Lens Power Unit Reference Tool

Description

Compare supplied signed optical-power units to an explicit reference without a prescription or lens recommendation.

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.

Compare supplied signed optical-power units to an explicit reference without a prescription or lens recommendation.

When to use this tool

Use Lens Power Unit Reference 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 reportedPower, suppliedDioptersPerUnit, referenceDiopters. Use the units and conventions below.
Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
Read convertedDiopters, gapDiopters. Use the output convention below.

For positive suppliedDioptersPerUnit return convertedDiopters=reportedPower*factor and gapDiopters=convertedDiopters-referenceDiopters.^[1]

Input field	Meaning and units	Accepted input
reportedPower	Reported Power	Required. Finite number.
suppliedDioptersPerUnit	Supplied Diopters Per Unit	Required. Finite number; strictly above 0.
referenceDiopters	Reference Diopters	Required. Finite number.

Output field	Interpretation	Returned shape
convertedDiopters	Converted Diopters	Required. Finite number.
gapDiopters	Gap Diopters	Required. Finite number.

json

{
  "input": {
    "reportedPower": -2,
    "suppliedDioptersPerUnit": 1,
    "referenceDiopters": -1.5
  },
  "output": {
    "convertedDiopters": -2,
    "gapDiopters": -0.5
  }
}

Limitations and assumptions

Factor is diopters per source power unit and signs are preserved. Unit identity, instrument calibration, optical interpretation, and appropriateness of a prescription are not verified.
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

Calculation and input contract: optometry/lens-power-unit-reference — tool.io

Similar or alternative tools

Lens Cylinder Axis Unit Flag
Convert a supplied axis unit and optionally normalize a 180-degree orientation; no prescription calculation.
Lens Axis Wrapped Angle
Wrap an explicitly supplied unoriented research axis to a half-turn coordinate; no prescription is generated.