Choosing the correct EyeSpace Scleral back optic zone radius (BOZR) is essential to ensure an even post-lens tear thickness (PLTT) over the first 9.00 mm of the cornea. Choosing the incorrect BOZR will have a detrimental effect in the mid-periphery of the cornea.
In the example above, the top picture's lens has a BOZR that is too flat in relation to the corneal curvature. The result is an increase post-lens tear thickness (PLTT) over the mid-peripheral cornea, reducing oxygen flow and increasing lens suction.
The bottom picture shows the opposite. The lens BOZR is too steep in relation to the cornea causing the lens to touch the mid-peripheral cornea. Touching the cornea can lead to many adverse effects, like late afternoon hyperemia, lens decentration, incorrect SLZ observations, and long term can cause scarring and neovascularization.
To choose the correct BOZR you can observe the radius of the diagnostic lens relative to the curvature of the eye using the slit lamp or OCT and adjust the final lens BOZR based on your clinical judgment.
A more accurate method is to use the best fit sphere (BFS) value from the Medmont topographer. Choose the original pre-fit corneal map and switch to the elevation map. The BFS can be recorded directly from the screen.
Alternatively you can use the scleral fitting wizard found in the EyeSpace desktop software. After importing the original pre-fit topography map from your Medmont, Oculus Keratograph or Pentacam topographers, EyeSpace will guide you through the step by step process to design your EyeSpace Scleral lens.
At step six, the EyeSpace Scleral fitting wizard will calculate the optimal BFS value of the final lens and display the tear layer profile over the 9.00 mm diameter of the cornea. You can choose to alter the BOZR and EyeSpace will automatically adjust the tear lens profile allowing you real-time feedback to your changes. As a bonus, it will also calculate the final back vertex power (BVP) of the lens in step seven.
Choosing the correct BOZR is key to ensuring a long-term healthy and hassle-free fit.