There has traditionally been the perception that toric lenses are too difficult to design and fit. Fortunately, this is not the case. Fitting toric lenses is not significantly different than fitting spherical GPs. With the availability of bitoric diagnostic lenses and the increasing technology in manufacturing, these lenses can be relatively simple to fit, resulting in both a good lens-to-cornea fitting relationship and optimum vision.
A helpful fitting aid is the “Advanced GP Fitting Video” available from the CLMA (1-800-344-9060).
- Spherical fitting on <2D of corneal astigmatism
- Consider use of a cookbook method such as the Mandell-Moore Bitoric Fitting Guide
- Consider use of diagnostic lenses
- If no residual astigmatism exists, a bitoric lens can rotate freely on the eye without visual reduction (i.e., spherical power effect – SPE)
Photo of spherical lens on highly astigmatic cornea. Fitting a spherical lens on a highly astigmatic cornea can result in the following:
- Corneal flattening/distortion in the meridian of corneal bearing (even when good centration is obtained)
- Corneal desiccation
- Flexure/variable vision
- Bitoric fitting on >2D of corneal astigmatism
The Mandell-Moore Guide is a valuable resource to determine base curve radii and powers of bitoric lens. Follow the steps below along with the Fit Factor Guide to determine bitoric parameters.
Mandell-Moore Bitoric Lens Guide – Per Eye
|Spectacle Rx (Minus Cyl Form)||x|
|1. Enter K|
|2. Enter Spectacle Power|
|3. Vertex Corrected|
|4. Add Fit Factor||(-)||(+)||(-)||(+)|
|5. Final CL Rx
|Base Curve||Power||Base Curve||Power|
– OR –