Light Hurts Your Eyes More Than Others. Your Genes May Explain Why.

Your COMT gene encodes an enzyme that breaks down dopamine and norepinephrine in your prefrontal cortex. These are your brain’s main stress and arousal chemicals. When COMT works normally, it clears these neurotransmitters at a balanced rate, allowing your brain to stay calm and focused without overreacting to stimuli.

The Val158Met variant is present in roughly 25% of people with European ancestry who are homozygous for the slow version. Here’s what happens: if you carry two copies of the Met allele (slow COMT), your brain clears dopamine and norepinephrine much more slowly than average. Your prefrontal cortex becomes hyperaroused, making you more sensitive to all incoming sensory information, including light. Your visual system perceives brightness as more intense and more threatening.

In everyday life, this means bright environments feel overwhelming before others around you even notice. A sunny day indoors, fluorescent office lighting, or a bright screen triggers immediate discomfort. Your nervous system is essentially stuck in a heightened state of alertness, interpreting light as a stronger signal than it actually is.

Your SLC6A4 gene codes for the serotonin transporter protein, the molecular machine that recycles serotonin back into neurons after it’s been released. Serotonin is your brain’s main volume control. It dampens excessive sensory input and keeps you from being overwhelmed by visual, auditory, and tactile information. Without adequate serotonin recycling, your sensory gates stay open too wide.

The 5-HTTLPR short allele is carried by roughly 40% of people. If you have one or two copies of the short variant, your neurons recycle serotonin less efficiently. Serotonin accumulates in the synapse temporarily, then drops lower between pulses, leaving your brain in a state of unstable sensory filtering. The result is heightened sensitivity to all visual stimuli, especially changes in brightness and flicker.

You likely notice that light sensitivity worsens with stress or poor sleep. Both deplete serotonin. In these states, your visual processing becomes even more chaotic. Bright or flickering light feels unbearable. You may also experience anxiety or low mood alongside your photophobia.

Your MTHFR gene encodes the enzyme that converts dietary folate into methylfolate, the active form your cells actually use. This step is critical because methylfolate fuels the production of nitric oxide, a molecule that keeps blood vessels in your retina dilated and well-perfused. Poor retinal blood flow starves photoreceptors of oxygen and accelerates oxidative stress in the eye.

The C677T variant is present in roughly 40% of people with European ancestry. If you carry two copies of the T allele (homozygous), your MTHFR enzyme functions at only 40% efficiency. Your cells struggle to convert folate into the active form, leading to elevated homocysteine, impaired nitric oxide production, and reduced blood flow to the retina. Photoreceptor cells become hypoxic and increasingly stressed.

This manifests as glare sensitivity and difficulty adapting from dark to bright environments. Your retinal cells are already running on low oxygen, so a sudden bright light feels like an assault. You may also notice that your eyes tire quickly in bright conditions, and you’re more prone to floaters or visual disturbances.

Your BDNF gene codes for brain-derived neurotrophic factor, a protein that supports the growth and survival of neurons and allows your brain to rewire itself in response to experience. BDNF is especially important in the visual cortex, where it helps your brain learn to filter and prioritize relevant visual information while ignoring background noise. Without adequate BDNF, your visual system stays stuck in a state of heightened reactivity.

The Val66Met variant is carried by roughly 30% of people. If you have one or two copies of the Met allele, your brain produces less BDNF, particularly in response to stress. Your visual cortex becomes less able to adapt to bright light or to down-regulate its response to visual stimuli over time. Instead of habituating to light, you remain acutely sensitive to it. Your brain’s stress response to brightness doesn’t diminish.

You’ve probably noticed that you don’t adapt to light the way others do. Even after wearing sunglasses and staying out of bright light, your eyes don’t seem to ‘learn’ that brightness is safe. Your brain can’t reprogram its threat response to visual input. This makes photophobia more persistent and exhausting.

Your VDR gene encodes the vitamin D receptor, a protein found throughout your retina that regulates calcium signaling in photoreceptor cells. Vitamin D and proper calcium balance are essential for photoreceptors to modulate their response to light appropriately. When VDR function is impaired, photoreceptor cells lose their ability to properly regulate their light-sensing machinery, leading to exaggerated responses to brightness.

The BsmI and FokI variants are present in 30-50% of people depending on ancestry. If you carry variants that reduce VDR efficiency, your photoreceptors struggle to maintain proper calcium levels. They become hypersensitive to light, firing more intensely in response to the same brightness that triggers a normal response in others. This overamplification of the light signal reaches your visual cortex as excessive stimulation.

You likely experience photophobia that worsens in winter or when you’re indoors frequently, because both conditions reduce sun exposure and vitamin D synthesis. Your light sensitivity is dynamic: worse when vitamin D is low, better when you’ve had consistent sun exposure at safe times. You may also notice that you’re more prone to dry eyes in bright light, which compounds the discomfort.

Your SOD2 gene codes for superoxide dismutase 2, the main antioxidant enzyme inside mitochondria. Photoreceptor cells are metabolically demanding and live in direct exposure to light, which generates reactive oxygen species (free radicals) continuously. SOD2 is your retina’s primary defense against this oxidative assault. When SOD2 function is reduced, photoreceptor cells accumulate damage and become increasingly irritable and dysfunctional.

The Val16Ala variant is present in roughly 40% of people homozygous for the variant form. If you carry two copies of the Ala allele, your SOD2 protein is less stable and degrades more quickly. Your photoreceptor cells have reduced antioxidant capacity, allowing free radicals from light exposure to accumulate and damage the light-sensing machinery. Over time, this accelerates retinal aging and increases light sensitivity.

This manifests as photophobia that worsens as the day goes on. Morning light feels tolerable. By afternoon, after hours of accumulated light exposure and oxidative stress, brightness becomes unbearable. You may also notice that your eyes feel fatigued and strained after light exposure, and recovery takes longer than it should. Your retina is essentially running on fumes.