Inner Retina Changes in ABCA4-Related Retinopathy: Structure-Function Relationship.

Purpose: The aim of this retrospective study was to evaluate the inner retinal changes in patients with ABCA4-related retinal dystrophy (ABCA4-RD), and correlate these changes with the photopic negative response (PhNR), a cone ERG component reflecting inner retinal activity, previously reported as altered in ABCA4-RD. Methods: Nineteen ABCA4-RD patients (21 eyes) and 20 age-matched controls (20 eyes) were included in the study. A detailed ophthalmological examination, a spectral domain optical coherence tomography with volumetric segmentation of retinal layers, as well as electrophysiological recordings of the ERG PhNR, were obtained in all patients and controls. The patient data were compared individually with normal values (mean and 95% confidence limits) and evaluated by Pearson's and linear correlation analyses. Results: The spectral domain optical coherence tomography examination showed in the perifoveal retina a laminopathy with thinning (<95% normal confidence limits) of the outer nuclear (18/21 eyes) and the ganglion cell layer (11/21 eyes), and relative sparing or slight thickening of the inner nuclear layer. The PhNR amplitude was reduced (<95% normal confidence limits) in 20 of the 21 study eyes. In the same eyes, PhNR losses were always greater than the cone b-wave amplitude losses. The ganglion cell layer volume was positively correlated with the PhNR amplitude (r = 0.69; P < 0.01). Conclusions: The present results show in ABCA4-RD patients a correlation of inner retinal anatomical changes with corresponding functional abnormalities, as detected by the PhNR. These findings may be interpreted as a causal relationship between anatomical and functional changes in the inner retina. Longitudinal studies on the natural history of ABCA4-RD should consider the role of inner retina both on the disease progression and the efficacy of treatments selectively focused on restoring the ABCA4 function and the photoreceptors' health.