Accuracy of different topographic instruments in calculating corneal power after myopic photorefractive keratectomy

Abstract

Purpose: To compare the corneal power measurements obtained using different topographic instruments after myopic photorefractive keratectomy (PRK). Methods: Patients with myopia who were candidates for corneal refractive surgery were sequentially included. Pre-PRK and six months post-PRK corneal powers were measured using Javal manual keratometer, Orbscan II, Galilei, Tomey TMS4, and EyeSys 2000 topographers. Measured values were compared with those obtained using the clinical history method (cHM). Results: This study included 66 eyes of 33 patients. The lowest keratometric measurements were obtained using the Galilei topographer (42.98 ± 1.69 diopters, D) and the highest measurements were obtained using the Javal manual keratometer (43.96 ± 1.54 D) preoperatively. The same order was observed postoperatively. Effective refractive power (EffRP) measured using EyeSys was most similar to the values obtained using cHM (Icc, intraclass correlation coefficient = 0.951), followed by the total corneal power measured using the Galilei system (Icc = 0.943). The values obtained using the adjusted EffRP formula (EffRP – 0.015*Δ Refraction – 0.05) were more consistent with the values obtained using cHM (Icc = 0.954) compared to those obtained with the adjusted average central corneal power formula measured using the Tomey system (Icc = 0.919). Conclusion: Post-PRK corneal powers measured using the adjusted EffRP formula were the most similar to values obtained using cHM.

Keywords

• Corneal Topography; EyeSys Corneal Analysis System; Galilei Dual Scheimpflug Analyzer; Photorefractive Keratectomy