Introducing a new ratio useful in the estimation of preoperative corneal power in patients with myopic LASIK based on postoperative corneal data.
OBJECTIVE
The aim of this study was to establish a new constant ratio for the calculation of preoperative total corneal power using postoperative corneal data alone in patients after laser in situ keratomileusis (LASIK).


METHODS
Preoperative anterior and posterior corneal radii from 192 pre-LASIK eyes were analyzed to derive a constant ratio in the first part of the study. In the second part of the study, with a set of post-LASIK patients (98 eyes), this ratio was used to estimate preoperative total corneal power. This estimated total corneal power was compared with the true value obtained from direct preoperative measurement.


RESULTS
The ratio (R(roc)) between the preoperative anterior central 10-mm corneal curvature and the posterior peripheral 7- to 10-mm corneal curvature was 1.166 +/- 0.049. Estimated mean preoperative total corneal power was 43.42 +/- 2.21 D, whereas the true preoperative mean keratometric value (SimK) was 43.40 +/- 2.64 D. The mean difference was 0.02 +/- 2.65 D (P = 0.942).


CONCLUSIONS
The pre-LASIK corneal power can be estimated using post-LASIK data together with R(roc). This will be useful in post-LASIK patients requiring cataract surgery but without the availability of pre-LASIK corneal data for the estimation of the preoperative keratometric power when the double-K technique was used to calculate the intraocular lens power.
Cheng
Arthur C K
AC
Department of Ophthalmology, Guy Hugh Chan Refractive Surgery Center, Hong Kong Sanatorium & Hospital, Hong Kong. artcheng@netvigator.com
Ho
Thomas
T
Lau
Silvania
S
Lam
Dennis S C
DS
D000328:Adult; D003315:Cornea / Q000473:pathology* / Q000503:physiopathology*; D019781:Corneal Topography; D006801:Humans; D020731:Keratomileusis, Laser In Situ; D008954:Models, Biological; D009216:Myopia / Q000473:pathology / Q000503:physiopathology / Q000601:surgery*; D011184:Postoperative Period