Vision loss
Vision loss or
visual loss is the absence of
vision where it existed before, which can happen either
acutely (i.e. abruptly) or
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.
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,
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.
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;
macular disease (
e.g.,
macular degeneration); and
retinal vascular occlusions, the most important of which is central retinal artery occlusion.
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.
The
optic nerve can be affected by
optic neuritis,
retrobulbar neuritis,
papillitis,
papilledema,
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 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
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).
*
Living with Vision Loss - American Foundation for the Blind*
International Standards: "Visual Standards - Aspects and Ranges of Vision Loss" - International Council of Ophthalmology*
Blindness*
Eye examination*
Low vision*
Visual acuity*
Visual impairment
