Optimizing Success With Irregular Cornea Patients, Part 2
BY EDWARD S. BENNETT, OD, MSED, SHAWNA HILL, OD, & ROBERT M. GROHE, OD
Irregular cornea patients benefit from the ongoing introduction of more sophisticated manufacturing technology. In Part 1 we discussed options that are beneficial when you need to tuck in the inferior lens edge. Here we'll discuss lens designs that have quadrant-specific curvatures for managing highly irregular corneas that vary greatly in curvature in every quadrant.
New Design Technology
Several quadrant-specific periphery designs are a result of newer CNC (computer numeric control) lathing technology. The QuadraKone lens (Tru-Form Optics) has variable curvatures in each of the four primary quadrants (0, 90, 180, 270 degrees). After evaluating the fluorescein pattern of a QuadraKone lens, make sure to steepen region(s) of excessive peripheral pooling by a minimum of 3.00D to 4.00D. Likewise, flatten areas of sealoff or near sealoff.
Recently, Lens Dynamics introduced its Quadrant Specific Design or Quad Sym, a technology successful in Europe. This technology is available for both peripheral edge treatment (PC) and for base curve treatment (BC).
Previous manufacturing methods were unable to match the front radii cuts to the various back surface radii to produce the required power. Computer ray tracing and data analysis made it possible for this software to be developed.
The edge treatment Quad Sym PC option allows practitioners to flatten or steepen the edge treatment differently in all four quadrants to match the peripheral cornea. The BC option allows the lens to have up to four separate base curve radii.
Figure 1. The fluorescein pattern of a Quad Sym design right after dispensing is shown in Figure 1a (left); the same lens after two weeks of wear is shown in Figure 1b.
You can use a Dyna Intra-Limbal (Lens Dynamics) for trial purposes with the goal to align, at minimum, one quadrant before performing an over-refraction. Document the fluorescein pattern in the other three meridians and provide this information, along with the topography map, to the laboratory, which will determine curvature in the other meridians.
Figure 1a shows a Quad Sym design upon dispensing to a pellucid marginal degeneration patient. We used this design because an area of bearing at 4 o'clock to 6 o'clock was present with all previous GPs. Figure 1b shows the same lens, which exhibits an improved lens-to-cornea fitting relationship after two weeks of wear. It's important not to change parameters too quickly, but to allow adaptation to occur.
Better Options Available
Use the best resource available when fitting these challenging cases: laboratory consultants.
The combination of advancing technology in evaluating corneal topography and newer lathing technology to manufacture designs that simulate these unusual curvatures results in increased quality of life for patients and, in some cases, can prevent or delay the need for a corneal surgical procedure. CLS
Dr. Bennett is an associate professor of optometry at the University of Missouri-St. Louis and is executive director of the GP Lens Institute.
Dr. Hill specializes in contact lenses, refractive surgery co-management and ocular disease at the Wang Eye Institute and Laser MedSpa in Nashville, TN.
Dr. Grohe specializes in contact lenses and anterior segment in his suburban Chicago practice while also being associated with the Northwestern University School of Medicine.