Optical Evaluation of Intracorneal Ring Segment Surgery in Keratoconus

Abstract

Purpose: The purpose of this study was to assess the impact of different intracorneal ring segments (ICRS) combinations on corneal morphology and visual performance on patients with keratoconus.

Methods: A total of 124 eyes from 96 patients who underwent ICRS surgery were analyzed and classified into 7 groups based on ICRS disposition and the diameter of the surgical zone (5- and 6-mm). Pre- and postoperative complete ophthalmological examinationswere conducted. Corneal geometry, volume, and symmetrywere studied. Zernike polynomials were used to build a virtual ray-tracing model to evaluate optical aberrations and the Visual Strehl (VS).

Results: ICRS induced significant flattening across the cornea, being more pronounced on the anterior (+0.38 mm, P < 0.001) than on the posterior (+0.15 mm, P < 0.001) corneal radius. Asphericity experienced a larger change for a 6-mm surgical zone diameter (from -1.23 +/- 1.1 to -1.86 +/- 1.2, P < 0.001) than for a 5-mm zone (from -1.99 +/- 1.1 to -2.10 +/- 1.5, P = 0.536). Mean astigmatism was reduced by 2.05 D (P < 0.001). Combination four was the most effective in reducing astigmatism. Coma decreased by 30% on average and combination one produced an average reduction by 51% (P< 0.05). Patients experienced significant improvement in visual performance, best corrected visual acuity increased from 0.57 +/- 0.21 to 0.69 +/- 0.21 and VS changed from 0.049 +/- 0.02 to 0.065 +/- 0.041.

Conclusions: ICRS combinations implanted within 5mmdiameter zone aremore effective in flattening the cornea, whereas those implanted on 6 mm diameter are as effective in reducing astigmatism and are a good choice if the asymmetry and the intended flattening are smaller. Combinations with asymmetrical implants are the best option to regularize corneal surface.

Translational Relevance: This study uses methods and metrics of optical research applied to daily clinical practice.