Rigid contact lens fitting based on keratometry readings in keratoconus patients: predicting formula
AIM: To find a simple mathematical correlation between the lens base curve (BC) and keratometry findings (Krf). METHODS: This retrospective study included 350 patients (400 keratoconic eyes) previously fit with rigid contact lenses at an academic eye center over a five years period. The patients were classified into five groups based on the keratometry findings [Krf < 7; Krf: 7-8; Krf > 8; Krf - Krs (difference between two keratometry; flat and steep) = 0.3-0.6; Krf- Krs > 0.6mm] as groups 1 to 5, respectively. Multivariate linear regression and Munro's correlation coefficient were employed to defer the formulas. RESULTS: A linear correlation could be found in all groups except for patients in group 3. For group 1, BC = 0.211 × Krf+ 5.904. For group 2, BC=0.456 × Krf+ 4.160. For group 4, BC = 0.321 × Krf + 5.219. For group 5, BC = 0.337 × Krf + 5.090. CONCLUSION: The development of new formulas for RGP fitting enables ophthalmologists to work with confidence and prevents unnecessary and frequent lens trials. The customary lens fitting methods are needed to be replaced by new formulas, which help to save time and costs.