Corneal Microstructural Alterations in Vernal Keratoconjunctivitis and Keratoconus Assessed by In Vivo Confocal Microscopy

Vernal keratoconjunctivitis (VKC) is a chronic inflammatory ocular surface disease that may coexist with keratoconus (KC), resulting in structural and nerve damage in the cornea. This study used in vivo confocal microscopy (IVCM) to evaluate corneal changes in VKC, KC, and VKC with KC. A total of 88 eyes were examined, including healthy controls (30 eyes), VKC cases classified as mild, moderate, or severe (39 eyes), KC alone (3 eyes), and VKC with KC (16 eyes). Corneal epithelial (CE), stromal, endothelial, and sub-basal nerve layers were analysed, while nerve parameters were quantified using ACCMetrics software. No significant differences were observed in CE or endothelial cell densities among the groups. Keratocyte density showed a significant overall difference, although pairwise comparisons were not. Although CNFW and fractal dimension demonstrated overall variability, no significant pairwise differences were identified. In contrast, several sub-basal nerve parameters demonstrated marked alterations, including corneal nerve branch density (CNBD; p=0.0001), corneal nerve fiber length (CNFL; p=0.0064), corneal total branch density (CTBD; p=0.0008), and corneal nerve fiber area (CNFA; p=0.0036). Reductions in CNBD were evident in moderate and severe VKC and in VKC with KC overlap, while the highest decline in CNFL was observed in VKC with KC. Inflammatory dendritic cells were frequently detected near altered nerve fibers in moderate-to-severe VKC and VKC with KC. IVCM-derived nerve parameters may serve as sensitive indicators of inflammatory corneal involvement in VKC and VKC-associated ectatic disease