Vertex Distance Calculator and Power Chart

Vertex distance, typically ranging from 12-14 mm, is the measurement from the spectacle lens to the corneal surface. At the corneal plane, high minus lenses become less minus and high plus lenses become more plus. Ignoring this shift at powers around ±4.00 D (and always ≥ ±6.00 D) risks blur, headaches, and poor adaptation when moving from glasses to contacts.

Begin compensating near ±4.00 D and always compensate at or beyond ±6.00 D. Use Fc = F / (1 - dF) (F in diopters, d in meters). For cylinders, vertex each principal meridian separately, then recombine or transpose. Round to available 0.25 D steps after the math.

Proper vertexing preserves acuity, reduces eyestrain, and smooths the SRx→CLRx transition. It also cuts remake rates and reinforces patient confidence in your precision. Document the assumed vertex so future refits remain consistent.

Use the chart below for quick estimates.