Photophobia (also light sensitivity) or fear of light, is a symptom of excessive sensitivity to light and the aversion to sunlight or well-lit places. In medical terms, it is not fear, but an experience of discomfort or pain to the eyes due to light exposure.

Light sensitivity is usually due to too much light entering the eye, which causes over stimulation of the photoreceptors in the retina and subsequent excessive electric impulses to the optic nerve. This leads to a reflex aversion to light, and discomfort or pain. Too much light can enter the eye if it is damaged, such as with corneal abrasion and retinal damage, or if a pupil(s) is unable to normally constrict (seen with damage to the oculomotor nerve).

Patients may develop photophobia as a result of several different medical conditions related to the eye or the nervous system.

• Albinism
• Anticholinergic drugs may cause photophobia by paralyzing the iris sphincter muscle.
• Aphakia
• Burns to the eye
• Cataracts
• Chiari malformation
• Chikungunya
• Conjunctivitis
• Conjunctivitis
• Corneal abrasion
• Corneal ulcer
• Cystinosis
• Drugs such as Atropine, Cyclopentolate, Hydroxypropyl cellulose, Doxercalciferol, Metipranolol, Nabilone, Nilutamide, Nitisinone, Pramipexole, Travoprost, Trimethadione
• Encephalitis
• Encephalitis
• Eye disease, injury, or infection such as chalazion, episcleritis, glaucoma, keratoconus
• Hangover
• Idiopathic anterior uveitis/iritis
• Influenza
• Iritis
• Keraconjunctivitis sicca (dry eye)
• Lightly pigmented eye
• Meningitis
• Migraines
• Mydriatic use
• Retinal detachment
• Subarachnoid haemorrhage

Patients with photophobia will avert their eyes from direct light (sunlight and room lights), or may seek the shelter of a dark room or wear sunglasses.

• Pain in the eye
• Headache
• Nausea
• Neck stiffness
• Blurred vision
• Sore or wound in eye
• Redness
• Itching
• Swelling
• Dizziness
• Numbness or tingling elsewhere in the body
• Changes in hearing

Photophobia is also a behavior demonstrated by insects or other animals which seek to stay out of the light.

• Swelling

• Heliophobia, fear of sunlight
• Photosensitivity, the amount to which an object reacts upon receiving photons of light
• Erythropoietic protoporphyria, a disease manifesting itself with painful photosensitivity
• Photic sneeze reflex, a medical condition by which people exposed to bright light sneeze