The Impact of Different Optical Zone Diameter on Corneal Astigmatism Correction Using Femtosecond Laser Corneal Relaxing Incisions: 8 mm vs 9 mm

Abstract

Purpose: To compare the impact of 8 mm versus 9 mm optical zone (OZ) diameters on corneal astigmatism correction and to evaluate the impact of incision depth percentage after femtosecond laser corneal relaxing incisions (CRIs) combined with cataract surgery.

Methods: Thirty-nine eyes from 39 patients were enrolled and randomly assigned to two groups based on the OZ diameter: 8 mm and 9 mm. Corneal astigmatism and CRI depth were measured using Pentacam and anterior segment optical coherence tomography. Vector analysis was performed using Alpins method.

Results: In the 8 mm group, postoperative corneal astigmatism was reduced by 0.77 ± 0.61 diopters (D), significantly greater than the reduction of 0.42 ± 0.40 D in the 9 mm group (p < 0.05). The 8 mm group exhibited greater surgically induced astigmatism (SIA), net corneal changes, and a smaller angle of error (AE) (p < 0.05). At 3 months postsurgery, the correction index (CI) values were 0.84 ± 0.39 for the 8 mm group, exceeding the 0.52 ± 0.32 observed in the 9 mm group (p < 0.05). The mean incision depth percentage was significantly higher in the 9 mm group (79.30 ± 10.76%) compared to the 8 mm group (72.58 ± 8.73%) (p < 0.05). In the 8 mm group, CI values closer to 1.00 were associated with lower percentages of incision depth.

Conclusions: CRIs with an 8 mm OZ diameter demonstrated superior efficacy in correcting corneal astigmatism with shallower incision depths compared to those with a 9 mm diameter.

Keywords: Corneal astigmatism correction; femtosecond laser corneal relaxing incisions; incision depth; optical zone diameter.