Corneal Layer Thickness Mapping With Optical Coherence Tomography in Different Stages Reveals Pathologic Processes of Keratoconus

Purpose: The aim of this study was to characterize the corneal layer thickness profile in different stages of keratoconus (KC). Methods: Patients with clinical or subclinical KC without a history of contact lens use were retrospectively enrolled. We evaluated 164 eyes, including 69 clinical KC, 32 topographic KC (no clinical signs), 22 very asymmetric ectasia with normal topography and no clinical signs of ectasia (VAE-NT), and 41 control eyes. The corneal epithelial, stromal, and total thicknesses in a 10-mm diameter were evaluated using swept-source anterior segment optical coherence tomography. Results: The epithelial thickness in the control and VAE-NT groups was thicker inferiorly than superiorly. While epithelial thickness parameters between the VAE-NT and control groups did not differ, significant stromal thinning was observed in the paracentral inferior and midperipheral temporal areas. The epithelium in the topographic and clinical KC groups was thinner than that in the control and VAE-NT groups, with focal thinning of the epithelium in the inferior-temporal area. In clinical KC, stromal thinning increased mainly in the central and paracentral inferior/temporal areas. With KC progression, the thinnest epithelial points tended to be placed temporally and inferiorly. Conclusions: Corneal layer thickness mapping using swept-source optical coherence tomography in a 10-mm diameter cornea across various severities of KC, from very mild to advanced, revealed that epithelial and stromal thicknesses changed with KC severity and was involved in the pathogenesis of KC progression. Pathological changes in the stroma may precede those in the epithelium. Epithelial compensatory mechanisms in clinical and topographic KC may not have fully emerged in VAE-NT.