A comparative study of masking fluids for excimer laser phototherapeutic keratectomy.

Several fluids of different viscosity were used to mask deeper tissues while exposing protruding irregularities during therapeutic keratectomy of an irregular anterior corneal surface with the 193-nm argon fluoride excimer laser. A model of an irregular anterior corneal surface was developed in deepithelialized calf eyes using grade 8-0 sandpaper. Therapeutic keratectomy was then performed on 28 eyes at a fluence of 180 mJ/cm2, a repetition rate of 10 Hz, and 500 pulses per eye. Solutions of 0.3% hydroxypropylmethylcellulose 2910 and a 0.1% dextran 70 solution, 1% carboxymethylcellulose sodium solution, or 0.9% saline solution were applied to the corneal surface of 21 eyes. Seven control eyes underwent ablation without the addition of fluid. Scanning electron microscopy demonstrated that corneas treated with dextran 70 had the least surface irregularity, and those treated with carboxymethylcellulose or saline solution had intermediate surface irregularity. Corneas that were ablated without additional fluid had the greatest surface irregularity. The application of a moderately viscous solution during therapeutic excimer laser keratectomy enhances the smoothing effect of surface ablation.