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Ranges of vision loss 
Various scales have been developed to describe the extent of vision and vision loss based on visual acuity. Early editions of the World Health Organization's ICD described a simple distinction between "legally sighted" and "legally blind". The ICD-9 released in 1979 introduced the smallest continuous scale which consisted of three tiers: normal vision, low vision, and blindness.
Acute visual loss 
Acute visual loss may be dramatic in presentation. It may be caused by media opacities, retinal disease, optic nerve disease, visual pathway disorders, or functional disorders, or it may be in fact an acute discovery of chronic visual loss.
Media opacity 
Opacities of the clear refractive media of the eye such as the cornea, anterior chamber, lens, and vitreous humor may cause acute visual loss as manifested by blurry vision or reduced visual acuity. While pupillary reflexes may be affected, these conditions generally do not cause a relative afferent pupillary defect.
Retinal disease 
Retinal diseases may cause sudden visual loss. Because the retina is being affected, there is usually a concomitant relative afferent pupillary defect. Conditions that affect or destroy the retina include retinal detachment; macular disease (e.g., macular degeneration); and retinal vascular occlusions, the most important of which is central retinal artery occlusion. Current research (2013) has raised the possibility of complete regeneration of the retina. (see Retinal regeneration)
Optic nerve disease 
Diseases which affect the optic nerve may cause acute visual loss. Signs include an abnormal pupillary reflex, with an afferent pupillary defect when the optic nerve disease is unilateral. It can also be caused by strobe light.
The eye is very sensitive to restriction of its supply of oxygen. A dimming of vision (a brownout or greyout) accompanied by loss of peripheral perception may result from low blood pressure, shock, g-LOC (an aviation related problem) or simply standing up suddenly, especially if sick or otherwise infirm. Vision usually returns readily once the conditions restricting blood flow are lifted.
Visual pathway disorder 
Also traumatic causes can lead to Acute Vision Loss.
Functional disorder 
The term functional disorder is now used where hysterical and malingering were historically used. This shift recognizes the inherent inability of the physician to identify the subjective experience of a patient (and thus whether that patient can truly see or not).
See also 
- International Council of Ophthalmology. "International Standards: Visual Standards — Aspects and Ranges of Vision Loss with Emphasis on Popular Surveys." April 2002.
- World Health Organization. International Classification of Diseases, 9th Revision (ICD-9), World Health Organization, Geneva, 1977.
- AFB Senior Site Expanding possibilities for people with vision loss
- CDC's "Learn the Signs. Act Early." campaign - Information for parents on early childhood development and developmental disabilities such as vision loss
- Living with Vision Loss - American Foundation for the Blind
- VisionAWARE - Self Help for Vision Loss Independence for adults with low vision
- Living with sight loss (RNIB)
- International Standards: "Visual Standards - Aspects and Ranges of Vision Loss" - International Council of Ophthalmology
- Catalan Association for the Blind and Visually Impaired
- LowVision.com Low Vision online informational resource center and referral hub
- Center for the Partially Sighted Low Vision Information and Resources
- Cleveland Sight Center Services for people with vision loss