|A well-fit aspheric multifocal gas permeable lens.|
If you want to offer your patients GP lenses, become comfortable with prescribing them. A good place to start: aspheric multifocal designs for GP lens wearers who are new presbyopes. If you follow the manufacturers fitting philosophy guide, you should, in most cases, achieve good centration, and the patient will gain some add power. And, very shortly, youll gain confidence to fit more patients, including those who require higher adds or more intermediate correction.
Good candidates for aspheric multifocal lenses not only include early presbyopes but:
Individuals who can benefit from a progressive add. These include computer users and anyone else with visual demands at more than two distances.
Athletes. (Yes, presbyopes still play sports.) The relatively tight-fitting aspheric designs minimize dislodgment in the tennis, softball, racquetball and basketball player.
Individuals whose lid anatomy is not conducive to segmented, translating bifocals.
Translating GP bifocals still should have a prominent role in the presbyopic contact lens practice. These executive, crescent and similar type of prism-ballasted designs are an excellent alternative for individuals who want excellent vision at distance and near (intermediate vision is also available in many of the newer designs).
To be successful with a segmented translating design, the patients lower lid should be no lower than 1mm below the inferior limbus. These weighted, or ballasted, lenses need to fit on or near the lower lid so that the lens is pushed up as the patient looks down. If the patients lower lid is too far below the limbus, the lenses wont translate properly. Likewise, if the lower lid is too flaccid, translation will not likely occur upon downward gaze.
|A well-fit, crescent segmented gas permeable bifocal.|
Aspheric multifocals that provide higher adds are perhaps the most exciting breakthrough in recent times. Traditionally, we considered the simultaneous vision of an aspheric lens to be a disadvantage because the patient had distance and near correction in front of the pupil at the same time. Over time, however, we learned that for an aspheric design to be successful, it must translate (i.e., shift up) to assist in providing the patient with add power.
Also, some of the newer lens designs provide a smaller effective center distance zone, an anterior paracentral near zone, or both to provide the higher add that advanced presbyopes (and relatively early presbyopes who have a small pupil size) require.
Another group to consider: soft lens wearers who might benefit by correcting their presbyopia with GP lenses. We often associate soft lenses with comfort and GPs with lens awareness. However, through my clinical experience, I have found that soft lens wearers can adapt to GPs, wear them comfortably and achieve excellent visual results.
Those visual results, of course, start in the exam room. Research has shown that how we present GP lenses to a new wearer may affect the patients satisfaction and success. If we present GPs with genuine interest and a positive and realistic attitude, patients are more likely to succeed in GP wear during the initial critical period.3
Whenever I see new presbyopes who have been soft contact lens wearers, I mention four options for correcting them: reading glasses worn over their soft lenses, monovision, soft bifocal contact lenses and gas permeable bifocals. If the patient is a satisfied soft lens wearer and wishes to stay in that modality, I fit him or her in soft bifocal contact lenses, which I prefer to monovision. Several published studies show that soft bifocals provide better quality of vision than that of monovision.4,5 Their success should only increase with the introduction of silicone hydrogel bifocals.
The availability of disposable lenses allows me to send the patient home, armed with different designs to determine what lens provides him or her with the best vision. If the patient is not satisfied with the vision offered by soft bifocals, I once again encourage him or her to consider GP bifocals. (Whenever patients ask me about my own preference, I tell them that I prefer GP bifocals because they offer the best visual results.)
Two advantages to GPs: A higher quality optical surface than soft lenses and the additional near assistance a patient may experience due to the translating effect of the lens.
Whichever contact lens they choose, I do not promise patients that they will never need to wear glasses. Although most patients will not require them, its always best to under-promise and over-deliver.
Occasionally, you may have a patient who feels his or her vision while driving at night is somewhat compromised with aspheric multifocals. You might offer that patient a pair of low-minus power glasses to wear over his or her contact lenses when driving at night to achieve sharper vision. Or, you may have a patient who wants optimum distance vision and requires over-readers for reading small print or viewing other small details, particularly under low illumination. Again, these examples are typically the exception to the rule.
Of course, we all probably encounter patients whose motivation not to wear glasses from a cosmetic standpoint allows them to accept compromised vision in bifocal contact lenses. Thats where the concept of 20/happy comes in. If these patients distance vision is significantly compromised in a soft bifocal design or monovision, encourage them to try GPs.
Making the Fit
Here are several clinical pearls that can help you achieve successful GP bifocal fits:
Before fitting the patient, carefully evaluate pupil size, lid relationship to the cornea and tear film. Patients who have large pupils (greater than 5mm in normal room illumination) are not good candidates for these lenses. As the pupil enlarges at night, the patient starts to see through the near zonepossibly compromising visionespecially when driving.
As with any contact lens patient, ensure sufficient tear volume. This is especially important for presbyopic patients, because tear volume decreases with age.
Start with a topical anesthetic. When fitting a new contact lens patient or soft lens wearer into GPs for the first time, instill a topical anesthetic to make the experience more comfortable for the patient. Then, let the anesthetic wear off so that the patient gradually experiences lens awareness.
My colleagues and I performed a study and found that the use of a topical anesthetic at the fitting visit for first-time wearers of GP lenses results in significantly fewer dropouts, improves initial comfort, enhances perception of the adaptation process and leads to greater overall satisfaction after one month of lens wear than when eyes are not anesthetized.6
We selected 80 new GP lens wearers and randomly assigned them to receive either a topical anesthetic or placebo immediately prior to the fit. Those who received an anesthetic rated their overall comfort as higher both at the dispensing visit and two-week follow-up. They also exhibited significantly greater overall satisfaction with GP lens wear at two and four weeks and perceived their adaptation, sensitivity and adaptation time to be significantly better at the one-month visit.
Always follow the fitting guide that comes with your diagnostic set. Doing this will get you very close to the exact fit.
With aspheric lenses, its possible for you, the optometrist, to feel comfortable with the diagnostic fitting process after as few as three fits. That allows you the opportunity to then fit empirically, which has the benefit of often providing the patient with very good vision in his or her first experience with GP multifocal lenses.
For segmented, translating lens fits, diagnostic lens fitting is all but required to assess seg position (this should be located at or very near to the lower pupil margin), lens rotation (if present) and translation with downward gaze. These diagnostic sets usually have an average seg height and an average prism amount that typically brings you very close to the optimum fit.
Choose a flat or steep base curve radius, depending on the lens design. Translating bifocals should be fit a little flatter than K, because you want these lenses to move down and rest on or near the lower lid.
For fitting aspheric multifocals, the base curve is often selected approximately 1.00 to 1.50D steeper than K to obtain good centration with no more than about 1mm of movement. The back surface geometry of aspheric lenses is likely to achieve that. With an aspheric design, any time the lenses fit steeply, youre likely to achieve good centration. If the lens moves excessively on the eye, youll need to go to a steeper base curve.
Let the patient try viewing different distances. When I fit patients in GP bifocals, I have them walk around the clinic and look around, read a newspaper or magazine, look at a computer screen and look outside. They report back to me what looks clear and what is not satisfactory to them.
Use flipper bars or loose trial lenses to fine-tune the fit. I try to tailor the final Rx to the patients most important needs, such as viewing a computer screen. A 0.25D change (plus or minus) can sometimes make a big difference in the patients vision, so the use of trial lenses is especially important.
|Tips for Troubleshooting Translating Designs|
Keep these additional pearls in mind when fitting translating, segmented lenses:
When the patient blinks, the lens should remain relatively stable on the eye. A lens that moves up with the blink and is slow to stabilize can create problems, especially when patients are driving. As these designs have a thin upper edge and a thick bottom, little movement with the blink is expected. If movement is a problem, try increasing the prism.
In assessing translation, have the patient view inferiorly and lift the upper lid. The lens should be pushed so that the near zone is in front of the pupil (or as you view it, the seg line should, at minimum, bisect the pupil).
If the lens doesnt translate, try a flatter base curve. This increases the edge clearance, or lift, which brings that edge onto the lower lid a little more. As a result, the lens is more likely to stay on the lower lid, so that when the patient looks down, the lower lid will help the lens up.
If changing the base curve doesnt work, the patients lid may be too loose and flaccida normal occurrence with the aging process. When this occurs, you may need to fit the patient in a different lens.
If you decide to order a prism ballasted, truncated lens, remember the effect of the prism ballast. The effect is decreased for a thick, higher-minus lens when it is truncated (i.e., more prism necessary) and is increased when a plus or low-minus power lens is truncated (i.e., less prism necessary).
If there is excess rotation of the seg line with the blink, try a flatter base curve. If you fit a lens excessively steepespecially on a cornea that has with-the-rule astigmatismthe lens will try to center on the eye. We dont want these lenses to center on the eye. Rather, we want them to ride somewhat inferiorly. The upper lid is twisting a lens that rotates, so you want to move it away from the upper lid. This is particularly true of a lens that rotates nasally, which is the common finding.
Advise the patient to shift his or her eyes (not head) inferiorly when viewing through a segmented lens. This ensures that he or she is viewing through the segment.E.S.B.
It is not necessary to maintain an inventory of GP bifocals and multifocals in order to achieve success. Once you feel comfortable fitting these lenses, you may order empirically, or you may prefer using diagnostic fitting sets. Also, many labs will help design a lens for you if you send refractive and topographic information.
While trying to find your comfort zone when fitting bifocal GPs, your laboratory consultant can be your best friend. Most laboratories offer several bifocal designsboth aspheric and translating lenses.
There are numerous resources available to assist in the patient selection, fitting and troubleshooting of GP bifocal lenses. These include a new comprehensive presbyopic patient, staff and a practitioner education module from the GP Lens Institute (www.gpli.info).
Todays GP bifocal lenses continue to come in improved designs and offer improved vision. These lenses can play a great role in building your practice and providing improved vision and satisfaction to your presbyopic patients. In my case, at least, they also make dining out a more pleasant experience.
Dr. Bennett is executive director of the Gas Permeable Lens Institute and is co-chief of the contact lens service and director of student services at University of Missouri-St. Louis College of Optometry.
1. Rakow PL. Presbyopic correction with contact lenses. Ophthalmol Clin North Am 2003 Sep;16(3):365-81.
2. Woods C, Ruston D, Hough T, Efron N. Clinical performance of an innovative back surface multifocal contact lens in correcting presbyopia. CLAO J 1999 Jul;25(3):176-81.
3. Bennett ES, Stulc S, Bassi CJ, et al. Effect of patient personality profile and verbal presentation on successful rigid contact lens adaptation, satisfaction and compliance. Optom Vis Sci 1998 Jul;75(7):500-5.
4. Kirschen DG, Hung CC, Nakano TR. Comparison of suppression, stereoacuity, and interocular differences in visual acuity in monovision, and Acuvue bifocal contact lenses. Optom Vis Sci 1999 Dec;76(12):832-7.
5. Rajagopalan AS, Bennett ES, Lakshminarayanan V, Henry VA. Performance of presbyopic contact lenses under mesopic conditions. ARVO Abstract #3679, 2003.
6. Bennett ES, Smythe J, Henry VA, et al. Effect of topical anesthetic use on initial patient satisfaction and overall success with rigid gas permeable contact lenses. Optom Vis Sci 1998 Nov;75(11):800-5.