Changes in Corneal Dynamics and Effective Optical Zone After Transepithelial Photorefractive Keratectomy for Myopia

Abstract

Objectives: The objective of this study was to analyze the changes in the effective optical zones (EOZ) using topographic techniques on the tangential curvature difference map at post-operative 1-year following transepithelial photorefractive keratectomy (T-PRK) and to identify parameters linked to the EOZ alterations.

Methods: The study comprised 55 eyes of 55 myopic patients who underwent T-PRK. EOZs were measured using the tangential curvature difference map of the Scheimpflug tomography system. Correlations between the EOZ alterations and relevant parameters were assessed.

Results: The EOZ was significantly lower than the programmed optical zone (p<0.001). The decrease in the EOZ was significantly relevant to the decrease in mean keratometry (p=0.01, B/95% confidence interval [CI]: 0.139/0.033 and 0.244, standardized Beta: 0.346) and the increase in maximum keratometry (p=0.003, B/95% CI: 0.072/0.026 and 0.118, standardized Beta: 0.406).

Conclusion: The EOZ decreased in the 1^st year after T-PRK in eyes with myopia. The decrease in the EOZ was correlated positively with the decrease in mean and maximum keratometry. T-PRK may be an effective and safe surgery for the correction of mild-to-moderate myopia.

Keywords: Effective optical zone; high-order aberrations; transepithelial photorefractive keratectomy.

Figure 1

An example of the tangential anterior curvature difference map. When the cursor is at 0 D on 30° (white arrow in a), the r value expressed in the upper left corner of the map is 3.04 mm, which is used to calculate the optical zone at 30–210 corneal meridian. When the cursor is at 0 D on 60° (white arrow in b), the r value expressed in the upper left corner of the map is 3.06 mm, which is used to calculate the optical zone at 60–240 corneal meridian.