Distribution Pattern of Total Corneal Thickness in Keratoconus versus Normal Eyes Using an Optical Coherence Tomography

To evaluate the total corneal thickness distribution pattern using a high‑resolution spectral‑domain optical coherence tomography (HR SD‑OCT) for distinguishing normal eyes from keratoconus (KCN).

One hundred and forty‑four patients were enrolled in three groups (55 normal, 45 mild KCN, and 44 moderate‑to‑severe KCN eyes) in this prospective diagnostic test study. Total corneal thickness was measured in 8 semi‑meridians using HR SD‑OCT (Heidelberg Engineering, Heidelberg, Germany) in 5 and 7 mm zones. The central corneal thickness (CCT), corneal focal thinning (minimum thickness[Min], min minus median and maximum [Min‑Med, Min‑Max]), and asymmetry indices (inferior minus superior[I‑S] and supranasal minus infratemporal[SN‑IT]) were calculated. One‑way analysis of variance and the area under the receiver operating characteristic curve (AUC) were used for the analysis.

Thinner CCT, lower Min thickness, more negative Min‑Max, Min‑Med, and greater I‑S and SN‑IT were found in KCN eyes compared to the control group (P < 0.001). The inferior and IT semi‑meridians were the thinnest locations in KCN cases in the 5 mm central zone (P < 0.001). CCT followed by Min‑Med had the highest discriminative ability for differentiating mild KCN (AUC, sensitivity and specificity: 0.822, 87.0%, 60.37% and 0.805, 82.93%, 66.0%, respectively) and moderate‑to‑severe KCN (0.902, 87.82%, 73.08% and 0.892, 85.37%, and 78.85%, respectively) from normal corneas.

The inferior and IT sectors of the cornea with the largest thickness changes in the 5 mm zone are the most common thinning sites in keratoconic corneas, and CCT and Min‑Med are the most sensitive indices for the diagnosis of KCN.