ophthalmology neurology general-medicine

LogMAR ⇄ Snellen Visual Acuity Converter

Maps distance visual acuity (Snellen line, better eye) to its LogMAR value and the WHO ICD-11 distance visual-impairment category (WHO uses presenting acuity; UK certification uses corrected acuity and the visual field). LogMAR = log₁₀(1 / decimal acuity); each step on a standardised ETDRS chart is 0.10 log units (5 letters). Counting fingers and hand movements have conventional values (≈1.9 and ≈2.3); light perception (2.7) and no light perception (3.0) are imputed, not measured.

Used in: Acute Red Eye

Score interpretation

6/12 or Better — No Distance Visual Impairment -0.3–0.3

LogMAR 0.30 or better (WHO ICD-11: no distance impairment).

→ Routine optometry follow-up. DVLA Group 1 driving permitted if the binocular corrected acuity is 6/12 or better (with adequate visual fields and the number-plate test). No CVI registration warranted.

Mild Visual Impairment (worse than 6/12, to 6/18) 0.31–0.48

Worse than 6/12 down to 6/18 (WHO ICD-11 mild).

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

Moderate Visual Impairment — WHO Category 1 (worse than 6/18, to 6/60) 0.49–1

Worse than 6/18 down to 6/60 (WHO ICD-11 moderate).

→ Refer for low-vision assessment. Optimise refraction; treat reversible cause (cataract, AMD, DR). Sight impaired (SI) certification via CVI depends on acuity and field: 3/60–6/60 with a full field, up to 6/24 with a moderately contracted field, or 6/18 with a marked field defect. Below the DVLA Group 1 standard — do not drive.

Severe Visual Impairment — WHO Category 2 (worse than 6/60, to 3/60) 1.01–1.3

Worse than 6/60 down to 3/60 (WHO ICD-11 severe).

→ Sight impaired (SI) certification via CVI is usually appropriate (3/60–6/60 with a full field); severely sight impaired (SSI) if the visual field is also contracted. Low-vision rehabilitation; mobility training; benefit entitlements. Treat underlying disease aggressively.

Blindness — WHO Categories 3–4 (worse than 3/60, to light perception) 1.31–2.7

Worse than 3/60 (WHO ICD-11 blindness, categories 3–4).

→ Severely sight impaired (SSI) certification (worse than 3/60). 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 2.71–3

No light perception (WHO ICD-11 category 5).

→ 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

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.

Score interpretation

References

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