Contact Lens Vertex Calculator

Spectacle to Contact Lens Conversion

Eyeglass lenses sit 12–14 mm from the eye (back vertex distance, or BVD). Contact lenses rest on the cornea, so the effective lens power changes. Vertex compensation converts spectacle prescription power to the equivalent contact lens power.

Vertex Compensation Formula

where:

• \(F_{\text{spectacle}}\) — spectacle lens power in diopters (D)
• \(d\) — vertex distance in meters (e.g. 12 mm = 0.012 m)
• \(F_{\text{contact}}\) — compensated contact lens power in diopters

Example: +8.00 D spectacles at 10 mm vertex distance give \(F_{\text{contact}} = 8 / (1 - 0.01 \times 8) \approx +8.70\,\text{D}\).