[The accuracy of posterior curvature method in corneal power calculation after LASIK surgery].
OBJECTIVE
To estimate the accuracy of posterior curvature method in corneal power calculation after LASIK surgery.


METHODS
Corneal power calculation in 11 eyes that underwent Intraocular Lens (IOL) implantation after LASIK surgery (10 cases of Phaco + IOL, 1 case of IOL displacement), all of which used posterior curvature method, was analyzed retrospectively. The differences between post-operative stable refraction and target refraction were calculated, the actual corneal powers were deduced, and the expected refractive errors using other corneal power evaluation methods (auto-keratometry, corneal topography, spherical equivalent method, anterior curvature method, Equivalent K Reading method provided by Pentacam) were analyzed. In addition, refraction of 23 eyes underwent LASIK surgery were done on their 6 months follow-up. The theoretical corneal powers were deduced by subtracting the change of refraction before and after LASIK surgery from the pre-operative corneal powers. The differences between calculated corneal powers using posterior curvature method and the theoretical corneal powers were analyzed, and were compared with other corneal power evaluation methods.


RESULTS
The mean uncorrected post-operative visual acuity of IOL implantation eyes using posterior curvature method was 0.8 +/- 0.2, with mean absolute refractive error from target of (0.36 +/- 0.36) D (-0.63 to +0.85 D). The ratio of eyes with absolute error within 0.25 D, 0.50 D, and 1.00 D was 55%, 73%, and 91% respectively. This result was significantly lower than that of the auto-keratometry (2.50 +/- 1.08) D, corneal topography (1.90 +/- 0.88) D, and those obtained from spherical equivalent method (2.09 +/- 1.62) D (P < 0.01) or anterior curvature method (1.45 +/- 1.10) D (P < 0.05). It also showed less bias (-1.13 to 0.85 D) when compared to the Equivalent K Reading (-1.10 to 1.80 D), but the difference was not significant (P > 0.05). For the 23 post LASIK eyes, the absolute difference between the corrected corneal power using posterior curvature method and theoretical power was (0.67 +/- 0.45) D, also showed least bias compared with other methods.


CONCLUSIONS
It is a practical and accurate way to calculate the corneal power after LASIK surgery using posterior curvature method.
Department of Ophthalmology, Xinhua Hospital Affiliated to Shanghai Jiao Tong University, Shanghai 200092, China. damihyq@hotmail.com
Yi-qian
YQ
Hu
Xiu-li
XL
Zhou
Yin
Y
Li
Cheng-hui
CH
Xu
Lin-lu
LL
Tian
Jie-yu
JY
Feng
Huang
H
Zhu
Yao-hua
YH
Sheng
D003315:Cornea; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D007910:Lenses, Intraocular; D008297:Male; D008875:Middle Aged; D011184:Postoperative Period; D012029:Refraction, Ocular; D012189:Retrospective Studies