What Prescription is Legally Blind?
What prescription is legally blind? Understanding this threshold can be crucial for those with significant vision impairments. In this article, we’ll explore the world of prescriptions, eyesight, and diopters and help clarify the point at which someone is considered legally blind.
Table of Contents
- Understanding Eyesight and Prescriptions
- Defining Legal Blindness
- Diopters and Legal Blindness
- Impact on Daily Life
- Resources and Support
Understanding Eyesight and Prescriptions
Before delving into what prescription is legally blind, let’s first understand the basics of eyesight and prescriptions. Our eyesight, or visual acuity, refers to the ability of our eyes to see objects clearly at a specific distance. A prescription is a numerical representation of the lens power needed to correct vision impairments.
Here are some key terms associated with prescriptions:
- Sphere (SPH): This number indicates the lens power needed to correct nearsightedness or farsightedness.
- Cylinder (CYL): This number represents the lens power needed to correct astigmatism.
- Axis: This number indicates the angle (in degrees) at which the CYL correction should be applied.
Defining Legal Blindness
Now, let’s address the main question: what prescription is legally blind? Legal blindness is determined based on two factors:
- Visual acuity: A person is considered legally blind if their best-corrected visual acuity (BCVA) is 20/200 or worse in the better-seeing eye. This means that they can see at 20 feet what a person with normal vision can see at 200 feet.
- Visual field: A person is considered legally blind if their visual field is 20 degrees or less in the better-seeing eye.
It’s important to note that legal blindness is not the same as complete blindness. Many people who are legally blind still have some vision, albeit significantly impaired.

Diopters and Legal Blindness
Diopters are a unit of measurement used to express the power of a lens. In terms of diopters, a person with a prescription of -10.00 diopters or more (for nearsightedness) or +10.00 diopters or more (for farsightedness) is often considered to have a significant vision impairment. However, it’s important to remember that diopters are not a direct measure of legal blindness. Legal blindness is determined by visual acuity and visual field, as mentioned earlier.
Impact on Daily Life
Being legally blind can have a significant impact on an individual’s daily life. Some of the challenges faced by those with significant vision impairments include:
- Difficulty reading or seeing objects at a distance
- Difficulty recognizing faces
- Difficulty navigating their environment
However, there are many resources and tools available to assist those who are legally blind, including:
- Assistive technology: Devices like screen readers, magnifiers, and braille displays can help individuals with significant vision impairments access information and communicate more easily.
- Orientation and mobility training: This type of training teaches individuals how to navigate their environment using a white cane or a guide dog.
- Support services: Organizations like the American Foundation for the Blind and the National Federation of the Blind offer resources, support, and advocacy for individuals with vision impairments.

Resources and Support
If you or a loved one is experiencing vision impairment, it’s essential to seek professional help. An optometrist or ophthalmologist can determine the cause of the vision loss and recommend appropriate treatments or interventions. They can also provide guidance on available resources and support services for individuals who are legally blind or have significant vision impairments.
In conclusion, understanding what prescription is legally blind can be crucial for those with significant vision impairments. Legal blindness is determined by visual acuity and visual field rather than diopters. Despite the challenges faced by those with significant vision impairments, there are numerous resources and support services available to help improve their quality of life.
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