Join Now | Sign in

Visual Disturbances Health Article

Save

Marketplace

Licensed from

Page: < Back 1 2

Blindness

Blindness is the partial or complete loss of vision. The leading causes of blindness are glaucoma, cataracts, and diabetic retinopathy. Blindness can also result from eye diseases, optic nerve disorders, or brain diseases involving visual pathways or the occipital lobe of the brain. The patterns of visual field reduction depend on the area that is being affected by disease. Damage to visual pathways as a result of macular degeneration, retinal detachment, or optic nerve atrophy can affect one or both eyes. In contrast, damage to the optic nerve chiasm or the pathway beyond it affects both eyes. There are many eye diseases that can cause visual abnormalities or/and blindness, including retinal detachment, cataracts, retinal disorders (often inherited), and macular degeneration.

Macular degeneration is the leading cause of blindness for those over age 55 in the United States. The macula is the central portion of the retina that records images and sends them from the eye to the brain via the optic nerve. If the macula deteriorates, the eye loses the ability to see in fine detail. The cause of macular degeneration is not fully understood, but risks for the disorder increase with age. Other abnormalities in the central retina can lead to blurry vision or can affect color perception. Color blindness can also originate from the lack of one or more type of cones, a type of light receptor on the eye. Total color blindness (monochromatic vision) is very rare; most commonly, varying levels of single color deficits are found among people with color blindness. Central vision can also be destroyed by small hemorrhages in the retina as a result of the aging process or diabetic retinopathy.

The neuronal diseases affecting the optic nerve and causing blindness can result from developmental abnormalities (hereditary or sporadic), abnormalities in the blood vessels causing an insufficient blood supply to the eyes or optic nerve, glaucoma, and demyelinating and inflammatory diseases such as multiple sclerosis, tumors, toxic agents, and trauma.

Optic nerve damage

Papilledema, the swelling of the optic nerve, can result from increased intracranial pressure or optic nerve deterioration (optic neuropathy). Inflammation, lack of adequate blood supply to the optic nerve, and certain diseases such as multiple sclerosis can cause the optic nerve to deteriorate. A brain tumor, bleeding or blood clots in the brain, brain swelling due to encephalitis or trauma, or a blockage in cerebrospinal fluid circulation can cause an increase in pressure inside the skull (intracranial pressure). The condition is often life threatening, and correct diagnosis of papilledema is important.

Papilledema arising from increased intracranial pressure is often accompanied by other symptoms, including diplopia, nausea, headache, and reduction of the visual field. When diagnosing papilledema, the physician looks for swelling of the optic disc (the area where the optic nerve enters the eye). The early signs include slight changes in appearance of the edge of neural tissue. Later, the disc rises from the retinal surface and can appear pale or can show signs of hemorrhages in severe cases. Persistent, chronic papilledema can cause atrophy of the optic nerve head and result in blindness.

The optic nerve can also be damaged by increased intraocular pressure (IOP) as in glaucoma. The pressure develops in aqueous area of the eye and is transmitted to the back of the eye, causing an initial reduction in peripheral vision and leading eventually to blindness. Glaucoma is often a complication arising from diabetes.

Additionally, optic neuritis, or inflammation of the optic nerve, can cause permanent loss of vision. Demyelinating diseases such as multiple sclerosis, systemic infections, diabetes, and hereditary factors can cause optic neuritis. Optic neuritis can also be a secondary complication of diseases such as meningitis, sinusitis, or tuberculosis, or reactions to toxins or trauma.

Other important causes of blindness are tumors affecting the optic chiasm (the area in the brain where the optic nerves cross) such as gliomas, cerebral tumors, and pituitary adenomas. In these cases, the transfer of visual stimuli through the optic nerve and visual pathways is directly affected and results in blindness.

BOOKS

Acheson, James, and Paul Riordan-Eva. Fundamentals of Clinical Ophthalmology: Neuro-Ophthalmology. London: BMJ Books, 1999.

Glaser, J. D. (ed). Neuro-ophthalmology, 3rd ed. Philadelphia: Lippincott Williams and Wilkins, 1999.

OTHER

"Double Vision (Diplopia)." InteliHealth Inc. February 28, 2004 (June 3, 2004). <http://www.intelihealth.com/IH/ihtIH/WSIHW000/9339/23796.html>.

"Understanding Nystagmus." Royal National Institute of the Blind. February 28, 2004 (June 3, 2004). <http://www.rnib.org.uk/xpedio/groups/public/documents/publicwebsite/public_rnib003659.hcsp>.