Vision Prescription Converter
Convert your spectacle (glasses) prescription to contact lens prescription.
Accounts for vertex distance adjustment.
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Contact Lens Prescription
Spectacle to contact lens conversion is needed because contact lenses sit directly on the eye, while glasses sit about 12mm away (vertex distance).
Vertex distance formula:
Contact Lens Power = Spectacle Power / (1 - (d × Spectacle Power))
Where d = vertex distance in meters (typically 0.012m or 12mm).
Key points:
- Prescriptions of -4.00D to +4.00D usually need no conversion (difference is negligible)
- The higher the prescription, the bigger the difference
- Contact lens prescriptions also omit the ADD power differently (in multifocals)
- Cylinder (astigmatism) adjustments may differ for toric contacts
- Always verify with your eye care professional
Example: A -8.00D glasses prescription converts to approximately -7.27D for contacts.