Comparative Efficacy Of Three Surgical Planning Strategies Using Intracorneal Ring Segments In Snowman Phenotype Keratoconus

To compare the efficacy of three intracorneal ring segment (ICRS) implantation strategies in patients with snowman phenotype keratoconus, assessing improvements in visual acuity, keratometric flattening, and refractive, topographic, and aberrometric changes. Both intra-group and inter-group differences were analyzed to determine the functional, refractive, and optical performance of each surgical approach.

Cornea and Keratoconus Unit, Department of Ophthalmology, Hospital Universitario Virgen del Rocío, Seville, Spain.

Retrospective comparative study including 30 patients with snowman phenotype keratoconus, defined by low asphericity, irregular topographic astigmatism, and a 30°–60° divergence between topographic and comatic axes. Patients were allocated into three groups according to surgical planning: Group 1, two asymmetric segments; Group 2, one symmetric segment; Group 3, two symmetric segments. Evaluated variables included visual acuity (VA), spherical equivalent (SE), K1, K2, mean keratometry (Km), maximum keratometry (Kmax), astigmatism, asphericity (Q), spherical aberration (Z4⁰), and coma. Measurements were recorded preoperatively and at 1 and 4 months postoperatively. Intra-group and inter-group analyses were performed.

Visual acuity improved in all groups, reaching significance only in the single symmetric segment group at 4 months (p=0.011). Spherical equivalent decreased without significant differences. Significant keratometric flattening (K1, K2, Km) occurred in the two asymmetric and one symmetric groups, and K2 in the two symmetric group (p<0.001). Kmax decreased in both double-segment groups. Astigmatism decreased in double-segment groups. Asphericity shifted toward less prolate values in all groups. The single symmetric segment induced greater coma reduction and showed differences in spherical aberration versus two symmetric segments.

In snowman phenotype keratoconus, the number and design of intracorneal ring segments differentially influence visual and optical outcomes. When high coma predominates, implantation of a single symmetric segment provides the greatest visual acuity gain and most consistent coma reduction, suggesting superior optical regularization for this morphological pattern. Conversely, in snowman phenotypes with predominant high astigmatism, double-segment implantation, particularly asymmetric segments, induces greater keratometric flattening and astigmatism reduction. ICRS selection should be guided not only by corneal topography but also by the aberrometric profile of the snowman phenotype.