contact lens case reports
Designing Your Own GP Lenses
BY PATRICK J. CAROLINE, FAAO, & MARK P. ANDRÉ, FAAO
Have you ever wanted to create your own GP design? The software program OrthoTool (www.orthotool.com) allows you to custom design every parameter of a GP lens and then visualize that lens on a simulated corneal surface. The software lets you create any spherical, aspherical, toric, multifocal, keratoconic, or reverse geometry design.
How the Software Works
Our patient is a 24-year-old female with a history of high unilateral astigmatism. Her spectacle prescription is OD −3.75 −1.00 × 010 and OS −3.50 −3.00 × 175.
Step 1. Create the simulated corneal surface by entering the central K readings and the corneal eccentricity along the flat corneal meridian. If eccentricity is not available, we default to a 0.40e. Next, enter the non-vertexed refractive data (Figure 1).
Figure 1. Patient's corneal topography and refractive data.
Step 2. Use the drop down menu to select the desired lens design and material. We chose a spherical design for our patient's right eye and a toric for the left (Figure 2).
Figure 2. Lens design parameters and tear profile.
Step 3. The software creates a lens for the cornea, allowing you to adjust each curve and width until the desired shape has been achieved. The posterior lens profile and tear film thickness are continually refreshed and displayed along the flat corneal meridian (Figure 2).
Clinical experience with OrthoTool has taught us that lens performance is optimized when the lens profile provides apical clearance of 10 to 20 microns, secondary curve clearance of approximately 30 microns, and peripheral curve clearance of 100 and 120 microns. Preferred lens designs can be programmed into the software so that when activated, the system automatically defaults to the desired, predetermined lens profile (Figure 3).
Figure 3. A pre-programmed reverse geometry design.
The software also incorporates a cross-cylinder calculator, eccentricity calculator, diopter to millimeter conversion, and vertex conversion. CLS
Patrick Caroline is an associate professor of optometry at Pacific University. He is also a consultant to Paragon Vision Sciences. Mark André is an associate professor of optometry at Pacific University. He is also a consultant for CooperVision.