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

<b><i>Background:</i></b> 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. <b><i>Methods:</i></b> 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. <b><i>Results:</i></b> 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). <b><i>Conclusions:</i></b> 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').

**<i>背景：</i>** 脑卒中后常出现同侧偏盲性视野缺损（homonymous visual field defects，VFD），其部分或完全恢复的具体机制尚未明确。临床实践中，经视野计检查显示视野恢复的患者通常被认为知觉视觉功能正常。然而已有研究表明，脑卒中合并同侧偏盲性视野缺损的患者存在对比敏感度（contrast sensitivity，CS）损伤。本研究旨在探讨脑卒中所致同侧偏盲性视野缺损患者视觉对比敏感度丧失的起源。我们提出如下假说：在累及视交叉后视通路的缺血性脑卒中患者中，其视野计检查看似正常的视觉区域仍存在对比敏感度损伤，且此类对比敏感度损失的时空特性与“盲视（blindsight）”相符，这或许提示二者具有相似的潜在发病机制。**<i>方法：</i>** 本研究纳入7例因脑卒中导致同侧偏盲性视野缺损且保留黄斑视力的患者，以及20名健康受试者，采用汉弗莱静态视野计（Humphrey static perimetry）的SITA-Fast 24-2检测程序对患者进行视觉评估。需特别说明的是，合并视觉空间忽视的患者被排除在本研究之外。对比敏感度检测采用经改良的递增对比度检测法，并对反应时间进行校正。实验使用3种空间刺激，涵盖多种空间频率：（1）大尺寸正弦光栅；（2）中央凹Gabor补丁；（3）在疑似恢复的视野区域（紧邻同侧偏盲性视野缺损区）呈现的Gabor补丁。此外，本研究使用具有不同时间特性的刺激物，以选择性激活瞬态与稳态视觉通道，从而深入探究视觉损伤及/或恢复的机制。研究采用方差分析（analysis of variance，ANOVA）对检测结果进行分析，并对年龄及刺激偏心度进行校正。**<i>结果：</i>** 针对稳态光栅刺激的方差分析显示，患者存在方位选择性（水平方向）的对比敏感度损失（p=0.025）；而在中央视觉区域（中央凹Gabor补丁刺激）未观察到此类损伤。与未受累的半视野相比，脑卒中受累半视野中紧邻同侧偏盲性视野缺损区的局部对比敏感度有所降低（p≤0.005），尽管这些区域在视野计检查中看似正常。在这些区域中，与稳态刺激相比，瞬态刺激下的对比敏感度相对保留（采用威尔科克森符号秩检验）。**<i>结论：</i>** 本研究发现脑卒中所致同侧偏盲性视野缺损患者的看似正常的视野区域存在特异性对比敏感度损伤，这提示静态视野计检查无法充分评估此类患者的视觉功能，该结果对临床视觉检测工作具有明确的指导意义。研究结果与瞬态/大细胞视觉通道相对保留的现象相符。本研究发现尚需进一步验证。若在更大规模的纵向研究中得到证实，其将对视觉恢复的机制研究具有重要价值，同时或许可为视觉康复提供干预靶点——例如采用重复检测训练（即“知觉学习（perceptual learning）”）。