Contact Lens Vertex Calculator

Category: Physics
- March 19, 2025
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The vertex distance is the space between your eye and the back of your glasses lens. When switching between glasses and contact lenses, a power adjustment is needed for prescriptions stronger than Ā±4.00 diopters.

This calculator determines the equivalent contact lens power based on your glasses prescription and the vertex distance.

D
mm
? Standard vertex distance is 12-14mm. Check your optical measurements or use 12mm as a default.

Advanced Options

? Contact lenses typically come in 0.25D steps. Rounding to the nearest 0.25D is standard practice.

About Vertex Distance

Vertex distance is an important consideration when converting between spectacle (glasses) and contact lens prescriptions. It matters most for higher power prescriptions.

Why Vertex Distance Matters:
  • Optical Physics: Light rays are refracted differently depending on the distance from the eye to the corrective lens.
  • Effective Power: The same lens will have a different effective power when placed at different distances from the eye.
  • Higher Prescriptions: The effect becomes more significant as prescription strength increases (generally above Ā±4.00D).
Practical Guidelines:
  • Minimal Adjustment Needed: For prescriptions between -4.00D and +4.00D, vertex adjustments are usually minimal and often clinically insignificant.
  • Myopic Prescriptions: For high myopia (nearsightedness), contact lenses will generally have less minus power than glasses.
  • Hyperopic Prescriptions: For high hyperopia (farsightedness), contact lenses will generally have more plus power than glasses.
  • Standard Vertex Distance: The standard vertex distance for eyeglasses is typically 12-14mm from the cornea to the back of the lens.
Examples:
  • A -8.00D glasses prescription might convert to approximately -7.50D in contact lenses.
  • A +6.00D glasses prescription might convert to approximately +6.50D in contact lenses.
  • The difference increases as the prescription strength increases.

Contact Lens Vertex Calculator