POTS Light Sensitivity: Can POTS Make You Sensitive to Light?

Is Light Sensitivity Linked to POTS?

At least 1 study links them. Researchers measured light-sensitivity thresholds in 30 people with POTS, 30 with chronic migraine and 20 healthy controls. People with POTS became uncomfortable at lower light levels than both other groups, which the authors called unexpected (Cortez, 2021). Light sensitivity is also called photophobia. It's 1 small study at 1 center, measured at a single visit, so it shows that people with POTS reached discomfort at lower light levels, and it doesn't show why.

Photophobia is common with migraine, meningitis, concussion and a range of eye diseases (Burstein, 2019). For how it fits into migraine, see photophobia in migraine.

When light sensitivity comes up with POTS, our team looks at the same eye and brain pathways it checks after a head injury. The clinic counts more than concussion as brain injury. A fall from a horse or a hit on the basketball court can do it, and so can trauma tied to body chemistry or an infection. Our team thinks about light sensitivity in a similar way in all of them, starting with how well the brain controls the pupil. For the wider set of symptoms people with POTS report, see POTS symptoms by body system. Light sensitivity that comes on suddenly with a fever, a stiff neck or a severe headache needs emergency care.

How Does Your Pupil Control Light?

Your pupil is a built-in dimmer switch. In the dark it widens to let more light in. In bright midday sun it should narrow and hold there, which cuts the light reaching the back of the eye. That control helps you see clearly and judge depth, and most people never notice it working.

The control runs on a reflex. Light reaches the retina, and slow fibers in the optic tract carry the signal to the pretectal area. Nerve cells there pass it on to the Edinger-Westphal complex, where the nerve cells that tell the pupil to constrict begin (Hultborn, 1978). Our team holds that areas in the frontal lobe and prefrontal cortex govern that reflex, and that those areas also run planning and focus, so the pupil's response is one output of a larger system.

Why Does Light Sensitivity Follow a Head Injury?

Light sensitivity is common after a brain injury, and fewer people have it in the first 3 months, though for some it lasts a year or longer. A meta-analysis pooled studies of photophobia after traumatic brain injury (TBI) and found it in 30.46% of people at 1 week, 19.34% between 1 week and 1 month, and 13.51% between 1 and 3 months after the injury (Merezhinskaya, 2021).

For the full picture of symptoms that linger after a concussion, see our page on post-concussion syndrome treatment.

Damage to the visual pathway that carries signals from the eye into the brain can cause photophobia, along with vision loss and gaps in the visual field (Maher, 2023).

Concussion also changes how the pupil reacts to light. 3 studies found the reflex differs after concussion, though they disagree on direction and use different tools (Ciuffreda, 2017; Carrick, 2021; Hsu, 2021). In adults with mild TBI, some pupil measures separated people with light sensitivity from those without it (Ciuffreda, 2017), while in children with concussion, those with and without light sensitivity had similar pupil responses (Hsu, 2021).

In our team's view, a flashlight check of the pupils is a window into those reflexes. For more on what a concussion does to the pupils, and when unequal pupils need the ER, see pupils different sizes after head injury. For care after a concussion, see post-concussion syndrome treatment and post-concussion treatment at the clinic.

What Are the 2 Ways Light Starts to Hurt?

Our team separates light sensitivity into 2 causes. In the first, the pupil can't hold its squeeze. Instead of narrowing in bright light and staying there, it tires and widens, so more light gets in than usual, and that extra light can reach a level that hurts. In the second, the nerve cells that sense light are too sensitive to begin with, so a normal amount of light feels like too much. The 1 study in POTS fits the second pattern: the authors found lower thresholds for light and for pain on the forearm, and they read it as a nervous system turned up across several senses (Cortez, 2021). No study has tested pupil control as a cause of light sensitivity in POTS.

2 ways light can start to hurt, in our team's view

Cause	What happens	What it feels like	What testing looks for
Pupil control tires (our team's working model; not tested in research)	The pupil can't hold its squeeze in bright light, so it drifts wide and lets extra light in.	Light that becomes too much while the eyes hold a position, as in reading or driving.	Pupils that pulse bigger and smaller when you look up in steady light.
Light sensors too sensitive	The nerve cells that sense light overreact to a normal amount of it.	A normal amount of light feels like too much.	No pupil pattern; in POTS research it shows up as a lower light threshold (Cortez, 2021).

Why Does Looking Up Make the Pupil Pulse?

The structures that move the eyes up sit in the dorsal midbrain. When that area is damaged, as in Parinaud's syndrome, upward gaze fails and the pupils respond poorly to light (Ortiz, 2021). That's structural damage, and it looks different from the pulsing our team describes. In our team's view, the circuits that control the pupil share some structure with the ones that move the eyes up and hold them there, so in a healthy person, looking up shouldn't change pupil size unless the light changes.

Our team tests this in the dark with VR goggles, so the light stays the same the whole time. You look straight ahead, then up. Your eyes should hold steady, and your pupils shouldn't change. If the eyes can't hold, that points to a problem in the hardware that runs eye position. If the eyes hold but the pupils pulse, growing and shrinking in a wave, the system that keeps the pupil narrow is tiring. Our team compares it to holding a weight up: as your arm tires, it drifts down and you pull it back up. For how the eye movement part of testing works, see what part of the brain controls eye movements.

Healthy Tired

Replay

Daily life asks for this all the time. Reading, scrolling, looking up at a board in a classroom, working at a computer and driving with light coming through the windshield all ask your eyes to hold a position. If the pupil pulses while they do, our team expects it to let in bursts of too much light, which raises the odds the light will hurt.

Is Blurry Vision Part of the Same Problem?

Our team checks for several causes of blur, and they can come from several parts of the eye control system. If your eyes don't point at exactly the same target, the 2 images land slightly apart and look a little blurred. Eyes that tire from reading or scrolling get less accurate as they move, and that reads as blur. Turning, tipping or tilting your head may change how clear things look, which our team links to the way the neck talks to the balance system in the brain. Less blood flow to the eye, or a lens or pupil that doesn't engage well, can blur vision too. Research supports part of the picture: damage to the pathways that move the eyes mainly causes misaligned eyes and double vision (Maher, 2023).

Blur or blackout when you stand up is a separate pattern, covered in why your vision goes black when you stand up and OCHOs. Blur that shows up with reading or phone use, from focusing up close or turning the eyes in, is covered in why reading and screens can make you dizzy. A sudden change in vision needs prompt medical care, as our page on intracranial hypertension and POTS explains.

How Does Our Team Approach Light Sensitivity?

Our team goes after the mechanism under the symptom. When testing shows the pupil can't hold, the work is to strengthen that control pathway, so the loop runs better and the pupil holds while the eyes look up, read and track. The goal is a system that can do more with the eyes before the pupil fails, and fewer symptoms as a result. The plan depends on what testing shows for each person.

POTS Light Sensitivity: FAQ