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Visual acuity conversion

Converts visual acuity between common notations and classifies visual impairment using WHO categories.

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Check the population, units and version. The result shows the formula or classification; it does not make an automatic treatment decision.

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Method · Limits of application

Snellen/decimal/logMAR conversion; ETDRS 1982 0.02 per letter; Holladay 2004 conventions

Conversion requires a positive Snellen fraction and preserves the original measurement; it does not perform a new examination. Compare results with testing distance, eye, optical correction and chart documented. The progression of 0.1 logMAR per line and 0.02 per letter corresponds to the ETDRS structure, not every chart. Holladay 2004 recommends averaging in logMAR, not taking the arithmetic mean of Snellen fractions. Counting fingers and hand movements depend on distance and must not be assigned fixed decimal equivalents through this conversion.

Conditions of use

Check the population, units, inclusion and exclusion criteria, and version in the original source. A result alone does not establish a diagnosis, discharge decision or prescription.

Documented parameters

Entered notation
Value (Snellen: denominator only)

5/5 reference cases checked. Numerical tests are not clinical validation.

Sources and documentation

Documented formula

Transcribed from the source or a recorded revision; this is not a clinical recommendation.

Decimal = Snellen numerator ÷ denominator (20/40 = 0.5). logMAR = −log₁₀(decimal) = log₁₀(MAR), where MAR is the minimum angle of resolution in arcminutes. Each ETDRS chart line is 0.1 logMAR (5 letters of 0.02).

References

Identifier: conversao-de-acuidade-visual

Original clinical content: Brazilian Portuguese.

Method version

Snellen/decimal/logMAR conversion; ETDRS 1982 0.02 per letter; Holladay 2004 conventions

conversao-de-acuidade-visual@native-2026-10-05+3d8f421d32e0

Source for the active edition

The bibliographic edition identifies the source. By itself, it proves neither full conformity of the formula nor clinical approval.

Synthetic cases checked (5)

Synthetic cases for checking the implementation, with no patient data.

Case 1

reference-001

Inputs

Entered notation: Snellen 20/x (feet)
Value (Snellen: denominator only): 40

{
  "modo": "s20",
  "valor": 40
}

Expected result

{
  "dec": 0.5,
  "logmar": 0.301
}

Actual result

{
  "dec": 0.5,
  "logmar": 0.3010299956639812,
  "snellen20": 40
}

Case 2

reference-002

Inputs

Entered notation: Snellen 6/x (meters)
Value (Snellen: denominator only): 60

{
  "modo": "s6",
  "valor": 60
}

Expected result

{
  "dec": 0.1,
  "logmar": 1
}

Actual result

{
  "dec": 0.1,
  "logmar": 1,
  "snellen20": 200
}

Case 3

reference-003

Inputs

Entered notation: logMAR
Value (Snellen: denominator only): 0

{
  "modo": "log",
  "valor": 0
}

Expected result

{
  "dec": 1,
  "snellen20": 20
}

Actual result

{
  "dec": 1,
  "logmar": 0,
  "snellen20": 20
}

Case 4

reference-004

Inputs

Entered notation: Decimal
Value (Snellen: denominator only): 0.04

{
  "modo": "dec",
  "valor": 0.04
}

Expected result

{
  "snellen20": 500,
  "logmar": 1.398
}

Actual result

{
  "dec": 0.04,
  "logmar": 1.3979400086720375,
  "snellen20": 500
}

Case 5

reference-005

Inputs

Entered notation: Snellen 20/x (feet)
Value (Snellen: denominator only): 3

{
  "modo": "s20",
  "valor": 3
}

Expected result

{
  "error": true
}

Code and reproducibility

This tool’s code on GitHub

Download code and tests

Sources, version and reproduction instructions

README

Local installation

Code license: Apache-2.0

Guidelines and conditions

This repository’s license applies to the code. Third-party instruments, questionnaires, data and models remain subject to their owners’ conditions.

The code tests are technical checks. Clinical approval and professional translation review are recorded separately.

Relationship with cancer research

General context — relationship to be defined

A resource for general clinical contexts. This edition does not assign a specific oncological relationship; selecting it for a study requires a justified question, population and purpose.