Types of Low Vision

Low Vision is a term which contains a broad spectrum of users with various types of with disabilities including the following.

Reduced Contrast and Glare

Achromatopsia

Achromatopsia means to see 'without colour' or 'no colour'. It is also known as Rod Monochromatism. This condition is associated with color blindness, visual acuity loss, extreme light sensitivity and nystagmus. Individuals who are born with lack of color vision have cones that do not function properly, leaving them with reduced visual acuity, reduced color vision and difficulty seeing in bright light. There are two primary forms, complete achromatopsia and incomplete achromatopsia. lowvision.org

Albinism

Albinism is associated with reduced visual acuity (ability to see fine detail) and light sensitivity (Photophobia). People with albinism do not have clear vision due to an underdevelopment of the central part of the retina called the macula. Since eyes with albinism have insufficient pigment (melanin) to effectively absorb light, sunlight and brightly-lit environments may be uncomfortable or even painful and cause even more difficulty seeing. (Need Source)

Aniridia

A person who has aniridia is born without a fully developed iris. Aniridia can affect the entire anatomy - the cornea, the fovea or retina, as well as the lens. As a result, ocular conditions can include glaucoma, foveal hypoplasia, nystagmus, strabismus, dry eye, corneal degeneration, and cataracts. Although people with aniridia always have vision problems, the degree varies greatly and is dependent upon which complications, in addition to the lack of iris, an individual has. Ocular conditions can include glaucoma, foveal hypoplasia, nystagmus, strabismus, dry eye, corneal degeneration, and cataracts. Vision For Tomorrow Foundation

Optic Atrophy

Optic atrophy means the loss of some or most of the nerve fibers in the optic nerve. The effects range from visual change to severe visual loss. Symptoms include blurred vision, abnormal side vision, abnormal color vision, decreased brightness in one eye relative to the other. Manocha Eye Hospitals

Corneal Dystrophies and Degeneration

Corneal dystrophy means one or more parts of the cornea (transparent front part of the eye) loses clarity due to a buildup of cloudy material. Abnormal material accumulates in the cornea — the clear, round dome covering the eye's iris and pupil. Most corneal dystrophies affect both eyes. It affects vision in differing ways. Some people with corneal dystrophy may have severe visual impairment, while in some cases no visual problems are experienced. (Need Source)

Corneal degeneration is the term used for the breakdown of the cornea.

Cataracts

Cataracts are a clouding of the eye's natural lens, which lies behind the iris and the pupil. For people who have cataracts, seeing through cloudy lenses is a bit like looking through a frosty or fogged-up window. Most cataracts are related to aging. Mayo Clinic

Age-related cataracts can affect vision in 2 ways:

1. Clumps of protein reduce the sharpness of the image reaching the retina, clouding the lens and reducing the light that reaches the retina. The clouding may become severe enough to cause blurred vision. Cataracts typically progress slowly, so vision gets worse gradually. Over time, the cloudy area in the lens may get larger, and the cataract may increase in size. Vision may get duller or blurrier.
2. As the clear lens slowly colors with age, vision may acquire a brownish shade. At first, the amount of tinting may be small and may not cause a vision problem. Over time, increased tinting may make it more difficult to read and perform other routine activities. This gradual change in the amount of tinting does not affect the sharpness of the image transmitted to the retina. (Need Source)

Peripheral (Side) Vision Loss

Glaucoma

Glaucoma is a condition that causes damage to the eye's optic nerve and gets worse over time. It's often associated with a buildup of pressure inside the eye. The most common types of glaucoma — primary open-angle glaucoma and angle-closure glaucoma — have completely different effects on vision. MedlinePlus

Primary open-angle glaucoma effects include:

• Gradual loss of peripheral vision, usually in both eyes
• Tunnel vision in the advanced stages

Acute angle-closure glaucoma effects include:

• Sudden onset of visual disturbance, often in low light
• Blurred vision
• Halos around lights

Retinitis Pigmentosa

Retinitis pigmentosa (RP)is a group of retinal diseases that damage the light-sensitive rods and cones located in the retina, the back part of the eye. Rods, which provide side (peripheral) and night vision are affected more than the cones that provide color and clear central vision. (Need Source)

Effects include:

• Loss of peripheral vision
• Night blindness

Progressive loss of visual fields a hallmark. The visual field loss often begins as a donut like ring in mid-periphery. As it progresses both centrally and peripherally and results in tunnel vision.

People with RP can experience light and glare problems, double vision, cataracts, and decreased visual acuity.

Hemianopsia

Hemianopsia is loss of half of the field of view on the same side in both eyes. People who have a stroke or traumatic brain injury, may lose one half of their side vision to the right or left. The Low Vision Centers of Indiana

Effects include:

• Half of the visual field is lost. Can't to see to either the left or right from the centre of a person's field of vision.

Central Visual Field Loss

Macular Degeneration

Macular Degeneration is caused by the deterioration of the central portion of the retina, the inside back layer of the eye that records the images we see and sends them via the optic nerve from the eye to the brain. The retina’s central portion, known as the macula, is responsible for focusing central vision in the eye, and it controls our ability to read, recognize colors, and see objects in fine detail. American Macular Degeneration Foundation

Macular Dystrophy

Macular dystrophy affects the retina in the back of the eye. It leads to damage of cells in an area in the retina called the macula. The macula is responsible for central vision. When the macula is damaged, people have difficulty seeing straight ahead. This makes it difficult to read. A pigment builds up in cells of the macula. Over time, this substance can damage cells that are critical for clear central vision. Vision often becomes blurry or distorted. Typically, people with macular dystrophy maintain peripheral vision. Side vision is usually fine. Disabled World

Cone-Rod Dystrophy

Cone-rod dystrophy results from a primary loss of cone photoreceptors, followed by loss of rods. An initial loss of color vision and of visual acuity (due to loss of cone function) is followed by nyctalopia (night blindness) and loss of peripheral visual fields (due to loss of rod function). Foundation Fighting Blindness

Effects include:

• Decreased visual acuity
• Difficulty seeing small details
• Central scotoma appears first, preventing fluent reading
• Patchy losses of peripheral vision follow

Diabetic Retinopathy

Diabetic Retinopathy is caused by damage to small blood vessels in the eye as a result of diabetes. It can affect vision in various ways. Proliferative diabetic retinopathy, or abnormal blood vessel growth in the eye, can result in severe vision loss due to bleeding into the eye, or a detachment of the retina. National Eye Institute

Effects include:

• Difficulty seeing small details or distortion of vision.
• Blurred vision. This may occur when the macula—the part of the retina that provides sharp central vision—swells from leaking fluid. This condition is called macular edema.
• Blocked vision. This may occur f new blood vessels grow on the surface of the retina and bleed into the eye.
• Spots can "float" in a person's vision due to specks of blood

Visual Acuity

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Functional Effects of Low Vision

1. acuity
   1. central reduced
   2. difference between eyes
   3. distance reduced
   4. general reduced
   5. fluctuating
   6. near reduced
2. color vision
   1. loss of color
   2. reduced
   3. shades of gray
3. Confusion, visual
4. Contrast Sensitivity, reduced
5. Detail
   1. fine vision loss
   2. loss
   3. (see Fatigue)
6. Discomfort
   1. closing eyes
   2. dizziness
   3. eye pain
   4. eye redness
   5. eye rubbing
   6. general
   7. headache
   8. making eye contact
   9. nausea
   10. tearing
   11. vertigo
7. Distortion
   1. binocular vision reduced
   2. blurred vision
   3. central
   4. depth perception reduced
   5. double vision
   6. general
   7. flaring of images
   8. fractured / scattered light
   9. glare (internal)
   10. images
   11. low light induced
   12. movement of stationary objects
   13. multiple images
   14. peripheral
   15. scattering light
   16. streaking
8. exacerbation, medicine existing visual impairment
9. Fatigue
   1. close work
   2. detailed tasks
   3. eye
   4. visual
10. Field Loss
    1. central
    2. fovea involvement
    3. general
    4. hemispheric
    5. monocular blindness
    6. peripheral
    7. recognition of large objects at close range
    8. unaware of missing visual information
    9. variable
11. Fixation (image capture)
    1. difficulty with
    2. not steady
12. Fluctuation
    1. acuity
    2. fatigue induced performance loss
    3. focus - some in and some out
    4. light related visual ability
    5. near better than distance
    6. near vision reduced
    7. night vision reduced
    8. slow recovery from changes in light
    9. uncontrolled eye movements increased pattern induced
    10. visual field
    11. visual performance
13. perception, impaired (visual cortex)
14. Rigidity
    1. focal distance change
    2. light change
15. reading difficulty
16. Sensitivity
    1. glare
    2. light
17. Tracking / Scanning
    1. difficulty
    2. fast-moving objects difficulty
    3. loses place in visual tasks
18. Visual-Motor
    1. abilities reduced
    2. eye-hand coordination
    3. reach impaired
    4. steps, drop-offs

References

• NoCoffee Vision Simulator (Chrome extension) "NoCoffee can be helpful for understanding the problems faced by people with slight to extreme vision problems" - Aaron Leventhal
• Low Vision - University of Michigan Kellogg Eye Center Kellogg Eye Center
• Types of Low Vision - The Chicago Lighthouse
• Common Types of Low Vision - American Optometric Association
• Visual Disabilities - Low Vision - WebAIM
• What is Low Vision? - American Foundation for the Blind
• Types of Visual Impairment - Freedom Scientific
• Eye Health and Low Vision - WebMD

TODO

While we need to define specific visual impairments many people with low vision don't have a specific named visual impairment. There are general things that we might have that are common across visual impairments and I think it is helpful to document those. For example

• Nystagmus
• Glare sensitivity
• Foveal hypoplasia (reduces fine detail vision)
• Decreased contrast
• Myopia (to the degree that it affects corrected acuity, e.g. may cause decreased contrast or with glasses makes text smaller)