Reorganization of Visual Processing in Macular Degeneration Depends on Foveal Loss

Purpose—When individuals with central vision loss due to macular degeneration (MD) view stimuli in the periphery, most of them activate the region of retinotopic cortex normally activated only by foveal stimuli – a process often referred to as ‘reorganization’. Why do some show this reorganization of visual processing whereas others do not? We reported previously that six individuals with complete bilateral loss of central vision showed such reorganization, while two with bilateral central vision loss but with foveal sparing did not, and we hypothesized that the effect occurs only after complete bilateral loss of foveal vision. Here we conduct a stronger test of the dependence of reorganization of visual processing in MD on complete loss of foveal function, by bringing back one (called MD6) of the two participants who previously did not show reorganization, and who showed foveal sparing. MD6 has now lost all foveal function, and we predicted that if large-scale reorganization of visual processing in MD individuals depends on complete loss of foveal input, then we will now see such reorganization in this individual. Methods—MD6 and two normally sighted controls were scanned. Stimuli were gray-scale photographs of objects presented at either the fovea or at a peripheral retinal location (i.e., the MD participant’s preferred retinal locus – PRL, or the control participants’ matched peripheral location). Results—In MD6, visual stimulation at the PRL significantly activated not only the expected “peripheral” retinotopic cortex, but also the deprived “foveal” cortex. Crucially, MD6 exhibited no such large-scale reorganization five years earlier when she had some foveal sparing. By contrast, in the control participants, stimulation at the matched peripheral location produced significant activation in peripheral retinotopic cortex only. Conclusions—We conclude that complete loss of foveal function may be a necessary condition for large-scale reorganization of visual processing in individuals with MD. Corresponding author: Daniel D. Dilks, Emory University, Department of Psychology, 36 Eagle Row, Room 469, Atlanta, GA 30332, [email protected]. The authors have no conflicts of interest. NIH Public Access Author Manuscript Optom Vis Sci. Author manuscript; available in PMC 2015 August 01. Published in final edited form as: Optom Vis Sci. 2014 August ; 91(8): e199–e206. doi:10.1097/OPX.0000000000000325. N IH -P A A uhor M anscript N IH -P A A uhor M anscript N IH -P A A uhor M anscript