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New bifocal contact lens broadens choices for presbyopic patients
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The Acuvue bifocal by Vistakon represents a significant step forward in the quest to successfully provide presbyopic contact lens correction to our patients. Although not a panacea, its unique design characteristics, easy accessibility to a full range of powers, convenience and minimal financial risk form a powerful package.
Approved for 2-week daily wear and 1-week extended wear replacement cycles, the Acuvue bifocal offers UV blocking, a visibility tint and an inversion mark. The new "1-2-3" inside-out mark uses new technology to provide a very comfortable tool to assist patients in determining lens orientation. According to Vistakon, the lens is available now to limited accounts and will be available nationally in the fourth quarter.
The Acuvue bifocal is a simultaneous-vision, distance-center lens with a unique multizone concentric ring de sign. The center distance zone is surrounded by alternating rings of near and distance focus. The outermost ring provides distance correction to assist night-time viewing.
The total of five alternating zones provide superior function, in part due to the precise tooling employed to fabricate the design. The crisp transition from zone to zone across the lens surface minimizes halos and blur. The zone sizes have been arrived at based on extensive study of pupil size and dynamics during varying light levels. Vistakon describes this as a "Pupil Intelligent" design.
Provided in a 14.2-mm diameter and 8.5-mm base curve, the Acuvue bifocal is available in sphere powers from +4 D to –6 D (in 0.25-D steps) and adds of +1.00 D, +1.50 D, +2.00 D and +2.50 D.
Having had the opportunity to work with the Acuvue bifocal for more than 2 years, I want to share some thoughts about my experience and offer help to maximize your success with this lens.
Educate patients
When presenting the Acuvue bifocal, or any presbyopic contact lens for that matter, be positive but realistic. It is important that the patient understand that any form of visual correction re quires adaptation and compromise.
For example, bifocal spectacles re quire the patient to view objects in down gaze, the lenses fog with temperature change and the frames can slide down the nose. Similarly, bifocal contact lenses will require some adaptation and compromise.
All soft bifocal contact lenses now on the market are simultaneous vision designs. Due to the presence of zones focusing at multiple distances all within the pupil at the same time, some softening of detail will invariably occur at times. However, the patient will be able to view distance and near tasks in any direction, enjoy unobstructed peripheral vision and won’t have to suffer with frames pinching and sliding.
I stress to the patient: "My goal is to meet most of your visual needs most of the time with your presbyopic contact lenses." Clarifying this at the start squelches many potential problems.
Selecting lens power
Distance power is simply the vertexed spectacle refraction. Patients with 1 D or more of astigmatism are not good candidates. For low astigmatic patients, Vistakon recommends adjusting the distance power by selecting the equivalent sphere power. I prefer to perform a sphere-only refraction on these patients to explore whether they, in fact, prefer added minus to center the interval. I feel this is important because the most common mistake the novice Acuvue bifocal fitter will make is give the patient too much minus power in the distance, thus compromising near vision. Any procedure that will help avoid this will enhance performance.
Add power is selected simply by choosing the spectacle add finding. If the spectacle add falls between the adds offered, choose the next higher add. For example, a patient with a +1.25 D spectacle add is fit with a +1.50 D add Acuvue bifocal.
It is important to allow these lenses to settle 10 to 15 minutes before assessing vision. In addition to stabilizing performance during evaluation, it provides an opportunity for the patient to get out of the exam room and explore his or her vision with the Acuvue bifocal in a more natural setting. Our patients are escorted out to the reception area and are instructed to look out the window and pick up a magazine. The feedback they provide when they return to the examining room a short time later guides me during my assessment. For example, if they have distance vision complaints, I know I need to channel my efforts in this direction.
A helpful clinical tool to get a handle on near vision performance is to ask the patient to "trombone" a near acuity card and tell me at what distance his or her near vision is the clearest. If this falls near a normal reading distance, I know I’m close to the proper near power. If he or she must hold the chart near arm’s length to see best, I know I need to cut minus in the distance or strengthen the add.
If the patient has no visual complaints, I know I’m not going to change the power much, if any.
I encourage you to assess vision under binocular conditions. This provides a truer measure of real-life visual performance. Monocular acuity testing can be helpful for troubleshooting, but tends to underestimate performance under day-to-day conditions.
If over-refracting monocularly be hind a phoropter, nearly all patients will take more minus in the distance correction. Such an approach will often not truly enhance distance vision performance, but will degrade near vision significantly. Remember, giving the patient too much minus in the distance correction will be the most common mistake made by those new to fitting the Acuvue bifocal.
To avoid this mistake, I encourage you to use the ±0.25 D and ±0.50 D flippers Vistakon provides with the Acuvue bifocal fitting set. These are so handy I find I’m using them with nearly all patients to demonstrate small changes in correction.
I recommend you begin by holding +0.50 over both eyes while a patient views a distance acuity chart. The patient should report this blurs distance vision. If not, add plus to the distance portion of the contact lenses. This obviously will not degrade distance vision and will also help at near.
All other changes in power should be symptom-driven. Instead of fixating on achieving 20/20 vision, strive for 20/happy. Increase minus in the distance only if the patient has distance vision complaints. Doing otherwise will likely reduce near vision performance. Increase the add only if the patient has near vision complaints. Doing otherwise will only degrade distance vision. The goal is to arrive at a balance that provides good visual performance at all distances.
If a symptom does exist, make the smallest change necessary to solve the problem. Small changes can have profound effects on distance and near vision. If a 0.25-D change elicits a visual re sponse similar to a 0.50-D change, make a 0.25-D change. If –0.25 D in the lens on the dominant eye improves distance vision similar to –0.25 D in both eyes, just change the lens in the dominant eye.
Addressing distance vision
As with all simultaneous vision designs, the stronger the add in the Acuvue bifocal, the greater the potential to interfere with distance vision. For this reason, higher add patients are often served better using a modified bifocal approach. In this case, a lower add lens is placed on the dominant eye, and a full strength add is placed on the non-dominant eye. The lower add on the dominant eye assists in achieving ample distance vision as well as providing a nice boost to vision at intermediate distances.
In some patients, any add power in the lens on the dominant eye compromises distance vision to an unacceptable level. In this case, applying a single vision lens on the dominant eye and a bifocal lens on the non-dominant eye will often achieve the correct balance. This is referred to as enhanced monovision.
If enhanced monovision is not successful, I consider attempting straight monovision.
The Acuvue bifocal has created a fundamental shift in how I provide contact lens care to presbyopic patients. The success I have achieved is comparable to that experienced with monovision, but patients are experiencing a higher level of visual performance. Many of these patients are not only satisfied, they are enthusiastic. Such enthusiasm has moved monovision from being my first choice for presbyopic correction to my last.
With attention given to the issues discussed here, I am confident you will find the Acuvue bifocal an effective tool to provide quality presbyopic contact lens correction to your patients.
For Your Information:
- Thomas G. Quinn, OD, MS, is in group practice in Athens, Ohio, and has served as a faculty member and research associate at The Ohio State University College of Optometry. A diplomate in the Cornea and Contact Lens Section of the American Acadamy of Optometry, Dr. Quinn also serves on the academy's Admittance Committee. He can be reached at 416 West Union St., Athens, OH 45701; e-mail: tquinn@eurekanet.com. Dr. Quinn has no direct financial interest in any products mentioned in this article. He is a clinical investigator for Vistakon and on the company's speaker's bureau.
- The Acuvue bifocal is available from Vistakon, P.O. Box 10157, Jacksonville, FL 32247; (904) 443-1000.