Contact Lens Design & Materials
Lens Options for Astigmats
BY RONALD K. WATANABE, OD, FAAO
I am sometimes asked, “What is the best contact lens for someone who has 3.00D of astigmatism?” I answer, “It depends.” That always evokes a groan. But there are several factors that help determine the best contact lens option for a patient.
Selecting a Design
If the astigmatism is irregular, the patient will probably need a GP lens, and though the patient may have 3.00D of astigmatism, a spherical GP design will probably work in most cases. If not, you may need a specialty GP design. Alternatively, there are new specialty soft lens designs such as the KeraSoft (Bausch + Lomb) and NovaKone (Alden Optical) that can help mask corneal irregularity. Otherwise, for regular astigmatism, either a GP or soft toric lens can work well.
Next, whether the astigmatism is corneal or lenticular is important for GP toric design selection, though for soft lenses it may not be as critical. Also, if the patient has a large spherical refractive component, he may tolerate less precise astigmatic correction. However, if the spherical component is near plano, the cylinder will have to be near perfect. The same is true if the patient has a low tolerance for cylinder misalignment. In either case, a GP design would provide better correction of the cylinder power and axis. On the other hand, if a 3.00D astigmat is relatively tolerant to under-correction of the cylinder, he may be able to wear a disposable brand with −2.25DC.
Finally, if the patient does a lot of physical activity, GPs may be less feasible than soft lenses.
Soft Toric Options
Regardless of the previous answers, most of the questions I get are about soft torics. There are many good custom soft toric options today, starting with Cooper-vision’s Proclear and Frequency 55 Toric XR. These are closer to “stock” designs because they are continuations of their disposable counterparts. They are available with up to −5.75DC in five-degree steps and two base curves.
Beyond that, many independent laboratories offer truly custom lenses. Some great examples are Art Optical’s Intelliwave Toric, Metro Optics’ MetroSoft Toric, Unilens’ C-Vue Advanced Custom Toric, and X-Cel’s Flexlens Toric, all of which are available in traditional hydrogel and Definitive (Contamac) silicone hydrogel materials. Other great examples are SpecialEyes Torics, Alden HP Torics, Kontur Torics, and a host of others. All of these designs are available in seemingly endless parameter ranges for virtually any refractive error and corneal dimensions.
The labs I have worked with have excellent consultants who can help fitters learn and understand how to fit their products, which is important because they all have slightly different ways to select parameters. It is important to have accurate keratometry readings, subjective refraction, and corneal diameter data ready when speaking with a consultant. Corneal topography can be helpful in detecting unusual corneal shapes and ruling out irregular corneas.
Custom labs usually send an initial pair of lenses with generous return and exchange policies, which can help decrease anxiety and increase success with difficult-to-fit patients. Another option for today’s custom soft torics is frequent replacement, either quarterly or monthly, once the initial lens fit has been finalized. Additional multipacks have reduced pricing to make them affordable. Finally, some labs don’t even require returning lenses that did not work, which makes life easier for your lens technician.
Many Good Options
The bottom line is that there are many good soft toric lens options today for high astigmats, so don’t be afraid to try one the next time a high astigmat asks you if he can wear contact lenses. CLS
|Dr. Watanabe is an associate professor of optometry at the New England College of Optometry. He is a Diplomate in the American Academy of Optometry’s Section on Cornea and Contact Lenses and Refractive Technologies and is in private practice in Andover, Mass. You can reach him at email@example.com|