Many people believe that being legally blind means having no vision at all, but that isn’t quite accurate. Some individuals who are legally blind can still see light, shapes, or objects - just not clearly. In fact, only about 15% of people with eye conditions are considered completely blind.
Understanding whether you are legally blind is very important, as it affects eligibility for benefits such as tax exemptions or Social Security disability support. It can also determine whether you are allowed to hold a driver’s licence.
In the guide below, we explain what prescription qualifies as legally blind, the criteria used to determine legal blindness, common causes of legal blindness, and practical tips to help protect and care for your vision.
What Does 'Legally Blind' Mean?
Legally blind does not always mean complete darkness or total loss of vision. Many people who are legally blind can still see shapes, colours, or light. The term 'legally blind' is a legal definition used by governments and medical authorities. It helps decide who qualifies for disability benefits, special education support, or vision-related assistance.
In most countries, including the USA and the UK, legal blindness is defined using two main factors. These factors are visual acuity and visual field. Visual acuity means how clearly a person can see. Visual field means how wide an area a person can see while looking straight ahead.
Understanding Eye Prescription and Vision Numbers
Before we answer what prescription is legally blind, it is important to understand how eye prescriptions work. Eye doctors use numbers like 20/20, 20/40, or 20/200 to describe vision clarity. These numbers are called visual acuity measurements.
If a person has 20/20 vision, it means they can see clearly at 20 feet what a normal person should see at 20 feet. If someone has 20/200 vision, it means they can see at 20 feet what a normal person can see at 200 feet. This shows very poor vision.
Eye prescriptions also include values like minus or plus numbers. These numbers show how strong glasses or contact lenses must be to correct vision. Higher numbers usually mean worse vision.
What Prescription Is Legally Blind According to Medical Standards?
Now let us clearly answer what prescription is legally blind. A person is considered legally blind if their best corrected vision is 20/200 or worse in the better eye. Best corrected vision means vision after wearing proper glasses or contact lenses.
This means that even after using the strongest suitable glasses, if the person still sees only 20/200, they are legally blind. This level of vision makes it very difficult to read, drive, or recognise faces from a distance.
Another way a person can be legally blind is through visual field loss. If a person’s visual field is 20 degrees or less, they are also considered legally blind. A normal visual field is about 180 degrees. A narrow field feels like looking through a tunnel.
How Do You Know If You Are Legally Blind?
To receive an accurate diagnosis of legal blindness, you should have a professional eye examination with an optician or eye care specialist. One of the main assessments used is a visual acuity test, often performed with a Snellen eye chart. If you are unable to read beyond the top line of the chart—even while wearing corrective lenses—you may meet the criteria for legal blindness.
Your optician may also carry out a visual field test. During this exam, one eye is covered at a time while you focus straight ahead. The optician will check whether you can see fingers or objects placed in different areas of your peripheral vision. This assessment, known as a confrontational visual field exam, helps determine whether your field of vision is significantly restricted.
Is Eye Prescription Number Alone Enough to Decide Legal Blindness?
Many people think that a high glasses number means legal blindness. This is not fully correct. Prescription power like minus 10 or minus 15 does mean very weak eyesight, but legal blindness depends on corrected vision, not prescription number alone.
Some people with very high prescription numbers can still see well with glasses. On the other hand, some people with lower prescription numbers may have eye diseases that cause poor corrected vision.
So, when asking what prescription is legally blind, remember that doctors look at how well you see with correction, not just the glasses number.
Most Common Causes Of Legal Blindness
Age-related macular degeneration (AMD)
This condition affects the retina and most often develops in people over the age of 50. It occurs in two forms: dry AMD, where the macula gradually thins, and wet AMD, where abnormal blood vessels grow beneath the retina. If left untreated, AMD can lead to rapid vision loss and, in severe cases, legal blindness.
Glaucoma
Glaucoma is caused by increased pressure inside the eye, which can damage the optic nerve over time. This pressure buildup often occurs when fluid does not drain properly from the eye. Without early detection and treatment, glaucoma can result in permanent vision loss and legal blindness.
Diabetic retinopathy
This condition develops as a result of prolonged high blood sugar levels in people with diabetes. It causes the blood vessels in the retina to swell, weaken, and leak. If not managed effectively, diabetic retinopathy can progress and lead to legal blindness.
Eye injuries and genetic conditions
Certain genetic disorders, such as Usher syndrome, can also cause legal blindness. In addition, serious eye injuries—often resulting from sports or physically demanding jobs where protective eyewear is not used—can lead to partial or total vision loss.
Difference Between Legally Blind and Totally Blind
It is important to understand the difference between legally blind and totally blind. 'Totally blind' means no light perception at all. This is very rare.
Legally blind people usually have some usable vision. They may see shadows, colours, or movement. With training and tools, many legally blind people live independent lives.
So when discussing what prescription is legally blind, it does not mean the person cannot see anything. It only means their vision meets the legal definition of blindness.
How To Protect Your Eyes From Becoming Blind
Manage blood sugar levels.
Vision loss related to diabetes is considered up to 90% preventable with proper blood sugar control. Keeping levels within a healthy range can significantly reduce the risk of diabetic eye disease.
Maintain a healthy diet.
Eating a balanced diet rich in vegetables and nutrient-dense foods helps support overall eye health. Foods high in omega-3 fatty acids, such as fatty fish, have been linked to better vision and eye function.
Maintain a healthy weight.
Being overweight increases the risk of developing diabetes, which can negatively affect eyesight. Maintaining a healthy weight can help lower this risk and support long-term vision health.
What Support Is Available To The Legally Blind?
Assistive equipment
A wide range of tools can help individuals who are legally blind manage everyday tasks more independently. These include bright lighting, white canes, magnifiers, screen readers, large-print keyboards, and liquid level indicators, all of which can improve safety and usability in daily life.
Guide dogs
Guide dogs provide valuable support by helping with mobility and navigation. They can assist with identifying obstacles, locating objects, using public transport, and increasing overall safety and confidence when moving around.
Support groups
Visually impaired support groups offer a space to share experiences, discuss challenges, build friendships, and receive emotional and practical support from others who understand similar situations.
Vision rehabilitation
Vision rehabilitation programmes help individuals adapt to vision loss by teaching practical skills and strategies to maintain independence and improve quality of life.
Final Thoughts
Understanding what prescription is legally blind helps remove fear and confusion. Legal blindness is a medical and legal term, not a judgement of a person’s ability or worth. Many legally blind people lead successful and fulfilling lives.
If you or someone you know has serious vision problems, consult an eye specialist. Proper guidance, treatment, and support can make a big difference.
FAQs
What prescription is 'legally blind' in simple terms?
A person is legally blind if their best corrected vision is 20/200 or worse in the better eye, or if their visual field is 20 degrees or less.
Is minus 6 eyesight considered legally blind?
No, minus 6 eyesight alone is not legally blind. Legal blindness depends on how well you see with glasses, not just the prescription number.
Can glasses fix legal blindness?
In some cases, glasses can improve vision. But if vision remains poor even with glasses, the person may still be legally blind.
Is legal blindness permanent?
It depends on the cause. Some conditions can be treated, while others cause permanent vision loss.
Can a legally blind person see anything?
Yes. Most see light, shapes, or blurry images. Total darkness is very rare.
Can LASIK cure legal blindness?
Only if poor vision is solely due to high spectacle power. LASIK cannot fix damage from diseases like glaucoma or retinal problems.
Can driving be allowed if someone is legally blind?
No. The visual requirements for a driver's licence are much stricter. Legal blindness means vision is too poor to meet the safe driving standards set by authorities.
Does legal blindness get worse over time?
It depends on the cause. Conditions like glaucoma or macular degeneration may progress. Regular monitoring by an eye doctor is essential to manage the condition.
Can children be legally blind?
Yes, children can also be legally blind. Some children are born with eye conditions, while others develop vision problems early in life. Early diagnosis helps in better learning support.
Does legal blindness qualify for disability benefits?
Yes, in many countries, legal blindness qualifies as a visual disability and allows access to government benefits and support programmes.
