Comparison of 3 different corneal thickness measurements in eyes with keratoconus

Abstract

Abstract: : Purpose: Three different central corneal thickness (CCT) measurements using Orbscan II scanning–slit topography, Topcon SP–2000P noncontact specular microscopy, and ultrasonic pachymetry have been compared and reported for normal eyes and post–LASIK eyes. In this study, we compared CCT measurements of 3 pachymetry devices in eyes with keratoconus. Methods: CCT was measured in 21 eyes with keratoconus. Eyes with apparent corneal opacity were excluded. Scanning–slit topography, noncontact specular microscopy, and ultrasonic pachymetry were used in this sequence. The acoustic equivalent correlation factor was used for Orbscan readings. Results: Three devices gave significantly different CCT readings (P < .005, ANOVA). Orbscan measurements (449.5 ± 43.2 [SD] µm) were significantly smaller than those of noncontact specular microscopy (476.7 ± 28.3 µm; P = .002, Bonferroni multiple comparison) and ultrasonic pachymetry (485.0 ± 29.3 µm; P < .001). There were significant linear correlations between scanning–slit topography and the noncontact specular microscopy (Pearson’s correlation coefficient r = 0.880, P < .0001, best fit line; y = 105.8 + 0.765 x), noncontact specular microscopy and ultrasonic pachymetry (r = 0.811, P < .0001, y = 214.4 + 0.584 x), and ultrasonic pachymetry and scanning–slit topography (r = .741, P < .0001, y = 265.3 + 0.489 x). Conclusions: Orbscan II scanning–slit topography system significantly underestimated CCT in eyes with keratoconus compared to other two devices. Measurements taken by noncontact specular microscopy and ultrasonic pachymetry were considered to be same. Three devices had significant linear correlations with each other.

Keywords: keratoconus • cornea: clinical science