Interocular differences of the Pentacam measurements in normal subjects


Dr Khalil Ghasemi Falavarjani
Eye Research Center
Rassoul Akram Hospital
Sattarkhan-Niayesh Street
Tehran 14455-364


Purpose:  The aim of this study was to determine the interocular differences of the Pentacam corneal measurements in a normal population.

Methods:  A retrospective analysis was performed on 550 eyes of 275 consecutive subjects evaluated for refractive surgery at the Rassoul Akram Hospital, Iran University of Medical Sciences. A Pentacam Scheimpflug camera was used for corneal measurements. Statistical analysis was performed to determine the normal levels of the difference between the two eyes.

Results:  One hundred and four men and 171 women with a mean age of 29.1 ± 7.73 years were evaluated. The mean (range) interocular difference was 2.17 (zero to 21) µm for maximum anterior elevation (AEmax), 3.62 (zero to 31) µm for maximum posterior elevation (PEmax), 8.42 (zero to 30) µm for minimum corneal thickness (CTmin), 0.06 (zero to 0.4) mm3 for three millimetre corneal volume (CV3), 0.19 (zero to 1.2) mm3 for five millimetre corneal volume (CV5), 0.44 (zero to 2.9) mm3 for seven millimetre corneal volume (CV7), 0.24 (zero to 2.5) dioptres for the mean keratometry (Km) and 0.39 (zero to 2.5) D for measurements of the corneal dioptric power in the steepest meridian (Kmax).

Conclusions:  Individuals with differences greater than 17.4 µm in AEmax, 29.1 µm in PEmax, 29.6 µm in CTmin, 2 D in Km, 2.27 D in Kmax, 0.32 in CV3, 1.05 in CV5, and 2.6 in CV7 between eyes represent less than 0.5 per cent of the population. An interocular difference outside the normal range should alert the clinician to examine for other parameters that are more predictive of post-refractive surgical ectasia.