Combining fMRI with Video Automated Perimetry in Patients with Brain-based Visual Impairments

For clinical diagnosis of brain-related vision deficits, it is advantageous to obtain behavioral visual field perimetry in conjunction with functional magnetic resonance imaging (fMRI) maps of visual cortex function. Ideally, these data should be obtained simultaneously to ensure that both measures are closely correlated. To facilitate this goal, we have developed a video automated perimeter (VAP) that will allow conventional or custom visual field testing inside the fMRI environment. To validate the system, data were obtained using both the VAP and a conventional Humphrey field analyzer (HFA) for 4 patients having localized visual field defects. Flashing spots of 0.4deg were presented on a grid of 76 test points (identical to the Humphrey 30-2 grid) using a modified staircase protocol to estimate detection thresholds. Overall, detection thresholds obtained with the two systems were similar though the VAP was 2 dB less sensitive, on average. Most importantly, though, the spatial pattern of visual sensitivity matched well in the two tests with a median cross correlation coefficient of 0.71, comparable to correlations obtained between repeated runs using the HFA. Thus the VAP system provides visual field maps comparable to those obtained with Humphrey perimetry but that can be administered between runs while the patient is in the MRI scanner, thus reducing test time and ensuring that both measures are obtained under closely matched conditions