Visual performance after excimer laser photorefractive keratectomy for high myopia

Abstract

Purpose: To evaluate the efficacy, safety, predictability, and visual performance of excimer laser photorefractive keratectomy (PRK) for myopia greater than -8 diopters (D).

Methods: Fifty-four patients (104 eyes) with myopia from -8D to -13D and cylinder up to -4D received surface ablation technique with the Allegretto wave version 1009-1 excimer laser to correct their refractive error. The patients were examined on days 1, 3, 7, and 14 and 1, 3, 6, and 12 months postoperatively. Visual acuity, manifest refraction, corneal haze, topography, intraocular pressure, contrast sensitivity, and wavefront aberration were evaluated.

Results: Twelve months postoperatively, 95% of eyes were within 1D of the intended correction. In addition, 94% of eyes had attained uncorrected distance visual acuity of 20/25 or better, and 98% of eyes had improved or remained their corrected distance visual acuity. All eyes exhibited barely detectable corneal haze which peaked during the 1^st month with a gradual reduction in the 3^rd month. Ninety-five percent of patients had no or only mild degree of night glare.

Conclusions: Excimer laser PRK is an effective and predictive treatment for high myopia greater than -8D with or without astigmatism up to -4D. The incidence of complication is low. All patients who are candidates for laser in situ keratomileusis can be candidates for surface ablation, especially those with preoperative thinner cornea or higher risk of corneal flap complications.

Keywords: Excimer laser; myopia; photorefractive keratectomy.

Figure 1

(a) The cumulative percentage of preoperative and postoperative uncorrected distance visual acuity. Eyes with target of low myopia or whose preoperative corrected distance visual acuity <20/20 were not included in the postoperative calculation. (b) The change in corrected distance visual acuity after the operation. Most eyes had corrected distance visual acuity equal to or better than preoperative corrected distance visual acuity. Only 1.9% eyes lost two or more lines. (c) The attempted and achieved spherical equivalent. The black line is the slope of attempted versus achieved spherical equivalent for all eyes plotted in Figure 1c. Most eyes had slight tendency to undercorrection. (d) The postoperative spherical equivalent refraction. 91% eyes were within 0.5D and 95% eyes were within 1.0D. (e) The preoperative and postoperative refractive astigmatism. Most eyes had much improvement in refractive astigmatism after the operation. (f) The mean spherical equivalent at the baseline and 1, 3, 6, and 12 months after the surgery. Most eyes reach the stable refraction at the postoperative 1 month. (g) The postoperative contrast sensitivity. The mean contrast sensitivity of 3, 6, 12, and 18 cycles/degree mild decreased at postoperative 12 months with glare test off and on (P = 0.04 and 0.02, respectively)