Excimer Laser Photore fractive Keratectomy[PRK]for Low and Mode rate Myopia using VIXS STAR Excimer Laser System

Choi, Nam Young; Hahn, Tae Won

Abstract

Excimer laser photorefractive keratectomy[PRK]for low and moderate myopia[-2D~-6D]has been performed recently as a predictable and effective method for correcting myopia. We analyzed refractive change, postoperative visual acuity, and postoperative complications of 168 eyes[104patients]for 6 months and 33 eyes among them for 1 year after excimer PRK using VISX STAR excimer laser system from February 1997 to February 1998.Among the patients male were 8 patients, and female were 96patients.The myopic range was from-2.00 diopters[D]to -6.00D with astigmatism less than 3D.Uncorrected visual acuity of 4/5 or better was achieved in 91%postoperatively ;corrected visual acuity of 4/5 or better in 97%postoperatively.Eighty-eight eyes received spherical photorefractive keratectomy[PRK]to correct myopia ;80 eyes received photoastigmatic refractive keratectomy[PARK]to correct both myopia and astigmatism.In spherical PRK group the mean spherical equivalent was -4.67 +/-1.69D preopratively, 0.11 +/-0.93D 6 months after PRK, -0.31 +/-0.80D 1 year after PRK ;in photoastigmatic refractive keratectomy[PARK]group these figures were -4 .9 4 +/-1.42D, -0.37 +/-0.81D, -0.62 +/-0.78D, respectively.In the PARK group13.8%were undercorrected but in the spherical PRK group only 5.7% were undercorrected.So we report the ndercorrection rate of PARK group was relatively higher than that of spherical PRK group, but statisticallyinsignificant[Chi-Square test, p=0.075, but Relative Risk=2.65].We evaluated the surgically induced astigmatism by using both Jaffe and Clayman's vector-corrected methods.In the spherical PRK group the mean surgically induced astigmatism[SIA]was 0.83 +/-0.49D 6 months after PRK, 0.72 +/-0.47D 1 year after PRK ;in the PARK group these figures were 1.36 +/-0.71D, 1.29 +/-0.72D, respectively.The differences between the two groups were statistically significant[unpaired T-test.p=0.001].Astigmatism greater than 0.25D was reduced in 23.86%and induced in 55.68%of eyes that received spherical PRK and astigmatism greater than 0.25D was reduced in 80%and induced in 3.75%of eyes that received PARK.There were several complications including transient punctate keratopathies[6 eyes, 3.5%], undercorrection [-1D][16 eyes, 9.5%], and overcorrection[-1D][28 eyes, 16.67%].The decrease in the best corrected visual acuity in 10 eyes[5.9%] may be the result of a grade 2 or more corneal haze[15 eyes]and central island[2 eyes].