Enter the perceived power of the wearer, the actual power of the lens, and the distance between where you want the lens and where it is to determine the vertex correction.

## Contact Lens Vertex Formula

The following formula is used to calculate a contact lens vertex correction

Fc = F / (1-xF)
• Where Fx is the power corrected vertex distance
• F is the original lens power
• x is the change in vertex distance in meters

To calculate the contact lens vertex, divide the original lens power by the result of 1 minus the change in vertex distance.

## Vertex Distance Correction Definition

A vertex distance correction is a power that a lens needs to focus light on the same location after it has been moved a distance x.

## Example

How to calculate vertex distance correction?

1. First, determine the original lens power.

Determine the original lens power.

2. Next, determine the change in position of the lens.

Calculate or measure the change in distance x the lens has been moved.

3. Finally, calculate the required power lens.

Calculate the required power lens needed to achieve the same results of the original lens before it was moved.

## FAQ

What is a vertex distance?

A vertex distance is a distance between the back surface of a lens and the front of the cornea.