point - TOPIC: Soft GP Multifocals
Fit Soft Multifocals for Comfort, Ease of Fit, and Quick Adaptation
By Thomas G. Quinn, OD, MS, FAAO
One of the most compelling reasons to fit a soft rather than a GP multifocal lens is the real likelihood that the patient is already wearing a soft lens. Nichols (2010) stated that in 2009, hydrogel and silicone hydrogel lenses combined to claim a commanding 89 percent of the contact lens market. If a newly symptomatic presbyope is already adapted to a single vision soft lens, the first treatment approach would logically be to stay with that mode of correction in a presbyopic design.
Over time, not only does our focusing ability decline, our tear production does, too (Moss et al, 2008). A lens with the best possible optics won't be worn if it feels too dry on the eye. Fortunately, some of today's multifocal soft lenses incorporate agents to enhance on-eye moisture retention.
Another ocular change that occurs with time is astigmatic orientation. Infants tend to have against-the-rule (ATR) astigmatism, which shifts to with-therule in the middle years. This change is thought to be induced by the pressure of the eyelids on the corneal surface. After age 40, as the eyelids become more flaccid, astigmatic orientation tends to shift back to ATR (Lyle, 1971; Baldwin and Mills, 1981).
What's the relevance? GP lenses tend to decenter laterally on ATR corneas. This decentration is particularly problematic with multifocal optics, leading to compromised visual performance.
Additionally, patients who have ATR astigmatism are more likely to have residual astigmatism with spherical GP lenses because of astigmatism induced by the crystalline lens. We now have toric soft multifocal designs for these patients.
What About Vision?
Soft multifocal fitting is steadily rising, a strong indicator that visual performance is improving with today's designs. After years of monovision being the dominant fitting approach for lenswearing presbyopes, multifocal fittings now outnumber monovision fittings (Nichols, 2010).
If clear vision is a top priority, let's not forget about vision in glasses when contact lenses are not being worn. Many of today's GP multifocal designs have an aspheric back surface, which can often result in spectacle blur. Our goal should be to provide clear vision to our patients at all times, both with contact lenses and with spectacles. GP lenses can sometimes make it harder to deliver on the second half of this quest.
The availability of full soft lens multifocal fitting sets allows same-day fitting of interested patients. In most cases, GP multifocals need to be ordered and then dispensed at a future time.
What if the first parameters chosen don't do the trick? Changes as small as 0.25D can impact visual performance with any multifocal contact lens. When fitting a soft multifocal design, simply access your in-office fitting set to claim the prize. With GP multifocals, it's back to the lab again. This can be a real drain on your time, the patient's time, and the patient's potential enthusiasm for pursuing multifocal contact lens correction.
I recognize the benefits of GP multifocals. I wear them, and they're great. However, I wore single vision GP lenses prior to reaching my more mature years. That's simply not the case with most of the patients we work with. Combine this reality with the comfort, improving clarity, and wonderful convenience of soft multifocal lenses, and it makes sense to recommend soft over GP as your multifocal modality of choice. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #179.
Dr. Quinn is in group practice in Athens, Ohio. He is a diplomate of the Cornea and Contact Lens Section of the American Academy of Optometry, an advisor to the GP Lens Institute, and an area manager for Vision Source. He has served as an advisor or consultant to Coopervision, Ciba Vision, and Vistakon and has received research funding from AMO, B&L, Ciba Vision, Coopervision, and Vistakon. You can reach him at email@example.com.
counterpoint - TOPIC: GP Multifocals
Go With GP Multifocals for Better Vision and More Design Options
By Douglas P. Benoit, OD, FAAO
As more and more people reach the presbyopic stage, everyone seems to want a piece of the giant disposable income pie that supposedly surrounds these baby boomers. Contact lens companies are no different. Each would like to have the presbyopic design that conquers the market. Many claim to have the best design, and some do work better than others—both soft and GP designs. This array of choices gives us the ability to satisfy our patients, but is there a panacea lens? If we could have only one type of material to use for presbyopic designs, what should it be? GP or soft?
In the multifocal contact lens category, I think GP materials win out for a number of reasons.
The Best Vision
First, GP lenses can give patients sharper vision, especially if they have 0.75D or more of corneal astigmatism. We can even do bitoric designs for those patients who have high amounts of corneal astigmatism, as well as back toric and front toric designs. Most labs can provide nearly unlimited power ranges for hyperopia, myopia, and presbyopia. Thus, there is a higher likelihood of fully correcting patients' visual needs with a GP design.
Second, there are more design choices with GP materials. There are both simultaneous image designs and alternating image designs. Aspheric and concentric designs fall under the simultaneous image category. These lenses are great for patients who work at multiple distances during their day because they provide a range of vision, much like a progressive addition spectacle lens would do. As an added bonus with these lenses, patients report less distortion than with their spectacles.
Segmented, or translating, designs are in the alternating image category. These lenses work more like a traditional bifocal spectacle lens in that they have two distinct focal distances. These lenses are better for patients who have exacting visual demands. Patients generally get good vision at both distance and near, but intermediate may be blurred.
Third, GP lenses can fit a larger group of physiologic variables. Patients who have drier eyes can often wear a GP lens over a normal wearing day with less discomfort compared to a soft lens.
Fitting GP Multifocals
Pupil size is important with multifocal contact lenses. If pupils are extremely large, the patient may experience flare and glare at night with soft multifocals and some GP multifocal designs. As a rule, aspheric and concentric GP lenses work better if pupils are 5mm or less.
Segmented designs are less affected by pupil size, but more dependent on lid architecture. If the lower lid is too far below the lower limbus, the lens may not translate up into the proper position. If the lower lid is too far above the lower limbus, the near power may always be in front of the visual axis, resulting in poor distance vision. Lid laxity, which can increase with age, also affects the ability of all GP lenses to translate up on downgaze.
Both simultaneous and alternating image designs need to translate up to access the proper power area for near and/or intermediate vision. Soft multifocal lenses generally do not translate (the one exception being the Triton Translating Soft Bifocal from Gelflex), which can limit their ability to provide clear vision.
Lastly, GP lenses last longer than their soft counterparts, making them more cost effective in most cases.
All in all, GP multifocal contact lenses provide a larger array of design options and parameters, and therefore a greater likelihood of satisfying patients' visual needs, when compared to soft multifocal lenses. This can result in better success rates and happier patients. CLS
Dr. Benoit practices in a multi-subspecialty ophthalmology group in Concord, NH. He is a Diplomate of the Section on Cornea, Contact Lenses and Refractive Technologies of the American Academy of Optometry. He is currently vice-chair of the Section.