Related Experiment Video
Updated: Feb 8, 2026

Eye-tracking to Distinguish Comprehension-based and Oculomotor-based Regressive Eye Movements During Reading
Published on: October 18, 2018
Comparison of Different Corneal Power Readings From Pentacam in Post-laser In Situ Keratomileusis Eyes
Alex L K Ng1, Tommy C Y Chan, Arthur C K Cheng
1Department of Ophthalmology (A.L.K.N.), LKS Faculty of Medicine, The University of Hong Kong, Hong Kong; Department of Ophthalmology and Visual Sciences (T.C.Y.C.), The Chinese University of Hong Kong, Hong Kong; and Department of Ophthalmology (A.C.K.C.), Hong Kong Sanatorium and Hospital, Hong Kong.
Objectives:
To compare the various Pentacam-measured K-readings with the clinical history method (CHM) in eyes that have undergone myopic laser in situ keratomileusis (LASIK).
Methods:
In this prospective study, Pentacam examination was performed in 71 eyes 1 month after myopic LASIK. The true net power (TNP) 4 mm, total corneal refractive power (TCRP) 4 mm, equivalent K-reading (EKR) 4.0 mm, and EKR 4.5 mm obtained from the same scan were compared with the K derived from CHM.
Results:
The average baseline spherical equivalence was -5.44±2.38 D. After LASIK, the mean KCHM was 37.67±2.13 D, TCRP4mm was 37.14±1.79 D, TNP4mm was 36.88±1.76 D, EKR4.0mm was 37.58±1.94 D, and EKR4.5mm was 37.51±1.94 D. TCRP4mm, TNP4mm, and EKR4.5mm showed a statistically significant deviation from the KCHM, with the mean error being 0.53 D, 0.79 D, and 0.16 D, respectively (P<0.05). Only the EKR4.0mm showed no statistically significant difference from the KCHM (mean error 0.09 D, P=0.23). The EKR4.0mm also had the narrowest 95% limits of agreement (LoA) (-1.10 to +1.28 D), whereas both TCRP4mm and TNP4mm had a wider LoA (-0.88 to +1.95 D and -0.62 to +2.20 D, respectively). All four Pentacam K-readings had a strong and statistically significant correlation with the KCHM.
Conclusions:
Using the CHM as reference, the EKR4.0mm demonstrated the closest agreement when compared with the EKR4.5mm, TNP4mm, and TCRP4mm obtained from the same scan.
Related Concept Videos
Uncertainty in Measurement: Reading Instruments
The Sense of Self: Reflected Self-Appraisal and Social Comparison
Power
Multiple Comparison Tests
It would be easy to compare two samples using a significance alpha level of 0.05. In other words, there is only one sample pair to be compared. However, it would be difficult to identify a significantly different sample if the number...
Nuclear Power
Nuclear Fuels
Nuclear fuel consists of a fissile isotope, such as uranium-235, which must be present in sufficient quantity to provide a...
Power and Energy
Power, defined as the time rate of expending or absorbing energy, is quantified in units called watts (W). The relation between power and energy is mathematically given as

