Vision loss
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'''Vision loss''' or '''visual loss''' is the absence of [[Visual perception|vision]] where it existed before, which can happen either [[Acute (medical)|acutely]] (i.e. abruptly) or [[chronic (medicine)|chronically]] (i.e. over a long period of time). The effects of visual loss can, before the acquisition of alternative adaptations and skills, be devastating; especially when a person's vision disappears over a short period of time.
==Ranges of vision loss==
Various scales have been developed to describe the extent of vision and vision loss based on [[visual acuity]].<ref name="ICO">International Council of Ophthalmology. [http://www.icoph.org/pdf/visualstandardsreport.pdf "International Standards: Visual Standards — Aspects and Ranges of Vision Loss with Emphasis on Popular Surveys."] April 2002.</ref> Early editions of the [[World Health Organization]]'s [[ICD]] described a simple distinction between "legally sighted" and "legally blind".<ref name="ICO"/> The ICD-9 released in 1979 introduced the smallest continuous scale which consisted of three tiers: normal vision, [[low vision]], and [[blindness]].<ref>World Health Organization. ''International Classification of Diseases, 9th Revision (ICD-9)'', World Health Organization, Geneva, 1977.</ref>
==Acute visual loss==
''Acute visual loss'' may be dramatic in presentation, and is almost always alarming to the person experiencing the loss.
It may be caused by media opacities, [[retina]]l disease, [[optic nerve]] disease, [[#visual pathway disorder|visual pathway disorder]]s, or [[#Functional disorder|functional disorder]]s, 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 (anatomy)|lens]], and [[vitreous humor]] may cause acute visual loss as manifested by blurry vision or reduced [[visual acuity]].
While [[pupillary reflex]]es may be affected, these conditions generally do not cause a [[relative afferent pupillary defect]].
Causes of media opacity include [[corneal edema]], [[hyphema]], [[cataract]] and [[vitreous hemorrhage]].
===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]]; [[macula]]r disease (''e.g.'', [[macular degeneration]]); and [[retinal vascular occlusion]]s, the most important of which is central retinal artery occlusion.
===Optic nerve disease===
Diseases which affect the optic nerve may cause acute visual loss.
[[Sign (medicine)|Sign]]s include an abnormal pupillary reflex, with an afferent pupillary defect when the optic nerve disease is unilateral. can ao be caused by [[strobe light]]
The [[optic nerve]] can be affected by many diseases including [[optic neuritis]], [[retrobulbar neuritis]], [[papillitis]], [[papilledema]], [[glaucoma]], [[ischemic optic neuropathy]], and [[giant cell arteritis]].
===Hypoxia===
The eye is very sensitive to restriction of its supply of oxygen. A dimming of vision (a [[brownout (medical)|brownout]] or [[brownout (medical)|greyout]]) accompanied by loss of peripheral perception may result from low blood pressure, [[Shock (medical)|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===
Visual pathway disorders are any problems that may impede the [[visual pathway]].
Rarely, acute visual loss is caused by [[homonymous hemianopia]] and, more rarely, [[cortical blindness]].
===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).
==References==
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==External links==
*[http://www.afb.org/seniorsite AFB Senior Site] Expanding possibilities for people with vision loss
*[http://www.cdc.gov/ncbddd/autism/actearly/vision_loss.html CDC's "Learn the Signs. Act Early." campaign] - Information for parents on early childhood development and developmental disabilities such as vision loss
*[http://www.afb.org/visionloss.asp Living with Vision Loss - American Foundation for the Blind]
*[http://www.visionaware.org VisionAWARE - Self Help for Vision Loss] Independence for adults with low vision
*[http://www.icoph.org/standards/visionres.html International Standards: "Visual Standards - Aspects and Ranges of Vision Loss" - International Council of Ophthalmology]
*[http://www.accdv.org/en/ Catalan Association for the Blind and Visually Impaired]
==See also==
*[[Blindness]]
*[[Eye examination]]
*[[Low vision]]
*[[Visual acuity]]
*[[Visual impairment]]
[[Category:Blindness]]
[[Category:Ophthalmology]]