Vertex distance calculator
Converts a spectacle refraction to the corneal plane for contact lens prescribing. Sphere and cylinder are corrected independently by principal meridian at your entered back vertex distance, then rounded to the nearest 0.25 D. Free to use — no sign-in required.
Clinical decision support only
This calculator applies vertex distance only. Product selection, stock feasibility, multifocal options, and lens recommendations belong in the Contact Lens Recommender.
Correction is applied to both principal meridians. Clinically significant for powers ≥ ±4 D. Output is rounded to the nearest 0.25 D; axis is retained.
Enter the spectacle Rx for one or both eyes, then calculate the estimated CL Rx.
When vertex correction matters
- Vertex correction becomes clinically significant from around ±4.00 D — myopes need less minus at the cornea, hyperopes need more plus.
- Correcting each principal meridian independently (sphere and sphere+cylinder) is more accurate for higher astigmatism than correcting the sphere alone.
- Results are rounded to standard 0.25 D contact lens steps; check the value against the lens family's actual stock range before ordering.
OptoGuide™ continues this workflow: matched AU stock lens recommendations, contact lens clinical guidance, prescribing support and referral tools.