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

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.

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.

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).

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.