Introduction: The purpose of this study was to derive a modified equation for contact lens method (CLM) in
calculating post myopic laser refractive surgery corneal power. Methods: A total of 93 subjects who
underwent myopic laser refractive surgery at IIUM Eye Specialist Clinic were recruited. The accuracy of
postoperative corneal power using the standard CLM and newly-derived contact lens modified method
(CLMmod) were compared to the standard comparison method ; the historical method (HM). The CLMmod
equation was derived by adjusting postoperative corneal power of CLM according to amount of refractive
change. Results: The mean postoperative corneal power using standard CLM was significantly higher than
HM (mean difference: -0.24 D, p < 0.001). Fifty seven percent (n = 53 eyes) of the standard CLM results were
within ±0.50 D of HM results. The difference between postoperative corneal power using standard CLM and
HM increased significantly with the amount of refractive change (r = 0.835; p < 0.001). The mean
postoperative corneal power of CLMmod showed that there was no statistical significant difference compared
to the HM results (mean difference: 0.00 D, p= 0.964). Eighty eight percent (n = 82 eyes) of the CLMmod
results were within ±0.50 D of HM results with improvement of 31% from the standard CLM results.
Conclusion: The CLMmod equation provides more accurate calculation in determining post myopic laser
refractive surgery corneal power. In near future, this modified equation can be used as an alternative
equation to calculate postoperative corneal power when the preoperative data is unavailable.
Introduction: The purpose of this study was to evaluate inter-session repeatability, inter-examiner
reproducibility and inter-device agreement of corneal power measurements from manual keratometer,
autokeratometer, topographer, Pentacam high resolution and IOLMaster. Methods: Two sets of mean
corneal power measurements (n=40) were compared for inter-session repeatability and inter-examiner
reproducibility in each instrument. Repeatability and reproducibility were evaluated by within-subject
standard deviation (Sw), coefficient of variation (COV) and intraclass correlation coefficient (ICC). A oneway
repeated measures analysis of variance was conducted to compare differences in the corneal power
between each instrument pair. The Bland and Altman analysis and Pearson’s correlation were employed to
assess agreement and determine strength of relationship between measurements. Results: There were no
significant differences in mean corneal power measurements between 2 different visits (p > 0.05). The Sw
and COV values between 2 visits were lower than 0.09 D and 0.20 % respectively. The ICCs were stronger
than 0.99 in all instruments. For reproducibility of each instrument, differences of the measurements
between 2 different examiners were also insignificant (p > 0.05). The Sw and COV values between 2
examiners were lower than 0.11 D and 0.23 % respectively. The ICCs were 0.99 and above in all instruments.
The 95% limit of agreement between instruments ranged from -0.29 to 1.13 D and the r-values were stronger
than 0.84. Conclusion: The corneal power measurements using these 5 instruments were repeatable and
reproducible. These instruments can also be used interchangeably, however the topographer should be used
with caution.