Excimer laser smoothing of a reproducible model of anterior corneal surface irregularity

A reproducible model of an irregular corneal surface was developed to test the ability of the excimer laser to treat such surfaces. Using a 193-nm argon fluoride excimer laser set at a fluence of 160 mJ/cm2, repetition rate of 10 Hz, and 185 pulses, fresh de-epithelialized pig eyes underwent phototherapeutic ablations through a piece of stainless steel wire screen that masked the cornea. This yielded an uneven corneal surface in a grid-like pattern, with the peaks 50 microns higher than the troughs. The eyes then underwent further treatment in an attempt to smooth the center of the irregularity. Hydroxypropyl-methylcellulose 0.3% protected the valleys in 12 eyes; 2 eyes were ablated without a protecting fluid. The same laser, at the above noted settings, was used, except that both 2 Hz and 10 Hz frequencies were used. Immediately after treatment, the eyes were processed for scanning electron microscopy. The eyes treated at 2 Hz showed less surface irregularity than did those treated at 10 Hz. The eyes treated without a protecting fluid, regardless of repetition rate, had the greatest irregularities. This model is simple and reproducible, and the authors' results suggest that modifying the repetition rates of the excimer laser can influence its effectiveness in smoothing irregular corneas.