Total blindness is a term used to describe those who have complete lack of light perception, documented as no light perception (NLP). Only about 15% of people with eye disorders have total blindness, the majority of those with visual impairment have some level of vision.
Low vision is a term used to describe those whose vision cannot be fully corrected by conventional method such as glasses, contact lenses, medicine, surgery, magnification aids or assistive technology.
Visual impairment is a functional term to describe those whose decreased visual function interferes with the ability for one to perform their activities of daily living, such as reading, driving, and watching TV. Visual impairment is defined based on function, instead of using visual acuity or visual field cutoff values. Visual impairment includes those who have low vision or who are blind.
The types of visual symptoms you may experience include:
- Blurred vision
- Wavy or spots in central vision
- Restricted peripheral vision
- Poor night vision
- Difficulty seeing colors
Legal blindness is a term defined by the United States Social Security Administration (SSA) to determine those who are eligible to receive disability benefits, tax exemption programs, and rehabilitation training. SSA uses visual acuity or visual field results to determine this eligibility. A person is considered legally blind if he/she has central visual acuity of 20/200 or worse in the better-seeing eye with best correction (using glasses or contact lenses) at a distance, or if he/she has visual field restriction where the widest diameter is 20 degrees or less in the better-seeing eye. The tests used to measure visual acuity or visual fields have been outlined as follows:
- Visual acuity testing for distance is carried out using Snellen visual acuity chart or another test that is comparable to the Snellen methodology. In 2007, SSA updated the criteria for measuring the visual acuity by allowing newer low vision test charts to be used instead of Snellen acuity charts alone. Under this update, if a person cannot read at least one letter on the 20/100 line, he or she will be classified as legally blind.
- Acceptable tests for visual field testing include automated static perimetry such as Humphrey Field Analyzer (HFA) 30-2, HFA 24-2, and Octopus 32, kinetic perimetry such as Goldmann perimetry or HFA "SSA Test Kinetic." Screening tests including confrontation tests, tangent screen tests, and static screening tests are not accepted forms of testing to determine legal blindness.
World Health Organization classifies visual impairment into the following categories based on visual acuity or visual field of the better seeing eye.
Near Normal visual impairment: 20/30-20/60
Moderate visual impairment: 20/70-20/160
Severe visual impairment: 20/200-20/400, or 11-20 degrees on visual field
Profound visual impairment: 20/500-20/1000 visual acuity, or 6- 10 degrees on visual field
Near total visual impairment: Counting fingers, Hand motion, Light perception, or 5 degrees or less on visual field
Total visual impairment: No light perception
Earn CME credit as you help guide your clinical decisions.
There can be many different causes of blindness. The leading causes of blindness worldwide are cataracts, age-related macular degeneration, glaucoma, diabetic retinopathy, and trachoma.
- Cataracts, a condition that causes yellowing and hardening of the lens in the eye, is the leading cause of blindness worldwide in developing and developed countries.
- Age-related macular degeneration, a condition that damages a part of the retina known as the macula, is the leading cause of blindness in Caucasians and those aged 65 and older.
- Glaucoma, a condition that damages the optic nerve, is the leading cause of blindness in African Americans.
- Diabetic retinopathy, a condition due to systemic diabetes, is the leading cause of new blindness in adults between 25 and 64 years of age.
- Trachoma is also on the list of leading causes. However, thankfully, the incidence is decreasing due to public health action.
The number of persons with reduced vision due to uncorrected refractive error exceeds that of those with the conditions mentioned above, however, uncorrected refractive errors can be easily treated or "cured" with proper vision correction.
Estimates are that approximately 90% of the visually impaired population live in developing countries or low-income circumstances and about 80% of all visual impairment worldwide can be prevented, treated, or cured with proper access to eye care.
The most common causes of blindness are as follows:
- Cataracts (51%)
- Glaucoma (8%)
- Age-related macular degeneration (5%)
- Corneal opacification (4%)
- Childhood blindness (4%)
- Refractive errors (3%)
- Trachoma (3%)
- Diabetic retinopathy (1%)
- Undetermined (21%)
According to the World Health Organization (WHO), there are approximately 285 million people with a visual impairment. Of those, 39 million are blind, and 246 million have low vision. Of those who are blind, 90% live in developing countries. For each blind person worldwide, an average of 3.4 people has low vision, with the country and regional variation ranging from 2.4 to 5.5 people. (WHO)
More than 82% of all people who are blind are 50 years of age and older. Due to the expected number of years lived in blindness, childhood blindness is a significant problem, with an estimated 1.4 million blind children below age 15. Females have a significantly higher risk of being visually impaired than males.
Conditions causing visual impairment vary widely. It can be a genetic, congenital, or acquired conditions. Vision loss can occur gradually or suddenly, and can result in central vision loss, peripheral vision loss, overall blur, a decrease in contrast sensitivity, color vision difficulties, night vision blindness, glare or light sensitivity issues. The cause of the vision loss determines whether it involves one type alone or a combination of presentations.
History and Physical
Performing a thorough case history is essential. Case history should include:
- Patient visual and ocular history
- Family visual and ocular history
- Patient medical history, including medications
- Family medical history
- Social history
- Vocational, educational, and hobby history
After a thorough case history, an ocular examination is necessary to assess the patient's current visual status and function.
- Visual acuity (distance and near)
- Pupils, motility, and binocular vision
- Visual fields
- Glare testing, color vision, contrast sensitivity
- Ocular health exam with dilated fundus exam
In addition to taking a good history, it is vital to perform a thorough evaluation. Ocular health exam should typically include visual acuity, visual field, extraocular muscles, pupil, binocular vision testing, intraocular pressure, anterior segment, and posterior segment evaluation with dilated fundus exams. Supplemental testing such as formalized visual field testing, color vision tests, contrast sensitivity tests, visual evoked potential, electroretinography, electrooculography, optical coherence tomography, fluorescein angiography, genetic testing may be necessary to help determine the etiology, monitor and properly manage the condition.
Treatment / Management
Comprehensive eye examinations are necessary to prevent, detect, treat, and manage the ocular conditions that can lead to blindness. Eye exams should include ocular health exams and not just vision and sight checks for glasses or contact lens prescription.
Many international, national, and local organizations are working to bring more awareness about vision and eye health, provide access to health care, and fight blindness. Research is being done worldwide to study the etiologies of many eye conditions causing permanent vision loss, and to develop a proper treatment to control or cure these conditions. The World Health Organization (WHO) is the leader in working to monitor trends, raise awareness, and coordinate efforts to fight blindness.
Low vision rehabilitation services are available to help patients maximize their remaining vision, maintain their independence and imrove their quality of life. These services are provided by a multisciplinary team of low vision professionals including low vision doctors (optometrists or ophthalmologists), low vision therapists, occupational therapists, rehabilitation teachers, orientation and mobility specialists, vocational rehabilitation specialists, social workers, and other rehabilitation low vision professionals. Please refer to the review article titled "Low Vision Rehabilitation" for additional information.
- Acute angle-closure glaucoma
- Corneal ulcer
- Exudative retinal detachment
- Giant cell arteritis
- Globe rupture
- Intraocular foreign body
- Migraine headache
Depending on the condition, vision can be stable or progressive in nature. Conditions such as age-related macular degeneration only causes central vision loss, thus these patients will not experience total blindness. Whereas, retinitis pigmentosa can cause peripheral vision loss leading to central vision loss and total blindness. Conditions causing blindness may be prevented with early detection, proper diagnosis and treatment. It is recommended to have a comprehensive eye examination every 1-2 years for all ages. For infants, InfantSEE is a free public health program available to provide comprehensive infant vision and eye health assessment within the first year of the infant's life.
Enhancing Healthcare Team Outcomes
Blindness in all its forms and severities confers serious morbidity to those affected, whether total blindness or visual impairments that include transient blindness or partial loss of field of vision. The assessment, diagnosis, and management of vision loss requires an interprofessional team approach, including physicians, specialists, specialty-trained nurses, optometrists, and pharmacists, all collaborating across disciplines to achieve optimal patient results. [Level V]
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