Abstract
Current initiatives to restore vision emphasize the need for objective assessments of visual field (VF) defects as pursued with functional magnetic resonance imaging (fMRI) approaches. Here, we compared population receptive field (pRF) mapping-based VF reconstructions to an fMRI method that uses more robust visual stimulation (on-off block design) in combination with individualized anatomy-driven retinotopic atlas-information (atlas-based VF). We investigated participants with sizable peripheral VF-deficits due to advanced glaucoma (n = 4) or retinitis pigmentosa (RP; n = 2) and controls (n = 6) with simulated scotoma. We obtained (1) standard automated perimetry (SAP) data as reference VFs and 3T fMRI data for (2) pRF-mapping [8-direction bar stimulus, fixation color change task] and (3) block-design full-field stimulation [8-direction drifting contrast patterns during (a) passive viewing (PV) and (b) one-back-task (OBT; reporting successions of identical motion directions) to probe the impact of previously reported task-related unspecific visual cortex activations]. Correspondence measures between the SAP and fMRI-based VFs were accuracy, assisted by sensitivity and specificity. We found an accuracy of pRF-based VF from V1 in patients [median: 0.62] that was similar to previous reports and increased by adding V2 and V3 to the analysis [0.74]. In comparison to the pRF-based VF, equivalent accuracies were obtained for the atlas-based VF for both PV [0.67] and, unexpectedly, the OBT [0.59], where, however, unspecific cortical activations were reflected by a reduction in sensitivity [0.71 (PV) and 0.35 (OBT)]. In conclusion, in patients with peripheral VF-defects, we demonstrate that previous fMRI procedures to obtain VF-estimates might be enhanced by: (1) pooling V1-V3 to enhance accuracy; (2) reporting sensitivity and specificity measures to increase transparency of the VF-reconstruction metric; (3) applying atlas-based procedures, if pRF-based VFs are not available or difficult to obtain; and (4) giving, counter-intuitively, preference to PV. These findings are expected to provide guidance to overcome current limitations of translating fMRI-based methods to a clinical work-up.
Highlights
Visual field (VF) testing is of critical importance for diagnosis and follow-up in ocular diseases
This approach is based on the retinotopic layout of the visual information in the visual cortex, which can be directly obtained from functional magnetic resonance imaging (fMRI) data via (i) individualized visual field (VF)-mapping, e.g., population receptive field mapping (Dumoulin and Wandell, 2008), or (ii) indirectly via the application of a group-informed retinotopic atlas to the individual anatomy (Benson et al, 2014). (i) Individualized VFmapping has been widely applied to map and investigate normal visual cortex functioning in healthy individuals (Harvey and Dumoulin, 2011; Wandell and Winawer, 2015; Prabhakaran et al, 2020), and to provide insights on the interplay of visual cortex stability and plasticity in vision disorders (Baseler et al, 2011; Barton and Brewer, 2015; Hoffmann and Dumoulin, 2015; Ahmadi et al, 2020, 2019)
In patients with advanced peripheral VF defects and controls with artificial scotomas, we investigated the scope of fMRI as an objective tool for VF-predictions
Summary
Visual field (VF) testing is of critical importance for diagnosis and follow-up in ocular diseases. Given the recent therapeutic advances at the level of the visual cortex with cortical implants (Beauchamp et al, 2020), one option for an objective VF assessment is the reconstruction of VF-coverage and identification of VF defects from the response patterns in the visual cortex obtained with functional magnetic resonance imaging (fMRI) This approach is based on the retinotopic layout of the visual information in the visual cortex, which can be directly obtained from fMRI data via (i) individualized VF-mapping, e.g., population receptive field (pRF) mapping (Dumoulin and Wandell, 2008), or (ii) indirectly via the application of a group-informed retinotopic atlas to the individual anatomy (Benson et al, 2014). Ritter et al reported for the pRF-based reconstruction of peripheral VF defects (similar to the present study’s patient cohort) in retinitis pigmentosa (RP) from V1 a median accuracy of 0.85 [range: 0.49–0.98 (n = 7)] (Ritter et al, 2019) It should be noted, that this approach is subject to the availability of reliable pRFmapping data and the patient’s reliable fixation of the central fixation target.
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