Photorefractive keratectomy to treat myopia and astigmatism after radial keratotomy and penetrating keratoplasty.

Fifteen eyes with an initial myopia between -5.00 diopters (D) and -12.00 D were treated with radial keratotomy (RK) followed by photorefractive keratectomy (PRK) at least 6 months later and observed for 6 months to 24 months. Five eyes that had penetrating keratoplasty (PKP) were treated for residual ametropia by PRK and followed for up to two years. For the RK-treated eyes, mean pre-PRK refraction was -4.00 D sphere and + 1.25 D cylinder, which improved to -0.52 D sphere and + 0.73 D cylinder. Incidence of complications, including corneal haze, was extremely low in both the RK and PKP groups. In summary, PRK is a valuable method for correcting ametropia following RK and PKP, with risks similar to that for eyes having PRK as the initial refractive procedure.

The correction of high myopia using the excimer laser.

OBJECTIVE: To determine the safety and efficacy of excimer laser photoablation as a treatment to correct high myopia that is defined as a spherical equivalent refractive error greater than -8.00 diopters (D). DESIGN: Using a multizone (4.0-, 5.0-, and 6.0-mm) photorefractive keratectomy protocol for correction of high myopia, 23 eyes in 18 patients were treated at one clinical center with an excimer laser (VISX Inc, Santa Clara, Calif). Preoperative spherical equivalent refractions ranged from -8.00 to -19.50 D (mean +/- SD, -11.83 +/- 2.92 D); the mean attempted ablation depth was 93.0 +/- 20.2 microns. RESULTS: At the last postoperative examination (mean +/- SD, 7.5 +/- 3.7 months), the mean +/- SD spherical equivalent refraction was -1.09 +/- 2.08 D, including results from two repeated procedures; visual acuity in 52% of the eyes was 20/40 or better uncorrected; 65% of the eyes improved or did not change best corrected acuity, whereas two eyes lost 2 Snellen lines; 39% of the eyes were +/- 1.00 D; and 65% were +/- 2.00 D of attempted correction. Corneal haze (corneal clarity score of > or = 1.5) was observed in 47% of the eyes at some time postoperatively. CONCLUSIONS: Photorefractive keratectomy for high myopia was found to be not nearly as efficient or predictable as it is for low myopia. A greater incidence of regression of refractive effect and corneal haze were noted in these cases compared with reported studies of low to moderate myopia. A multizone approach to reduce ablation depth during photorefractive keratectomy for myopia that is greater than 8.00 D does not appear to prevent subsequent haze or refractive regression.

Effect of PMMA and silicone lens materials on normal rabbit corneal endothelium: an in vitro study.

Various silicone elastomer intraocular lens materials were compared to PMMA intraocular lens material to ascertain the relative degree of damage caused by each to the rabbit corneal endothelium in vitro. The soft elastomer materials which had been surface treated by electrical molecular rearrangement appeared to cause the least damage and would therefore possibly be most successful for intraocular lens manufacture.