Structural and microvascular retinal changes in keratoconus: an OCT and OCT angiography study

Abstract Background: Keratoconus is increasingly recognized as a condition that may affect not only corneal structure but also posterior segment parameters. This study aimed to evaluate alterations in central macular, choroidal, and peripapillary retinal nerve fiber layer thicknesses, as well as peripapillary vessel densities (VDs), in eyes with keratoconus using optical coherence tomography (OCT) and OCT angiography (OCTA). Methods: This cross-sectional study included eyes with keratoconus and healthy control eyes. Participants underwent Scheimpflug corneal tomography (Pentacam HR) to assess central corneal thickness (CCT) and keratometry; spectral-domain OCT (SD-OCT) for central macular thickness (CMT), choroidal thickness, and peripapillary retinal nerve fiber layer thickness (RNFLT) measurements; and swept-source OCT angiography (SS-OCTA) to quantify peripapillary VD centrally and across four quadrants at the superficial and deep capillary plexuses (pSCP, pDCP), the peripapillary choriocapillaris (pCC), and the global radial peripapillary capillary plexus (nRPCP). Results: Eighty-six eyes with keratoconus and ۸۶ age-, sex-, axial-length-, and laterality-matched healthy controls (all P > ۰.۰۵) were analyzed. The keratoconus group showed significantly higher spherical equivalent, higher keratometry parameters, higher astigmatism, and lower CCT, along with worse best-corrected distance visual acuity (all P < ۰.۰۰۱). Mean choroidal thickness was significantly greater in eyes with keratoconus (P < ۰.۰۰۱), whereas CMT, global RNFLT, and most quadrant RNFLT measures were comparable (all P > ۰.۰۵), except for a thinner inferonasal RNFLT (P < ۰.۰۵). Central VD in the pSCP, pDCP, pCC, and global nRPCP were significantly reduced (all P < ۰.۰۵). Eyes with keratoconus additionally demonstrated a non-significant (all P > ۰.۰۵) but characteristic pattern of regional VD alterations across peripapillary sectors. Conclusions: Keratoconus was associated with significant microvascular and structural alterations extending beyond the cornea, including reduced VDs in central peripapillary plexuses, localized thinning of inferonasal RNFL, and increased choroidal thickness. These findings support a broader pathophysiologic framework in which keratoconus involves not only anterior corneal remodeling but also measurable changes in blood supply within the macular and lamina cribrosa regions. The characteristic, though nonsignificant, regional VD patterns further underscore potential sectoral vulnerability. Future longitudinal and multimodal imaging studies are warranted to clarify the temporal evolution, clinical relevance, and prognostic utility of these microvascular changes in keratoconus. Keywords: choriocapillaris choroids retina macula luteas optical coherence tomography optical coherence tomography angiography optic nerves peripapillary retinal nerve fiber layer retinal nerve fiber layer keratoconus