Challenges in Fitting Astigmatic Lenses… Do They Still Exist?
Today's toric contact lens technology bears little resemblance to earlier generations, as this lively exchange at SECO 2012 revealed.
W. Lee Ball Jr, OD, FAAO: Having worked together at VISTAKON, Dr Routhier and I've found that some of our experiences in optometry school were quite different, even though we graduated less than 10 years apart. Specifically, she had exposure to some technologies that I did not. Today, we're going to model a conversation that you may already have heard in your practices, especially if there's a generation gap between you and your associates. The basis for our conversation is the question: Do challenges in fitting toric lenses still exist?
Dr Ball: I learned that you can mask up to 1D of astigmatism with a soft spherical contact lens.
Janelle Routhier, OD, FAAO: I learned that you can mask astigmatism, too, but the toric lenses I learned to fit can correct as little as 0.75D of cylinder.
Dr Ball: Are there that many patients in our practices who have 0.75D of cylinder?
Dr Routhier: Believe it or not, many of our patients have astigmatism. A study by Graeme Young1 showed that almost half of our patients have at least 0.75D of astigmatism in one eye, while a third have a full diopter in one eye, and 24 percent have 0.75D in both eyes (Figure 1). So, there really are many patients who could benefit from a toric lens.
Figure 1. Almost half of a practice's patients have at least 0.75D of astigmatism in one eye, while a third have a full diopter in one eye, and 24 percent have at least 0.75D in both eyes.
Dr Ball: I hear what you're saying, but I'm not the only one who believes we can mask astigmatism with a spherical lens. Nearly a third of optometrists think a soft spherical lens can handle 0.75D of astigmatism.2 What's more, nearly 25 percent of our patients who have astigmatism are wearing spherical equivalent lenses,2 and I don't hear anyone complaining.
Dr Routhier: Patients don't complain, because they're what some practitioners call 20/happy (Figure 2). The eye chart at the top represents the vision of our 20/happy patients. They can read the 20/20 line, but it's not crystal clear. The letters on the chart at the bottom are much clearer, and that represents what vision would be like for a patient who isn't just 20/happy, but who can clearly see 20/20 or 20/15.
Figure 2. The top slide represents what “masked” astigmats who have been given the spherical equivalent of their sphero-cylindrical prescription would see -2.00/-0.75 X 180 (with -2.25D sphere). In the bottom image, it's clear that correcting even just a small degree of astigmatism can make a big impact on a patient's clarity of vision.
A topography map (Figure 3) shows an eye with about 2.50D of corneal cylinder. When we put a soft spherical lens on that eye, most of the corneal astigmatism still shows through. Even if we apply a higher modulus lens, such as a silicone hydrogel, the astigmatism shows through. So, essentially, instead of correcting the astigmatism the way a GP lens does when the tear layer fills in, we're simply placing a blur circle directly on the retina.
Figure 3. Topography maps help demonstrate that a spherical lens merely places a blur circle on the retina. It doesn't truly correct the astigmaism.
Dr Ball: I still don't think fitting soft toric lenses is worth the extra chair time. The visual improvement is minimal, and patients don't appreciate the extra time we spend with them. In fact, nearly half of optometrists spend an additional 5 minutes fitting a toric lens, and as many as a quarter of us spend 15 minutes.2 I can do another full examination in 15 minutes.
Dr Routhier: That may have been true in the past, but with today's toric lens technology and designs, you should be able to place a lens on an eye and the lens should be properly oriented by the time you move behind the slit lamp.
Dr Ball: That's definitely an improvement, but toric lenses are expensive. Our patients — especially those with low astigmatism — don't want to pay the extra money. They just want the cheapest option available. In fact, nearly 25 percent of optometrists think that only one of every 10 patients will appreciate what we're doing for them and be willing to pay for toric lenses.2
Dr Routhier: How do you know what your patients want if you don't ask them? Believe it or not, when asked by their doctor, two-thirds of current contact lens wearers would be open to switching to daily disposables, and 75 percent of spectacle wearers would be open to trying them.3 And keep in mind, some of those spectacle wearers may be contact lens dropouts who would like to give it another try with contact lenses.
Dr Ball: You make a good point. After I started offering daily disposables to nearly all of my patients, I was amazed at the number who wanted to try them. But why should I prescribe a soft toric daily disposable contact lens? To be frank, there isn't a lens on the market that's consistent or that I'm confident prescribing, nor is there one that's comfortable for my patients to wear the entire day.
Dr Routhier: I think the latest technology will change your mind. Let's start by discussing BLINK STABILIZED Design.
BLINK STABILIZED DESIGN
Dr Routhier: To appreciate BLINK STABILIZED Design, we need to understand the mechanics of the blink. During a blink, the upper lid moves up and down, and the lower lid moves horizontally toward the nose. BLINK STABILIZED Design harnesses the power of the blink, allowing the eyelids to work with the lens. This design has four zones of interaction, which helps decrease rotation due to gravity if a patient isn't looking straight ahead. Whether wearers are looking up, down or side to side, these zones of interaction help to keep the lens in proper position.
As Figure 4 illustrates, the blue areas are accelerated slopes that are activated when the lens is out of alignment. If the lens rotates, the accelerated slopes work with the eyelids, with the blink, to reposition the lens quickly. The lens is symmetrically weighted, so that if it's applied at 180º, it's really not upside down. It's essentially the same either way. This helps to limit the influence of gravity.
Figure 4. The BLINK STABILIZED Design of 1-Day Acuvue Moist Brand Contact Lenses is the same successful technology as in Acuvue Oasys Brand Contact Lenses for Astigmatism, but optimized for the daily disposable modality.
Another important aspect of this design is the thin profile. When a patient is wearing a traditional prism-ballast lens and the lower lid travels horizontally during a blink, there's potential for interaction with the thicker area of the lens. Lenses with BLINK STABILIZED Design have a thinner profile at the bottom, so there's less interaction with the lower lid.
Dr Ball: When I was in optometry school, I read about an experiment where optometry students wearing prism-ballast lenses placed their heads in an upside-down position, and the lenses didn't move at all. Are you saying gravity doesn't affect this lens?
Dr Routhier: That was quite a while ago, and it's true when a patient was 180º upside down, the lens didn't rotate; it just sagged. In more realistic situations, however, gravity plays a bigger role in the position of a toric lens. Recent studies have shown that when patients are in a recumbent position or have a 90-degree head tilt, the rotational stability provided by the BLINK STABILIZED Design is superior to peri-ballast and prism-ballast lenses.4-7
Dr Ball: And fitting this new technology lens takes less time to fit than older toric lenses?
Dr Routhier: Yes. We call it the “60-second fit.” One study found that nine out of 10 patients fitted with this BLINK STABILIZED Design lens were fit within 10 degrees of rotation within 60 seconds. At the 1-week evaluation, the lenses demonstrated consistent stability with 99 percent having less than a 10-degree change from the initial fit.2
Dr Ball: Another shortcoming of toric soft lenses is a lack of parameters. It's frustrating to talk to my patients about correcting their astigmatism and then learn that the needed parameters aren't available. The range of options is just too narrow. Nearly half of our colleagues believe there aren't enough parameters for their patients.2
Dr Routhier: The new lens I've been describing has nearly three times more parameters than any other daily disposable toric lens on the market. There are twelve axes and four cylinders, with minus powers from plano to –9.00D and plus powers from +0.25D to +4.00D. When combined with its spherical counerpart, we can fit 95 percent of our patients.2 What's more, the fitting kit contains extensive parameters, making it easy to fit patients that same day.
Not only does the lens orient on the eye quickly, the kit is designed so that you can locate the proper lens quickly. Each of the drawers is divided by axis, but before you open the drawer, you can see by the check marks whether or not the lens you need is in the kit. If it's not available in the kit, a guide on the drawer tells you if the parameter is available to order.
Dr Ball: You've told me about some great features of this lens, but what is it?
Dr Routhier: It's 1-DAY ACUVUE MOIST for ASTIGMATISM. We've already discussed its BLINK STABILIZED Design, the 60-second fit and the wide range of parameters, but what I haven't mentioned yet is that it's made with LACREON Technology. LACREON Technology, which is also found in 1-DAY ACUVUE MOIST spherical contact lenses, permanently embeds the wetting agent into the lens, so it won't leach out over time. That means your patients will have just as much wetting agent in their lenses when they throw them away at the end of the day as when they first apply them in the morning.
Dr Ball: Does this lens have UV protection like the other products in the ACUVUE family?
Dr Routhier: It certainly does. It provides Class II UV blocking* to help protect your patients' eyes.
Dr Ball: So, it's no longer necessary to mask low astigmatism with a spherical lens?
Dr Routhier: That's exactly what I'm telling you. The new toric designs are more predictable and reliable, and extensive research tells us that our patients with astigmatism have the same visual demands as any of our other patients. When performing life tasks, they need a product that will help them do what they need to do.
ACUVUE® Brand Contact Lenses are indicated for vision correction. As with any contact lens, eye problems, including corneal ulcers, can develop. Some wearers may experience mild irritation, itching or discomfort. Lenses should not be prescribed if patients have any eye infection, or experience eye discomfort, excessive tearing, vision changes, redness or other eye problems. Consult the package insert for complete information. Complete information is also available from VISTAKON® Division of Johnson & Johnson Vision Care, Inc., by calling 1-800-843-2020 or by visiting www.jnjvisioncare.com.
*WARNING: UV-absorbing contact lenses are NOT substitutes for protective UV-absorbing eyewear such as UV-absorbing goggles or sunglasses because they do not completely cover the eye and surrounding area. You should continue to use UV-absorbing eyewear as directed.
NOTE: Long-term exposure to UV radiation is one of the risk factors associated with cataracts. Exposure is based on a number of factors such as environmental conditions (altitude, geography, cloud cover) and personal factors (extent and nature of outdoor activities). UV-blocking contact lenses help provide protection against harmful UV radiation. However, clinical studies have not been done to demonstrate that wearing UV-blocking contact lenses reduces the risk of developing cataracts or other eye disorders. Consult your eye care practitioner for more information.
ACUVUE®, ACUVUE® OASYS®, 1-DAY ACUVUE® MOIST®, LACREON® Technology, BLINK STABILIZED™ Design, and VISTAKON® are trademarks of Johnson & Johnson Vision Care, Inc.
1. Young G, Sulley A, Hunt C. Prevalence of astigmatism in relation to soft contact lens fitting. Eye Contact Lens. 2011;37:20-25.
2. Data on file. Johnson & Johnson Vision Care Inc. 2011.
3. Data on file. Survey of 1,300 soft contact lens and spectacle wearers, Dec. 2009-Jan. 2010. Johnson & Johnson Vision Care Inc.
4. Zikos GA, Kang SS Ciuffreda KJ et al. Rotational stability of toric soft contact lenses during natural viewing conditions. Optom Vis Sci. 2007;84:1039-1045.
5. Young G, Mcllraith R, Hunt C. Clinical evaluation of factors affecting soft toric lens orientation. Optom Vis Sci. 2009;86:1259-1266.
6. McIlraith R, Young G, Hunt C. Toric lens orientation and visual acuity in non-standard conditions. Cont Lens Anterior Eye. 2010;33:23-26.
7. Chamberlain P, Morgan P, Moody KJ, Maldonado-Codina C. Fluctuation in visual acuity during soft toric contact lens wear. Optom Vis Sci. 2011;88:E534-E538.
|Dr Ball is Associate Director of Professional Affairs for Vistakon, a division of Johnson & Johnson Vision Care Inc.|
|Dr Routhier is Manager of Medical Affairs for Vistakon, a division of Johnson & Johnson Vision Care Inc.|