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Calculations of actual corneal astigmatism using total corneal refractive power before and after myopic keratorefractive surgery

Authors
 Kyoung Yul Seo  ;  Hun Yang  ;  Wook Kyum Kim  ;  Sang Min Nam 
Citation
 PLOS ONE, Vol.12(4) : e0175268, 2017 
Journal Title
PLOS ONE
Issue Date
2017
MeSH
Adult ; Astigmatism/diagnosis* ; Astigmatism/surgery* ; Cornea/pathology* ; Cornea/surgery* ; Female ; Humans ; Keratomileusis, Laser In Situ ; Lasers, Excimer ; Male ; Myopia/diagnosis ; Myopia/surgery ; Photorefractive Keratectomy ; Postoperative Period ; Preoperative Period ; Refraction, Ocular ; Young Adult
Abstract
PURPOSE: To calculate actual corneal astigmatism using the total corneal refractive astigmatism for the 4-mm apex zone of the Pentacam (TCRP4astig) and keratometric astigmatism (Kastig) before and after photorefractive keratectomy or laser in situ keratomileusis.

METHODS: Uncomplicated 56 eyes after more than 6 months from the surgery were recruited by chart review. Various corneal astigmatisms were measured using the Pentacam and autokeratometer before and after surgery. Three eyes were excluded and 53 eyes of 38 subjects with with-the-rule astigmatism (WTR) were finally included. The astigmatisms were investigated using polar value analysis. When TCRP4astig was set as an actual astigmatism, the efficacy of arithmetic or coefficient adjustment of Kastig was evaluated using bivariate analysis.

RESULTS: The difference between the simulated keratometer astigmatism of the Pentacam (SimKastig) and Kastig was strongly correlated with the difference between TCRP4astig and Kastig. TCRP4astig was different from Kastig in magnitude rather than meridian before and after surgery; the preoperative difference was due to the posterior cornea only; however, the postoperative difference was observed in both anterior and posterior parts. For arithmetic adjustment, 0.28 D and 0.27 D were subtracted from the preoperative and postoperative magnitudes of Kastig, respectively. For coefficient adjustment, the preoperative and postoperative magnitudes of Kastig were multiplied by 0.80 and 0.66, respectively. By arithmetic or coefficient adjustment, the difference between TCRP4astig and adjusted Kastig would be less than 0.75 D in magnitude for 95% of cases.

CONCLUSIONS: Kastig was successfully adjusted to TCPR4astig before and after myopic keratorefractive surgery in cases of WTR. For use of TCRP4astig directly, SimKastig and Kastig should be matched.
Files in This Item:
T201701383.pdf Download
DOI
10.1371/journal.pone.0175268
Appears in Collections:
1. College of Medicine (의과대학) > Dept. of Ophthalmology (안과학교실) > 1. Journal Papers
Yonsei Authors
Seo, Kyoung Yul(서경률) ORCID logo https://orcid.org/0000-0002-9855-1980
URI
https://ir.ymlib.yonsei.ac.kr/handle/22282913/154405
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