Purchase this article with an account.
J. Frolo, T. Plank, A. B. Renner, S. Brandl-Rühle, H. Helbig, M. W. Greenlee; Neural Correlates of Eccentric Fixation in Patients With Central Visual Field Scotomas. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3616.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Patients with central visual field scotomas are reliant on using their intact peripheral retina for fixation, but they differ in their strategies of eccentric viewing. Some of them use only one new "preferred retinal locus" (PRL) consistently that functions as a pseudo-fovea and achieve high eccentric fixation stability. Others use several peripheral areas and fixate in a less stable fashion. We used functional Magnetic Resonance Imaging (fMRI) to determine possible neural correlates of the stability of eccentric fixation in retinotopic and associational visual cortex.
The data of 16 patients with central scotomas due to retinal dystrophy (Stargardt disease, cone-rod dystrophy; age 19-66 yrs; scotoma diameter 10-20°) and of 10 normal sighted controls were analysed. Fixation behaviour and perimetry were measured with an MP-1 Nidek microperimeter. Patients with stable eccentric fixation were assigned to the "stable pseudo-fovea" group (n=9, fixation stability [% in 2°] above 80%), patients with unstable eccentric fixation were assigned to the "unstable eccentric fixation" group (n=7, fixation stability [% in 2°] below 80%). MRI was performed using a Siemens 3T Allegra scanner. We stimulated the PRL and a comparable peripheral location on the retina in the opposite hemifield (OppPRL) with object pictures as stimuli in a block design. Data were analyzed using SPM5 (GLM, ROI analysis with Marsbar to obtain % signal change for striate and extrastriate cortical areas, as well as higher areas of the ventral pathway: fusiform gyrus, inferotemporal gyrus). Significant clusters were combined with anatomical ROIs defined using the WFU Pickatlas.
Results show that direct stimulation of the patients’ pseudo-fovea with object pictures leads to significantly increased activation in striate and extrastriate cortices, as well as in higher visual areas (fusiform gyrus, inferotemporal gyrus) in comparison to stimulating a matching peripheral area in the opposite hemifield. This difference is not seen in controls. Patients with stable eccentric fixation show a more pronounced difference between PRL and OppPRL in fusiform and inferotemporal gyrus than patients with unstable eccentric fixation.
Patients with central scotomas benefit from developing high eccentric fixation stability in one pseudo-fovea. This advantage is reflected in increased activation in higher areas of the visual cortex associated with object recognition.
This PDF is available to Subscribers Only