The Road to GP Comfort
GP LENS COMFORT
The Road to GP Comfort
GP lens comfort has never been easier to deliver, but you must make the right choices along the way.
By Roxanna Potter, OD
Dr. Potter is currently in private practice in Sylvania, Ohio. She has designed and participated in numerous research projects and has given lectures to both students and optometrists on eye-related topics.
The benefits of GP lenses are numerous. They provide better optics, easier handling, excellent oxygen transmission and tear exchange, and fewer ocular health complications. GP lenses can also boost practice growth through patient loyalty and can even increase profit margins.
However, when ideal GP lens candidates ask about their contact lens options, many of us are hesitant to recommend GPs even knowing these benefits. What often holds us back is either the fear that patients will be reluctant to try GPs — whether because of bad memories of older materials or of horror stories from poorly fit friends — or our own notions of GP lens discomfort. Ideally, the choice to start a new fit with a GP lens should be based not on these feelings, but rather on the potential for optimal vision in a comfortable modality, yielding a successful, satisfied patient.
Fortunately, we have support on our journey toward this goal. From the relentless work of GP researchers in materials, designs, manufacturing and solutions, we have advances in every area of GP lens fitting that are just waiting to be utilized. It's never been easier to back up our promises of comfort and satisfaction to a potential GP lens patient, but it does take a few conscious decisions along the way to create the right lens for each patient.
Getting Started: Patient Selection and Examination
I used to hesitate when recommending a GP lens to patients who have many years of soft lens wear in their history, fearing that they would immediately react negatively to GP lens application. I was much more likely to recommend GPs to a younger patient with no previous lens experience. But whether because of decreased corneal sensitivity with aging, additional patient education about adaptation delivered in a positive and upbeat manner, or the immediate, overwhelming improvement in vision, my experienced soft contact lens patients have been surprisingly indifferent upon initial GP lens application.
Regardless of age, I recommend utilizing one often underused tool to gather some data prior to the lens order: the manual keratometer. Topographers provide excellent information on irregular or limbal-extending astigmatism, but for most patients manual readings provide great results with the first lens attempted. You can also assess the patient's tear film stability just by paying attention to the keratometry mires. You can use this direct assessment to quickly measure tear break-up time or to dynamically observe the behavior of the tear film. For example, mires that are clear after a blink but then distort can indicate a volume deficiency or evaporative cause; mires that distort immediately after the blink and clear the longer the eye is held open may indicate a lipid or oily imbalance. This information may affect your decisions on the next leg of the fitting process.
Plan Your Route: Material Selection
There is no single material that is successful for every patient. Factors such as surface wetting, resistance to deposits, oxygen transmissibility and flexure must be considered when selecting a material. We've all learned the old rule that lower-oxygen-permeability (lower-Dk) lenses are more stable and wettable; however, with new technologies and fluorosilicone acrylate material advances, we are very close to making this rule obsolete. The newest hyper-Dk materials are now boasting excellent stability, deposit resistance and inherently wettable surfaces despite having Dk values greater than 100.
With a Dk of 141 (ISO/Fatt) and availability in a large range of parameters and designs, Bausch & Lomb's Boston XO2 is a welcome new member to the growing Boston materials family. Menicon Co. Ltd's Menicon Z offers the highest Dk available in GP contact lens materials today as well as continuous wear approval, which may be appealing to many new GP lens wearers. Another beneficial trait of this contact lens material for a novice GP lens patient is its superior resistance to physical damage, breakage or scratches due to a unique siloxanylstyrene component.
When wettability is a concern, Contamac's Optimum line of materials reports some of the lowest wetting angles of all the hyper-Dk materials and comes with a one-year performance guarantee to back up this claim (when used with Lobob Laboratories' Optimum GP solution). With a Dk of 125, Optimum Extreme has a wetting angle of just 6 degrees (receding dynamic contact angle), and the only slightly less oxygen-permeable Optimum Extra (100 Dk) features a remarkable wetting angle of 3 degrees. The upcoming release of Optimum HR, a range of high-refractive-index materials, will likely prove useful in many new designs.
This isn't to say that older materials don't have a place in our GP lens fitting armament. There are occasions when flexure is a desirable outcome, or when a patient has a history of problems with fluorinated materials. Younger patients who have higher oxygen needs or patients with high prescriptions will require higher-Dk materials, whereas wettability should be a priority for presbyopes or for patients who are prone to deposits.
GP laboratories have consultants who can recommend their favorite materials, or you can find a comprehensive listing of materials and their properties on the Gas Permeable Lens Institute's Web site (www.gpli.info). It's important to determine which materials have breakage warranties or replacement guarantees because new GP wearers are more likely to break a lens during the first few months of handling and caring for their new lenses.
Construction Ahead: Design Options
Computer-guided lathes and more stable materials have helped usher in a wave of new lens designs that can provide better comfort in numerous ways. Manufacturing techniques are also now so consistent and repeatable that designs can be reproduced perfectly and reliably on every lens ordered. In general, thinner, lighter lenses are often more comfortable and are usually lenticulated.
Art Optical offers a design called Thinsite that, in place of a standard lenticular, uses junctionless aspheric front and back surfaces to reduce lens mass by up to 48 percent when compared to a standard tricurve GP lens (Figure 1). Thinsite also increases oxygen transmission because of thinner lens centers in plus powers and thinner edges in minus powers, and the junctionless front surface reduces initial lid interactions. In high powers, Thinsite can help achieve centration for heavy and low-dropping lenses. I often use this design if I desire the benefits of a large diameter without the extra weight and thickness. Most laboratories have at least one or more thin lens designs available.
There are also peripheral curve design options that can enhance initial comfort in some patients. The Naturalens from Advanced Vision Technologies features Variable Inverse Periphery (VIP) technology that uses an innovative peripheral curve design to help improve the relationship between the posterior surface of the lens and the corneal surface. The VIP uses a channel of peripheral tear reservoirs that help enhance tear exchange and oxygen delivery without the need for increased edge lift. By keeping edge lift to a minimum, lens awareness experienced with the lid over the edge of the lens can be reduced, as can excessive midperipheral bearing (Figure 2). The Naturalens also helps provide better overall tear distribution, which may benefit patients who have suffered from 3 o'clock and 9 o'clock staining or dryness issues in the past.
Figure 1. Thinsite (Art Optical) vs. a standard tri-curve lens.
Figure 2. Traditional midperipheral bearing of a standard spherical design (left) and Naturalens Variable Inverse Periphery (VIP) Technology design (right).
Many laboratories utilize inventive designs to create lenses that are more comfortable than the standard tricurve lenses of the past. Don't be afraid to ask consultants what their most comfortable designs are and what parameters and materials are available in those designs.
Another factor that may seem obvious but is often overlooked is: for patients who have corneal cylinder >2.50D, plan on fitting a toric GP lens. Remember that doing so will not only provide better vision, but will also help the lens fit more comfortably on the anterior corneal surface. When there's less corneal cylinder but significant residual astigmatism over a spherical lens on over-refraction, consider trying one of the many aspheric designs available today rather than going to a thicker and less comfortable front toric. If you've already achieved an ideal fit with a spherical lens or if you own a spherical fitting set, then ask your preferred laboratory upon ordering if it can add a panafocal polish to the front peripheral surface of the lens. In mild cases of residual astigmatism, this aspheric polish can improve vision without the need for a front toric design.
Are We There Yet? Finishing Touches
Plasma Treatment Of particular interest for new GP lens patients, plasma treatment is an option to help maximize initial GP wetting and therefore comfort upon dispensing. Utilizing cold gas plasma, this process is able to remove residues and contaminants from a finished lens, resulting in a hydrophilic surface with lower wetting angles (Figure 3). Be careful when discussing this treatment with your patients to not describe it as an extra "coating" or "layer." Rather, I like to explain the process as a way to "super clean" a lens after it's made to provide the cleanest and freshest surface possible.
The value of plasma treatment lies not in long-term comfort, but only in initial wetting; the longer a plasma-treated lens is worn and handled, the more the surface is contaminated and the treatment loses its effectiveness. As soon as the lens leaves the plasma chamber it is an exposed surface, so handle it as little as possible before dispensing to the patient. Plasma-treated lenses are wet-shipped, but use caution prior to patient dispense, as cleaning and exposure to solution preservatives will immediately start to affect the vulnerable surface. However, the treatment is inexpensive, and any additional wetting and comfort we can provide our patients with their first GP lens is valuable.
Figure 3. Non-plasma-treated GP lens (left) and a plasma-treated GP lens (right).
GP Lens Care The perfect GP lens must be cared for with a compatible solution, so help your patients understand which solutions are appropriate for their needs. Some deposits require the mechanical abrasives in Boston Original or Boston Advance (both B&L) to break them down before soaking, whereas the solution properties of Lobob's Optimum or Menicon's Menicare GP can more easily remove lipid coatings.
It's amazing to me how few of my patients are aware that peroxide-based solutions can also be used on GP lenses. Clear Care (CIBA Vision) is something I recommend for any GP wearer who has a history of allergies, deposits, wetting difficulties or solution sensitivities. However, some patients prefer the more viscous GP-specific solutions on application, so in these cases I recommend Clear Care for an occasional deep clean that can help remove what other cleaners may have left behind.
Be careful not to recommend solutions with abrasive cleaners (such as Boston Original or Advance) for lenses made of the newer fluorosilicone acrylate materials or for lenses that have been plasma-treated, as the cleaners can damage the surface integrity of the lens. When educating your patients about lens care, keep in mind recent FDA guidelines that caution using tap water to rinse lenses and cases. Many public water systems are full of petroleum waste by-products that can cause complications such as foggy or filmy vision and non-wetting. A new multipurpose solution from Advanced Vision Technologies called Naturalens RDS (Rinsing Disinfecting and Storing) is now available specifically as a no-tap-water rinsing system. This solution has the potential to improve and maintain long-term patient comfort and provide an increased consistency of vision when used correctly.
Lens Dispensing On the day of the initial dispensing, prepare for the patient's arrival. Make sure the lenses have been verified, cleaned and have been soaking for at least four hours (preferably longer if possible) prior to application. If this isn't possible, have the laboratory wet-ship the lenses to you so that they are maximally hydrated before the initial application.
If a patient does report an excessive amount of lens awareness on application, don't hesitate to rerinse or perform a quick edge polish if not contraindicated. Be ever aware of the often overlooked solution sensitivity reactions, and use a topical anesthetic to allow for a comfortable period of gradual adaptation during lens settling time.
Large-Diameter GPs: A Growing Trend
One final trend that's important to mention is the recent growing interest in larger-diameter GP lenses, which other articles in this issue emphasize. Previously reserved for irregular corneas (and often as a last resort when other designs had failed), limbal, corneal-scleral and scleral lenses are beginning to show promise as successful initial designs for patients who have potential comfort issues. The basis for this trend is that larger diameters tend to be more comfortable because they evenly distribute the weight and bearing of the lens across the corneal and scleral surfaces. This trait contributes to the comfort of soft lenses.
Art Optical has partnered with Dakota Sciences to offer the SO2 Clear corneal-scleral lens, which has an average diameter of 14.0mm (Figure 4). Although relatively new, this lens has demonstrated promising comfort and vision on both irregular and regular corneas.
Similarly, Valley Contax offers a lens for enhanced comfort and centration called Comfort XL. It's available in diameters of 11.0mm to 12.5mm. If you're hesitant to initially use the larger scleral lenses, then start with a lens of 10.0mm or so, such as the Naturalens or the Comfort Zone 5 from ABBA Optical. I've come to appreciate the benefits of larger diameters so much that I rarely fit any regular cornea with a lens diameter less than 9.5mm.
Figure 4. SO2 Clear lens (left) and SO2 Clear lens-to-cornea fitting relationship (right).
What Are You Waiting For?
It's clear that there's never been a better time to recommend GP lenses for the first time to any patient. With new materials and designs, we can confidently speak with our patients about the advances that have been made to provide excellent vision without sacrificing comfort. CLS
I would like to acknowledge Keith Parker of Advanced Vision Technologies for information used in this article.
Contact Lens Spectrum, Issue: October 2008