Measurement of White-to-White Distance Using Pentacam Scheimpflug Imaging versus IOLMaster

Purpose
The aim of this study was to assess white-to-white (WTW) horizontal corneal diameter using Pentacam versus IOLMaster and determine whether the two instruments were interchangeable.
Patients and methods
Twenty eyes were included in this prospective clinical study conducted in I-care Eye Centre, Alexandria. Measurement of WTW horizontal corneal diameter was taken using Pentacam (internal and external measurements) and IOLMaster.
Results
The mean WTW measured using IOLMaster was 11.66 ± 0.27 mm, ranging from 11.30 to 12.30 mm. The mean WTW externally using Pentacam was 11.93 ± 0.43 mm, ranging from 11.01 to 12.66 mm. The mean WTW internally using Pentacam was 11.20 ± 0.39 mm, ranging from 10.56 to 11.93 mm. The diameters measured using IOLMaster were significantly less than that measured using Pentacam externally and significantly more than that measured using Pentacam internally. There was no correlation between WTW measured using the two machines.
Conclusion
Although horizontal corneal diameter (WTW) can be measured using Pentacam or IOLMaster, WTW measurement is significantly different between the two instruments and they should not be used interchangeably. Pentacam measurement depends on manual placement of calipers on the Scheimpflug digital image.