The Vertex Distance Calculator simplifies vertex distance calculation, helping you adjust lens power accurately for various eye and lens positions.
Vertex Distance Calculator
More Calculators
What is vertex distance?
The vertex distance is defined as the straight-line measurement in millimeters from the back (vertex of the ocular surface) of a lens to the vertex of the cornea. In simpler terms, it is the distance from the back of any spectacle lens, whether it is in spectacles or not, to the vertex of the cornea. This measurement is of crucial importance in the field of ophthalmic optics as it influences the effective power of spectacle lenses. Use our Vertex Distance Calculator that helps you adjust lens power accurately for various eye and lens positions.
Vertex Distance Calculation
A. Definitions:
Vertex Distance: The straight line measurement from the back surface of a mounted lens to the apex of the cornea.
Lens Power Compensation: Adjusting the lens power to account for changes in vertex distance to maintain the correct optical prescription.
B. Basic Calculation Formula:
The primary vertex distance formula used to calculate the compensated lens power is:
what changes when vertex distance changes
If the vertex distance changes, the effective refractive power of the lens changes for the following reasons:
- For Plus Lenses (+):
- Closer to the Eye: The lens appears stronger (increased power).
- Farther from the Eye: The lens appears weaker (decreased power).
- For Minus Lenses (−):
- Closer to the Eye: The lens appears weaker (decreased power).
- Farther from the Eye: The lens appears stronger (increased power).
In both cases, the lens power must be compensated to maintain the correct vision prescription.
Vertex distance conversion table
To help you with the conversion of vertex distance calculation, you will find here a vertex distance table with the conversion of the lens power for common vertex distances. This table shows how the power of a lens changes with the distance changes. For illustration purposes, the values are based on a lens power of +2.00 D and -2.00 D. Adjust the values for other strengths if necessary.
| Original Vertex Distance | New Vertex Distance | Change in Power (for +2.00 D) | Change in Power (for -2.00 D) |
|---|---|---|---|
| 10 mm | 10 mm | 0.00 D | 0.00 D |
| 10 mm | 12 mm | -0.02 D | 0.02 D |
| 10 mm | 14 mm | -0.04 D | 0.04 D |
| 10 mm | 16 mm | -0.07 D | 0.07 D |
| 12 mm | 12 mm | 0.00 D | 0.00 D |
| 12 mm | 14 mm | -0.03 D | 0.03 D |
| 12 mm | 16 mm | -0.06 D | 0.06 D |
| 14 mm | 14 mm | 0.00 D | 0.00 D |
| 14 mm | 16 mm | -0.03 D | 0.03 D |
| 16 mm | 16 mm | 0.00 D | 0.00 D |
