Description
Prentice thin-lens prism product with millimeters converted to centimeters; sign follows the supplied lens power and displacement, without patient base-direction assignment.
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.
Prentice thin-lens prism product with millimeters converted to centimeters; sign follows the supplied lens power and displacement, without patient base-direction assignment.
When to use this tool
Use Prism Power Decentration Prentice Term 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 lensPowerDiopters, decentrationMm. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read signedPrismDiopters, decentrationCm. Use the output convention below.
Return decentrationCm=decentrationMm/10 and signedPrismDiopters=lensPowerDiopters*decentrationCm.1
Prentice's rule combines lens power in diopters with decentration in centimeters to obtain prism diopters. The millimeter input is divided by ten before that multiplication.2
| Input field | Meaning and units | Accepted input |
|---|---|---|
| lensPowerDiopters | Signed lens power in diopters. | Required. Finite number. |
| decentrationMm | Signed decentration in millimeters. | Required. Finite number. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| signedPrismDiopters | Power times centimeter decentration, with sign inherited from inputs. | Required. Finite number. |
| decentrationCm | Decentration Cm | Required. Finite number. |
{
"input": {
"lensPowerDiopters": 4,
"decentrationMm": 5
},
"output": {
"signedPrismDiopters": 2,
"decentrationCm": 0.5
}
}Limitations and assumptions
- This is the scalar Prentice relation using lens power in diopters and displacement in centimeters. Prism sign depends on supplied coordinate and power conventions; no base direction, full meridional optics, prescription, or clinical adjustment is determined.
- 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/prism-power-decentration-prentice-term — tool.io
-
Prentice's Rule — American Academy of Ophthalmology
Similar or alternative tools
- Prism Base Axis Sign Token
Relabel supplied prism components under explicit signs without deriving a lens prescription.
- Astigmatic Power One Meridian Term
Paraxial sphero-cylinder meridian power S+C*sin²(theta-axis) in radians, without a prescription recommendation.