Corneal thickness measurements in normal and keratoconic eyes: Pentacam comprehensive eye scanner versus noncontact specular microscopy and ultrasound pachymetry

PurposeTo compare central corneal thickness (CCT) measurements taken with the Pentacam comprehensive eye scanner (CES), noncontact specular microscopy (SM), and ultrasound pachymetry (UP) in normal and keratoconic corneas.SettingDepartment of Ophthalmology, Ankara University School of Medicine, Ankara, Turkey.MethodsIn a prospective study, 3 CCT measurements were taken with the Pentacam CES, SM, and UP in that sequence from 1 eye of 45 consecutive patients with myopia (group A) and 62 consecutive patients with keratoconus (group B). Eyes with keratoconus were further divided into 3 subgroups, mild, moderate, and severe, according to the mean keratometry readings.ResultsPentacam CES (r = 0.994) and UP (r = 0.993) demonstrated very high and comparable reproducibility in group A. In group B, Pentacam CES displayed better reproducibility (r = 0.988) than UP (r = 0.969) and SM (r = 0.901). The mean CCT measurements of Pentacam CES and UP were not significantly different in group A (P = .37) and in eyes with mild keratoconus (P = .29), whereas significant differences between all instrument pairs were evident in group B and in moderate and severely keratoconic eyes (P<.05). Noncontact SM measurements were significantly smaller than those of Pentacam CES and UP in all groups (P<.05) when a measurement could be obtained. There were significant linear correlations between CCT measurements of Pentacam CES, UP, and noncontact SM in groups A, B, and mildly keratoconic eyes (P<.001).ConclusionsResults suggest that whereas Pentacam CES and UP may be used interchangeably in normal eyes in the clinical setting for the measurement of CCT, one should be cautious interpreting corneal thickness data from Pentacam CES, UP, and particularly SM in eyes with keratoconus. Whereas, in normal and mildly keratoconic eyes, Pentacam CES and UP demonstrated very high and comparable reproducibility, in moderately keratoconic eyes, Pentacam CES readings showed better reproducibility than UP.