The effect of astigmatism axis on visual acuity

Area of Science:

• Ophthalmology
• Refractive Surgery
• Corneal Optics

Background:

• Astigmatism is a common refractive error affecting visual quality.
• Laser refractive surgery aims to correct refractive errors, including astigmatism.
• Understanding the impact of astigmatic axis on visual outcomes is crucial for surgical planning.

Purpose of the Study:

• To investigate the influence of the astigmatic axis on uncorrected distance visual acuity (UDVA) in emmetropic eyes post-laser refractive surgery.
• To compare UDVA across different astigmatic axis groups: with-the-rule (WTR), oblique, and against-the-rule (ATR).

Main Methods:

• Retrospective analysis of 17,416 eyes undergoing laser in situ keratomileusis or photorefractive keratectomy.
• Eyes with a 3-month postoperative spherical equivalent of -0.5 D to 0.5 D were included.
• Eyes were categorized into WTR, oblique, and ATR astigmatic axis groups for UDVA comparison.

Main Results:

• WTR astigmatism eyes (n=10,651) demonstrated significantly better UDVA (logMAR 0.01 ± 0.08) compared to oblique (n=3,141) and ATR (n=3,624) eyes (p<0.001).
• The oblique WTR subgroup showed superior UDVA over the oblique ATR subgroup (p<0.001).
• Astigmatic axis accounted for 15% of the UDVA variance (p=0.04).

Conclusions:

• The astigmatic axis exerts a statistically significant, albeit minor, influence on UDVA in emmetropic eyes.
• With-the-rule astigmatism is associated with better visual outcomes than oblique or against-the-rule astigmatism.
• Surgical correction of astigmatism may benefit from aiming for a WTR outcome.