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Sing-Hang Cheung, Ronald A. Schuchard, Sheng He, Yonghua Tai, Gordon E. Legge, Xiaoping P. Hu; Limited retinotopic reorganization in age-related macular degeneration. Journal of Vision 2005;5(8):299. doi: https://doi.org/10.1167/5.8.299.
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Purpose: Age-related macular degeneration (AMD) afflicts the central 5° to 10° of the retina. Studies of retinotopy of the primary visual cortex (V1) among normally sighted humans have shown that the central retinal area projects to a disproportionately large area at the posterior end of V1. It is not yet known what happens to the retinotopy in AMD patients with central visual field loss (CFL). The current study investigates the possible retinotopic reorganization in AMD patients using fMRI.
Methods: Four AMD patients aged 81 to 84 were studied. Macular perimetry was performed using a scanning laser ophthalmoscope prior to the fMRI session. Averaged size of CFL in the tested eye was 11°. Two stimulus sequences were used. (1) Full-field vs. control vs. fixation. A change detection task at the 1.5° fixation cross was used to encourage stable fixation. The whole display (42° × 30°) was filled with flickering checks during the full-field blocks. A check-filled 2° disc was presented to the estimated foveal location in the CFL area during the control blocks. (2) Whole-field scene vs. blank. Participants performed a 1-back picture matching task with free viewing of the pictures during the scene blocks. Functional and anatomical MR images were obtained with a Siemens 3T TRIO system and analyzed using BrainVoyager software.
Results: Macular perimetry confirmed that all participants used a preferred retinal locus (PRL) for fixation outside the CFL area. Posterior V1 showed activation in one of the four patients for both full-field and scene conditions. Anterior V1 showed activation in all four patients for both full-field and scene conditions. No V1 activation was detected in the control condition.
Conclusions: A substantial region of V1 remains unresponsive to visual stimulation in the majority of patients, suggesting the lack of extensive retinotopic reorganization in the elderly with AMD, despite evidence for behavioral adaptation in the use of a non-foveal PRL.
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