Blindness

The Five Senses and Beyond: The Encyclopedia of Perception - Jennifer L. Hellier 2017


Blindness

Blindness is a condition of poor visual perception. There is a range of vision loss as defined in the International Classification of Diseases (ICD) of the World Health Organization (WHO). ICD-10 states the categories as: (1) normal vision, (2) moderate visual impairment, (3) severe visual impairment, and (4) blindness. Blindness can be acquired at birth or in life due to injury, genetics, and other life events. As of August 2014, according to WHO, there were an estimated 285 million people who are visually impaired worldwide, of whom 39 million are blind.

History

Blindness is a condition that has been frequently noted in history. Many cultures have viewed blindness in different aspects of mythology, social value, and legal definition. No one person can be attributed with the discovery of this condition, but many have recorded individuals in stories, official documents, and personal entries. An important figure in the history of blindness is Louis Braille (1809—1852). Braille was a French educator who became blind at age three as a result of an eye injury. He created the tactile system used by the visually impaired and blind to read and write, known simply as braille.

Types and Symptoms

The more common diseases that can cause blindness are cataracts, glaucoma, age-related macular degeneration (AMD), and pregnancy-related issues. Blindness can result from genetic defects, certain chemicals, eye injuries, and abnormalities of related tissues, such as the optic nerve.

Cataracts are the change in lens color that leads to clouding. This is associated with aging, smoking, and diseases such as diabetes. Early changes in lens color do not affect vision, but vision is impaired over time as the clouding becomes thicker.

Glaucoma is a disease in which retinal cells are damaged as a result of increased pressure within the eye. When aqueous humor, the liquid within the eyeball, is drained slower than it is produced, it can lead to increased pressure within the eye. This can also compress the optic nerve, which is responsible for transporting information about light received by the retina to the brain for processing. This disease is a major cause of irreversible blindness. Late signs of the disease include blurred vision, headaches, and reported halos around sources of light.

Age-related macular degeneration (AMD) is the progressive deterioration of the retina. It affects a specific region on the retina called the macula lutea, a pigmented region that deals with high acuity vision. There are two forms of AMD: wet and dry. In the “wet” form new blood vessels grow and cause retinal detachment by scarring, and in the “dry” form excessive accumulation of visual pigments causes many more to die off.

Treatments and Outcomes

Cataracts can be surgically corrected. The removal of the clouded lens and implantation of an artificial lens can restore effective vision. Long-term exposure to ultraviolet radiation may play a role in developing cataracts, so wearing sunglasses is recommended by many experts as a preventive measure to delay the onset.

Glaucoma can be caught early; however, it takes sight away so slowly and painlessly that many do not realize the damage until it is done. An examination for high inner eye pressure is done by administering a directed puff of air toward the cornea to measure the deformation of the sclera, the white area of the eye. The amount of deformation can detect possible glaucoma. A glaucoma exam should be performed annually after age 40 since it affects 2 percent of people over that age (Marieb et al., 2011). If caught early, glaucoma can be treated with eye drops that either increase drainage or decrease production of the aqueous humor.

AMD is mostly untreatable, but laser treatment can remove some of the growing blood vessels to slow the progression of the disease in “wet” form. To date, there are no viable treatments for the “dry” form.

Prevention and Research

The majority of these diseases have few effective preventive measures. Most are successful in the early stages of these diseases, thus most experts recommend annual eye exams, especially for persons over age 40 as many diseases seem to manifest around this age. Additionally, examinations should always be performed after any trauma to the eyes or head to ensure eye health and vision will not be affected.

A study published in the New England Journal of Medicine (Bainbridge et al., 2008) shows the potential of gene therapy to improve vision in subjects with an inherited blindness called LCA (Leber’s congenital amaurosis). The gene therapy involved using a virus to deliver a gene into the eyes of patients with LCA, with most reporting improved vision.

In summary, several diseases that can render their victims blind may not have exact known causes or effective treatments. Ongoing research is currently exploring the effects of techniques such as gene therapy to help restore vision and reverse the effects of vision-impairing diseases. Prevention can be limited, but early signs of these sight-stealing diseases can be caught with routine eye examinations.

Eric B. Moore

See also: Optic Nerve; Optic Nerve Hypoplasia; Retina; Visual Fields; Visual Perception; Visual System

Further Reading

Bainbridge, James W., Alexander J. Smith, Susie S. Barker, Scott Robbie, Robert Henderson, … & Robin R. Ali. (2008). Effect of gene therapy on visual function in Leber’s congenital amaurosis. New England Journal of Medicine, 358, 2231—2239. http://dx.doi.org/10.1056/NEJMoa0802268

International Council of Ophthalmology. (2002). Visual standards: Aspects and ranges of vision loss with emphasis on population survey [Report prepared for 29th International Congress of Ophthalmology]. Retrieved from http://www.icoph.org/downloads/visualstandardsreport.pdf

Marieb, Elaine N., Patricia B. Wilhelm, & Jon Mallatt. (2011). Human anatomy (6th ed.). San Francisco, CA: Pearson Benjamin Cummings.

World Health Organization. (2014). Visual impairment and blindness. Retrieved from http://www.who.int/mediacentre/factsheets/fs282/en/