Slit lamp image of cornea, iris and lens.

5 Most Common Conditions Leading to Blindness

Blindness is a condition when a person lacks visual perception. Blindness may be caused by physiological as well as neurological factors. The term “blindness” is often used in cases when a person suffers from severe visual impairment, although still retains some residual vision. In case of total blindness (also known as NLP), a person has completely no light perception.One does not have to be totally blind to be considered “legally blind” in the United States. Any person with a visual acuity of 20/200 or less in the better eye with best possible correction, is considered legally blind. “20/200” means that a person needs to stand 20 feet away from an object to see it (with correction) with the same clarity a healthy person would see it from 200 feet. Having a tunnel vision (also known as Kalnienk Vision) – a visual field of 20 degrees diameter or less (in the better eye) also classifies a person as legally blind. The leading cause of monocular blindness (blindness in one eye) in the U.S. is not a disease, but an eye injury. 1.1 million people in the U.S. and 42 million around the world are blind.

Normal vision
Normal vision
Same scene viewed by a person with diabetic retinopathy Source NIH national Eye Institute
Same scene viewed by a person with diabetic retinopathy
Source: NIH national Eye Institute

5) Diabetic retinopathy

Retinopathy is damage to the retina. Diabetic retinopathy is the most common diabetic eye disease. It is basically damage to the small blood vessels in retina resulting from a complications of diabetes mellitus. Every person with diabetes is at risk and should undergo a dilated eye exam at least one a year. The general rule is that the longer  a person has diabetes, the higher the risk of diabetic retinopathy. Most of the diabetics will develop some signs of diabetic retinopathy. Approximately 28% of the people with diabetes over the age of 40 have diabetic retinopathy, and about 4% of all diabetic have advanced diabetic retinopathy, which could lead to the severe loss of vision. There is no cure to this condition. Laser treatment (photocoagulation) is effective at preventing vision loss if done before the severe damage to the retina has been made. Another treatment found to be effective at improving vision (also in the case when retina has not been seriously damaged) is vitrectomy, or the removal of the vitreous gel (also called vitreous humor).

Single port 19-gauge vitrectomy
Single port 19-gauge vitrectomy

4) Corneal opacity

Cornea is a transparent structure at the front of the eye. In this condition, normally transparent, cornea becomes opaque. There are many causes of corneal opacity, with the most common being various infections, inflammation and injury. Additionally, risk factors include: measles, Vitamin A deficiency, Herpes simplex virus (it can be transmitted to the eyes and cause viral keratitis – a viral infection of the cornea) and wearing contact lenses for an extended period of time (it may lead to inflammation and infection). Treatments are: eye drops (containing antibiotics and/or steroids), oral medications and in some cases surgical removal of the scar tissue. Cornea transplant is also an option in the most severe cases.

Slit lamp image of cornea, iris and lens.
Slit lamp image of cornea, iris and lens.

3) Macular degeneration

This is the leading cause of the loss of vision in the people over 60 years of age in the United States. Age related macular degeneration has two forms, wet (neovascular) and dry (central geographic atrophy). Dry AMD (more common – 85% of all cases) causes a gradual loss of central vision. Wet AMD results in a rapid loss of vision, if left untreated. Over 1.7 million of U.S. residents currently suffer from the advanced age-related macular degeneration and the associated loss of vision. Certain nutrients and vitamins (beta carotene, vitamins C and E) help prevent or slow down dry macular degeneration. Wearing sunglasses with UV protection is recommended for people with this condition.

A fundus photo showing intermediate age-related macular degeneration.
A fundus photo showing intermediate age-related macular degeneration.

2) Glaucoma

Glaucoma is a disease where damage to the optic nerve occurs, leading to the progressive and irreversible loss of vision, if left untreated. Glaucoma may be associated with an increased pressure of the fluid in the eye. There are two types of glaucoma. Open-angle glaucoma (accounts for over 90% of cases) is called the “silent thief of sight”, because the loss of eyesight is gradual and takes place over an extended period of time. Because of that, it is often only recognized at an advanced stage. Closed-angle glaucoma is characterized by sudden decreased vision, pain, red eye, often accompanied by nausea and vomiting. Closed-angle glaucoma accounts for about 10% of all cases of glaucoma. Risk factors include: increased pressure within the eye (ocular hypertension), African descent, old age, family history of glaucoma, prolonged use of steroids, severe diabetic retinopathy, ocular trauma and uveitis. About 4 million people in the U.S. have glaucoma. There is no cure for this condition. When vision is lost, it can’t be regained. It is possible, however, to slow down the progression.

A scene as it might be viewed by a person with glaucoma.
A scene as it might be viewed by a person with glaucoma.

1) Cataracts

A cataract is a clouding of the lens in the eye, usually related to aging. More than half of all Americans by the age of 80 have had a cataract. There are also different types of cataract, other than the age-related. Secondary cataract may form after surgery or as a result of glaucoma, diabetes or steroid use. Traumatic cataract may develop after an eye injury. Exposure to some types of radiation may lead to radiation cataract. Cataract affect over 20 million Americans over the age of 40. Surgery is the treatment of choice. Working as a commercial airline pilot increases the chances of developing cataracts by 300% due to the exposure to the radiation from the outer space.

Magnified view of cataract in human eye, seen on examination with a slit lamp using diffuse illumination
Magnified view of cataract in human eye, seen on examination with a slit lamp using diffuse illumination

Further reading

WebMD page on Glaucoma
WebMD Eye Health Center
The Glaucoma Foundation
National Health Service page on Cataracts
National Eye Institute Eye Health Information