Bright light and migraine

Photophobia is a symptom

Photophobia means abnormal sensitivity to light. It is part of the ICHD-3 criteria for migraine without aura: during the headache, nausea or vomiting, or photophobia together with phonophobia (sound sensitivity).

It can also start before the pain. The Migraine Trust lists being more sensitive to light among prodrome symptoms, which can appear hours or days earlier. Some people also feel discomfort from light between attacks (Wilkins 2021).

So when light seems to set off an attack, there are two possible orders of events:

• light came first, and the attack followed;
• the attack had already started, and light became painful as a result.

From the inside, these can feel the same. The Migraine Trust says it can be hard to tell whether light is a trigger or a symptom.

What studies show

• Self-report. 38.1% of 1,207 clinic patients named lights as a trigger at least occasionally (Kelman 2007).
• Provocation. 27 people with migraine with aura were exposed in a lab to the triggers they reported: 30 to 40 minutes of bright, flashing or flickering light, or strenuous exercise. No one developed an attack after light alone. Exercise brought on migraine in 4 of 12 (Hougaard 2013). The authors said confirmation is needed. The study covered only migraine with aura, and the reports of it describe no control group.
• Premonitory phase. Among 1,010 people with migraine at a Hamburg clinic, those with light sensitivity before the headache named flickering or bright light as a trigger significantly more often than others (p under 0.0001). The authors suggest that many such triggers may be misread symptoms, though recall bias is possible (Schulte 2015).
• Review. Sensitivity to light is among the premonitory symptoms that may mimic triggers (Marmura 2018).

A negative lab test does not exclude light in daily life. The threshold idea holds that several factors may need to combine, which a single exposure in a lab does not reproduce.

Mechanism

Research explains how light worsens a headache better than how it might start one.

A pathway from the retina to thalamic neurons that respond to migraine activity carries light signals to cortical areas, based on animal and human observations (Burstein 2019). In tests, green light worsened migraine headache less than white, blue, amber or red light (Noseda 2016). The American Migraine Foundation mentions green light, but this research concerned worsening of an existing headache, not prevention.

Researchers disagree on the site. Wilkins 2021 calls retinal findings inconsistent and favours a cortical explanation.

How to check it in your diary

1. Write the order. Was light already bothering you before the exposure?
2. Describe the exposure: sunlight, glare, flicker or a screen, and for how long.
3. Log early symptoms the same day, such as tiredness or yawning.
4. Count exposures with no attack, such as a bright day outdoors with nothing after it.
5. Log the rest of the day. Sleep, heat and skipped meals can coincide with a day outdoors.

For the general method, see how to test a suspected trigger.

When to see a doctor

Tell your doctor if sensitivity to light is new or stays between attacks, because it also occurs in other conditions. Sudden severe headache and new neurological symptoms, including loss of vision, need urgent care.