Contact Lens Vertex Calculator
Convert spectacle prescription to contact lens prescription by adjusting for vertex distance. Essential for accurate contact lens fitting.
Published by:
isCalculator Editorial Team
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How to use this tool?
Follow these steps to calculate the contact lens power from your spectacle prescription:
- Enter Spectacle Rx (D): Type the spherical power of your glasses prescription in diopters (e.g., -4.00). Use a decimal point if needed.
- Enter Vertex Distance (mm): Type the distance from your cornea to the back of the spectacle lens in millimeters (usually 10–15 mm, e.g., 12). Must be between 0 and 30.
- Click "Calculate": The result shows the required contact lens power in diopters.
- Review the steps: A step-by-step breakdown of the formula is displayed below the result for verification.
Note: All measurements must be in metric (diopters and millimeters). The formula adjusts for the change in vertex distance when switching from spectacles to contact lenses.
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Frequently Asked Questions
Vertex distance is the distance between the back surface of a spectacle lens and the front surface of the cornea. It typically ranges from 10-15 mm. Adjusting for vertex distance is crucial for accurate contact lens power calculation, especially for high prescriptions.
Spectacle lenses sit at a distance from the eye, while contact lenses sit directly on the cornea. The difference in vertex distance changes the effective power of the lens, especially for prescriptions above ±4.00 diopters. This calculator provides the correct contact lens power.
For high prescriptions (e.g., above ±6.00 D), the vertex distance adjustment becomes more significant. This calculator handles any value, but always consult with an eye care professional for final prescription.
