Astigmatic vector analysis after combined surgery for forme fruste keratoconus.

Purpose: The Alpins vector analysis approach was used to assess astigmatic changes in eyes with forme fruste keratoconus following combination treatment with photorefractive keratectomy (PRK) and corneal collagen crosslinking (CXL).

Methods: This retrospective study was performed in 27 eyes from 20 patients with forme fruste keratoconus undergoing treatment with a combination of PRK, followed immediately by corneal collagen CXL. Spherical error, corneal astigmatism, and manifest astigmatism were assessed preoperatively and at 12 months postoperatively. Scheimpflug imaging was used to determine the thinnest corneal thickness, maximum keratometry (Kmax), steep keratometry (K2), and flat keratometry (K1). Alpins vector analysis was used to evaluate the corneal and refractive astigmatism vectors.

Results: The patients ranged in age from 18 to 35 years, with a mean of 22.00 ± 1.16 years. Unilateral surgery was performed in 7 patients, whereas 13 patients underwent bilateral surgery. After surgery, logMAR corrected distance visual acuity improved from 0.22 ± 0.04 to 0.06 ± 0.01 (p < 0.001). On examination of corneal astigmatism, the difference vector (DV) mean was 0.49 diopters (D) at axis 13°, the arithmetic mean was 0.96 D, and the correction index (CI) geometric mean was 0.64. On examination of manifest or refractive astigmatism, the DV mean was 0.10 D at axis 16°, the arithmetic mean was 0.63 D, and the geometric mean CI was 0.89.

Conclusion: Patients with forme fruste keratoconus with sufficient corneal thickness may benefit from a combination of surface ablation and crosslinking surgery. Astigmatic changes induced by this treatment can be examined more objectively using Alpins vector analysis.