Eye Health NepalClinical tools and eye care resources
Eye Health Nepal
Vertex Distance Calculator
Calculate estimated contact lens power from a spectacle prescription using optical vertex distance compensation. This tool supports eye care education, contact lens planning, and quick high-power prescription checks.
Calculator
Enter the spectacle lens power and standard vertex distance to estimate the equivalent power at the corneal plane.
Result
Review the compensated lens power, the raw calculation, and the formula inputs used for the estimate.
Estimated converted power
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Enter a spectacle power and vertex distance, then calculate.
F₂ = F₁ / (1 − d × F₁)
F₁ = original lens power, d = vertex distance change in meters, F₂ = compensated power.
Clinical notes
Vertex distance compensation is most useful when spectacle powers are higher, especially around plus or minus four diopters and above.
Minus prescriptions usually become less minus when converted from spectacles to the corneal plane, while plus prescriptions usually become more plus.
This calculator supports estimation only. Final contact lens selection still depends on full refraction, corneal findings, fit, material, and available lens parameters.
Eye Health Nepal provides this vertex distance calculator as a practical online eye care tool for spectacle to contact lens power estimation. For prescriptions with higher plus or minus values, vertex distance compensation can improve the accuracy of contact lens planning by accounting for the distance between the spectacle lens and the eye.