How do you convert Snellen 20/200 to LogMAR?

LogMAR = log10(Snellen denominator / Snellen numerator) = log10(200/20) = log10(10) = 1.0; for Snellen 20/20: LogMAR = log10(1) = 0; worse acuity = higher LogMAR.

What visual acuity defines legal blindness in the US?

Legal blindness in the US: best corrected VA ≤20/200 (Snellen) in the better eye OR visual field ≤20 degrees diameter; in the UK: worse than 6/60 (Snellen) or <20 degrees visual field is severely sight impaired.

How many ETDRS letters correspond to each Snellen line?

Each Snellen line = 5 ETDRS letters; 20/20 = 85 letters; 20/40 = 70 letters; 20/200 = 35 letters; counting fingers = approximately 1.3-1.5 LogMAR; hand motions, light perception are below ETDRS scoring range.

What is the difference between Snellen and Landolt C acuity?

Snellen uses optotype letters calibrated for each line; Landolt C (ring with gap) is more internationally standardized and less literacy-dependent; both use angular resolution (20/20 = 1 arcminute gap resolution).

When is ETDRS preferred over Snellen for research?

ETDRS (Early Treatment Diabetic Retinopathy Study) chart is preferred for clinical trials due to letter-by-letter scoring, equal spacing between letters within lines, and better test-retest reliability; Snellen is sufficient for clinical practice.

Visual Acuity Conversion Calculator (Snellen / LogMAR / Decimal / ETDRS)

Converts between visual acuity notation formats: Snellen fraction (20/x), decimal fraction, LogMAR, and ETDRS letter count, with near vision equivalents and legal blindness thresholds.

Use the full interactive calculator below, or

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Visual Acuity Conversion Calculator (Snellen / LogMAR / Decimal / ETDRS)

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Frequently Asked Questions

How do you convert Snellen 20/200 to LogMAR?

What visual acuity defines legal blindness in the US?

How many ETDRS letters correspond to each Snellen line?

What is the difference between Snellen and Landolt C acuity?

When is ETDRS preferred over Snellen for research?