Visual Contrast Sensitivity Deficits in ‘Normal' Visual Field of Patients with Homonymous Visual Field Defects due to Stroke: A Pilot Study

Abstract

Background: Homonymous visual field defects (VFD) are common following stroke, and often recover, partially or fully, by unknown mechanisms. In clinical practice, visual field recovered on perimetry is often considered perceptually normal. However, studies have shown contrast sensitivity (CS) deficits in patients with stroke and homonymous VFD. This study investigated the origin of visual CS loss in patients with VFD due to stroke. We hypothesised that CS deficits would be found in visual field areas appearing normal on perimetry, in patients with ischaemic stroke affecting the retrochiasmal visual system, and that the spatiotemporal properties of this CS loss would be consistent with those of ‘blindsight', perhaps suggesting similar underlying mechanisms. Methods: CS measurements were made in 20 healthy participants, and in 7 patients with stroke causing homonymous VFD sparing foveal vision, measured using Humphrey static perimetry (SITA-Fast 24-2 procedure). Importantly, patients with concomitant visuospatial neglect were excluded. CS measurements were made using a modification of the method of increasing contrast, corrected for reaction time. Three spatial stimuli were used, at several spatial frequencies: (1) large sinusoidal gratings; (2) foveal Gabor patches; and (3) Gabor patches presenting in the putatively recovered visual field, near VFD. Stimuli with different temporal profiles were used to selectively stimulate transient and sustained visual channels, to provide insight into mechanisms of visual loss and/or recovery. Analysis of variance (ANOVA) was used in the analysis of the measurements, allowing for correction for age and stimulus eccentricity. Results: ANOVA for sustained grating stimuli showed orientation-selective (horizontal) CS loss (p = 0.025); no such loss was apparent in the central visual field (foveal Gabor stimuli). Localised CS close to VFD was reduced in stroke-affected hemifields compared with unaffected hemifields (p ≤ 0.005), though these areas appeared normal on perimetry. In these areas, CS was relatively preserved for transient compared with sustained stimuli (Wilcoxon signed rank tests). Conclusions: The finding of specific CS deficits in the normal-appearing visual field of patients with homonymous VFD due to stroke suggests that static perimetry provides an inadequate assessment of visual function in these patients, with clear implications for testing of vision in clinical practice. The results are consistent with relative sparing of the transient/magnocellular visual channel. These findings demand further investigation. If confirmed in larger, longitudinal studies, this will have important implications for the mechanisms of recovery, and may provide a target for visual rehabilitation - for example, using repeated detection practice (‘perceptual learning').

Useful Field of View Performance in the Intact Visual Field of Hemianopia Patients

“…As hypothesized, we found that patients had worse iUFOV2 and iUFOV3 scores than control participants, confirming that visual functioning of the intact visual field is in fact impaired. These results agree with previous research showing that the ipsilesional part of the visual field is affected in patients with hemianopia, [8][9][10][11][12] and extend the findings previously reported by Rizzo and Robin, 16 who measured UFOV size performed with the entire visual field.…”

Functional Connectivity of the Precuneus Reflects Effectiveness of Visual Restitution Training in Chronic Hemianopia

“…Interestingly, a previous report on the same cohort of patients showed similar improvements for both the perimetric defect and intact VF (Elshout et al, 2016), which suggest that also in the intact parts of the VF clinically relevant improvements can be obtained. This complements various reports that show perceptual deficits in the "intact" parts of the VF (for review: Bola et al, 2013;Cavézian et al, 2015;Clatworthy et al, 2013; Geuzebroek and van den Berg, 2017). Furthermore, is has been suggested that this observation partially accounts for the subjective visual impairment as experienced by the patients and should therefore also be considered when examining VRT effects (Bola et al, 2013).…”

Behavioral Consequences and Cortical Reorganization in Homonymous Hemianopia

“…Conversely to the case of blindsight, which has been extensively studied in hemianopia patients, vision quality in the central visual field and in the IVF of these patients has scarcely been assessed, and moreover, it has traditionally been assumed to remain intact. However, as recently proposed, neither the central visual field ( Cavézian et al, 2010 ; Perez et al, 2013 ), nor the IVF of hemianopic patients ( Bola et al, 2013a , b , Clatworthy et al, 2013 ; Cavézian et al, 2015 ) actually appear to be fully intact or functional. Moreover, as we recently proposed, and as discussed below, the nature of the task, the type of stimulus and the side of the occipital lesion might determine the central and ipsilesional visual deficit in hemianopic patients ( Cavézian et al, 2010 , 2015 ; Perez et al, 2013 ).…”

“…Indeed, Hess and Pointer (1989) proposed that spatial and temporal sensitivities in the IVF of hemianopic patients were lower than in control subjects. In the same vein, Clatworthy et al (2013) showed that hemianopic patients present visual contrast sensitivity deficits in their IVF. Similarly, Rizzo and Robin (1996) , and Poggel et al (2011) , suggested that hemianopic patients can exhibit lower sensitivity to signals, compromised processing of temporal information and longer reaction times in both hemifields, as compared to control participants.…”