Photophobia: Causes, Symptoms, Light Sensitivity and Management

What photophobia is, and what it is not

Clinicians use photophobia for abnormal intolerance of light: discomfort or pain in light levels that most people find comfortable. It is distinct from glare disability (reduced vision in bright light), from photosensitivity in the dermatological sense (skin reactions to light) and from the light-triggered seizures of photosensitive epilepsy. Some authors separate photophobia (light causes pain or discomfort) from photo-oculodynia (light causes eye pain specifically), but in practice the terms overlap.

Photophobia can be acute, as in a corneal abrasion or iritis, or chronic, as in migraine or blepharospasm. It may be present only during symptom episodes or persist between them.

Sources: [1], [2], [3]

Conditions associated with photophobia

Reviews group the causes into eye conditions, neurological conditions and a smaller set of medication, psychiatric and systemic causes. The list below is not exhaustive and the presence of photophobia alone does not identify which applies; that requires an examination.

• Eye surface and anterior segment: dry eye disease, corneal abrasion or ulcer, keratitis, uveitis and iritis, conjunctivitis, and after some eye surgery.
• Other ocular: cataract, retinal dystrophies such as cone dystrophy and achromatopsia, albinism, and dilated pupils.
• Neurological with normal examinations: migraine (the most common association), benign essential blepharospasm, and traumatic brain injury or concussion.
• Other neurological: meningitis and subarachnoid haemorrhage (medical emergencies), progressive supranuclear palsy, and some chronic pain conditions.
• Visual snow syndrome, in which photophobia is a frequent accompanying symptom.
• Medications and other factors: some drugs that dilate the pupil, and withdrawal states; anxiety and depression can lower the threshold for light discomfort.

Sources: [1], [2], [3], [10]

How light reaches discomfort and pain circuits

The retina contains rods, cones and a small population of intrinsically photosensitive retinal ganglion cells (ipRGCs) that express the photopigment melanopsin. ipRGCs respond to light directly, most strongly around 480 nm, and project to brain regions involved in circadian timing, the pupil reflex and, importantly for photophobia, to parts of the thalamus.

In an influential series of experiments, light signals carried by ipRGCs were shown to converge in the posterior thalamus of rats on neurons that also receive input from the dura, the pain-sensitive covering of the brain, and those neurons project widely to the cortex. The same study reported that blind people with migraine who retained ipRGC function still found light worsened their headache, while those with no light perception did not. This retino-thalamo-cortical route is the leading proposed mechanism for light-exacerbated headache.

Cone pathways also matter. Later work found that colour affects migraine photophobia: in laboratory testing, green light was the least aversive and could even reduce headache intensity at low levels, while blue, amber, red and white light increased it. Colour-selective discomfort has also been measured outside attacks. For eye-surface disease the route is different: irritation of trigeminal nerve endings in the cornea sensitises the same trigeminal system, so light discomfort and eye pain often co-occur.

Most of the circuit evidence comes from animal studies with indirect human support; it is best described as a well-supported proposed mechanism rather than settled physiology.

Sources: [4], [5], [6], [7], [8], [9]

How photophobia is assessed

A clinician will usually take a history (onset, triggers, time course, associated headache, eye pain, vision changes and medications), examine the eye surface, pupils and the back of the eye, and look for neurological signs. Questionnaires that rate the impact of light sensitivity on daily activities are used in research and some clinics. There is no single objective test for photophobia; the examination is directed at finding the cause.

Sources: [1], [3]

Management approaches in the published literature

Treatment is aimed at the underlying condition first: lubrication and anti-inflammatory care for eye-surface disease, specialist treatment for uveitis, preventive and acute therapy for migraine, and botulinum toxin for blepharospasm, among others. Light-related measures sit alongside that care, not instead of it.

• Avoid chronic dark adaptation. Specialists commonly advise against wearing dark sunglasses indoors, because the retina adapts to the darkness and sensitivity to normal light can increase.
• Adjust the environment: lower screen brightness and contrast, use warmer or dimmable lighting where fluorescent flicker is a trigger, and use brimmed hats and sunglasses outdoors.
• Wavelength-selective tints. A rose-coloured tint studied in children with migraine in 1991 reduced headache frequency compared with a blue tint in a small randomized trial; the FL-41 tint improved light sensitivity and blink measures in randomized crossover studies in blepharospasm. These are small studies and the populations differ.
• Thin-film notch filters centred at 480 nm, designed to reduce ipRGC stimulation, were compared with a 620 nm filter in a randomized crossover trial in chronic migraine: both groups improved and the two filters did not differ, so the specific wavelength effect remains unproven.
• Behavioural and psychological support can help where anxiety amplifies light avoidance.

Sources: [1], [2], [11], [12], [13]

Evidence: established versus emerging

Established

• Photophobia is a symptom with many causes; migraine, blepharospasm and traumatic brain injury are the commonest associations when examinations are normal.
• ipRGCs exist in the human retina, express melanopsin and project to non-image-forming brain regions.
• Treating the underlying cause is the first step in management.

Emerging or unresolved

• The ipRGC to posterior thalamus route for light-exacerbated headache is based mainly on animal data with indirect human support.
• Colour-specific effects on migraine photophobia come from laboratory studies and have not been translated into proven treatments.
• Evidence for tinted and notch-filter lenses rests on small randomized studies in specific populations; no large multicentre trial exists.

Questions and evidence-based answers

Continue reading

• Glasses for photophobia and light sensitivity
• Migraine and photophobia
• Melanopsin, ipRGCs and neural responses to light
• Spectral transmittance and wavelength-selective filters

References

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3. Wu Y, Hallett M. Photophobia in neurologic disorders. Translational Neurodegeneration, 2017. PMID 28932391. DOI 10.1186/s40035-017-0095-3.
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5. Noseda R, Bernstein CA, Nir RR, et al.. Migraine photophobia originating in cone-driven retinal pathways. Brain, 2016. PMID 27190022.
6. Nir RR, et al.. Color-selective photophobia in ictal vs interictal migraineurs and in healthy controls. Pain, 2018. PMID 29905657. DOI 10.1097/j.pain.0000000000001303.
7. Burstein R, Noseda R, Fulton AB. Neurobiology of photophobia. Journal of Neuro-Ophthalmology, 2019. PMID 30762717. DOI 10.1097/WNO.0000000000000766.
8. Hattar S, Liao HW, Takao M, Berson DM, Yau KW. Melanopsin-containing retinal ganglion cells: architecture, projections, and intrinsic photosensitivity. Science, 2002. PMID 11834834.
9. Berson DM, Dunn FA, Takao M. Phototransduction by retinal ganglion cells that set the circadian clock. Science, 2002. PMID 11834835.
10. Eren OE, Ruscheweyh R, Straube A, Schankin CJ. Quantification of photophobia in visual snow syndrome: A case-control study. Cephalalgia, 2020. PMID 31865761. DOI 10.1177/0333102419896780.
11. Good PA, Taylor RH, Mortimer MJ. The use of tinted glasses in childhood migraine. Headache, 1991. PMID 1960058. DOI 10.1111/j.1526-4610.1991.hed3108533.x.
12. Blackburn MK, Lamb RD, Digre KB, et al.. FL-41 tint improves blink frequency, light sensitivity, and functional limitations in patients with benign essential blepharospasm. Ophthalmology, 2009. PMID 19410958. DOI 10.1016/j.ophtha.2008.12.031.
13. Hoggan RN, Subhash A, Blair S, et al.. Thin-film optical notch filter spectacle coatings for the treatment of migraine and photophobia. Journal of Clinical Neuroscience, 2016. PMID 26935748. DOI 10.1016/j.jocn.2015.09.024.