Vision, disorders of
The most widespread visual disorders are refractive errors, such as ant stigmatism (the abnormal curvature of the front of the eye), myopia (short sightedness), and hypermetropia (long sightedness), which can almost always be corrected by contact lenses or glasses. Other types of disorder affecting vision include amblyopia (lazy eye); double vision; and disorders of the eye or optic nerve, of the nerve pathways connecting optic nerves to the brain, and of the brain itself.
Causes in the eye
The eye can lose its transparency through corneal opacities, cataract, or vitreous haemorrhage (bleeding into the gel of the eye behind the lens). Defects near the centre of the retina cause loss of corresponding parts of the visual field. Floaters, which are often insignificant, can indicate a retinal tear or haemorrhage, or they may herald a retinal detachment. Optic neuritis (inflammation of the optic nerve) can cause a blind spot in the centre of the visual field.
Causes in the brain
Damage to the brain (for example, from a stroke) can cause visual impairment such as hemianopia (loss of half the visual field), agnosia (failure to recognise objects), visual preservation (in which a scene continues to be perceived after the direction of vision has shifted), and visual hallucinations.