Changes in retinal and choroidal thickness and blood density in participants with keratoconus.

Purpose: Keratoconus causes progressive myopia and irregular astigmatism, leading to vision impairment. This study investigated choroidal and retinal variations and their influence in participants with keratoconus.

Methods: This case-control study assessed 33 keratoconic and 33 axial length-matched healthy myopic eyes. Choroidal and retinal parameters between the two groups were compared using general linear models. Correlations between keratoconus choroidal/retinal parameters and ABCD grading or tomographic keratoconus classification (TKC) staging were assessed. Multivariable linear regression models were used to investigate the factors affecting changes in keratoconus choroidal/retinal thickness and blood flow.

Results: Keratoconus participants exhibited 2.3% lower macular inner retinal thickness (mean difference: -4.97 μm, p = 0.02), along with 8.0% and 2.3% higher superior and mean retinal vessel (mean difference: 2.71%, p = 0.03; mean difference: 3.22%, p = 0.01) densities, respectively, compared with controls. The blood flow density of the choroidal capillaries was 15.5% higher (mean difference: 5.72%, p = 0.01), while the large choroidal vessel density was 4.8% lower (mean difference: -3.38%, p = 0.03) at the macula in the keratoconus group. In the keratoconus group, higher deep retinal vessel density correlated with more severe A grading (r = 0.49, p = 0.006), while lower large choroidal vessel density correlated with more severe B grading (r = -0.48, p = 0.006); notably, higher deep retinal vessel density was positively correlated with more severe TKC staging (r = 0.50, p = 0.004). Furthermore, superior retinal vessel density was associated with the index of vertical asymmetry (IVA) (slope coefficient: 3.55%, p = 0.03) and the index of height asymmetry (slope coefficient: 0.07%, p = 0.04). Mean retinal vessel density was associated with IVA (slope coefficient: 4.82%, p = 0.01). Choroidal capillary density was associated with the keratoconus index (slope coefficient: 21.89%, p = 0.01). Large choroidal vessel density was associated with the steepest keratometry (slope coefficient: -0.61%/D, p = 0.009).

Conclusion: Participants with keratoconus exhibited choroidal and retinal parameter alterations associated with keratoconus severity, as well as corneal keratometry and irregularity, suggesting the potential pathophysiological mechanisms.