domingo, 25 de noviembre de 2018

Causes of visual impairment

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By Ananya Mandal, MDReviewed by April Cashin-Garbutt, MA (Cantab)

There are many causes that may lead to loss of vision or lead to impairment of vision.

Common causes that lead to vision loss or visual impairment include injury to the eye, inherited conditions, infections and so forth. (1-4)

Injury to the eyes

Injury to the eyes while playing or at work or due to accidents may result in vision loss and impairment.

Particularly injuries to the cornea are the commonest cause of vision loss.

Inherited conditions of blindness and vision impairment

Retinitis pigmentosa is the most common cause of inherited blindness.

Infections of the eyes

Sometimes if the mother has had a viral infection like German measles that is transmitted from the mother to the developing fetus during pregnancy the baby may be born with blindness or visual impairment.

Trachoma of the eyes caused by contagious microorganism called Chlamydia trachomatismay also damge eye sight. This is seen in the developing and underdeveloped countries with poor water and sanitation facilities.

Amblyopia

This is basically impaired vision in one eye due to lack of its use in early childhood.

This is seen in squint or “lazy eye” since both the eyes project differently and send in different messages to the brain the brain may then turn off or suppress images from the weaker eye.

This stops development of the weaker eye leading to amblyopia in that eye.

Cataract

Clouding of part or the entire lens of the eye.

Normally, the lens is clear to let in the light that focuses on the retina. Cataracts prevent light from easily passing through the lens, and this causes loss of vision.

This condition usually affects the elderly. Symptoms include cloudy or blurry vision, difficulty in seeing in dimly lit areas and bright lights, colors appear faded, double vision etc.

Cataract affects 20.5 million (1 in 6) Americans age 40 and older. By 80 years of age, more than one half of Americans have cataract.

Cataract is the leading cause of blindness in the world (47.8%) compared to other eye disorders.

Diabetic retinopathy

Diabetes affects the small blood vessels in the retina. When damaged this leads to impairment of vision.

This is the commonest cause of blindness and visual impairment in the United States.

An estimated 23.6 million people in the U.S. have diabetes.

Of those, 5.7 million are undiagnosed. Currently, 1 in 10 individuals has diabetes. Between 40% to 45% of all people with diabetes have diabetic retinopathy.

Glaucoma

This condition results due to raised pressure within the eyes. The increased pressure impairs vision by damaging the optic nerve.

This may be seen in older adults and in some babies as well who are born with the condition.

Approximately 2.3 million Americans (1.9%) age 40 and older, have glaucoma.

African-Americans (age 40 and over) are 4 to 5 times more likely than any other ethnic group to have glaucoma

Age related Macular degeneration

Age related Macular degeneration or AMD that is a progressive loss of the visual acuity due to damage to the macula that is the most sensitive part of the retina.

AMD affects more than 1.75 million individuals in the U.S. This number is expected to increase to almost 3 million by 2020 due to the rapid rise in the aging of the U.S. population.

The center of the visual field appears blurry or opaque. The patient is unable to focus clearly. This mainly occurs in the elderly.

The risk of AMD rises in those exposed to excess sunlight and those who smoke excessively.