INFLUENCE OF CORNEAL TOPOGRAPHIC CHARACTERISTICS ON VISUAL ACUITY AFTER LASER CORRECTION IN PATIENTS WITH MYOPIA

Abstract

Purpose – to assess the effect of changes in corneal topographic characteristics changes on functional outcomes after laser correction of myopia.

Material and methods
The study included 54 patients (108 eyes) with moderate to high myopia (≥ 3.25D). Biometric parameters were obtained using Wave light Allegretto Oculyzer (Alcon, Germany). Changes in parameters due to laser correction were determined by calculating the difference between pre-and post-operative values. Visual acuity and corneal keratotopographic characteristics were evaluated before surgery and three months postoperatively. The parameters assessed included central corneal thickness (CT), surface variance index (ISV), vertical asymmetry index (IVA), height asymmetry index (IHA), and height decentration index (IHD).

Patients were divided into two groups based on these indices. The first group included those with values within the normal range, while the second group consisted of individuals with above-normal values. Preoperative and postoperative uncorrected visual acuity was compared between the groups using a two-sample t-test with unequal variances.

Results
Among patients with different corneal thicknesses and topographic indices, visual acuity outcomes did not differ significantly (p ≥ 0.21). However, a statistically significant difference (p = 0.02) was observed in patients with different levels of the IVA index (< 0.28 and > 0.28), where uncorrected visual acuity was 0.062 ± 0.001 and 0.094 ± 0.005, respectively. Groups with normal and pathological topographic indices demonstrated significant differences in visual acuity outcomes.

Conclusion
In patients with myopia, preoperative visual acuity is significantly influenced by vertical corneal asymmetry (IVA < 0.28 and > 0.28, corresponding to uncorrected visual acuity of 0.062 ± 0.001 and 0.094 ± 0.005, respectively). Postoperatively, optimal visual acuity is observed in cases where corneal thickness ranges from 458 to 560 μm, and the indices remain within ISV < 38, IVA < 0.28, and IHA < 19.