What eye prescription is legally blind in the UK?

'Legally blind' is not a UK legal term, but the phrase is often used to mean **severely sight impaired (SSI)** — the modern equivalent of 'blind' on the UK's Certificate of Vision Impairment (CVI). This guide explains what actually counts, why your glasses prescription alone does not determine it, and what registration means in practice.

The legal definitions

In the UK, sight impairment is defined by visual acuity and visual field, measured in the **better eye with the best possible correction** (glasses or contact lenses on). The two categories are:

- **Severely sight impaired (blind)** — visual acuity worse than 3/60, OR 3/60 to 6/60 with a very contracted visual field, OR 6/60 or better with a very contracted field.

- **Sight impaired (partially sighted)** — visual acuity of 3/60 to 6/60 with a full field, OR 6/24 with a moderately contracted field, OR 6/18 or better with a marked field defect.

Snellen 6/60 means you can see at 6 metres what a normally sighted person sees at 60 metres. Registration is voluntary and is completed by a consultant ophthalmologist on the CVI form.

Why your glasses prescription is not the answer

Patients often ask 'what prescription counts as legally blind?' — but a spectacle prescription (e.g. −8.00 dioptres) describes the refractive error, not the vision. Someone with a very high prescription who sees 6/6 with glasses on is **not** sight impaired. Registration depends on the acuity you achieve with your best correction, not the strength of the lens.

That said, patients with prescriptions above roughly −10 or +8 dioptres often have other eye complications (myopic maculopathy, retinal thinning, cataract) that can reduce best-corrected vision, and those complications are what may bring them into the sight-impaired category.

Conditions that most commonly lead to registration in the UK

The commonest UK causes of sight impairment registration are:

- **Age-related macular degeneration (AMD)** — the leading cause in adults over 60

- **Glaucoma** — permanent field loss if untreated; see our glaucoma section for detail

- **Diabetic retinopathy**

- **Cataract** — but this is reversible with cataract surgery, so it should not lead to registration unless surgery is contraindicated

- **Inherited retinal disease** (e.g. retinitis pigmentosa)

Uncorrected refractive error should never leave someone sight impaired in the UK — a proper refraction and glasses (or, where appropriate, laser eye surgery or lens replacement) should be the first step.

What registration does for you

Being certified as sight impaired or severely sight impaired gives access to:

- Low-vision aids and rehabilitation from your local sensory team

- The Blind Person's Personal Tax Allowance

- Reduced TV licence fee (50% for SSI)

- Free NHS eye tests and, in many cases, help with transport costs

- Priority for Personal Independence Payment (PIP) and other benefits assessments

- Symbol cane or long-cane training

Registration is a supportive process — it is not a driving licence flag on its own, but the DVLA vision standard is a separate legal test and must be met to keep a licence.

Driving vision standards

You must be able to read a UK number plate in good daylight from 20 metres away (with glasses or contacts if you wear them) and have a visual acuity of at least 6/12 with both eyes open. Losing this standard means you must tell the DVLA and stop driving until reassessed.

When to see a consultant

If your vision is dropping despite up-to-date glasses, or if an optometrist has raised concerns about the macula, glaucoma or diabetic changes, ask for a referral to an ophthalmologist. Early treatment prevents avoidable sight loss in most UK cases.

You can book a private consultation at my London practice or call **020 3137 3237** if you would like a specialist assessment sooner than the NHS pathway allows.