prescribing for astigmatism
Astigmatism and Presbyopia: Contact Lens Double Jeopardy?
BY WALTER L. CHOATE, OD, FAAO
We all know the population is continuing to age. Many sources estimate that there are currently at least 70 million presbyopes in the United States alone. Of these, about 25 to 30 percent have astigmatism requiring correction.
When faced with the astigmatic component of a presbyope's Rx with hydrogel contact lenses, many practitioners default to fitting toric monovision. This system can be a cost-effective and satisfactory method of approaching presbyopic correction with concurrent cylinder needs. It may work well for emerging presbyopes with low near demands.
However, the more mature presbyope will have difficulty with this correction as focal imbalance becomes more acute with higher add powers. This problem can be even more significant with computer users. Some distance-oriented patients may prefer a distance toric contact lens fit using spectacles for near to maximize quality of vision at both distances. Indeed, a Gallup poll survey by Bausch & Lomb in 1999 indicates that most consumers who become presbyopic would prefer to wear bifocal contact lenses when given a choice.
TABLE 1: UltraVue 2000 Parameters
Power: +8.00D to 8.00D in 0.25D steps
Cylinder: 0.75D to 2.75D in 0.25D steps
Axis: 0 to 180 degrees in 1-degree steps
Addition: 1.00D to 4.00D in 0.25D steps
Base Curve: 8.3mm, 8.6mm, 8.9mm
Toric Multifocal to the Rescue
Over the past few years, we have seen an improvement in hydrogel multifocal lens design, comfort, quality and reproducibility. However, until recently, we haven't had a product that could reliably approach our needs in providing both multifocal and toric optics. One such lens is the UltraVue 2000 Toric Multifocal by Opti-Centre, which has been available for a year and a half. It works on the same principle as the UltraVue 2000 Multifocal, using inverse optics for the multifocal component: one UltraVue D lens (dominant eye, distance in the center and near in the periphery) and one UltraVue N lens (non-dominant eye, near in the center and distance in the periphery). Toric optics are lathed on the back surface and the lens is stabilized rotationally using dual thin zones, with axis markers at 3 and 9 o'clock.
The reproducible lens system allows the lens to be prescribed empirically. In patients with 0.75D cylinder or greater, begin with the D lens on the dominant eye and the N lens on the non-dominant eye, prescribing the determined cylinder and add powers. Patients with heavy near demands may prefer two N lenses, and conversely, patients who have heavy distance demands may prefer two D lenses. If the toric fits works well, then adding the multifocal optics does not complicate the fit.
Over the past year I achieved success rates similar to Opti-Centre's published success of 65 to 70 percent. These numbers assume properly screened patients with appropriate expectations and proper fitting and follow-up care. I have found the UltraVue 2000 Toric Multifocal is a great tool in managing presbyopes with too much cylinder to succeed with many multifocal disposable lenses. Although monovision is still a great tool, today's presbyope has a greater variety of near working distances than before, leading to earlier complaints of focal imbalance. I think multifocal lenses first and then resort to monovision. The UltraVue 2000 Toric Multifocal makes this process much easier.
Dr. Choate is in private practice in Nashville, TN, a charter member of the AOA Contact Lens Section and an adjunct faculty member at Southern College of Optometry and University of Houston College of Optometry.