Knowledge Base
2. Linking EyeSpace to your topographer

4. Back Optic Zone Radius (BOZR)

5. Forge Ortho-KCharl Laas

The Back Optic Zone Radius or BOZR is responsible for the amount of refractive change induced by the Forge Ortho-K lens. EyeSpace will automatically calculate the required BOZR based on the entered spectacle prescription.


Formula: SimK (D) + Spec Rx + Jesson Factor = BOZR

eg. 42.00 + (- 3.00) + (- 0.75) = 38.25(D) = 8.82 mm****


Every 0.05 mm change on BOZR = 0.25D refractive change.
A flatter BOZR (higher numeric value in mm) will create more myopic correction.

A steeper BOZR (lower numeric value in mm) will create less myopic correction.

Optical analysis

The optical analysis tab helps to visualise the optics of the cornea, tear lens system, and the final lens power. The plot shows the power of each element in air along each corneal meridian.

  1. The Ocular Refraction power (OR) shows the patient's contact lens prescription (vertexed spectacle prescription). For example, a patient with spectacle prescription -3.00D and vertex distance 12.0 mm will have an ocular refraction -2.90D.
  2. Tear power is the power of the tear lens formed between the cornea and the posterior surface of the contact lens.
  3. Ideal BVP is the ideal back surface power of the lens required to correct the patient's refractive error. This needs to take into account the tear power and is simply the ocular refraction minus the tear power.