[Corneal opacity after photorefractive keratectomy with an excimer laser. Cause, objective measurement and functional...

A marginal loss of corneal transparency or 'haze' is a phenomenon commonly experienced after photorefractive keratectomy using excimer lasers (193 nm). The putative causes of this phenomenon are the presence in the surgical site of (1) activated keratocytes, (2) vacuoles and (3) newly synthesized collagen. A CCD camera device was employed in order to measure the corneal transparency. Both scattered and reflected light in the slit image of patients' corneas was measured using polarizing filters and image analysis software. We observed an increase in reflected and scattered light until the second postoperative month, followed by a subsequent decline. However, the combined signal generated by reflected and scattered light showed a second increase at 4 months postoperatively, whereas the signal generated by scattered light alone stayed at lower levels. These objective measures of changes in corneal transparency were correlated with changes in visual performance using psychophysical tests measuring visual acuity at different contrast levels (100%, 20% and 5%). In all patients we observed a good correlation between the signal generated by scattered light alone and the reduction in the 5% contrast visual acuity performance. These disturbances in low contrast visual performance were only significant during the first 3-4 months postoperatively, and thereafter most patients returned to their preoperative value. Eighteen percent of our patients discontinued topical steroids postoperatively. No difference in corneal transparency was observed.