Visual stimuli in the form of a high contrast striped grating pattern can be highly disturbing for patients who have suffered a concussion. This is felt to be the result of cortical hyperexcitability.
Dr. Patrick Quaid recently reintroduced the “Bihemispheric Dissonance Test (BDT),” created by the late Dr. Merrill Bowan, and has reminded us of the strong discomfort and physical aversion a concussed individual can exhibit when simply looking at striped patterns.1
Investigating the visual stress response and illusionary mirages observed when viewing striped patterns as it pertains to people with migraines and reading disabilities, Dr. Bowan felt that this may be the result of dissonance between the parvo-, magno- and koniocellular functions. He referred to this as “visual aliasing.”2
Dr. Bowan’s work was based upon the foundation developed by Dr. Arnold Wilkins, who used repetitive grating patterns as a probe of visual hypersensitivity with regard to epilepsy. Wilkins called his test the “Pattern Glare Test.”3
Regardless of the name used, the concussed patient is presented with a striped pattern at about 40 cm. and instructed to look at the center of the target. Usually, this results in the immediate strong response described above.
We use the 2.0 CPCM LEA Grating Paddle held at 40 cm. in front of a concussed patient as a way to elicit a response. 4 Usually, this stimulus creates a reaction that is immediate, dramatic and extremely uncomfortable for the concussed patient.
- Quaid P, Diagnosis before Prognosis: Going beyond visual acuity in visual rehabilitation. NORA
Annual Meeting, Sept. 22, 2019 Scottsdale, Arizona.
- Wilkins AJ, Darby CE, Binnie CD. Neurophysiological aspects of pattern-sensitive epilepsy. Brain 1979;102:1-25.