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ophthalmology neurology general-medicine

LogMAR ⇄ Snellen Visual Acuity Converter

Maps the patient's distance visual acuity (best-corrected, better eye, presenting acuity) to its LogMAR equivalent and the WHO 2019 ICD-11 visual-impairment category. Single common reference for documentation, DVLA decisions, certification of vision impairment (CVI), and study endpoints. LogMAR = log₁₀(1 / decimal acuity); each step on a standardised ETDRS chart is 0.10 log units (5 letters).

Used in: Acute Red Eye

Score interpretation

Normal vision — meets DVLA Group 1 standard (≥6/12) -100–30

→ Routine optometry follow-up. DVLA Group 1 driving permitted (with adequate visual fields). No CVI registration warranted.

Mild visual reduction (better than 6/18) 31–47

→ Consider refraction, cataract assessment, or referral if recent change. Below 6/12 — does not meet DVLA Group 1; counsel patient and report if concerns. Group 2 (HGV/PSV) requires 6/7.5.

Moderate visual impairment — WHO Category 1 (6/18 to 6/60) 48–99

→ Refer for low-vision assessment. Consider Sight Impaired (SI / 'partially sighted') registration via CVI if best eye 6/24–6/60. Optimise refraction; treat reversible cause (cataract, AMD, DR). Inform DVLA — driving not permitted.

Severe visual impairment — WHO Category 2 (6/60 to 3/60) 100–129

→ Severely Sight Impaired (SSI / 'blind') CVI registration usually appropriate (best eye <6/60). Low-vision rehabilitation; mobility training; benefit entitlements (PIP, Blind Person's Allowance). Treat underlying disease aggressively.

Blindness — WHO Categories 3–4 (3/60 to LP) 130–270

→ SSI registration. Multidisciplinary visual rehabilitation, social services, ECLO referral. Confirm no treatable cause (RD, vitreous haemorrhage, NAION, CRAO/CRVO). Counsel re: end-stage support and assistive technology.

No light perception — WHO Category 5 271–300

→ SSI registration. Confirm by direct ophthalmoscopy and bright-light testing both eyes. Investigate reversible causes (occipital lobe stroke, NA-AION, severe ROP, end-stage glaucoma). Bilateral NLP — consider neuro-ophthalmology if uncertain aetiology.

Interpretation bands for the LogMAR / Snellen. Apply clinical judgement and local guidance.

References

Related

Curated clinical cross-links plus same-class fallbacks.

Pathways

Decision support only — verify against a current formulary, NICE, or your local guideline before clinical use.