The effects of fixation stability, corneal density, and epithelial hyperplasia on the efficacy of astigmatism correction by transepithelial photorefractive keratectomy.

BACKGROUND

Transepithelial photorefractive keratectomy (transPRK) can be safely and predictably performed to correct low-to-high astigmatism. This study explored the effects of fixation stability, corneal density (CD), ocular residual astigmatism (ORA), and the surgically-induced change in the epithelial thickness (ΔET) on the efficacy of astigmatism correction by transPRK.

METHODS

Eighty-three consecutive patients who underwent transPRK to correct myopia and myopic astigmatism were divided into two groups according to refractive astigmatism [high refractive astigmatism (RA) group: ≥ 2.0 D, n = 31; low RA group: < 2.0 D, n = 52]. Fixation stability was evaluated by measuring the lateral movement of the pupil center on the eye tracker images. The CD was measured using a Pentacam Scheimpflug imaging system, epithelial thickness mapping was performed using optical coherence tomography, and the ORA was determined using vector analysis. Multiple linear regression analyses were performed to identify factors associated with the correction index (CI) and angle of error (AOE).

RESULTS

At 6 months postoperatively, the RA was higher in the high RA group (- 0.66 ± 0.44 D) than in the low RA group (- 0.29 ± 0.29 D, P < 0.001), whereas no significant differences were found in CI or AOE between two groups. Multiple linear regression analyses showed that for the low RA group, preoperative anterior CD of the central 2 mm (CD, β =  - 0.482, P = 0.011) and ΔET (β = 0.295, P = 0.041), were associated with CI, whereas the vector length of the pupil center shift (PCVL, β =  - 0.404, P = 0.005) and ΔET (β =  - 0.293, P = 0.036) were associated with AOE. For the high RA group, ΔET (β = 0.519, P = 0.038) was associated with CI, whereas static cyclotorsion (β =  - 0.493, P = 0.040) was associated with AOE. No significant associations were found between ORA and CI or AOE.

CONCLUSIONS

Postoperative changes in epithelial thickness were associated with the efficacy of transPRK in both the low and high RA groups, whereas the pupil center shift and anterior CD were associated with the efficacy of transPRK in the low RA group.