'Haze' in photorefractive keratectomy: Its origins and consequences

A marginal loss of corneal transparency or 'haze' is a phenomenon experienced after photorefractive keratectomy using excimer lasers (193 nm). In this study, the authors present a review of the current literature relating to this phenomenon and illustrate this with an example of pathology from a two-week postoperative human eye. They also report the functional implications of postoperative changes in corneal transparency using psychophysical tests measuring visual acuity at different contrast levels (100, 20 and 5%). The data were collected from 103 patients at various postoperative intervals with a maximum follow-up time of one year. At 100% contrast, the authors found only slight disturbances in the first six to eight weeks postoperatively. At 20% contrast most patients had a decrease of visual acuity in the first six weeks but all returned to the normal range by 14 weeks postoperatively. At the 5% level, all patients showed significant disturbances in the first 12 to 14 postoperative weeks, but again most were back in the normal range after this period. However, some patients showed a second wave of decrease of visual performance at the low contrast level commencing at four months, peaking at nine months, and thereafter again regressing to the normal preoperative level. This second wave of visual disturbance may correlate with cellular responses subsequent to cessation of steroid therapy at three months.