Purpose:

To evaluate abnormal corneal thinning using optical coherence tomography (OCT) pachymetry mapping in keratoconus patients.

Material and Method:

In this prospective study, 57 eyes of 33 keratoconus patients and 50 eyes of 25 control subjects without ocular pathology were compared. After routine ophthalmologic examination, corneal topography and corneal pachymetry mapping by OCT with anterior segment module were performed in all subjects. Central corneal thickness (CCT), minimum corneal thickness (Min), superior-inferior (S-I), minimum-median (Min-Med), superonasal-inferotemporal (SN-IT), superotemporal-inferonasal (ST-IN), minimum-maximum (Min-Max) and minimum corneal vertical localization(MCVL) parameters were evaluated from the OCT pachymetric maps. Measurements were performed three times in all patients, and the means of these data were used for statistical analysis and comparisons. Cut-off values were determined for all OCT-derived parameters. Sensitivity, specificity, and area under the receiver operating characteristic (AROC) curve were also calculated for these parameters.

Results:

Keratoconic corneas were thinner. Minimum corneal thickness was 425±63 µm in the keratoconus group, and 513.7±3 µm in the control group (p<0.001). The thinnest corneal location was inferiorly displaced in the keratoconus group. MCVL value was -845.6±427.9 µm in the keratoconus group and -419.6±240.1 µm in the control group (p<0.001). Min-med was -46.3±23.8 µm and 18.4±16.3 µm in keratoconus and control groups, respectively. Corneal thinning was more asymmetric in the keratoconus group ( S-I, SN-IT, ST-IN parameters were statistically different between the groups, p<0.001). Sensitivity, specificity, and AROC values of the OCT pachymetric parameters were within the range of 82-92%, 54-89%, and 0.674-0.922, respectively.

Discussion:

OCT pachymetry maps have high sensitivity and specificity for keratoconus diagnosis. OCT provides additional information in patients whose corneal topography was inconsistent with clinical signs and interpretation of both devices together would be more valuable in the diagnosis of keratoconus.

Keywords: Keratoconus, optical coherence tomography, pachymetry mapping, corneal topography