A case-control study identified a lower visual contrast sensitivity at 15 Hz among patients with visual snow syndrome (VSS). These findings were published in The Journal of Headache and Pain.
Patients with VSS experience debilitating symptoms of continuous television noise-like flickering dots covering their entire visual field and can be associated with palinopsia and photophobia. Although the pathophysiology of VSS is presumed to slightly overlap with migraine, especially migraine with aura, there is scientific data that suggest VSS is a distinct disorder of the visual and extra-visual system, the researchers explained.
Currently, there is no validated diagnostic test for VSS and patients are left with few treatment options.
The objective of the current study was to compare dynamic contrast thresholds at different frequencies between patients with VSS and age-, gender-, migraine-, and aura-matched control individuals, to control for the potential influence of migraine.
In order to better assess the symptomology VSS, a group of patients (n=20) was recruited from a self-help group for VSS called “Eye on Vision Foundation” between 2015 and 2019. Patients were matched with healthy control individuals (n=20) and all participants were evaluated by dynamic contrast threshold measurement (DCTM). The descriptive statistic used in the study was the Michelson contrast (MC) which was the ratio of the difference between the maximum and minimum luminance (cd/m2) divided by the sum at a particular frequency.
The patient and control group was comprised of 7 women and 13 men each, they were aged 30.5±10.1 and 34.3±10.4 years, 14 and 11 had comorbid migraine, and they had 1.88±4.67 and 1.37±2.04 monthly headache days, respectively. Compared with control individuals, the patient group had significantly higher depression scores (t, -5.67; P <0.00).
Patients with VSS exhibited an increase in contrast threshold (MC, 1.17%) compared with control individuals (MC, 0.77%; P =.0074) at a flicker frequency of 15 Hz. Other tested contrast thresholds (20, 25, 30, 35, 40 Hz) did not differ between groups.
Contrast thresholds did not appear to be affected by migraine status (P >.12).
Among all assessed frequencies, there was a correlation between log-contrast threshold and age among the patients (r, 0.69; P <.001) but not among the control individuals (r, 0.30; P =.20). This age affect was not due to disease progression, as no correlation was observed for disease duration (r, 0.19; P =.46).
Using a contrast threshold of 15 Hz, the researchers were able to differentiate between patients and control individuals with a receiver operating characteristic curve decision rate of 0.725, sensitivity of 1.0, and specificity of 0.45.
Study limitations included not evaluating additional lower temporal frequencies, however, due to the demanding nature of evaluation, the researchers chose to limit the total duration of the DCTM.
“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 researcher stated. This is near the optimum frequency of the major visual processing streams in the parvo- and magnocellular pathways. The researchers concluded, “Dynamic CT detection seems to be a promising neurophysiological test that may contribute to the diagnosis of VSS.”
Disclosure: Multiple authors declared affiliations with industry. Please refer to the original article for a full list of disclosures.
Eren OE, Straube A, Schöberl F, Ruscheweyh R, Eggert T, Schankin CJ. Age- and frequency-dependent changes in dynamic contrast perception in visual snow syndrome. J Headache Pain. Published online December 11, 2021. doi:10.1186/s10194-021-01355-y