Vertex Conversion

What is Vertex Conversion?

Vertex conversion is the process of adjusting spectacle lens power to determine the correct power for contact lenses. Since spectacles sit approximately 13 mm away from the eye and contact lenses sit directly on the cornea, a conversion is necessary—especially for higher prescriptions—because the effective power of a lens changes with distance from the eye.

When is Vertex Conversion Needed?

Vertex conversion becomes clinically important when the spherical power of the prescription is ±4.00 D or greater. At these powers, the difference between spectacle and contact lens prescriptions can significantly affect visual clarity and lens fit.

How It Works

The calculator uses a standard 13 mm vertex distance to adjust your spectacle prescription. This adjustment ensures that the contact lens provides the correct focus directly on the eye, maintaining optimal vision and comfort.

• Minus Sphere Powers: The resulting contact lens power is typically less negative.
• Plus Sphere Powers: The converted contact lens power is usually more positive.

Why Use This Calculator?

• To ensure accurate contact lens prescriptions
• To improve visual acuity and lens fit
• To aid professionals and patients in making informed decisions about lens power

Input Parameters

• Spectacle Power: Enter the sphere value from your glasses prescription.
• Sphere Type: Select whether the sphere is plus or minus.
• Vertex Distance: This tool assumes a fixed distance of 13 mm, the standard average used in clinical settings.

Output

The calculator will provide the converted contact lens power based on your input, adjusted for vertex distance.

Note

This tool is for informational and fitting guidance purposes. Final contact lens prescriptions should always be confirmed by a licensed eye care professional following a proper contact lens fitting.