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A team of researchers in Toronto have developed a new way to measure visual discomfort – also known as photophobia – that could help advance our understanding of debilitating light sensitivities.
"We all experience visual discomfort at some point in our lives, for example when coming out of a cinema during daytime," says Dr. Agnes Wong, a Senior Scientist at the Krembil Research Institute.
"However, for those with certain health conditions, such as a migraine headache, cataracts or damage to the eye, even normal light levels can be difficult to tolerate."
Dr. Wong developed a new test to provide clinicians and researchers with a more rigorous way to measure visual discomfort in patients. Current approaches typically involve questionnaires or polls, which are hard to interpret and can vary according to patients' mood, health or cultural background.
The researchers designed the test to take advantage of new research suggesting that visual discomfort may be influenced by a relatively unstudied cell in the retina known as an intrinsically photosensitive retinal ganglion cell (ipRGC).
"ipRGCs are a rare type of cell located in the back of the eye and are believed to provide the brain with a general readout of ambient light levels," says Marija Zivcevska, the lead author and a Master's student under Dr. Wong.
"Although several lines of evidence have implicated ipRGCs in photobias, to date there is limited clinical data to support this."
The test they developed uses a commercially available "flash stimulator" – a device that is normally used to test for vision disorders – and which was programmed to deliver tightly-controlled flashes of light of varying colours. This device was linked to two push buttons, through which patients could indicate when they experienced visual discomfort.
When the test was used on a small group of adults with no history of visual disorders, the results supported the idea that ipRGCs are involved in visual discomfort. For example, they revealed that blue light is more likely to induce visual discomfort than red light – which agrees with previous findings that ipRGCs are activated when exposed to blue light.
The test – the first of its kind – provides an objective way to assess the light conditions that cause discomfort. This work represents an important first step towards improving our understanding of photophobia and developing new therapies to treat this condition.