Thursday, April 18, 2024

Low Vision And Blindness Definition

What Are The Causes Of Blindness And Low Vision

What’s the difference between vision loss, low vision and legal blindness?

Your eye is a ball in a bony socket with muscles attached to it for your eye movement. From the front, it has a clear window or cornea. Behind that is the pupil, the fluid inside the eye, the lens and, lastly, a light-sensitive membrane called the retina that sends information to your brain through the optic nerve. Problems or damage to any part of the pathway from your cornea to your brain can affect your vision.

Blindness and low vision can be caused by conditions that only affect your eye or conditions that affect your whole body. Conditions that can cause blindness and low vision include:

  • genetic conditions such as retinitis pigmentosa.

Blindness and low vision can happen to anyone but it is more common in older people. The video below is about the common causes of vision loss.

What Support Is Available With Blindness And Low Vision

Living with blindness and vision loss can be challenging. It takes time and effort to learn to cope with low vision. Below are some support services and information for people affected by blindness and low vision and their family/whnau:

Blind + Low Vision NZ offers a range of services to people with blindness and low vision such as counseling, orientation and mobility services, adaptive daily living services, adaptive technology and employment support. Kp Mori Aotearoa New Zealand Inc. is a member-based society that is open to all people with a disability. The services they offer include vision support services, advice and information about disability services and peer support. Parents of Vision Impaired NZ Inc. supports parents who have blind or vision impaired children.Albinism Trust, NZ is a support group for people living with albinism. Retina New Zealand Inc. offers peer to peer support for people living with retinal disorders. Blind Citizens NZ is New Zealands oldest advocacy organisation in the disability sector. Glaucoma NZ provides resources and information about glaucoma and offers peer support groups for people living with glaucoma. Macular Degeneration NZ provides resources and information about macular degeneration and has a support helpline 0800 622 852.

Common Types Of Low Vision

Loss of central vision

A blur or blind spot in the center of what youre looking at occurs from a loss of central vision. This makes it difficult to read, recognize people and identify features at a distance. A persons side vision is mostly unaffected by the loss of central vision.

As long as the person has adequate side vision, mobility is still possible.

Loss of peripheral vision

Peripheral vision loss leaves a person with remaining central vision, allowing them to see straight ahead, read, watch TV and recognize faces. This is referred to as tunnel vision and can be caused by glaucoma, a brain tumor or injury.

Peripheral vision loss makes it difficult to differentiate objects on one or both sides, as well as items directly above and below eye level. Mobility is often hindered by a loss of peripheral vision.

Blurred vision

Blurred vision causes both near and far vision to be out of focus. When blurred vision is caused by refractive error, glasses, contact lenses and sometimes surgery can clear it up. However, certain conditions may cause blurred vision that cannot be corrected, such as macular degeneration, cataracts and diabetic edema.

Reduced contrast sensitivity

Glare/light sensitivity

There are two types of glare: discomfort glare and disability glare.

Those with disability glare cannot function in these lighting conditions, posing a danger of being in harms way.

Both types of glare can be helped by an IALVS low vision eye doctor.

Night blindness

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How Are The Terms Low Vision Visually Impaired And Blind Defined

Low vision is used to describe a loss of visual acuity while retaining some vision. It applies to individuals with sight who are unable to read a newspaper at a normal distance of viewing, even with the aid of glasses or contact lenses. People with low vision often need adaptations in lighting and/or enlarged print to read something. There are two specific types of low vision:

  • Myopic- Unable to see distant objects clearly, commonly referred to as “near-sighted.”
  • Hyperopic- Unable to see close objects clearly, commonly referred to as “far-sighted.”

Partially Sighted is usually used in educational contexts to describe a visual impairment that requires special education services. The partially sighted student meets the challenge of disability in much the same way as a totally blind student. Accommodations include the use of readers, audio taped texts, and raised-line drawings. The partially sighted student may be able to use large print books and a Closed-Circuit TV or other magnifying device. Some partially sighted students can take notes in class by printing very large with a felt tip pen or marker others will tape record lectures for later use.

Legally Blind refers to people that have less than 20/200 vision in the better eye or a limited field of vision that is 20 degrees or less at its widest point. People who are legally blind may have some useful vision.

The descriptions above were compiled using the following resources.

Diagnosis Of Low Vision

Types of Low Vision and Blindness

Low Vision Tests

Low vision tests are done at an eye exam with an optometrist or an ophthalmologist to determine the functional vision of a patient and their ability to perform daily activities. Visual acuity and amsler grids are low vision test charts used to determine central visual function or loss. Visual field tests aid in the low vision diagnosis to determine the field loss and remaining functional ability. A low vision diagnosis may also be made from an occupational therapist when they are conducting their in-home low vision assessment test.

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What Accessibility For The Visually Impaired

Like other disabilities, visual impairment takes different forms and to varying extents. Blind people resort to the use of their valid senses: hearing, touch, smell, but also the echolocation, cold drafts, temperature differences, etc. People who have low vision act a little differently in that they maximize their visual potential.

The difficulties encountered by blind or visually impaired people in public spaces concern:

Reading information,

Location and orientation in space,

The ability to cross the street safely,

The ability to detect dangers

In order to improve access to the environment and services for people with a visual impairment, the following recommendations should be applied:

Visible and legible signage, using large print and contrasting colors,

Accessible pedestrian signals at pedestrian crossings,

Audio beacons to identify important points of interest,

Audio dubbing of visual information, in particular announcements in public transport,

Tactile guide paths for orientation in large spaces,

Detectable warning surfaces to alert to a danger such as stairs, public transit platforms or pedestrian crossings,

Continuous handrails, contrasting risers and stair nosings to use the stairs safely,

Tactile signs with Braille and raised print in the elevators,

Maps using high-contrasting colors, large print and Braille and raised indications,

Homogeneous and glare-free lighting,

Staff trained in welcoming people with visual disabilities,

Using Low Vision Optical And Non

Low vision optical, non-optical, and electronic magnifying devices can make it possible for you to do a variety of everyday tasks, including

  • managing your medication
  • preparing meals
  • and managing your finances

To learn more about the many different types of reading options that are available, see Reading, Writing, and Vision Loss on the VisionAware website.

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What Is Legal Blindness

A person is considered legally blind if they cannot see at six metres what someone with normal vision can see at 60 metres or if their field of vision is less than 20 degrees in diameter.

Government departments use the term ‘legally blind’ to define a person whose degree of sight loss entitles them to special benefits.

NOTE: Another way to define 20 degrees in diameter is: the field of vision constricted to 10 degrees or less of arc around central fixation. This is the way Centrelink describes it. For further details go to the Centrelink website.

Low Vision Vs Legal Blindness

Blindness and Low Vision Studies Quick Facts

“Legal blindness” is a definition used by the United States government to determine eligibility for vocational training, rehabilitation, schooling, disability benefits, low vision devices, and tax exemption programs. It’s not a functional low vision definition and doesn’t tell us very much at all about what a person can and cannot see.

Part 1 of the U.S. definition of legal blindness states this about visual acuity:

  • A visual acuity of 20/200 or less in the better-seeing eye with best conventional correction .

This is a 20/200 visual acuity measurement, correlated with the Snellen Eye Chart :

  • If you can only read line 1 from 20 feet away while wearing your regular glasses or contact lenses, the doctor records your vision as 20/200 with best correction.
  • Update: In 2007, the Social Security Administration updated the criteria for measuring legal blindness when using newer low vision test charts with lines that can measure visual acuity between 20/100 and 20/200. Under the new criteria, if a person’s visual acuity is measured with one of the newer charts, and they cannot read any of the letters on the 20/100 line, they will qualify as legally blind, based on a visual acuity of 20/200 or less.

Part 2 of the U.S. definition of legal blindness states this about visual field:

  • OR a visual field of 20 degrees or less in the better-seeing eye.

This is a representation of a constricted visual field:

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Facts About Low Vision And Legal Blindness

Most surveys and studies indicate that the majority of people in the United States with vision loss are adults who are not totally blind instead, they have what is referred to as low vision. You may have heard the terms partial sight or partial blindness also used to describe low vision. Those descriptions are no longer in general use, however.

Here is one definition of low vision, related to visual acuity:

  • Low vision is a condition caused by eye disease, in which visual acuity is 20/70 or poorer in the better-seeing eye and cannot be corrected or improved with regular eyeglasses.

How Low Vision Devices Can Help

People with low vision can often live and work independently thanks to a number of tools and devices that can greatly improve their quality of life.

Our low vision optometrist prescribes all types of low vision glasses and devices, such as:

  • bioptic and full diameter telescope glasses
  • microscope glasses
  • and filters of all types
  • as well as a wide range of low vision aids ranging from hand-held magnifiers to electronic visual aids.

Large-type books, magazines, and newspapers, as well as books on tape, talking wristwatches, self-threading needles, and other products, can also help those with low vision.

Live your best life by contacting an IALVS low vision eye doctor to book a low vision evaluation and to determine the optimal low vision devices for your needs and lifestyle.

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Visual Acuity And Low Vision

Visual acuity is a number that indicates the sharpness or clarity of vision. A visual acuity measurement of 20/70 means that a person with 20/70 vision who is 20 feet from an eye chart sees what a person with unimpaired vision can see from 70 feet away.

20/70 can best be understood by examining a standard eye testing chart that you may have used in your own doctor’s office during an eye examination.

In the United States, the Snellen Eye Chart is a test that ophthalmologists and optometrists use to measure a person’s distance visual acuity. It contains rows of letters, numbers, or symbols printed in standardized graded sizes.

Your eye doctor will ask you to read or identify each line or row at a fixed distance , although a 10-foot testing distance is also used.

If you can read line 8 from 20 feet away while wearing your regular glasses or contact lenses, the doctor records your vision as 20/20 with best correction.

If the smallest print you can read is line 3 from 20 feet away while wearing your regular glasses or contact lenses, the doctor records your vision as 20/70 with best correction.

Please note: An actual Snellen Eye Chart is much larger than the one depicted here therefore, it’s not recommended that you use this chart to test your own visual acuity.

Eye Care Vision Impairment And Blindness

Tips for Coding Blindness and Low Vision

Eye conditions are remarkably common. Those who live long enough will experience at least one eye condition during their lifetime.

Globally, at least 1 billion people have a near or distance vision impairment that could have been prevented or has yet to be addressed. In the absence of timely detection, reduced or absent eyesight can have long-term personal and economic effects. Vision impairment affects people of all ages, with the majority being over the age of 50. Young children with early onset severe vision impairment can experience lower levels of educational achievement, and in adults it often affects quality of life through lower productivity, decreased workforce participation and high rates of depression.

Vision impairment and blindness impact the life of people everywhere. In low- and middle-income settings the burden of vision impairment can be even greater due to fewer opportunities to access the most essential eye care services.

Cataracts and uncorrected refractive errors are estimated to be the leading causes of vision impairment however, other causes for vision impairment cannot be ignored. Age-related macular degeneration, glaucoma, long standing systemic conditions like diabetes causing diabetic retinopathy, infectious diseases of the eye and trauma to the eye are all equally important causes for vision impairment that need to be addressed.

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What Is Low Vision

Vision impairment, or low vision, is a problem with your eyes that makes it hard to do everyday activities. It cant be fixed with contact lenses, glasses or other treatments such as medicine or surgery.

Low vision affects each person differently, and it requires an approach that focuses on the patients individual problem.

The sooner your vision loss or eye disease is found and treated, the more likely you are to keep your remaining vision. Once vision loss is diagnosed you should have regular comprehensive eye exams by an eye care professional.

How Are Blindness And Low Vision Diagnosed

Your doctor will ask you questions related to your vision, including how long you have had vision loss, how it affects your daily activities and whether you have any existing medical condition. Your doctor will then perform an eye examination to check your eye and vision. Your doctor may perform some tests which include using instruments such as magnifiers, slit lamp and special charts to check your vision, depth perception, visual field or pressure in your eye.

Visual acuity is used to test and check how well you can see from a specific distance. You may recall being asked to read a few letters from a distance by your ophthalmologist or optometrist before during an eye check. If you have a visual acuity of 6/24, it means that from a distance of 6 metres you can only see what a person with normal vision can see at 24 metres.

In New Zealand, about 30,000 people are blind, which means they have a visual acuity of 6/24 or less. Approximately 150,000 New Zealanders have low vision, which means they have a visual acuity between 6/126/23. Normal vision is 6/6.

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Facts About Low Vision

Most surveys and studies indicate that the majority of people in the United States with vision loss are adults who are not totally blind instead, they have what is referred to as low vision. You may have heard the terms “partial sight” or “partial blindness” or even “poor vision” also used to describe low vision. Those descriptions are no longer in general use, however.

Here is one definition of low vision, related to visual acuity:

  • Low vision is a condition caused by eye disease, in which visual acuity is 20/70 or poorer in the better-seeing eye and cannot be corrected or improved with regular eyeglasses.

Who Is Most At Risk Of Having Low Vision

Developing AI datasets with the blind and low vision community

Anyone can be affected by low vision because it results from a variety of conditions and injuries. Because of age-related disorders like macular degeneration and glaucoma, low vision is more common in adults over age 45 and even more common in adults over age 75. For example, one in six adults over age 45 has low vision one in four adults over age 75 has low vision.

The most common types of low vision include:

  • Loss of central vision: There is a blind spot in the center of one’s vision.
  • Loss of peripheral vision: The inability to see anything to either side, above, or below eye level. Central vision, however, remains intact.
  • Night blindness: The inability to see in poorly lit areas such as theaters, as well as outside at night.
  • Blurred vision: Objects both near and far appear out of focus.
  • Hazy vision: The entire field of vision appears to be covered with a film or glare.

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Low Vision Assessment And Rehabilitation

Low vision assessment and rehabilitation aim to assess your condition, reduce the impact of low vision on your daily activities and teach you how to make use of your remaining vision more effectively. Low vision assessment and rehabilitation services include:

  • an evaluation by your ophthalmologist or your optometrist
  • prescription for low-vision aids or devices
  • referral to an occupational therapist to learn new ways of managing your daily tasks
  • mobility and transport services to help you move around your area and unfamiliar places safely
  • support and training to help you manage your daily tasks and keep your independence.

The University of Auckland Optometry School offers low vision rehabilitation and some hospital eye departments have low vision clinics . Ask your GP, ophthalmologist, optometrist or the Blind + Low Vision Foundation, NZ for a referral to one of these low vision clinics.

Some optometrists also offer rehabilitation services. Ask your optometrist or find a list of optometrists who offer low vision rehabilitation here.

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