To establish a link between silent retinal progressive impairment and cortical reorganization in a cohort of 15 asymptomatic patients harboring the 11778G>A mutation with good visual acuity and normal ocular examination (pre-clinical phase). We aimed to phenotype preclinical silent degeneration from the psychophysical, neurophysiological and structural point of view. Moreveover we aimed to establish whether retinal measures could explain cortical reorganization.Methods
We studied RGC function at the population level using pattern electrophysiology and chromatic contrast sensitivity along three chromatic axes. We used optical coherence tomography to measure macular, RGC nerve fiber layer as well as inner and outer retinal layer thickness. We then asked whether such measures could explain previously identified cortical reorganization as assessed by cortical magnetic resonance imaging thickness measures in extrastriate visual cortex.Results
We found that compensatory cortical plasticity occurring in V2 and V3 is predicted by thickness of macular RGC axonal layer. This was also the most discriminative measure between carriers and controls, as revealed by ROC analysis. Moreover we found that the substantial cortical reorganization that occurs in the carrier state, can be used to provide statistical discrimination between carrier and normal groups to a level that is similar to measures of retinal dysfunction.Conclusion
We conclude that cortical compensatory plasticity in visual areas V2 and V3 is triggered by pathology in retinal ganglion cell axons.