Skip to main content icon/video/no-internet
icon backReturn to Entries

Visual Disorders: Blindness

Blindness is the complete absence or severe impoverishment of vision. The World Health Organization (WHO) defines blindness as acuity of less than 20/400 in the better eye (in case of unequal vision loss across the two eyes) or a visual field of less than 10° around fixation. Blindness is to be distinguished from low vision, which is defined as best-corrected acuity of less than 20/60, but better than 20/400. While blindness effectively renders vision ineffective for even the most basic tasks (such as obstacle avoidance), low vision permits some coarse visually guided skills, although it compromises more detail-oriented ones, such as reading and driving.

Over 35 million people across the world are blind, with the highest incidence (over 90%) in developing countries. Each year, 1 million blind people are treated, 6 million people die blind, and 8 million new cases are added. Thus, the net yearly increase of the blind population is 1 million. The economic cost corresponding to the loss of productivity caused by blindness is estimated to be in excess of $40 billion per year. This entry explores some of the primary causes of blindness, some scientific studies of perception in the blind, and frontiers in blindness research.

Primary Causes

Blindness can have a variety of etiologies, ranging from damage to the eye to brain trauma. Next, the causes that account for the bulk of global blindness are described.

Cataracts

A cataract is an opacity of the lens. The likelihood of an opacity increases with age. Although the precise causal factors are still not clearly understood, ultraviolet (UV) exposure, genetic predis-posers, smoking, and diabetes mellitus are all believed to heighten the risk. Cataract surgery is one of the great success stories of our time. A short procedure that involves removal of the lens done under local anesthesia (for adults) can almost completely restore clear vision.

Macular Degeneration

The macula is the central region of the retina that includes the fovea and that subserves high-acuity vision. Macular degeneration (MD) is a disorder that compromises the macula and thus severely impairs visual perception. The risk for MD worsens with age and prior familial incidence of the condition. Regrettably, no satisfactory preventive or treatment strategy for MD is currently available.

Diabetic Retinopathy

Overgrowth and/or hemorrhaging of retinal blood vessels associated with diabetes mellitus can lead to retinal damage and eventually blindness. Effective interventions exist, including laser-based cauterization of hemorrhaging vessels.

Glaucoma

Glaucoma is chronically increased intraocular pressure, which can lead to damage of the retinal tissue and, especially, the optic disk. Glaucoma might have genetic underpinnings in some individuals, and might be the outcome of trauma in others. Treatments that reduce intraocular pressure are effective in the early stages of glaucoma. Delay leads to permanent damage to the optic nerve fibers, and hence uncorrectable visual loss.

River Blindness

River blindness, or onchocerciasis, is a common cause of blindness in parts of Africa. The disease is caused by a skin-dwelling nematode whose larvae are transmitted across a population via biting black flies. The flies breed in running streams (hence the prevalence of the disease near rivers). The transmitted larvae migrate across a person's body. In the eyes, these larvae cause a host of problems, including corneal scarring, glaucoma, and cataracts, leading eventually to blindness. Population-based drug-distribution programs have been effective in reducing the incidence of onchocerciasis.

...

  • Loading...
locked icon

Sign in to access this content

Get a 30 day FREE TRIAL

  • Watch videos from a variety of sources bringing classroom topics to life
  • Read modern, diverse business cases
  • Explore hundreds of books and reference titles

Read next

More like this

Sage Recommends

We found other relevant content for you on other Sage platforms.

close

Have you created a personal profile? Login or create a profile so that you can save clips, playlists and searches

close
close
close Signed In to profile You are signed in as:
close
Logged in Institution Institution