Visual disturbances are most commonly associated with migraine headache. These symptoms can also be related to local eye conditions, such as glaucoma, which can produce a halo effect around objects. Visual disturbances may be warning signs of a stroke, and are termed "transient ischemic attacks." Although these ischemic attacks more commonly occur in older individuals, they can be confused with migraine-related disorders. In migraine, visual disturbances can occur before or during the headache. They may be related to the headache itself, in which case the occurrence of blurred vision and increased headache related to light, or photophobia, are most common.
The aura of migraine is most commonly visual, and precedes the migraine attack by 20 to 60 minutes. Occasionally, the migraine aura will persist into the headache phase of migraine, or may even start once the headache has begun.
Several major forms of visual phenomena can occur as migraine related auras. Photopsia is the occurrence of bright flashes of light in the visual field, similar to the effect that occurs when an old-fashioned camera flash bulb would go off. Fortification spectra or teichopsia are the bright, shimmering, jagged lines that can spread across the visual field. The name fortification spectra comes from the visual appearance that resembles the battlements or walls of archaic fortresses. Metamorphopsia is the distortion of visual images in their size, shape, and color. This has been termed the "Alice in Wonderland Syndrome," and is named after the events described in Lewis Carroll's book Through the Looking Glass, and as portrayed in original woodcuts by John Tenniel. Other visual effects may include the occurrence of scotoma or partial loss of vision, ranging from blank spots in the field of vision, or "tunnel" vision effects. Amaurosis Fugax, which appears as a loss of vision spreading from the top down, as if a shade were being drawn, can also occur, but is more commonly due to decreased blood flow due to disease causing narrowing in the carotid artery.
Some medications such as the tricyclic antidepressants may cause blurred vision and difficulty with focusing.