Vision, disorders of

The most common visual disorders are refractive errors, such as myopia, hypermetropia, and astigmatism, which can almost always be corrected by glasses or contact lenses. Other disorders include amblyopia; double vision; and disorders of the eye or optic nerve, of the nerve pathways connecting the optic nerves to the brain, and of the brain itself. The eye may lose its transparency through corneal opacities, cataract, or vitreous haemorrhage. Defects near the centre of the retina cause loss of the corresponding parts of the visual field (see macular degeneration). Floaters, which are usually insignificant, may indicate a retinal tear or haemorrhage, or they may herald a retinal detachment. Optic neuritis can cause a blind spot in the centre of the visual field. Damage to the brain (for example, from a stroke) may cause visual impairment such as hemianopia, agnosia, visual perseveration (in which a scene continues to be perceived after the direction of gaze has shifted), and visual hallucinations.