SOFT BIFOCAL LENSES
Know Your Soft Bifocal Lens Options
Troubleshooting problems becomes easier when you know the strengths of different lenses.
By Susan Kovacich, OD, FAAO
If practitioners and patients are waiting for "the perfect" bifocal contact lens, they may have a long wait. However, many good soft bifocal contact lens options are on the market today, and knowing the strengths of the different lenses will help you make the best initial lens selection and save valuable chair time. However, even after following manufacturers' fitting guides, you often need to make adjustments to optimize patients' vision. Flexibility in fitting bifocal contact lenses can mean the difference between success and failure.
After years of fitting monovision with its known compromises to binocular vision, it's easy for the pendulum to swing the other way and attempt to fit all patients with the best distance vision in both eyes using bifocal contact lenses.
Younger presbyopes who are easy to satisfy initially may become more complicated as they age and you may have to employ modifications to the distance and near prescription. Here I use "modified monovision" to describe a fit that shifts one or both lenses away from binocularity and toward favoring distance or near correction. Presbyopic progression may eventually make the strongest add power available ineffective, or higher add power designs may interfere with distance vision. Listening to the patient's complaints and knowing how to manipulate the lenses will often result in a satisfied patient. Because several manufacturers recommend unequal adds or have lenses built on a distance/near design, modified monovision and a little judicious creativity can work wonders.
Emmetropes who become presbyopic are some of the most particular patients to satisfy. Often, no lens in the dominant eye and a bifocal lens in the nondominant eye will make them happier than lenses in both eyes.
When fitting a patient with bifocal contact lenses it's important to establish reasonable expectations. The patient needs to know up front that this new visual system will not mimic the visual freedom that a 20-year-old patient enjoys. You can communicate this to the patient in many different ways. If you shy away from the negative connotations that the word "compromise" conveys, other terms such as "give and take" or "balance" work well. In general, if you correct a patient so that he can perform 80 percent of his daily activities well, consider that a success. If he needs readers to see the phone book or medicine bottles, this is acceptable.
It's important to note that making continual changes to the bifocal lenses can increase some patients' expectations that there truly is one perfect fit, which may make those patients harder to satisfy.
Fitting Do's and Don'ts
While each of the soft bifocal contact lenses has particular fitting characteristics, there are some do's and don'ts that work for all of the lenses. One of the main limitations of these lenses is that they won't work well for patients who have more than 0.75D or 1.00D cylinder (those patients will need soft toric bifocal lenses, GP bifocals or monovision).
Some other general rules are important for success in fitting bifocal contact lenses. Practitioners should determine the patient's dominant eye and should employ the best spectacle correction (using the spherical equivalent for cylinder up to 1.00D). The lighting in the examination room should be adequate for reading after the lenses have settled. Practitioners should take acuities with both eyes open and should make (small) changes to the prescription using loose lenses or flipper bars. Occluding one eye or putting the patient behind the phoropter may affect pupil size and the visual performance of the lenses.
Next let's look at the lens designs of Bausch & Lomb's SofLens Multi-Focal and PureVision Multi-Focal, CooperVision's Proclear Multifocal and Frequency 55 Multifocal, Vistakon's Acuvue Bifocal and CIBA Vision's Focus Progressives and Focus Dailies Progressives. All of these are simultaneous design lenses. The B&L and CIBA lenses are aspheric designs, and the Acuvue and CooperVision lenses are concentric designs.
B&L SofLens Multi-Focal and PureVision Multi-Focal
The SofLens Multi-Focal currently has the largest portion of the soft bifocal contact lens market share. The release of the PureVision Multi-Focal in March makes it the first silicone hydrogel soft bifocal lens on the market. This aspheric, center-near design comes in two add powers (high and low). The SofLens Multi-Focal has two base curves, and the PureVision Multi-Focal has one. B&L states that practitioners can switch 86 percent of SofLens Multi-Focal wearers directly into the PureVision Multi-Focal with no change in parameters, and 96 percent are within 0.25D. The same wide range of powers is available with both lens materials.
For initial lens selection, B&L recommends:
Distance: Full distance prescription in both eyes (spherical equivalent up to –1.00D cylinder).
Add selection: For up to a +1.50D add, use the Low Add OU. For a +1.75D to +2.25D add, use the Low Add for the distance eye and the High Add for the near eye. For up to +2.50D add, use the High Add OU.
Case #1 Patient #1 is a 51-year-old male who has been wearing SofLens Multi-Focal lenses successfully for years, going from two Low Adds to a Low Add and a High Add, and then finally, to two High Adds. His spectacle prescription is OD plano, OS –0.50DS, with a +2.50D add. His right eye is the dominant eye. Lens parameters include 8.5mm base curves, OD plano with a High Add and OS –0.50D with a High Add with visual acuity of 20/30 at near. The patient is unhappy with his near vision and he has the strongest add in both eyes. I modified his prescription to OD plano with a High Add and OS plano with a High Add, resulting in 20/25 at near. By cutting the distance prescription by 0.50D in the nondominant left eye, the patient is still happy at distance and can once again read comfortably at near.
Case #2 Patient #2 is a 64-year-old male who has worn monovision in the past and wants to try contact lenses again. There is a potential problem in that he is a maintenance manager who has to inspect work at several different intermediate distances in addition to working at a computer. His spectacle correction is OD +1.00DS, OS +0.75DS with a +2.50D add (Progressive). His right eye is dominant.
According to the SofLens Multi-Focal fitting guide, he should be fit with OD +1.00D with a High Add, OS +0.75D with a High Add. However, he has greater intermediate needs than average. I modified his prescription to OD +1.00D with a Low Add and OS +0.75D with a High Add. To meet his occupational needs, I reduced the add in his dominant eye. The patient was comfortable with his vision at all distances.
B&L recommends these fitting modifications:
1. Over-refract to increase distance visual acuity (DVA) (±0.25D steps) with handheld trial lenses.
Add plus or minus power to dominant eye if necessary (0.25D to 0.50D) for better distance.
2. Over-refract to increase near visual acuity (NVA) (+0.25D steps) with handheld trial lenses. Add plus power to non-dominant eye if necessary (0.25D to 0.50D) for better near.
Other suggestions include if a myopic patient is having problems with distance vision, push the minus in the dominant eye first, then in both eyes if necessary. If there's a distance complaint with two High Adds, drop the dominant eye to a Low Add. When a near complaint occurs with two High Adds, push the plus in the nondominant eye.
Strengths The aspheric design is useful for intermediate demands, such as computer use. The PureVision Multi-Focal is a silicone hydrogel lens, allowing significantly more oxygen transmission to the cornea and the added option of 30-day continuous wear for appropriate patients.
CooperVision Proclear Multifocal and Frequency 55 Multifocal
There are some important features to note with the CooperVision lenses. The company offers a multifocal design it describes as "Balanced Progressive Technology." This concentric design lens employs a center-distance design lens (D lens) for the dominant eye and a center-near lens (N lens) for the near eye. The D and N designation is important to note when fitting and ordering lenses. There are also four adds (+1.00D, +1.50D, +2.00D, +2.50D), which gives practitioners many parameters to choose from.
The Proclear (omafilcon) lens material is FDA approved for dry eye, which presbyopes are more likely to have. It may be difficult to fit a patient who has been wearing a Proclear lens (single vision or multifocal) successfully into another lens material if he has dry eye. The Frequency 55 Multifocal is approved for flexible wear.
CooperVision recommends the following (and has a fitting calculator available on its Web site):
Step 1: Determine the dominant eye.
Step 2: Using the spherical equivalent of the proper prescription (up to 0.75D cylinder), use the appropriate D lens in the dominant eye and appropriate N lens in the near eye.
Step 3: After allowing the lenses to settle, evaluate the lens performance in normal lighting conditions binocularly first, then monocularly.
To determine if the visual acuity will satisfy the patient, CooperVision recommends using this fitting matrix:
D Lens 20/20 N Lens 20/20
N Lens 20/40 D Lens 20/40
If the visual acuity does not match this matrix, adjust the appropriate lens for distance or near.
Case #3 Patient #3 is a 52-year-old housewife who does needlepoint and some computer work. She currently wears monovision. Spectacle prescription is OD +1.25 –0.50 x130, OS +1.00 with a +2.25D add. Her left eye is dominant. Her habitual lenses are Proclear with 8.6mm base curves, OD +3.25D and OS +1.00D. She has near complaints and was presented with the option of bifocal contact lenses.
I fit her with Proclear Multifocals with 8.7mm base curves, OD +1.00/+2.50N with visual acuities at 20/40 near, 20/40 distance; OS +1.00/+2.50D with visual acuities at 20/20 distance, 20/40 near. However, the patient still had near complaints. Using the matrix, I changed the nondominant eye to OD +1.50/+2.50N with visual acuities at 20/20 near and 20/40 distance. Pushing the plus in the distance portion of the nondominant eye solved the chief complaint.
There may be times when a patient (especially an early presbyope) wants better distance vision and two distance lenses may work better. Similarly, two near lenses may be necessary for an older presbyope who has a higher add and is exacting about near work and not as critical about his distance vision (but still needs correction well enough to function). Two near design lenses are the exception to the rule, but don't be afraid to try it if the patient complains about near vision. Again, flexibility is important.
Strengths The Proclear material is a great option for older patients with dry eyes. Also, many different parameters are available, with a distance-center and a near-center lens design as well as four add powers.
Vistakon Acuvue Bifocal
This concentric bifocal lens has five alternating rings beginning with a distance center, a good range of powers and one base curve.
As with the other lenses, determine the best spectacle correction (spherical equivalent), and allow the lenses to settle adequately. The company encourages unequal adds when appropriate.
The power of the four adds (+1.00D, +1.50D, +2.00D, +2.50D) is skewed strong, which you can see in the advised near power selection guide:
40 to 46 +1.00D
47 to 52 +1.50D
53 to 59 +2.00D
Case #4 Patient #4 is a 45-year-old professor currently wearing single vision lenses (parameters unknown) with near complaints. His spectacle prescription is OD –2.50 –0.50 x180, OS –2.50 –0.50 x180 with a +1.00D add. The left eye is dominant. We fit the patient with an aspheric soft bifocal, but he didn't like his vision at distance or near. We refit him with the Acuvue Bifocal at OD –2.75D with a +1.00D add, OS –2.75D with a +1.00D add. The patient was happier with distance vision, but still had near complaints. I modified the prescription to OD –2.75D with a +1.50D add, OS –2.75D with a +1.00D add. By increasing the add in the nondominant eye, the patient could see clearly at near.
For distance optimization in the dominant eye, adjust the distance vision appropriately first, and failing that, reduce the add power in that eye. For near optimization in the nondominant eye, adjust the sphere power first, and if no improvement occurs, increase the add power.
Strengths The Acuvue Bifocal has multiple adds, which are skewed strong. This lens may give patients who can't seem to get enough add power with other brands better near vision. It also offers ultraviolet protection.
CIBA Vision Focus Progressives and Focus Dailies Progressives
It's important to note that this aspheric design lens has only one add power (up to +3.00D), which is very concentrated in the center of the lens.
A formula is available to calculate the initial lens: Add the distance refraction to one-half of the add power. For example, for a –3.00D myope with a +2.00D add, the equation would be: –3.00D + one-half of the +2.00D add, which is –3.00D + (+1.00D) = –2.00D Focus Progressives.
Case #5 Patient #5 is a 56-year-old retired female. She heard about bifocal contact lenses and wants to try them. Her spectacle prescription is OD +1.50 –0.50 x040, OS +1.50 –0.50 x015 with a +2.25D add. Her right eye is dominant. We fit her with Focus Progressives OD +2.25D, OS +2.25D, but she was unhappy with her distance vision. After several trials, we fit her with OD +1.50D, OS +2.25D. This hyperopic patient kept taking more minus in the distance in her dominant eye, which wasn't expected. Keeping an open mind kept this patient in her lenses.
With only one add to choose from, practitioners should make small changes (beginning with 0.25D) according to patient complaints.
Strengths Anecdotal reports show this lens working better than other designs for hyperopic patients. Also, Focus Dailies Progressives are the only soft bifocals contact lenses available as daily disposables. Note that while the Focus Progressives lens is available in 8.6mm and 8.9mm base curves, the Focus Dailies Progressives lens is available only in an 8.6mm base curve.
Bifocal Contact Lens Candidates
Practitioners can use the same creativity and flexibility they use in fitting bifocal contact lenses when considering patients as bifocal contact lens candidates. Some patients can't use bifocal lenses for work because of distance or near demands, but they may be great candidates for occasional wear. We recently fit an emmetrope who has problems with her farther-than-average computer distance, although she probably won't wear the lenses for work. One of her main hobbies is hiking during which she needs to be able to read maps and a GPS for navigation, and one bifocal lens in her nondominant eye solves her near needs for that activity.
Also, consider younger patients who have accommodative problems. We successfully fit bifocal lenses on several college students who were experiencing accommodative problems and having problems going from distance to near in large lecture halls. They are happy to remain in contact lenses without the need for readers.
The five patients presented here demonstrate the great opportunity to grow a contact lens practice by offering soft bifocal contact lenses. Only one patient went from single vision lenses into bifocal contact lenses. Two patients tried monovision as they became presbyopic; one dropped out, and the other progressed into bifocal contact lenses. An emerging presbyope chose to wear bifocal contacts as a new wearer, and a mature presbyope chose bifocal lenses in her 50s. By knowing the soft bifocal options and how to troubleshoot problems, practitioners will continue to meet the contact lens needs of the growing presbyopic patient population.
Dr. Kovacich graduated from Indiana University School of Optometry and completed a hospital-based residency at the St. Louis VAMC. In 1998 she returned to IU as a Clinical Assistant Professor, currently working in the Cornea and Contact Lens Clinic.