Optimizing scleral lens prescriptions: a comparison of algorithmic and conventional refraction and over-refraction in irregular corneas.

Purpose: To compare the accuracy and consistency of subjective refraction using conventional methods versus an algorithm-based approach in patients with primary or secondary corneal irregularities, both with and without scleral lenses (SL).

Methods: Nineteen eyes of ten subjects with irregular corneas underwent non-cycloplegic refraction using (I) retinoscopy followed by conventional subjective refraction (Conventional Refraction) to achieve maximum visual acuity with the maximum positive prescription, and (II) a Hartmann-Shack wavefront aberrometer (WAM 800) followed by an algorithm-based semi-automatic phoropter (Vision-R 800). Refraction measurements were conducted with both techniques, without and with SLs. Outcomes included spherical equivalent (M) and astigmatic components (J0 and J45), and monocular high and low-contrast visual acuity (HCVA and LCVA).

Results: Without SLs, the mean difference in the spherical equivalent between methods was -0.80 ± 1.20 D (p = 0.001). With SLs, the mean difference was -1.04 ± 0.93 D (p = 0.001). Without SLs, monocular HCVA was 0.21 ± 0.20 LogMAR (range: -0.10 to 0.76) and 0.17 ± 0.14 LogMAR (range: -0.02 to 0.60) for Conventional Refraction and V-R 800 (p = 0.162), respectively. Monocular LCVA was 0.59 ± 0.22 LogMAR (range: 0.18 to 0.96) and 0.53 ± 0.20 LogMAR (range: 0.10 to 0.92) for Conventional Refraction and V-R 800, respectively (p = 0.060). With SLs, HCVA was 0.12 ± 0.16 LogMAR (range: -0.12 to 0.50) and 0.09 ± 0.11 LogMAR (range: -0.08 to 0.26) for Conventional Refraction and V-R 800 (p = 0.272), respectively. LCVA was 0.43 ± 0.20 LogMAR (range: 0.06 to 0.90) and 0.47 ± 0.15 LogMAR (range: 0.18 to 0.88), respectively (p = 0.287).

Conclusions: Algorithm-based refraction method provided a more positive spherical equivalent than conventional methods, and both techniques resulted in comparable HCVA and LCVA. Algorithm-based refraction may offer an alternative for over-refraction in patients with irregular corneas during SLs.