[Changes of higher order aberrations and contrast sensitivity after standard photorefractive keratectomy].

UNLABELLED

The aim of the prospective study was to evaluate higher order aberrations and contrast sensitivity after photorefractive keratectomy (PRK) using the standard photoablation profile.

MATERIALS AND METHODS

The group consisted of 37 patients (69 eyes), the mean age 27.2 +/- 4.5 years, who underwent PRK with target emetropia during the period January 2007 -December 2007. In 19 cases, it was correction of myopia, in 50 cases myopia with astigmatism.The preoperative spherical equivalent was -3.14 +/- 0.95 D. The PRK was performed by means of excimer laser system Technolas 217 (Bausch & Lomb) with the standard phoptoablation profile (PlanoScan 2000), using the 6.5 mm optical zone. The visual acuity, contrast sensitivity (CS; CSV-1000E, VectorVision) under mesopic circumstances and monochromatic aberrations (Zywave, Bausch & Lomb) were evaluated before the surgery, and 1,3, 6, and 12 months thereafter. The pair t-test, Wilcoxon test, and the Mann - Whitney U test (alpha = 0.05) were used for the statistical analysis.

RESULTS

The PRK showed high index of effectiveness and safety (0.98, respectively 1.03 in the first year after the procedure). The contrast sensitivity under mesopic circumstances was not significantly involved after the PRK. The main value of the CS remained during the whole follow-up period within the physiological range in all spatial frequencies. Postoperatively, the part of spherical aberration on the higher order aberrations increased from 13.1% preoperatively to 16.6% one year after the PRK. In one half of the cases, the change of the higher order aberrations was within the range +/- 0.1 microm. In 66% of cases, the change of the spherical aberration was +/- 0.05 microm. The higher order aberrations comparing to the preoperative values decreased or remained unchanged approximately in one third of the cases, and the spherical aberration in one quarter of the cases. There was not established dependence between monochromatic aberrations values and the contrast sensitivity.

CONCLUSION

Although the conventional RPK for low myopia treatment induces higher order aberrations including the spherical aberration, the impact on the contrast sensitivity under mesopic circumstances in our group were not significant. The contrast sensitivity of the most of patients was near the upper limit of the normal range.