New equivalent keratometry reading calculation with a rotating Scheimpflug camera for intraocular lens power calculation after myopic corneal surgery

Abstract

PURPOSE: To calculate the keratometric (K) reading in corneas modified by myopic keratorefractive surgery using the total corneal refractive power (TCRP) of the Pentacam rotating Scheimpflug camera. SETTING: University hospitals and private clinics, South Korea DESIGN: Evaluation of diagnostic test or technology. METHODS: The study comprised healthy eyes, eyes having myopic keratorefractive surgery, and eyes having cataract surgery after myopic keratorefractive surgery. The conversion equation from the TCRP in the central 4.0 mm zone (TCRP4) to a K reading was derived in normal corneas. This equation was rechecked and its application range extended in corneas modified by myopic keratorefractive surgery. Then, the predictability of the TCRP method, combining the K reading derived from the TCRP4 and the Holladay 2 formula, was evaluated in a case series of cataract surgery patients who had previous myopic keratorefractive surgery. RESULTS: The K reading derived from the TCRP4 was obtained by adding 0.7 diopter (D). This conversion factor was applicable after myopic keratorefractive surgery because changes in TCRP4 were equal to changes in refraction in the 4.0 mm zone. The TCRP method predicted intraocular lens power within ± 0.5 D in 83% and within ± 1.0 D in 94% of eyes having cataract surgery after myopic keratorefractive surgery. CONCLUSION: The TCRP4 of the rotating Scheimpflug camera was successfully converted into the equivalent K reading, and the TCRP method showed good predictability in corneas modified by myopic keratorefractive surgery. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.