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.

Determination of Corneal Power After Refractive Surgery with Excimer Laser: A Concise Review

“…In a recent study, Baradaran-Rafii et al determined that the corneal power obtained by applying an adjusted formula to the values of the Effective Refractive Power (EffRP) map with the EyeSys 2000® topographer (Eyesys Vision, Houston, TX 77060, United States) was closer than manual keratometry, and information from another 3 devices, to the power determined by the clinical history method [13]. However, within this adjustment, the refractive change caused by the procedure was included as a factor.…”

“…However, within this adjustment, the refractive change caused by the procedure was included as a factor. Therefore, the practical usefulness of this "Adjusted Effective Refractive Power" is very limited, since the vast majority of patients will lack preoperative information, as previously mentioned [13].…”