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Vertex Distance Calculator
Convert lens power between spectacle and contact lens planes using standard vertex distance formulas.
Vertex Distance Converter
Bidirectional conversion between spectacle and contact lens power
When to Use Vertex Conversion
- Powers ≥ ±4.00 D require vertex adjustment
- Standard spectacle vertex distance is 12mm
- Minus lenses: CL power is less minus than spectacle
- Plus lenses: CL power is more plus than spectacle
Understanding Vertex Distance
What is Vertex Distance?
Vertex distance is the distance from the back surface of a spectacle lens to the front surface of the cornea. This distance affects the effective power of the lens at the corneal plane.
Clinical Significance
- • Minus lenses: CL power is less minus than spectacle Rx
- • Plus lenses: CL power is more plus than spectacle Rx
- • Effect increases with higher powers
- • Generally significant at ±4.00 D or greater
Quick Reference Table
| Spec Rx | CL Rx (12mm) | Difference |
|---|---|---|
| -4.00 | -3.75 | 0.25 |
| -6.00 | -5.50 | 0.50 |
| -8.00 | -7.25 | 0.75 |
| -10.00 | -8.75 | 1.25 |