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T. Liu, W. Tang, X. Sun, J. Qian; FMRI-Based Implication of Receptive Field Size Expansion and Eccentricity Distribution of Visual Cortex in Glaucoma. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1616.
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© ARVO (1962-2015); The Authors (2016-present)
To compare eccentricity distribution and receptive field size of visual cortex in patients with glaucoma with those in age-matched controls using functional magnetic resonance imaging.
We recruited two patients with primary open angle glaucoma (both aged 70) and three age-matched controls in our study. Four scan sessions including one anatomical scan and three functional scans were acquired using a 3T scanner (GE signa VH/i) equipped with 8 channel head coil. Expanding annular rings (checkerboard pattern, 100%contrast, 4Hz counterphase, 0.75ºwidth, 0.4º/2s) swept the field of view extending 12 degrees periodically in two sessions. Borders of early visual areas were delineated using meridian stimuli in the third session. All functional sessions included an attention task to maintain fixation. The functional images lied perpendicular to the calcarine sulcus (TR:2s, TE:40ms, FOV:19cm, matrix:64×64, slice:3mm). Surface models of each subject’s occipital lobes were constructed from the anatomical data(1mm3 in resolution) using Freesurfer. Serial cross-correlation analyses with different reference functions (7 functions, width of duty cycle ranged from 12.5% to 87.5%) were used to indicate the whole receptive field size of a single voxel.
Both glaucoma patients and normal controls exhibited eccentricity distribution rules. However, when analyzed with different reference functions aiming at the shape of response profile, voxels of patients with glaucoma correlated better with wider reference functions than shorter ones. 28% of voxels in the occipital lobes correlated with the 56% width model, while only 11% correlated with the 12.5% width model. Normal controls had a relative flat distribution with a slight trend to the shorter width models. When viewed from the inflated hemisphere, more activation existed with wider models including the posterior pole of occipital cortex, while less activation with shorter models along with the absence of fovea area. This kind of transition was reversed in controls, but less significant within 12.5% to 50% range. With further investigation of this feature, we would quantify the width distributions of different visual areas and behavior changes.
Our results indicate that there is observable expansion of receptive field size in patients with glaucoma even when the automated visual field tests show normal function for the corresponding area, which is in accordance with the observation from experimental glaucoma.
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