Correlation between retinal vascularization and function in cone dystrophies: An optical coherence tomography angiography study

Purpose: Cone dystrophies (CDs) are a group of inherited pathologies characterized by cone dysfunction and loss. The aim of this study was to investigate the relationship between retinal vascularization and function in patients with CDs. Setting: Cross-sectional study conducted at the ophthalmology clinic, Department of Medicine and Science of Ageing, University “G. d’Annunzio” Chieti-Pescara, Chieti. Methods: Six patients (12 eyes) with previous diagnosis of cone dystrophy, confirmed by both clinical features and electrophysiological evidence, and 20 healthy controls (20 eyes) were enrolled. A complete ophthalmologic examination was performed including multifocal electroretinogram (mfERG) and pattern electroretinogram (PERG) with Retimax (CSO, Scandicci, Florence, Italy) as well as optical coherence tomography angiography (OCT-A) using XR Avanti (Angiovue, Optovue, Freemont CA, USA). Main outcome measures were: (i) foveal and parafoveal retinal thickness; (ii) superficial and deep plexus densities and choriocapillaris density which were tested in the whole, foveal and parafoveal areas; (iii) PERG P50 and N95 amplitude and latency; and (iv) mfERG N1 to P1 amplitude (from the first negative to the first positive peak) in the five recorded rings. Mann-Whitney U-test was performed to evaluate differences in functional and morphological parameters between cases and controls. Spearman’s correlation coefficient was calculated to evaluate correlation among functional and morphological parameters in the CDs group. All statistical tests were evaluated at an alpha level of 0.05. Statistical analysis was performed using IBM® SPSS Statistics v20 software (SPSS Inc, Chicago, IL, USA). Results: Analysis showed a reduction of retinal thickness in both foveal and parafoveal areas compared to controls (p < 0.001), a reduction of superficial plexus density in the foveal area (p = 0.010) and reduced deep plexus density mainly in the parafoveal area (p = 0.011). PERG and mfERG were both significantly reduced in CDs compared to controls (p < 0.01). A direct correlation was found between foveal thickness and superficial plexus density (Rho = 0.809; p = 0.001), as well as deep plexus density (Rho = 0.697; p = 0.012). PERG and mfERG were significantly correlated to parafoveal retinal thickness (p = 0.001). Superior and deep plexus densities in parafoveal area were both significantly correlated to PERG (Rho = 0.774; p = 0.003) and mfERG, mainly in Ring 5 (Rho = 0.755; p = 0.005). Conclusions: Our data showed that our cohort of CDs eyes was characterized by a reduced vascular density (mainly in the parafoveal area) which was related with retinal thickness. Moreover, we demonstrated in these pathologies a direct correlation between vascular density and loss of function. In conclusion, the main accent of this study was on capillary loss as a pathogenetic moment in CDs.