Distribution pattern of total corneal thickness in keratoconus versus normal eyes using an optical coherence tomography

Abstract

Purpose: 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). Methods: 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. Results: 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. Conclusion: 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.

Diagnostic Accuracy of Corneal and Epithelial Thickness Map Parameters to Detect Keratoconus and Suspect Keratoconus

“…Previous studies have shown that the apex of early KC focal steepening is compensated by corneal epithelial thinning, and the degree of potential epithelial remodelling is dependent on the severity of the keratoconus [20]. In this study, all ET variables showed statistically signifcant differences between KC and N eyes.…”

“…Epithelial thickness data may allow for an earlier diagnosis of KC, as epithelial changes may precede any changes produced on the front surface of the cornea. Such ET changes in KC have been examined by other groups [20][21][22][23][24][25]. Fuente et al evaluated total corneal thickness and corneal layers in 86 healthy young adults using SD-OCT, where they reported a central ET of 54.60 ± 4.25 μm [26].…”

“…To a lesser extent, SKC and N eyes comparisons showed signifcant diferences for all CT variables except Min CT (2_5), S-I CT (2_5), and Min-Max CT (2_5). In their study, Hashemi et al used highresolution spectral-domain OCT (Heidelberg Engineering, Heidelberg, Germany) to investigate the diagnostic ability of total corneal thickness in detecting KC, where they found that CCT and Min-Median variables were the most sensitive indices for the diagnosis of KC [5]. In the current study, the two CT variables showing the greatest AUC to detect KC were Min-Max CT (0_2) and Min-Max CT (2_5); AUC � 0.94 and AUC � 0.89, respectively.…”

“…Several studies from the Middle East have demonstrated a high prevalence rate of KC [2][3][4]. KC is typically characterized by thinning of the stroma with the largest thickness changes in the 5 mm zone [5].…”

Multi-modal imaging for the detection of early keratoconus: a narrative review

“…Heideri et al also evaluated the thicknesses of different corneal layers for identifying KC and SCKC using SD-OCT [52]. Total cornea and stroma in KC and SCKC, and epithelium in KC were significantly thinner compared to the control group.…”