Department of Neurology, LMU Munich, University Hospital - Großhadern, Marchioninistraße 15, 81377, Munich, Germany.
Department of Neurology, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland.
J Headache Pain. 2021 Dec 11;22(1):148. doi: 10.1186/s10194-021-01355-y.
Patients with visual snow syndrome (VSS) suffer from a debilitating continuous ("TV noise-like") visual disturbance. They report problems with vision at night and palinopsia despite normal visual acuity. The underlying pathophysiology of VSS is largely unknown. Currently, it is a clinical diagnosis based on the patient's history, an objective test is not available. Here, we tested the hypothesis that patients with VSS have an increased threshold for detecting visual contrasts at particular temporal frequencies by measuring dynamic contrast detection-thresholds.
Twenty patients with VSS were compared to age-, gender-, migraine- and aura-matched controls in this case-control study. Subjects were shown bars randomly tilted to the left or right, flickering at six different frequencies (15 Hz, 20 Hz, 25 Hz, 30 Hz, 35 Hz, 40 Hz). The contrast threshold (CT) for detection of left or right tilt was measured in a two-alternative adaptive forced-choice procedure (QUEST). The threshold was defined as the Michelson contrast necessary to achieve the correct response in 75% of the cases.
The CT increased for higher flicker frequencies (ANOVA: main effect frequency: F (5,180) = 942; p < 0.001), with an additional significant frequency*diagnosis interaction (ANOVA: F (5,180) = 5.00; p < 0.001). This interaction effect was due to an increased CT at a flicker frequency of 15 Hz in the VSS cohort (VSS: MC = 1.17%; controls: MC = 0.77%). At the other frequencies, group comparisons revealed no differences. Furthermore, in the VSS cohort we observed an increase of CT with higher age (r = 0.69; p < 0.001), which was not seen in controls (r = 0.30; p = 0.20).
This study demonstrates a lower visual contrast sensitivity exclusively at 15 Hz in VSS patients and demonstrates frequency-dependent differences in dynamic contrast vision. The peak sensitivities of both parvo- and magnocellular visual pathways are close to a frequency of about 10 Hz. Therefore, this frequency seems to be of crucial importance in everyday life. Thus, it seems plausible that the impairment of contrast sensitivity at 15 Hz might be an important pathophysiological correlate of VSS. Furthermore, the overall age-related decrease in contrast sensitivity only in VSS patients underscores the vulnerability of dynamic contrast detection in VSS patients. Dynamic CT detection seems to be a promising neurophysiological test that may contribute to the diagnosis of VSS.
患有视觉雪综合征（VSS）的患者会遭受衰弱性的持续（“电视噪声样”）视觉障碍。尽管他们的视力正常，但他们会报告夜间视力问题和残像。VSS 的潜在病理生理学在很大程度上是未知的。目前，它是一种基于患者病史的临床诊断，尚无客观检查。在这里，我们通过测量动态对比度检测阈值来检验 VSS 患者在特定时间频率下检测视觉对比度的阈值增加的假设。
在这项病例对照研究中，我们将 20 名 VSS 患者与年龄、性别、偏头痛和先兆相匹配的对照组进行了比较。受试者被显示向左或向右随机倾斜的条，以六种不同的频率（15Hz、20Hz、25Hz、30Hz、35Hz、40Hz）闪烁。通过二选一自适应强制选择程序（QUEST）测量左或右倾斜的检测对比度阈值（CT）。阈值定义为在 75%的情况下获得正确响应所需的米歇尔对比度。
随着闪烁频率的增加，CT 增加（方差分析：主要效应频率：F（5，180）=942；p<0.001），并且存在额外的显著频率*诊断相互作用（方差分析：F（5，180）=5.00；p<0.001）。这种相互作用效应是由于 VSS 队列中 15Hz 闪烁频率的 CT 增加（VSS：MC=1.17%；对照组：MC=0.77%）。在其他频率下，组间比较没有发现差异。此外，我们在 VSS 队列中观察到 CT 随年龄的增加而增加（r=0.69；p<0.001），而对照组则没有（r=0.30；p=0.20）。
本研究仅在 VSS 患者中显示出 15Hz 时较低的视觉对比度敏感度，并显示出动态对比度视觉的频率依赖性差异。视锥细胞和视杆细胞视觉通路的峰值敏感度都接近约 10Hz 的频率。因此，该频率似乎在日常生活中至关重要。因此，VSS 中 15Hz 对比度敏感度的损害可能是 VSS 的重要病理生理相关因素。此外，仅在 VSS 患者中，对比度敏感度随年龄的整体下降强调了 VSS 患者动态对比度检测的脆弱性。动态 CT 检测似乎是一种很有前途的神经生理学测试，可能有助于 VSS 的诊断。
