What Causes Light Sensitivity?

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What Causes Light Sensitivity?

The more you understand about a particular challenge, the better equipped to handle it you may become. Perhaps this is why so many people who suffer from photophobia or light sensitivity tend to become experts on the subject.

If you know what causes light sensitivity in the eye, perhaps you can avoid or mitigate those causes and enjoy life with fewer effects. This may be especially true for those whose photophobia tends to trigger migraines. As shown in two recent studies, the cause of light sensitivity may lie in a photopigment most of us have never heard of. Keep reading to learn more about melanopsin and what it has to do with photophobia.

How the Eye Responds to Light

For decades, it was believed that specific sets of cells, called rods and cones, were completely responsible for the eye’s ability to detect light. In bright light, cones have the role of mediating colors. In the darkness, rods enable you to be able to see your way. Indeed, the function of rods and cones are critical to your ability to see light and color.

However, within the last 20 years or so, research has discovered that these aren’t the only cells capable of sensing light. Between 1999 and 2002, researchers at Brown University and Johns Hopkins University discovered that a small subset of cells in the eye, called retinal ganglion cells (RGCs), express melanopsin; a photopigment which is also capable of detecting light. In fact, melanopsin is also instrumental in how the pupil reacts to bright light.

“Melanopsin contributes to the expansion and contraction of the pupil in response to changes in light intensity. Thus, a malfunctioning melanopsin system may contribute to conditions that involve sensing too much or too little light, such as migraine, concussion, insomnia, or seasonal affective disorder.”

This understanding set the tone for further study on what causes light sensitivity, and how melanopsin is related to both photophobia and migraine.

girl wearing Axon Optics migraine glasses

The Most Recent Research on Melanopsin & Migraine

More recently, the relationship between melanopsin and migraine has been given a closer look. A study published by the International Headache Society set out to define the role melanopsin may play in photophobia, and its contribution to migraine.

Published in late 2020, this study gathered information from both healthy controls and migraineurs. Paraphrased from the study:

Healthy controls and migraineurs were categorized according to the International Classification of Headache Disorders criteria. Photophobia was measured with migraineurs tested during their interictal headache-free period. Melanopsin-driven pupil responses quantified the photosensitivity in Retinal Ganglion Cell (ipRGC) function.

In plain language, this means that people with and without migraines were tested to measure how their Retinal Ganglion Cells (ipRGC) responded to specific spectrums of light known to activate the eye’s cone cells and melanopsin response. On migraineurs, the testing was conducted without an active headache present. Researchers then measured the eye’s response in both migraine and non-migraine groups.

The Results

Researchers found that within this light spectrum, people who suffer from migraines had a lower threshold for photophobia (∼0.55 log units; p < 0.001). They also had a larger post-illumination pupil response (p = 0.03) than the control or non-migraine group. 

This means that not only do people with migraine have a lower tolerance for bright light, but their eye’s response to that light can be longer lasting than those who don’t get migraines. If you suffer from migraine yourself, you can probably attest to the study’s finding that exposure to bright light can not only be bothersome in the moment, but also long after the exposure has passed.

When it comes to melanopsin specifically, the study revealed that it contributed ~1.5x more than cone luminance to the eye’s photophobia response. Remember — melanopsin contributes to how your pupil constricts, or shrinks, when you’re exposed to bright light. The pupil is responsible for how much of that light is allowed into the eye, designed to protect your retina and its ipRGC cells from overexposure.

We already knew that people with photophobia have hypersensitivity in the eyes’ ipRGC and cone luminance pathways. What researchers discovered in this study is that people with photophobia also show an abnormal response when melanopsin is activated by certain types of light. Combined, these factors are what causes light sensitivity.

What Does This Mean for You?

In the study conclusion, researchers suggest that, “artificial lighting strategies” designed to produce less of a melanopsin response might be used to, “limit the lighting conditions leading to photophobia.” 

In other words, restricting the spectrum of light most likely to excite melanopsin response may be used to reduce photophobia’s effects.

According to Dr. Bradley Katz, neuro-ophthalmologist and co-founder of Axon Optics, “These interesting findings lend further credibility to our long-held belief that both ipRGCs and melanopsin are important in photophobia. That’s why Axon Optics’ precision tint works — it filters out the spectrum of light most likely to cause this hyperactive ipRGC and abnormal melanopsin response. If you can tame that response, which is what causes light sensitivity, you can lessen your discomfort and the associated onset of migraine.”

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We love hearing about new research that indicates Axon Optics is on the right track to helping more migraine sufferers experience less pain. Even more exciting to us is the effect that revealed knowledge has in the lives of our customers. 

Do you have a story to share? Please send it to [email protected]

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