Since the release of the first silicone hydrogel toric lens for two-week replacement, Acuvue Advance for Astigmatism (Vistakon), the market has trended wisely toward monthly replacement regimens with more recent toric designs. Research has supported the suspected clinical fact that patients are more compliant with a monthly replenishment schedule, and the newer silicone hydrogel materials, with their superior protein deposit resistance, oxygen permeablility and improved performance in patients with marginally dry eyes, support this trend as well.1 Over the last year, we have seen the release of two more silicone hydrogel toric designs—Air Optix for Astigmatism (CIBA Vision) and Biofinity Toric (CooperVision)—joining the well-established monthly replacement toric lens, PureVision toric (Bausch + Lomb). Some practitioners also use the Acuvue Oasys for Astigmatism lens (Vistakon) as a monthly replacement lens, although the manufacturer recommends one- to two-week replacement.
Excluding patients with very high astigmia or ametropia, we now have the luxury of fitting our astigmatic patients in a planned replacement silicone hydrogel. All of these options are used in my practice to offer each patient the very best choice for their individual needs, but each of these lens designs has their strengths and weaknesses.
Although all of these lenses are available for the average patient’s distribution for power, corneal diameter and morphology, they do have individual characteristics that make each lens unique and therefore, better suited for certain individuals. Some of these factors are predictable, such as a high modulus lens being better suited for irregular astigmatism, or a larger lens being a better choice for a greater visible iris diameter. But, factors such as edge design comfort and tear film interaction are more difficult to predict. As eye care practitioners, we must get into the habit of comparing two different lenses side by side during the initial fitting experience to gather information more quickly and choose the best lens for each patient’s individual demands.
SiHy Toric Options
Acuvue Oasys for Astigmatism (8.6mm base curve, 14.5mm diameter) followed Acuvue Advance, the first silicone hydrogel for astigmatism. The lens is very comfortable initially and orients extremely quickly due to its accelerated stabilization design and low modulus. Because of the four zones of stability, at 2:00, 4:00, 8:00 and 10:00 o’clock, this lens can equilibrate in as little as three minutes. These characteristics also make the lens assume an ovoid shape off the eye, due to the variable edge thickness, which can be easily explained to patients. The 12:00 and 6:00 o’clock base positions are both marked with line indicators, which means that there is no set top or bottom to the lens, and these positions can interchange without affecting the fit. Parameters are somewhat limited, in that the -2.25D cylinder power is not available in most oblique axes (30, 40, 50, 60, 120, 130, 140, 150), is only available in axes 10, 20, 90, 160, 170 and 180 over -6.50D sphere powers and not available at all in the plus sphere powers. This lens is made in the senofilcon A 38% water material (Dk approximately 95), with the Hydraclear Plus wetting agent incorporated with the material as well as Class l UV blocking. It is approved for up to seven days extended wear.2 There is some question as to the durability of the wetting characteristics of this material; some patients notice significant coating or increased dryness as the weeks progress. But when initially placed on the eye, this is an extremely comfortable lens. Patients with high-viscosity tear film or ocular allergies with increased mucus secretions may need to replace this lens more often than biweekly. Of course, all silicone hydrogels attract oily deposits, and patients should be warned to avoid the use of moisturizers or oily make-up removers around the eyes. Recommend the use of water soluble mascara and diluted baby shampoo solution (five parts water to one part baby shampoo) for eye make up removal.
The PureVision Toric has the highest modulus of all the lenses in this group.3 A cast-molded, back surface toric made of balafilcon A with 36% water content, it is the only monthly replacement toric lens approved for up to 30 days continuous wear. It is the smallest diameter lens at 14.0mm, with an 8.7mm base curve and a Dk of 94. The lens is stabilized with a prism ballast, aspheric optic zone and a bicurve posterior design.4 The inferior base position of the lens is marked by three lines at 5:00, 6:00 and 7:00 o’clock. This lens also has a uniform mid-peripheral thickness at the apex, center and base of the optic zone.The manufacturer recommends allowing 10 minutes for the lens to stabilize before evaluating the fit. This lens can have excellent initial comfort—despite the high modulus—and can even be used in irregular astigmatism or pellucid marginal degeneration. Even some patients wearing piggy-back tandem lenses (rigid gas-permeable over soft carrier) have been able to obtain good vision with this lens when converted. The -2.25D cylinder is available around the clock in 10° increments in sphere powers ranging from +6.00D to -9.00D. To maintain wettability and resist deposits, an Argel design with Performa surface treatment is used to change the inherent wetting characteristics of the material, transforming the hydrophobic silicone to hydrophilic silicate.
Air Optix for Astigmatism is the lowest water content lens in this group, and therefore, it dehydrates less over time and during the normal monthly life of the lens due to the unique surface plasma coating. With the highest clinical oxygen permeability in the limbal zone and its 4:00 and 8:00 o’clock ballasting, the perilimbal conjunctival area remains extremely “white,” with less edema, even in high ametropias. This lens usually stabilizes in 30 seconds—especially if inserted near the correct orientation. It has been shown to absorb less lipids over time.5 The Air Optix lens for Astigmatism has limited high minus availability; -9.00D, -9.50D and -10.00D powers are available in limited axes, and the -2.25D cylinder is not available in any plus powers. Plasma treatment is used to create a permanent, chemically bonded wetting surface. The thickest points of the lens edge are at 8:00 and 4:00 o’clock to promote lens comfort and increase oxygen transmission at 6:00 o’clock. The lens material, lotrafilcon B 33% water, has a Dk of 112, with medium modulus and is approved for up to six nights of extended wear. Predictability and quality control with this lens are excellent; however, the axis indicator marks can be difficult to see in some cases—markings are at 3:00, 6:00 and 9:00 o’clock. This is a very durable workhorse lens with excellent optics. CIBA Vision has announced the expansion of parameters to all axes in 10° steps, in all available sphere powers and cylinder choices, as of November 2010.
The most recent entrant to the monthly silicone hydrogel toric market is the Biofinity Toric. This lens is a naturally hydrophilic lens due to inherent wettability without coatings, wetting agents or surface treatments. The material has the lowest modulus of this group, with the lowest wetting angle and the highest Dk of 128.6 The water content is the highest of the silicone hydrogels: Comfilcon A is 48% water, and this lens uses an optimized ballast design, which is consistent across all power ranges. The base is marked with a single line at 6:00 o’clock. Parameter availability is the most complete, with all cylinder powers (up to -2.25D) available in all sphere powers from +8.00D to -10.00D in 10° increments around the clock. This lens has been successful in refitting those stubborn hydrogel toric patients for whom none of the other silicone hydrogel toric options have been comfortable or successful. One drawback to this lens is that it can tear more easily than the other silicone hydrogels, so it pays to warn your patients to hydrate the lens before removal to prevent cracking and tearing, especially at the end of the day when dehydration is most prevalent. This lens is approved for six nights extended wear.
All silicone hydrogel toric choices are a great improvement over their hydrogel predecessors. Reliably, patients experience less conjunctival and limbal redness, less corneal edema and neovascularization as well as giant papillary conjunctivitis (GPC). And, as we now know, monthly replacement leads to simpler care regimens and better compliance. The lenses are all very easy to handle, and I have not found adaptation to be significantly different among these brands, as long as the trial lenses demonstrate good fitting characteristics.
But, how do we apply all these great products and knowledge clinically? Based on the patient’s physical characteristics and needs, select the two lenses that are most likely to fulfill these requirements and proceed with a diagnostic fitting. Comparing two different lenses side by side, one can compare the comfort, stability, wettability and vision for each individual patient.
In most cases, dispense the two different lenses for the first week or two. At the follow-up visit, one brand will emerge as the best choice for that patient. For example, if the patient has a smaller-than-average visible diameter and marked dryness at the end of the day, I would select the PureVision Toric and the Air Optix for Astigmatism to start. If the patient had been a previous failure with silicone hydrogels and was stuck with the poor physiological response associated with hydrogel lenses, I would choose the Biofinity Toric for one of the options. If the patient demonstrates microscysts or has long demands on wearing time, I would select the most permeable options: Biofinity Toric and Air Optix for Astigmatism. For any irregular astigmatism or handling difficulties, such as patients who tear their lenses more frequently, choose the lens with the highest modulus—Purevision toric. Patients who have unstable rotation with standard designs or are exquisitely sensitive to edge feel would be good candidates for the Oasys for Astigmatism or other lower modulus materials. Keeping all the comparative characteristics in mind, one can preselect the lens most likely to succeed. For the difficult patient, you can save chair time by comparing two lenses at once, rather than having the patient return each time for a trial with another design.
Cultivate Lasting Doctor-Patient Relationships
Refitting current toric patients from hydrogels into silicone hydrogel torics is a great opportunity to cement your relationship with your patient. By doing so, you demonstrate concern for your patient’s eye health and show that you are on the cutting edge of practitioners. Pave the way by inquiring if the patient has dryness at the end of the day, spectacle blur, ongoing redness or discomfort. Ask specific questions—if you ask whether everything is okay with the lenses, patients will likely say, “Sure!” But, if you ask whether their lenses get dry at the end of the day or their eyes get red, or if their lenses coat with protein as the weeks progress, patients will usually admit that they do. Then you might say, “I’d recommend that you be refit with new astigmatism-correcting lenses that breathe more, deposit less and generally improve comfort at the end of the day. It is a process to determine which lens is best for you, so we dispense diagnostic lenses for you to use and then evaluate them after two weeks to determine your final prescription. Your refitting fee will be X amount. These lenses are monthly (or planned) replacement, and the total cost of the lenses may be comparable to what you are currently paying.”
Early presbyopic patients in spherical lenses who have small amounts of residual astigmatism also present a significant pool of potential patients. Due to the decreased ability to accommodate and compensate for residual astigmatism, these patients have more blur from that uncorrected 0.75D of astigmatism. This patient could benefit from being refit into toric silicone hydrogels. Don’t hesitate to bring up the topic of switching lenses. To such a patient, you could say, “I see that your vision is no longer 20/20 with your contacts. You have a small amount of astigmatism that was not corrected with your soft lenses, and it is now causing more blur as your focusing ability has decreased. Toric soft lenses would give you better vision and less eye strain, and the newer lenses that we have are more comfortable and easier to wear than ever.”
SiHy Torics for All?
The most demanding patient, of course, is the one with high ametropia (greater than +6.00D or -12.00D) or astigmatism greater than -2.50D. For these patients, silicone hydrogel toric lenses are not currently available, which is ironic because these are the patients who need such products the most, as they are more dependent on their contact lenses and have greater physiological challenges with thicker, less permeable hydrogel lenses. Hopefully, a custom or expanded parameter silicone hydrogel toric contact lens becomes available in the very near future, and our patients can begin to realize the benefits this modality can offer.
1. Dumbleton K, Woods C, Jones L, et al. Patient and practitioner compliance with silicone hydrogel and daily disposable lens replacement in the United States. Eye Contact Lens. 2009 Jul;35(4):164-71.
2. Tyler’s Quarterly Soft Contact Lens Guide. March 2010.
3. Ross et al. 2005. Poster Presentation, BCLA.
4. Tyler’s Quarterly, March 2010.
5. CIBA Vision. Data on file. 2006.
6. CooperVision, Data on file. 2009.
Dr. Keech is currently in private practice in Shoreline, Wash.
Dr. Keech is currently in private practice in Shoreline, Wash.