Prof. Dr. Mark Greenlee
University of Regensburg

Prof. Dr. Stuart Anstis
University of California, San Diego
Department of Psychology

Patients with a hereditary form of macular dystrophy (Stargardt disease, Cone-rod dystrophy) usually develop scotomas (blind areas) of 10 degrees or larger in the central visual field. Many of these patients report that they do not consciously perceive this loss of vision, rather they experience a phenomenon of filling-in. Perceptual filling-in is a process where the brain tries to fill in missing information owing to the lack of input from parts of the visual field that correspond to the lesioned regions. In normal observers filling-in takes places in the blind spot, a photoreceptor-void region in the peripheral retina. Many studies have been conducted on the blind spot, but all of these are hampered by the poor acuity at that peripheral eccentricity (15 degrees). In this BaCaTeC cooperation we shall investigate filling-in of a blind area surrounded by a relatively high acuity retina location in young patients with juvenile macular dystrophy using psychophysics and objective tests of visual processing. In addition, we also will look at spatial distortions of geometric patterns (Amsler grid) and how individual scotomata effect these distortions. We expect to achieve a better understanding of cortical plasticity following retinal lesions and a better understanding of filling-in versus ignoring of information, which can help to improve methods of rehabilitation also for elderly people with central vision loss due to age related macular degeneration.

Final report:

Patients with juvenile retinal dystrophy often report that they are unaware of their central scotoma, suggesting the presence of perceptual filling-in. We used functional Magnetic Resonance Imaging (fMRI) to determine possible neural correlates of perceptual filling-in in patients with retinal distrophy and clinically established central scotoma in both eyes. The data of 5 patients (Stargardt disease, cone-rod dystrophy; mean age 45 yrs; scotoma diameter 10-20°) and of 5 normally sighted controls were analyzed. Fixation behaviour and perimetry were measured with a Nidek microperimeter. Magnetic resonance imaging was performed using a Siemens 3T Allegra scanner. We stimulated the central visual field (30deg) with a vertically oriented, low spatial frequency (1 c/deg) high-contrast sinewave grating that was either a) continuous, or b) was interrupted by a central grey disk. The disk was either slightly larger than the scotoma (detectable on 75% of trials) or slightly smaller (detectable on 25% of trials). To control for attention, an eccentric fixation task was performed during scanning. Data were analyzed using SPM8 (GLM with ROI analysis to obtain percent signal change for foveal projection zone). Results: for all patients, the BOLD signal in the foveal projection area was significantly higher for the small disk (i.e., condition leading to complete filling-in) than for the large disk (i.e., no filling-in). This effect was absent in the control subjects. Our findings support the existence of an active neural process that leads to filling-in in patients with central visual field scotomata.

Reference
Greenlee MW, Anstis S., Rosengarth K, Goldhacker M, Brandl-Ruhle S, Plank T. Neural correlates of perceptual filling-in: fMRI evidence in the foveal projection zone of patients with central scotoma. Abstract of paper to be presented at Annual Meeting of the Vision Sciences Society (VSS), May 11 – 16, 2012 in Naples, FL, USA.