Vertex Distance Adjustment Calculator
Adjust lens power when changing the vertex distance (e.g., from glasses to contacts or between different frame positions).
Inputs
D
mm
mm
Results
Adjusted Power
-4.75 D
Change Magnitude0.25 D
Effective Power at Cornea-4.72 D
How to Use This Calculator
- Enter the Original Lens Power in diopters (from the current glasses prescription or trial frame).
- Enter the Original Vertex Distance in mm — typically 12 mm for standard eyeglass frames.
- Enter the New Vertex Distance in mm — use 0 mm for contact lenses or the new frame's measured vertex distance.
- The formula P_new = P_effective / (1 + d₂ × P_effective) calculates the adjusted power.
- Review the Adjusted Power (rounded to the nearest 0.25 D) and Change Magnitude to determine whether a prescription update is clinically significant.
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Formula
New Power = P / (1 - d × P)Related Calculators
Glasses to Contacts Rx Calculator
Convert your glasses prescription to contact lens prescription using vertex distance adjustment for powers above ±4D.
Lens Thickness Calculator
Estimate center and edge thickness of eyeglass lenses based on prescription power, lens index, and frame size.
Prism Diopter Calculator
Calculate prism diopters from measured displacement and distance. Uses the standard prism diopter definition and Prentice's rule.
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