1. What is Vertex Compensation?

Vertex compensation is the adjustment made to lens power when converting between glasses and contact lens prescriptions. It accounts for the difference in position between glasses (typically 12-14mm from the eye) and contact lenses (on the corneal surface).

2. How Does the Calculator Work?

The calculator uses the vertex formula:

Where:

• \( d \) — Vertex distance (mm)
• \( n \) — Refractive index (typically 1.336 for cornea)
• \( power \) — Original lens power (diopters)

Explanation: The equation accounts for the effective power change when moving a lens closer to or farther from the eye.

3. Importance of Vertex Compensation

Details: Vertex compensation becomes clinically significant for powers above ±4.00D. Proper compensation ensures accurate vision correction when switching between glasses and contact lenses.

4. Using the Calculator

Tips: Enter vertex distance in mm (typically 12-14mm for glasses), refractive index (default 1.336 for cornea), and the original lens power in diopters.

5. Frequently Asked Questions (FAQ)

Q1: When is vertex compensation necessary?
A: For powers above ±4.00D when converting between glasses and contact lenses, or when comparing lenses at different vertex distances.

Q2: What's the typical vertex distance for glasses?
A: Standard vertex distance is 12-14mm from the corneal surface, though this varies by frame design and facial anatomy.

Q3: Why use 1.336 for refractive index?
A: 1.336 approximates the refractive index of the cornea. This value may be adjusted for specific applications.

Q4: Does vertex affect plus and minus lenses differently?
A: Yes - moving a plus lens closer to the eye increases its effective power, while moving a minus lens closer decreases its effective power.

Q5: How does vertex affect toric/astigmatic corrections?
A: Vertex compensation applies equally to all meridians, so cylinder power is compensated the same way as sphere power.