Description
Apply an explicit logMAR step without selecting a chart scoring convention.
Optical calculations distinguish lens power in diopters, prism notation, angular axes, geometric distances, and visual-acuity reporting scales. Sign conventions and length units are especially important when a formula combines power with decentration or vertex distance. A supplied model term is separate from a validated visual test or prescription.
Apply an explicit logMAR step without selecting a chart scoring convention.
When to use this tool
Use Optometric Acuity Log Scale Step Factor when you need this explicit optical, chart, frame, axis, or reference conversion with compatible supplied units.
How to use the tool and how it works
- Enter startLogMar, steps, logStep. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read endLogMar, decimalAcuity, decimalFactor. Use the output convention below.
Require nonzero signed logStep. Return endLogMar=startLogMar+steps*logStep, decimalAcuity=10^(-endLogMar), and decimalFactor=10^(-steps*logStep).1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| startLogMar | Start Log Mar | Required. Finite number. |
| steps | Supplied step count or fractional step increment. | Required. Safe integer. |
| logStep | Signed nonzero change in logMAR per step. | Required. Finite number. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| endLogMar | End Log Mar | Required. Finite number. |
| decimalAcuity | Decimal Acuity | Required. Finite number. |
| decimalFactor | Decimal Factor | Required. Finite number. |
{
"input": {
"startLogMar": 0.3,
"steps": 2,
"logStep": -0.1
},
"output": {
"endLogMar": 0.09999999999999998,
"decimalAcuity": 0.7943282347242815,
"decimalFactor": 1.5848931924611136
}
}Limitations and assumptions
- LogMAR steps are supplied, steps need not be an integer, and positive logMAR changes reduce decimal acuity. The calculation does not infer a chart's scoring convention, verify a measurement, or prescribe a clinical interpretation.
- Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
- Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.
Alternative or Complementary methods
Use the appropriate complete optical or measurement model when a scalar term is insufficient. Verify power, axis, length, notation, and reference conventions before applying the result within a broader assessment.
References
Similar or alternative tools
- Snellen Decimal Logmar Source Crosswalk
Numerical Snellen fraction, decimal and logMAR crosswalk, excluding counting-fingers or other non-Snellen categories and clinical interpretation.
- Chart Acuity Step Budget
Count supplied chart index steps inclusively; no visual acuity conversion or scoring is assumed.