To assess the validity and accuracy of a proposed formula for keratometry (K) readings after laser in situ keratomileusis (LASIK).
The Eye Center and the Eye Foundation for Research, Riyadh, Saudi Arabia.
This studied comprised 34 eyes that had LASIK surgery. Refraction and an automated K-reading (auto-K) were performed preoperatively. Refraction, auto-K, and K-reading assessment by the clinical history method and the proposed formula were performed 4 to 12 weeks postoperatively. The proposed formula is Kpostop = Kpreop – [(Nc – 1) × (Ra-postop – Ra-preop)/(Ra-postop × Ra-preop)], where Kpostop is the K-reading after LASIK, Kpreop is the K-reading before LASIK, Nc is the index of refraction of the cornea (1.376), Ra-postop is the radius of curvature of the anterior corneal surface after LASIK, and Ra-preop is the radius of curvature of the anterior corneal surface before LASIK.
Twenty patients (10 men, 10 women) were included in the study. The mean age of the patients was 30.58 years ± 17.68 (SD) (range 18 to 44 years). Preoperatively, the mean spherical equivalent (SE) was –4.99 ± 2.82 diopters (D) (range –1.12 to –15.00 D), the mean Ra was 7.76 ± 0.32 mm (range 7.33 to 8.50 mm), and the mean auto-K reading was 43.45 ± 1.73 D (range 39.62 to 46.00 D). Postoperatively, the mean SE was +0.02 ± 0.63 D (range –2.75 to +1.00 D), the mean Ra was 8.63 ± 0.53 mm (range 7.80 to 9.92 mm), and the mean K-reading assessed by auto-K, clinical history method, and the proposed formula was 39.17 ± 2.35 D (range 34.00 to 43.25 D), 38.79 ± 2.52 D (range 33.1 to 42.78 D), and 38.69 ± 2.51 D (range 33.1 to 43.0 D), respectively. The results obtained by the proposed formula were similar to those obtained by the clinical history method (P = .098). Auto-K readings significantly overestimated the K-values (P<.0001) when compared to the proposed formula and clinical history method.
The proposed formula was simple, objective, not dependent on refraction, and as accurate as the clinical history method in determining K-readings after LASIK.