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Photophobia 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 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.

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

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

• Meningitis
• Eye disease, injury, or infection such as chalazion, episcleritis, glaucoma, keratoconus
• Subarachnoid haemorrhage
• Albinism
• Burns to the eye
• Migraines
• Encephalitis
• Conjunctivitis
• Aphakia
• Iritis
• Corneal abrasion
• Corneal ulcer
• Cataracts
• Retinal detachment
• Chiari malformation
• Cystinosis
• Anticholinergic drugs may cause photophobia by paralyzing the iris sphincter muscle.
• Hangover
• Chikungunya

In folklore and mythology, many creatures suffer from photophobia - or heliophobia, a specific fear of sunlight.

• The Norse troll is said to either turn to stone or become trapped above ground when the sun rises.
• According to Paracelsus, gnomes explode when they go above ground^{[citation needed]}. As C.S. Lewis puts it, "if he thrust out his face…[it] would break into splinters, bursting as a man would burst in interstellar space." - though in fact, humans exposed to the vacuum of space experience no such spectacular effect.
• In English folklore, goblins are said to be unable to bear light.
• A common element of the vampire myth says that vampires perish, generally by burning or turning to ash, when exposed to direct sunlight.
• Gargoyles are often portrayed as purely nocturnal creatures, changing into stone if the sun shines upon them
• In the story of Hercules, his twelfth labour was to capture Cerberus. In one version of this story he had only to lead Ceberus to daylight.
• In Lithuanian and some other Eastern European folklore, devil is said to go back to hell whenever the sun rises.

• In J.R.R. Tolkien's works, goblins are said to get wobbly legs and become giddy in the head when outside, while trolls turn to stone.
• In Lemony Snicket's A Series of Unfortunate Events, the zombies from the movie Zombies in the Snow are forced to retreat during daylit hours.
• In the films Gremlins and Gremlins 2: The New Batch, both the Mogwai and Gremlins are incredibly sensitive to bright light; direct sunlight on their skin will kill them in a matter of seconds.
• It is common tradition in literature that vampires burn and/or explode when exposed to light, which was first introduced in the 1922 German film Nosferatu. Contrary to popular thought, Bram Stoker's Dracula did not originate this convention.
• In the films 'Blade', 'Blade 2' and 'Blade 3', Wesley Snipes plays a half vampire half human, known as 'The Daywalker', i.e. a vampire that can walk in the light without fear of burning/exploding.
• A character from the anime Ouran High School Host Club, Umehito Nekozawa, avoids light, and wears a hood all the time to protect himself from it. When exposed to light for a short time, he collapses, but he eventually gets over it. It is thought that he could possibly suffer light Photosensitivity.
• prot (lower-case is proper) from the planet K-PAX (upper case is proper), wears dark glasses while on our planet because he can see ultraviolet light and would be blind without them.
• In the films Pitch Black and The Chronicles of Riddick, the antihero protagonist, Richard B. Riddick is photophobic as a result of medical alterations to his eyes which give him superhuman night vision, but forces him to wear welding goggles in the light.

• 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^

Lewis, C.S. Poems: C.S. Lewis. U.S.: Harvest/HBJ, 1964. ISBN 0-15-672248-8.

• Photophobia (Light Sensitivity) at allaboutvision.com
• www.photophobia.tk