Convert Eyeglass to Contact Lens Prescription
Calculate the vertex distance correction when converting eyeglass prescriptions to contact lens prescriptions. Our calculator accounts for the different distances between lenses and eyes for accurate vision correction.
Easily adjust your eyeglass prescription for contact lenses.
Use our contact lens vertex calculator to convert your eyeglass prescription to the correct contact lens power. This tool ensures precise adjustment for optimal vision and comfort.
Typical values range from 10mm to 15mm.
The vertex distance is the space between the back of your eyeglass lens and your eye. When switching to contact lenses, which sit directly on the eye, adjustments are necessary—especially for prescriptions stronger than +/-4.00 diopters.
Our contact lens vertex calculator simplifies this process, providing you with the adjusted power needed for your contact lenses.
Always consult with your eye care professional to confirm the final prescription.
Vertex distance is the gap between the back of eyeglass lens and front of eye (typically 12-14mm). Contact lenses sit directly on the eye (0mm vertex). For strong prescriptions (±4.00D or more), this distance difference affects required lens power. Stronger prescriptions need larger vertex adjustments.
Contact lens power = Eyeglass power / (1 - vertex distance × eyeglass power). Positive prescriptions (farsightedness): contact lens power is weaker. Negative prescriptions (nearsightedness): contact lens power is stronger in absolute value. Example: -8.00D glasses at 12mm becomes approximately -7.00D contacts.
Professional fitting required: calculator provides estimate only, eye exams measure additional factors (base curve, diameter), astigmatism may need toric lenses, prescription validity differs (glasses vs contacts). Never self-prescribe contact lenses. This tool helps understand expected differences, not replace professional consultation.
