Looking to Monovision for Bifocal Improvement

BY LEONARD SEIDNER, OD
June 1999

Fitting presbyopic patients doesn't have to be an arduous task. This lens offers a new twist to monovision without the compromises.

My son, Stevie, a neonatologist in Texas, once said to me, "There are two ways to treat a common cold. One is with chicken soup. The other is with sulfur drugs. I prefer chicken soup."

Good advice. In my opinion, chicken soup is easier, people are comfortable with it and it works. Why complicate matters? When we set out to develop our new LifeStyle MV2 blisterpack bifocal contact lens, we didn't look to improve on existing bifocals, instead we looked to improve on monovision. Sound surprising?

I believe monovision to be the chicken soup of the presbyopic armamentarium. Most eyecare practitioners seem to initially fit emerging presbyopes with monovision. And in the big picture, it works. Patients adapt well to it and the staff pretty much has the routine down pat. Monovision clearly deserves a second look.

But what about the limitations of monovision? Emerging presbyopes who work on a computer all day need functional intermediate vision. And monovision falls short for moderate and mature presbyopes. And as baby boomers age, more of them are going to be coming through our doors looking for a solution.

Like it or not, it's going to take a bifocal contact lens to do the job. Still, we wanted a bifocal that would maintain all of the benefits of monovision without its shortcomings. It's a simple approach, and it worked like a breath of fresh air. We came up with something that has never been done before.

A First-of-Its-Kind Design

MV2 bifocal contact lenses are fit using the same prescription as monovision -- one eye for distance and one eye for near. Unlike monovision, MV2 bifocals give presbyopes of virtually any age exceptional intermediate vision, in addition to distance and near. How did we do it? We took into consideration the factors that make monovision so successful.

When fitting monovision, we give distance vision the better eye by either using the dominant eye for distance or by performing the swing test (+1.50 in front of each eye to see where it is more easily accepted). In other words, we balance the quality of distance and near vision between the two eyes, but we tilt it slightly toward distance. This may seem like a minor detail, but I believe it to be monovision's secret weapon. The next question then becomes: how do we apply it to a better bifocal design?

Perhaps the solution to accomplishing this favorable balance with a bifocal is as simple as making the distance section slightly larger than the near section. But then we would have to be very careful, because, as we all know, near vision has traditionally been a problem with bifocals. It doesn't take much to throw off the balance and end up with poor near vision. Such a delicate balance is hardly the simple solution we were looking for. Instead, we made MV2 bifocal lenses very similar to single-vision lenses, but with one important difference: we put an intermediate zone in the dead center (Fig.1). It was a bold move, but it worked. MV2 contact lenses correct one eye for distance and the other eye for near, yet both eyes benefit from the intermediate zone in the center.

FIG. 1: The center-intermediate design of the MV2 bifocal.

In the MV2 distance lens, the central intermediate zone is only surrounded by the distance zone. Likewise, in the MV2 near lens, the central intermediate zone is surrounded by nothing more than the near zone. The result was just what we were looking for. We could easily control the balance of distance and near, and get exceptional intermediate vision as well.

Age Friendly Intermediate Zones

The intermediate zone in a LifeStyle MV2 distance lens is always +0.50D more than the distance prescription. For example, let's say a patient has a
-3.00D distance prescription in both eyes. The power you would order for the distance lens would simply be a -3.00D. The intermediate zone of a -3.00D MV2 distance lens is always -2.50D (-3.00D + 0.50D = -2.50D).

On the other hand, the intermediate zone in the MV2 near lens always has a power -1.25D less than the near prescription. Say the above patient, with a distance prescription of -3.00D in both eyes, requires an add of +1.25D. The power you would order for the MV2 near lens would be -1.75 (the same near eye prescription as in monovision). The intermediate zone of a -1.75D MV2 near lens is always -3.00D
(-1.75D -1.25D = -3.00D).

The patient gets the benefits of four powers:
-3.00D and -2.50D in the distance eye, and -1.75D and -3.00D in the near eye. It's no coincidence that the patient has a distance prescription available in both eyes. Emerging presbyopes need more help in the distance range, and this is precisely what the MV2's center-intermediate zones deliver to them. But it doesn't stop here. The LifeStyle MV2's intermediate zones work in mysterious ways.

Try the simple calculation above, but substitute a moderate presbyope's add requirement of +1.75D. You'll find moderate presbyopes get a slightly different range than emerging presbyopes. Moderate presbyopes get their distance prescription in one eye and their near prescription in the other, but with the same intermediate prescription in both eyes -- just what a moderate presbyope needs according to his accommodation ability.

Now try the calculation with an add requirement of +2.50D. The mature presbyope, on the other hand, gets good distance and near vision, but with two different intermediate powers -- the TV range and the computer range. Again, this is just what the mature presbyope needs. The MV2's intermediate zones automatically adjust to specific degrees of presbyopia. With monovision, if there's a difference of 1.50D or more between a patient's distance and near eye, vision begins to break down. The gap becomes too much to handle. The MV2's intermediate zone ensures that you'll never have such a gap because it brings similar powers to both eyes.

The MV2 Paradox

When troubleshooting the fit of MV2 bifocal lenses, your first instinct may be to add minus to the distance eye for distance problems, and plus to the near eye for near problems. Instead, think monovision.

When vision is unsatisfactory with a monovision fit, it's best to reduce the disparity between the two eyes. The MV2 is no different. If distance vision is unsatisfactory, reduce the plus in the near contact lens. Likewise, if near vision needs improvement, reduce the minus in the distance contact lens. This simple technique, another gift from monovision, helps to keep the balance. Once you get in to this routine, you'll find it to be the easiest way to tailor the MV2 lens to patients' specific visual requirements.

Another Use for MV2 Lenses

Computer vision is creating the newest buzz in the industry. The time has come to give serious thought to the visual demands of spending hours in front of a computer monitor. Here, the MV2 contact lens can help in more ways than one.

Not only can MV2 lenses provide emerging, moderate and mature presbyopes with great intermediate vision, but they can also help those who are struggling with computer vision problems and are too young to be presbyopic. Try putting MV2 distance lenses on both of their eyes at the same time. Since they have a slight add of +0.50D in their center, they give younger computer users just the right amount of boost.

Other Bifocal Designs

Almost every specialist says that there is no one bifocal design that satisfies every patient, and we have to agree. Certainly, patients who are unable to effectively process different images at the same time may do better with a more conventional bifocal that corrects all of their ranges binocularly. But since these designs are more complicated, we feel that MV2 lenses are the better starting point.

The Nuts and Bolts of the MV2

MV2 bifocal lenses are blister-packed for monthly replacement and made from 38 percent water polymacon material (Fig.2). There's less dehydration with lower water content lenses, which is an important consideration since many presbyopes suffer from dry eyes. In addition, lower water content lenses generally give better overall vision and are easier to handle than high water content lenses.

FIG. 2: MV2 lenses, blister-packed for monthly replacement.

LifeStyle MV2 distance lenses are currently available in powers from -5.00D to +4.00D and MV2 near lenses in powers from -4.00D to +5.00D, though these powers will soon be expanding. The lens has a diameter of 14.5mm and is available with base curves of 8.50mm or 8.80mm.

Inventory Options and Fees

The most successful way to fit bifocals is to have a full inventory of trial contact lenses at the office. Lens selection is immediate and any problems with the initial fit can be solved quickly. For these reasons, low cost inventories of MV2 contact lenses are available to practitioners. Still, if you prefer to fit the LifeStyle MV2 per patient, individual trial contact lenses can also be ordered. LifeStyle MV2 bifocal lenses are available from The LifeStyle Company's customer service department or from your authorized LifeStyle distributor.

Fees are an important consideration of any practice. It may take you less time to fit the MV2 than traditional bifocals, but it's still a bifocal and your expertise in specialty fitting is valuable. We strongly urge you to set your fees for the MV2 in line with your usual bifocal fee schedule.

Keep it Simple and the Rest Will Follow

So that's the story. As it turns out, the trick to building a better bifocal has been staring us in the face for years: start with monovision, keep all its advantages and eliminate all its disadvantages. Could the solution to every problem be this simple?

Dr. Seidner, founder and CEO of The LifeStyle Company, has been known as the Father of the RGP lens since he first developed the material in the 1970s.