Contact Lens Vertex Calculator

Convert a spectacle prescription to a contact lens power.

Contact lens power (D) -5.597

Formula: F_c = F ÷ (1 − d·F)

Step-by-step with your numbers:

1. Values used:

2. Spectacle power = -6 D

3. Vertex distance = 12

5. Contact lens power = -5.597D

Did we solve your problem today?

Moving a lens closer to the eye (glasses to contacts) changes the effective power.

The math behind it

F_c = F ÷ (1 − d·F), where d is the vertex distance in metres. The effect grows for strong prescriptions.

−6 D at 12 mm → about −5.6 D as a contact lens.

When does vertex matter most?

For prescriptions stronger than about ±4 D.