contact lens business
Mixing Bifocal Designs
Using different lenses for distance and near can sometimes create excellent vision in difficult cases.
By Bruce Koffler, M.D.

When you're initially fitting a patient with bifocal contact lenses, it makes sense to stay with one company's lens design. Of course, if the patient doesn't achieve good vision in either eye with that lens design, you should be flexible and consider switching to another company's product (a far better option than declaring the patient "not a good candidate for bifocal lenses" and giving up).

Using this concept, one company -- CooperVision -- uses different lens designs for the dominant and non-dominant eyes in their Frequency 55 Multifocal lens pairs: The "D" lens is distance centered, and the "N" lens is near-centered. The lenses also have different central zone sizes: 2.3 mm and 1.7 mm respectively. (This works because the pupil constricts when focusing on a near target.) This allows for more distance coverage in the outer rings of the "N" lens, improving distance vision.

Of course, even this design may not work for some patients, in which case the same strategy -- using a lens from another manufacturer on the second eye -- is a worthwhile option.

Easy for the Patient (Worth It for You)

Using two brands instead of one doesn't have any appreciable negative consequences for the patient; if good vision is the result, the patient will be happy. Lens care is no different; all of the bifocal lenses we use are available as 2-week or 1-month disposables. They come in 6-packs, so the patient simply gets a box from one company for one eye and a box from another company for the other eye. (This may even make it easier for the patient to remember which lens goes in which eye.)

Using this option does require a little more effort on your part; you'll have to spend a little more time learning the pros and cons of the different lens designs and how to fit each one. (Of course, the more you fit, the more successful you'll be.)

In my experience, this isn't a big hurdle to overcome. Besides, it's in the best interest of the patients, which means it's also in the best interest of your practice. And it's very gratifying to achieve success with a tough patient.

Helpful Fitting Strategies

To make the fitting process as easy as possible:

Fit with both eyes open. When you're checking distance and near vision and making changes in powers, don't test with one eye closed. You're trying to get the patient to see binocularly, so fine-tune the lenses with both eyes open.

Try mixing spherical and bifocal lenses. For a high myope I'd initially try the traditional bifocal fit -- good bifocal vision in both eyes at the same time. But some patients in their mid-40s have never worn distance glasses. These patients may not like having simultaneous vision (two images coming in at the same time).

We give these patients a single vision lens for distance in the dominant eye and a bifocal lens on the reading or non-dominant eye. That way we don't take away so much of their distance vision, which remains sharp, while still helping them with their up-close vision. In our experience, this arrangement is easier than traditional monovision (although we've always had good success with that option, too).

Be flexible about which eye is near. Allow the dominant eye to be the reading eye, if this seems to work best on initial follow-up and the patient is comfortable with it.

Pick the right patients. Choose patients who are highly motivated and have minimal astigmatism (since these lenses don't have cylinder).

Don't prejudge patients. People have told me that emme-tropes and happy monovision patients aren't good candidates for switching to bifocals. However, a study we conducted found that both of those groups did just as well as anybody else.

Let the patient try them at home. Patients may use their eyes differently at home or at work than they do in your office.

Don't just add near power to the spherical equivalent. Often the dominant eye requires a little more minus power to sharpen up distance vision, and the near eye needs a little more plus power to help sharpen up reading vision.

Make sure the patient's expectations are realistic. As with any bifocal contact lenses, most patients will go through a period of adaptation. A little time spent teaching the patient about what to expect will go a long way toward producing good results.

Dr. Koffler is director of the Kentucky Center for Vision in Lexington, Ky., and associate clinical professor of ophthalmology at the University of Kentucky Medical Center. He is past president of the Kentucky Academy of Eye Physicians and Surgeons, and the Contact Lens Association of Ophthalmologists.