: There was no difference between the two groups in SMA+ cells at 4 weeks after surgery. The mean±standard deviation number of cells per field was 44±2.2 and 47±4.9 in the alcohol and mechanical groups, respectively (p = 0.14). Control group showed 1.33±0.5 cells per field. There was no difference in haze between the mechanical epithelial removal and ethanol epithelial removal groups (mean score of 2.3±0.6 and 1.83±0.4, respectively, p=0.057), although there was a trend towards more haze in the mechanical group. Control group presented grade zero for haze. Mechanical group versus control and ethanol group versus control comparisons were statistically different regarding haze and SMA+ cells (p<0.0001 for all comparisons).

Conclusions:: In this study, there was no difference in clinical haze or myofibroblast generation between mechanical and ethanol epithelial debridement in PRK.

Keywords: refractive surgery: PRK • wound healing • cornea: stroma and keratocytes