Contact Lens Vertex Calculator
Convert your spectacle prescription to contact lens power with precision
Contact Lens Prescription
Calculated on:
Understanding Vertex Distance
The Formula
The vertex compensation formula is:
Where:
- \(F_c\) = Contact lens power
- \(F_o\) = Original spectacle power
- \(d\) = Vertex distance change in meters
Frequently Asked Questions
What is BVD 12 on eye prescription?
BVD stands for back vertex distance, the distance from the back surface of the lens to your cornea. BVD 12 mm means the refraction prescription was measured at a 12 mm vertex distance.
What is the vertex of a contact lens?
The vertex distance is the distance between the lens and your eye. The vertex distance of a contact lens is zero since a contact lens rests on top of your cornea.
What happens when a plus lens is moved closer to the eye?
When a plus lens (converging lens) is moved closer to the eye, it loses perceived power because the new focal point falls behind the retina. Conversely, when a plus lens is moved away from the eye, it gains perceived power because the new focal point lies in front of the retina.