Visual impairment and blindness: how they are graded
- Topic
WHO grades visual impairment by the acuity of the better eye: mild, moderate, severe and blindness. The grade guides rehabilitation and certification.
See it in 3D: Retina · Optic nerve
What it is
The World Health Organization classifies distance vision impairment by the presenting visual acuity of the better eye, that is, with whatever correction the person actually uses. Near vision impairment is classified separately. A severely restricted visual field also counts as blindness, even with good central acuity. These categories are used in epidemiology, disability certification and to plan rehabilitation.
Key facts
- Mild: acuity worse than 6/12 but equal to or better than 6/18.
- Moderate: worse than 6/18 but equal to or better than 6/60.
- Severe: worse than 6/60 but equal to or better than 3/60.
- Blindness: worse than 3/60, or a visual field narrowed to less than 10 degrees around fixation.
- Near vision impairment: near acuity worse than N6 or M0.8 with existing correction.
In clinical practice
- Presenting acuity (with current glasses or none) shows the real burden; best-corrected acuity shows what correction could achieve.
- A person can be 'blind' by field loss (advanced glaucoma) while reading the 6/6 line.
- Disability certification in Colombia follows the Ministry of Health's procedure and uses the clinical findings recorded by the treating doctor.
Next step / Initial management
- Record presenting and best-corrected acuity of each eye, and the visual field when relevant.
- Moderate impairment or worse not correctable with glasses: refer for low vision rehabilitation.
- Help the person access disability certification and support services when appropriate.
- Look for the treatable cause first: refraction, cataract, diabetic retinopathy, glaucoma.
Test yourself
Think of the answer, then tap the question to see it.
How does WHO define blindness?
Presenting acuity worse than 3/60 in the better eye, or a visual field of less than 10 degrees around fixation.
Which eye is used to grade visual impairment?
The better eye, with the person's current correction (presenting acuity).
Can someone with 6/6 acuity be classified as blind?
Yes, if the visual field is constricted to less than 10 degrees around fixation.
Connections
See it in 3D2
The structures of Durgical's 3D anatomy where it is found.
Educational content; not a clinical guideline and no substitute for assessment by a health professional. For sudden visual loss, severe eye pain, a chemical burn or an eye injury, go to an emergency department at once.
Sources: Blindness and vision impairment: fact sheet (World Health Organization, 2023); Blindness (StatPearls Publishing (NCBI Bookshelf), 2024).
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Representative model, for educational purposes only.