The study evaluated the ray tracing method [total corneal refractive power (TCRP)] in a Pentacam apparatus (Oculus, Wetzlar, Germany) for postoperative keratometry measurement after myopic photorefractive keratectomy (PRK).
Manifest refraction (MR) and Pentacam analyses were performed preoperatively and at 6 months postoperatively after the PRK (STAR S4 IR CustomVue; Abbott Medical Optics/Visx) in 49 right eyes from 49 patients (age, 25.42 ± 3.51 years). Postoperative corneal power was calculated using the clinical history method (CHM) and compared with postoperatively measured simulated keratometry (simK), true net power (TNP) at 3 mm, and pupil-centered TCRP at the center, 1, 3, and 4 mm (TCRP0, TCRP1, TCRP3, and TCRP4). Vertex-distance-adjusted refractive change (delta-MR) at the corneal plane was also compared with various keratometric changes (delta-K).
Postoperative TCRP0, TCRP1, TCRP3, and TCRP4 showed no significant difference compared with that of the CHM. Postoperative simK was significantly higher than that of the CHM, whereas the TNP was significantly lower compared with that of the CHM. The delta-Ks measured by simK, TNP, and TCRPs were significantly smaller than delta-MR, and delta-TCRP4 showed the least difference [mean ± SD, 0.28 ± 0.55 diopters (D)] with delta-MR. The 95% limit of agreement between delta-MR and delta-TCRP4 was −0.85 to 1.31 D. The difference between delta-TCRP4 and delta-MR was <0.5 D in 55.1% and <1.0 D in 87.8% of the eyes studied.
Although postoperative TCRPs showed no significant difference with CHM, delta-MR was still underestimated after myopic PRK.
*Department of Ophthalmology, Dongguk University, Ilsan Hospital, Goyang, South Korea; and
†Department of Ophthalmology and Visual Sciences, Montefiore Medical Center, Albert Einstein College of Medicine, Bronx, NY.
Reprints: Choul Yong Park, Department of Ophthalmology, Dongguk University, Ilsan Hospital, 814, Siksadong, Ilsan-dong-gu, Goyang, Kyunggi do 410-773, South Korea (e-mail: firstname.lastname@example.org).
Supported in part by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (NRF 2010–0002532) (C.Y.P.), and an unrestricted core grant from the Research to Prevent Blindness (R.S.C.).
The other authors have no funding or conflicts of interest to disclose.
Received August 17, 2013
Accepted October 11, 2013