Seo Kyoung Yul, Yang Hun, Kim Wook Kyum, Nam Sang Min
Department of Ophthalmology, Institute of Vision Research, Eye and Ear Hospital, Severance Hospital, Yonsei University College of Medicine, Seoul, Korea.
SU Yonsei Eye Clinic, Seoul, Korea.
PLoS One. 2017 Apr 12;12(4):e0175268. doi: 10.1371/journal.pone.0175268. eCollection 2017.
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.
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.
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.
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.
使用Pentacam眼前节分析系统测量的4mm角膜顶点区域总角膜屈光性散光（TCRP4astig）和角膜曲率计测量的散光（Kastig），计算准分子激光角膜切削术或准分子原位角膜磨镶术后的实际角膜散光。
通过查阅病历招募了术后6个月以上的56例无并发症的眼睛。手术前后使用Pentacam眼前节分析系统和自动角膜曲率计测量各种角膜散光。排除3只眼，最终纳入38例顺规散光（WTR）受试者的53只眼。使用极坐标值分析研究散光情况。将TCRP4astig设定为实际散光时，使用双变量分析评估Kastig的算术或系数调整的效果。
Pentacam眼前节分析系统模拟角膜曲率计散光（SimKastig）与Kastig之间的差异与TCRP4astig和Kastig之间的差异密切相关。手术前后TCRP4astig与Kastig在大小而非子午线上存在差异；术前差异仅归因于后角膜；然而，术后差异在前部和后部均有观察到。对于算术调整，分别从Kastig的术前和术后大小中减去0.28D和0.27D。对于系数调整，Kastig的术前和术后大小分别乘以0.80和0.66。通过算术或系数调整，在95%的病例中，TCRP4astig与调整后的Kastig之间的差异在大小上小于0.75D。
在WTR病例的近视角膜屈光手术后，Kastig成功调整为TCPR4astig。对于直接使用TCRP4astig，SimKastig和Kastig应匹配。
