Back Vertex Distance
Precision Calculator
This professional tool calculates the adjusted lens power when changing the vertex distance, ensuring optimal visual correction for your patients.
How it works
Enter the current spectacle lens power and vertex distances to calculate the new lens power required. This calculation is essential when fitting contact lenses or when the frame position changes significantly.
Formula: P₂ = P₁ / (1 - (d₁ - d₂) × P₁)
Where P₁ is the original power, P₂ is the new power, d₁ is the original vertex distance, and d₂ is the new vertex distance (in meters).
Optical Visualization
Before
After
OS (Left Eye)
Astigmatism Correction (Optional)
Fixed distance from spectacle lens to cornea
Contact Lens Power
Note: This calculator converts spectacle lens powers to contact lens powers using a fixed vertex distance of 12mm. Enter sphere power only for spherical prescriptions, or include cylinder and axis for astigmatism correction. The calculation is most important for high-powered lenses (usually >±4.00D) where vertex distance changes have a more significant effect on effective power.
OD (Right Eye)
Astigmatism Correction (Optional)
Fixed distance from spectacle lens to cornea
Contact Lens Power
Note: This calculator converts spectacle lens powers to contact lens powers using a fixed vertex distance of 12mm. Enter sphere power only for spherical prescriptions, or include cylinder and axis for astigmatism correction. The calculation is most important for high-powered lenses (usually >±4.00D) where vertex distance changes have a more significant effect on effective power.
No Lenses to Recommend
Please complete your eye prescription calculation to see recommendations.