The Presbyopic Fitting Process
Satisfy your presbyopes with monovision, multifocal lenses or anything in between.
By Peter D.
Bergenske, OD, FAAO
Fitting presbyopes is never as simple as matching lens type with patient type. It is a process of finding acceptable compromise. Clearly the choices for presbyopes have expanded. We have not only monovision and multifocals, but also combinations of these as modified monovision. Think of the range of choices as a continuum, with monovision at one end and full binocular, bifocal correction on the other. Many, if not most, successful fits end up somewhere between these two poles. Successful fitters can flexibly adapt these options to a patient's needs and tolerances.
Some presbyopic contact lens wearers are satisfied with reading glasses, but this option is intolerable for many. For some patients you can slightly over-plus single vision contact lenses, allowing good near vision, then supplement with spectacles for long distance tasks such as driving. Many patients accept spectacles as a supplement as long as they are not entirely dependent upon them. Many monovision or multifocal wearers can perform 90 percent of their near tasks with just contact lenses and really don't mind using spectacles for the occasional challenging task.
Monovision allows the use of any lens type, is inexpensive and does not create compromise any greater than multifocal lenses do. It does depend on a flexible binocular system, and some patients simply do not adapt. Monovision requires that both eyes have essentially equal capabilities, and its success suffers if you cannot obtain clear corrected vision for each eye independently. Monovision success also declines in the higher add ranges.
One variation for high add demand is to over-plus both eyes, but to different degrees. This "school teacher's" correction allows good vision from desktop to across a small room. Supplement with distance spectacles for long distance viewing. Such correction can work well for office workers and even eyecare practitioners, who have all-day near demands and relatively little long distance viewing.
You can also combine one single vision lens and one multifocal lens. Set the single vision lens for either near or distance depending on patient need, then bias the multifocal lens for the other range.
The Multifocal Milieu
No other aspect of contact lens practice offers the variety we have with multifocals. Multifocal styles fall into four basic categories: annular, aspheric, multizone and translating. Annular and aspheric designs may be either center-near or center-distance. Effective optic zone size varies with the individual design and often with the add power.
The term "translating" applies only to rigid lenses. The position of the translating lens relative to the visual axis determines the focal length of the system. Soft lenses, on the other hand, move little and depend on simultaneous vision as well as centration and pupil size. The multizone design addresses this dependency, and the success of the Acuvue Bifocal testifies to the accuracy of that aim.
With most designs, other than the true alternating bifocals, distance vision and near vision tend to compete such that the better one is, the worse the other becomes. This challenges the fitter to find the balance point appropriate for the patient. Break from the idea that both eyes need full near correction. At least half of the successful soft multifocal fits consist of lenses with unequal adds (the so-called modified bifocal), and in the majority of both rigid and soft lens fits, the degree of add is less than what the spectacle correction called for. Just as with monovision, the less near correction you employ, the less you interfere with the distance vision.
|Figures 1 and 2. Pupil diameter can have significant effect on the view through a lens with a progressive additional optical zone, with large pupils potentially causing the near portion to overwhelm distance vision.|
|Figures 3 and 4. The multizone design decreases the effect of pupil size as the proportion of near and distance correction remain relatively fixed over a wide range of pupil diameters.|
FIGURES COURTESY OF PATRICK CAROLINE, FAAO, FCLSA
Matching Patients with the Right Option
With so many options, even just finding a starting point can be overwhelming. On the other hand, evaluating a presbyopic patient for contact lens correction is similar to evaluating single vision correction; however, accurately correcting each eye becomes more significant.
The astigmatism factor. When corneal astigmatism is present, make rigid lens fitting a theoretical first choice. You can even correct residual astigmatism in a rigid multifocal depending on the lens design. Astigmatism correction with soft contact lenses has improved. However, multifocal toric lenses have yet to reach mainstream, and price, availability and experience are limitations at this point in time. Ignoring astigmatism and fitting with equivalent sphere correction often creates too much compromise when attempting multifocal correction. Fitting monovision with toric soft lenses can be difficult, as monovision correction depends on stable and excellent vision in each eye.
Astigmatic patients who want or need soft lenses should anticipate some compromise in vision. Monovision with toric soft lenses can work, but is more likely to fail. Soft toric multifocals can also work, but expect a lengthy process. (You can trial fit with spherical lenses of the same multifocal design and over-refract for the cylinder to speed the process of elimination.) Some patients will present with significant astigmatism in only one eye. In such cases, try fitting a single vision toric lens on one eye (usually for distance vision) and a multifocal sphere on the other.
The add factor. Add needs are important in choosing correction. Think in terms of minimum, rather than optimum, near correction in many cases. For very low adds (+0.75D to +1.00D), almost any choice will likely work, including monovision, low add soft multifocals and rigid aspheric lenses. The need for astigmatic correction will likely drive the decision. For adds ranging from 1.25D to 1.75D, try rigid back surface aspheric multifocals. If astigmatism is not a factor, soft multifocals will work, but the patient may need unequal adds or slight over-plussing of one lens for adequate near correction while maintaining satisfactory distance vision. For add needs 2.00D or greater, try alternating rigid lens designs. Soft multifocal lenses may need some degree of monovision for success.
The pupil factor. Patients with very small pupils will have difficulty utilizing anything but the central portion of a relatively stationary lens. A lens that centers well over the pupil is advantageous, but may also be limiting. Consider pupil size in determining whether to use a center-near or center-distance design. Patients with exceptionally large pupils are more likely to have night vision problems with multifocal lenses and may be more suited to monovision. Multizone lenses are the least pupil dependent.
Pupils are almost always slightly decentered nasally. Most multifocal lens designs are symmetrical, and if they center on the cornea they will not center over the patient's pupil. Observe the red reflex through a retinoscope or direct ophthalmoscope to check for position of the multifocal components relative to the pupil.
The mental factor. The goal of presbyopic contact lens fitting is to reduce, rather than eliminate, the need for supplemental near correction. If patient and practitioner both accept this, they are more likely to reach success. Patients and practitioners should understand at the outset that fitting for presbyopia is not instant, automatic or particularly predictable. Successful modern presbyopic fitting is a process that results from an understanding of the lens designs and their appropriate application as well as adjustments and compromises that allow a balance to be achieved.
For the practitioner not actively involved with presbyopic fitting, even deciding what lenses to have in the office is challenging. Find out what lenses other practitioners most commonly use. Have at minimum disposable soft multifocal fitting sets in both center-distance and center-near designs. Disposables are preferable for accurate trial fitting and ease of parameter changes. For rigid lenses, obtain a fitting set for a back aspheric design. (Alternating designs are significantly more challenging to fit. Wait on this until you reach a level of comfort with fitting these other lenses.)
Study and understand the lens designs you are going to work with. There is usually a good reason that something does or does not work. The more you understand, the less guessing you will have to do.
Follow the fitting guides for these lenses and make use of consultation services. Most practitioners like to think they can figure these things out by themselves, but you will save time, money and frustration if you follow guidance based on trial and error and thousands of fits.
References are available upon request to the editors of Contact Lens Spectrum. To receive references via fax, call (800) 239-4684 and request document #73. (Have a fax number ready.)
Dr. Bergenske, a Past Chair of the American Academy of Optometry's Section on Cornea and Contact Lenses, has practiced for over 20 years in Wisconsin. He is now on the faculty at Pacific University College of Optometry.
"Additude" Trends in Contact Lens Fitting for Presbyopia
An article in the December 2000 Optometry presented data from a survey on monovision fitting. The survey was conducted in 1998, just before the big upswing in soft bifocal contact lens availability and promotion, and the data indicated very low rates of bifocal/multifocal fitting. We decided to survey the same group again to see how attitudes regarding multifocal fitting may have shifted from 1998 to 2001.
The original survey was mailed to Diplomates of the Section on Cornea and Contact Lenses of the American Academy of Optometry. We e-mailed our survey, and rather than asking all the questions relating to monovision, we simply asked this question from the original survey:
* Indicate treatments you ordinarily recommend for current contact lens-wearing patients who have recently begun to require assistance with reading (new presbyopes). Please specify the approximate proportion of patients for whom you recommend each treatment (such as monovision CLs = 20 percent) so that the total proportion adds to 100 percent.
The original survey was larger (we had only 99 e-mail addresses, whereas 179 original surveys mailed). The 1998 survey had 95 responses; we had 49, 40 of which we could use. We have no way of knowing how many of our respondents participated in the initial survey. We acknowledge that data obtained this way is notoriously unscientific. Only one of our respondents indicated that he submitted exact numbers from computer patient data. We also did not account for the steady increase of all kinds of presbyopic fits. Nevertheless, we felt the information showed an unmistakable change in attitude toward multifocal contact lens fitting over this time period.
Figures 1 and 2 graphically summarize the responses to the survey. Note the change in the "never" response. In 1998, approximately one third stated they "never" utilized a soft multifocal lens, over half "never" used a modified monovision approach, and over 20 percent "never" used a rigid multifocal. The 2001 data shows a great shift from this category into the other categories of utilization.
Respondents in 1998 clearly preferred monovision for managing presbyopes, with 53 percent of the respondents choosing monovision for at least 40 percent of presbyopic new fits, and 28 percent using this method over 80 percent of the time. The 2001 survey shows monovision dropping in popularity somewhat, with only 28 percent choosing it more than 40 percent of the time. None responded that they choose monovision over 80 percent of the time. On the other hand, 46 percent still use monovision between 20 and 40 percent of the time, and 28 percent use it over 40 percent of the time. It's not dead yet!
Where have the mono-fits gone? Over 40 percent of the 2001 respondents used rigid bifocals at least 20 percent of the time. Soft bifocals, used sparingly or not at all by the majority in 1998, are now fit at least 20 percent of the time by over 60 percent, clearly a change.
Note that all we have reported are estimated percentages, not absolute numbers. This tells us little, if anything, about the growth of the presbyopic market. The Diplomates we surveyed, well recognized as contact lens specialists, do not represent contact lens fitters in general, so we expect that their specialty fits are higher than is common in general practice. Diplomates are experienced and up-to-date, and their responses may indicate where the rest of the contact lens field will be in time. The survey does show a distinct change in attitude toward fitting multifocal lenses, testimony to the significant advances that have been made in this modality over the past few years. If you had less than great results fitting multifocals in the past, look once again at the opportunities that multifocal lenses offer your patients and practices.