Elisa Castaldi, Guido Marco Cicchini, Benedetto Falsini, Paola Binda, Maria Concetta Morrone
Residual Visual Responses In Patients with retinitis pigmentosa revealed by functional magnetic
CNR Annual Retreat 2019
Purpose: We evaluated the potential of magnetic resonance imaging in identifying signs of cortical visual processing with greater sensitivity than standard ophthalmological measures in RP patients at advanced stage. Methods: Eight patients affected with retinitis pigmentosa with only bare light perception and weak or absent visual evoked potential (VEP) or electroretinogram (ERG) responses to flashes of light were tested. Visual impairment was evaluated by means of psychophysical testing, where patient were asked to discriminate the drifting direction of a contrast modulated grating. Patients underwent MRI scanning and the behavioral performance was correlated with both Blood-Oxygenation-Level-Dependent (BOLD) signal elicited by flashes of lights and cortical thickness measured in primary visual area. Results: Contrast sensitivity to drifting gratings of very low spatial and temporal frequency was greatly impaired yet measurable in all patients. Weak luminance flashes elicited significant BOLD responses in striate and extra-striate cortex, despite the stimuli were not perceived during scanning. Importantly, patients with less severe impairment of contrast sensitivity showed stronger V1 BOLD responses. Striate cortical thickness did not correlate with visual sensitivity. Conclusions: BOLD responses provide a sensitive and reliable index of visual sparing more than VEPs or ERGs, often absent in RP patients. The minimal residual vision can be assessed by optimal visual stimulation in two alternative forced choice discrimination tasks and by BOLD responses. Imaging techniques can provide useful information to monitor progressive vision loss.