Visual impairments can vary greatly in severity and type, and they may impact how a person reads, writes, travels, accesses information, or interacts with the world. Visual impairments can arise from a wide range of causes, including:
  • Congenital conditions, such as albinism, optic nerve hypoplasia, anophthalmia, or congenital cataracts.
  • Eye diseases that develop later in life, such as glaucoma, diabetic retinopathy, macular degeneration, retinitis pigmentosa, or cortical visual impairment (CVI).
  • Injuries or trauma to the eye or brain that affect the visual system.
  • Neurological conditions, including damage to the visual pathways or occipital lobe.
It is also important to understand that total blindness is rare. Very few individuals have no light perception or complete functional vision. Many people who are legally blind still have residual or usable vision, which may help them detect shapes, movement, colors, or light. Others may rely on peripheral vision, central vision, or specific viewing strategies to maximize the vision they do have. Because visual impairments exist on a broad spectrum, each person's visual needs, strengths, and accommodations will be unique. Understanding the diversity of visual impairments helps educators, families, and service providers design appropriate supports, provide meaningful accommodations, and empower individuals to use their remaining vision effectively while also developing alternative skills for independence.

World Health Organization (WHO) Vision Classifications

​The World Health Organization (WHO) classifies levels of visual impairment based on the best-corrected visual acuity in the better eye (with the best possible glasses or contact lenses):
Visual Acuity (Better Eye with glasses)
WHO Classification
Description
20/30 to 20/60
Mild visual impairment
Near-normal vision
20/70 to 20/160
Moderate visual impairment
Moderate low vision
20/200 to 20/400
Severe visual impairment
Severe low vision
20/500 to 20/1,000
Profound visual impairment
Profound low vision
Less than 20/1,000
Near-total visual impairment
Near-total blindness
No light perception
Total visual impairment
Total blindness
In the United States, the term “legally blind” is a specific legal classification used to determine eligibility for certain services, supports, and benefits. It does not always reflect how much a person can or cannot see in daily life. A person is considered legally blind if they meet either of the following criteria:
  • Visual Acuity of 20/200 or Worse. This means that in the better eye (with the strongest possible correction such as glasses or contacts), a person can see at 20 feet what a person with typical vision can see at 200 feet. In other words, their vision is significantly less clear or sharp, even with corrective lenses. This reduced clarity may affect reading print, recognizing faces from a distance, or seeing details.
  • Visual Field of 20 Degrees or Less. The visual field refers to how wide an area a person can see when looking straight ahead. A typical visual field spans about 180 degrees, allowing people to see far to the left and right. If a person’s visual field is 20 degrees or less, they experience what is commonly referred to as “tunnel vision.” Even if their central vision is relatively sharp, the severe narrowing of peripheral vision can make mobility, safety, and visual awareness more difficult.
It’s important to know that legal blindness does not mean total blindness. Many individuals who are legally blind still have usable vision that can be supported with tools such as magnification, lighting adjustments, optical devices, or technology.
The legal definition provides a consistent way for agencies and professionals to determine access to:
  • Vocational Rehabilitation Services
  • Disability benefits (such as SSDI or SSI)
  • Accessible educational services and accommodations
  • Specialized low vision evaluations and devices
This classification ensures that individuals with significant vision loss receive the supports they need to participate fully and independently in school, work, and daily life.
Best-corrected visual acuity refers to the sharpest, clearest vision a person can achieve when using the most effective standard corrective measures available to them, typically prescription glasses or contact lenses. This measurement does not reflect how a person sees without correction; instead, it shows the maximum level of clarity achievable with optical devices. Best-corrected acuity is important because it provides professionals with a consistent, reliable way to assess how much of the visual system’s function can be improved and how much vision loss remains even after optimal correction.
"The only thing worse than being blind is having sight but no vision."  -Helen Keller

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