CONTACT LENS MATERIALS
Contact Lens Materials Update: Options for Most Prescriptions
New materials and lens designs offer more options for providing patients with good vision and healthy eyes.
By R. Alan Landers, OD, MS, and Andrew J. Rixon, OD
It's an exciting time in the realm of contact lenses. Patients who once believed they weren't good candidates for lens wear or who gave up wearing contact lenses for a variety of reasons can now wear them successfully despite their prescription or visual needs. We can attribute this advance to the research and development of new lens materials and designs. Existing lens wearers who have complaints of dryness, redness or end-of-day discomfort may benefit from these new materials as well.
Implementation of new hyper-oxygen transmissible materials, bifocal designs and materials that promote stable hydration represent just a few advancements in the contact lens arena. This article will look at some of the newer contact lenses on the market and indicate their clinical usefulness. We obtained information about packaging, parameters and clinical application from recent journal articles, the contact lens manufacturers, the December 2004 Tyler's Quarterly and Contact Lens Spectrum's Contact Lenses and Solutions Summary (www.clspectrum.com/CLASS).
Soft Hydrogel Lenses
Extreme H2O (hioxifilcon A, Hydrogel Vision Corp.) Many of you may know about Extreme H2O because it's been on the market for several years. However, this lens is now available in two options: G60S-thin and the new addition, G60S-Xtra. Table 1 provides the specifics of both lenses for a side-by-side comparison. The Extreme H2O contact lens is indicated for patients who have dry eye or who experience lens-induced dry eye, particularly toward the end of the day.
The water content of most hydrogel contact lenses changes upon application onto the eye, and throughout the course of the day, the contact lens begins to dehydrate. This loss of water can manifest clinically as decreased visual acuity, redness and dryness. These signs and/or symptoms result from poor lens movement and tear exchange secondary to tightening of the contact lens after dehydration. According to the manufacturer, the Extreme H2O contact lens retains its water saturation even while on the eye, which increases end-of-day comfort and overall stability of vision.
The "Xtra" option features a slightly increased center thickness in comparison to the "thin" version. This change may increase the lens's overall durability and ease of handling for patients.
Biomedics 55 Premier (ocufilcon D, CooperVision/Ocular Sciences Inc.) This recent two-week disposable soft lens features a front anterior surface that's designed to correct aberrations in the spherical lens as well as in the human eye. According to the manufacturer, this lens works especially well for patients who have low amounts of against-the-rule astigmatism. In addition, some patients in our clinic have reported improved comfort with this lens in comparison to their previous lenses. The improved comfort most likely results from the smoother, rounded-edge design that's 20 percent thinner than the standard Biomedics 55 design. Table 1 provides more detailed parameters for Biomedics 55 Premier.
Other items in this category worth mentioning include two contact lens name changes. Bausch & Lomb has renamed its Optima FW contact lens as SofLens 38 and its B&L Two Week lens as SofLens 59. This naming convention is consistent with the company's existing SofLens 66 contact lens, in which the 66 reflects the material's water content.
Figure 1. Hyperemia in a low-Dk lens wearer (top) and the reduction in limbal and bulbar hyperemia in the same wearer following 1 month of extended wear with high Dk silicone hydrogel lenses (bottom).
Silicone Hydrogel Lenses
Silicone hydrogel lenses became commercially available in 1998. Silicone rubber is highly oxygen permeable. However, it's also inherently hydrophobic, so lenses made of pure silicone tended to accumulate lipid deposits. To solve this problem, manufacturers combined silicone and conventional hydrogel materials, resulting in contact lenses that are highly oxygen permeable and have increased wettability and less affinity for lipids. Silicone hydrogel lenses have also nearly eliminated hypoxic complications (such as contact lens red eye, microcystic edema and the long-term effect of corneal neovascularization) (Figure 1) that commonly occur with traditional hydrogel materials, particularly in extended wear patients. Table 2 summarizes the parameters of three commercially available silicone hydrogel lenses.
O2Optix (lotrafilcon B, CIBA Vision) CIBA recently released the the O2Optix lens, which has approval for up to six nights of extended wear. This lens may prove a good option for patients who tend to overwear their current low-Dk/t contact lenses but who aren't interested in the 30-day continuous wear modality of the Night & Day lens (CIBA).
PureVision (balafilcon A, Bausch & Lomb) B&L will reintroduce its PureVision lens to the U.S. market in the near future. In addition, B&L has developed the PureVision Toric, the first toric silicone hydrogel, which is currently commercially available worldwide with the exception of the United States.
Acuvue Advance (galyfilcon A, Vistakon [Johnson & Johnson Vision Care, Inc.]) Vistakon has just launched Acuvue Advance for Astigmatism, the first toric silicone hydrogel lens available in the United States. It offers a unique accelerated stabilization design featuring the company's patented Stableview Technology. Acuvue Advance for Astigmatism also features the same material as Acuvue Advance with Hydraclear spherical daily wear lenses.
Soft Multifocal Lenses
Proclear Multifocal (omafilcon A, CooperVision) Over the past few years, several technological advances have occurred in the soft multifocal contact lens market. These advances have undeniably contributed to a more visually satisfied presbyopic patient. However, as a natural progression with age, many patients develop dry eye, which can result in contact lens-induced discomfort. The recent arrival of the Proclear Compatibles Multifocal offers a new alternative for presbyopic patients who experience dryness with contact lens wear. These multifocals feature the same material base as their proven spherical and toric predecessors. Omafilcon A is a Group 2 material that tends to resist dehydration and, in fact, remains the only material that's FDA approved for patients who have contact lens-induced dry eye.
This material can resist dehydration because it contains phosphorylcholine, a phosphorylated alcohol that's present in mammalian cell membranes and provides a biocompatibility that mimics a cellular interface. Based on the polar nature of the phosphate group in the phosphorylcholine molecule, you could deduce that it plays a role in hydrogen bonding with water molecules and, thus, hydration of the contact lens. In addition, the hydrophilicity of omafilcon A results in resistance to protein and lipid deposition.
Another advantage of this lens is that CooperVision has incorporated the same design it currently uses in its Frequency 55 Multifocal lenses. Table 3 lists the lens parameters. They're available in D lenses (center distance zone, aspheric intermediate zone and spherical near periphery) for the dominant eye and N lenses (center near zone, aspheric intermediate zone and spherical distance periphery) for the nondominant eye. Combining the near-centered and distance-centered lenses can create a more balanced visual state between the two eyes. We've found that this lens has proven advantageous for patients who can barely survive the discomfort of their contact lenses; by switching them to the Proclear Multifocal, most have become truly successful lens wearers.
Essential Solution (X-Cel Contacts Inc. and Blanchard Contact Lens, Inc.) The inherent difficulty that exists with any bifocal lens is the ability to provide patients with an acceptable happy medium between ideal vision and adequate vision. This challenge primarily results from a loss of near vision range that occurs with advancing stages of presbyopia. Alternating vision (translating) GP bifocals are advantageous to patients who require optimal near and distance vision. However, with the widespread vocational use of computers, the sacrifice of intermediate vision is often unacceptable to many patients.
In contrast, simultaneous vision aspheric lenses can provide patients with an adequate intermediate near range, but often cannot generate sufficient power at reading distances. Although modified monovision is often an option for these patients, some associated compromise in binocularity always occurs.
To address the lack of a system that completely encompasses the major three ranges of vision in maturing presbyopes, X-Cel Contacts Inc. and Blanchard Contact Lens, Inc. introduced the Essential Solution segmented aspheric multifocal. This lens combines the best attributes of X-Cel's Solution Segmented Bifocal lens and Blanchard's Essential Aspheric lens. Although you should fit this lens within the same selection criterion as required by other typical translating lenses, its value is undeniable for correct candidates and it can provide a seamless, confusion-free transition among focal points for many patients. Powers range from 10.00D to +6.00D at distance and +1.75D to +4.00D at near. The lens diameter is 9.3mm and seg heights are 1.0bcg and 1.5bcg. Furthermore, this lens uses the high-Dk Boston XO material (Polymer Technology).
Onsi-56 (onsifocon A, Lagado Corp.) One company has applied the same technology of silicone hydrogel lenses to rigid materials. The Lagado Corporation has developed Onsi-56, a rigid silicone hydrogel. Lagado has formulated this material to incorporate the better attributes of both types of lenses. Some of these attributes include the comfort and wetting properties of soft silicone hydrogels and the durability and permeability of rigid lenses.
According to Lagado, the lens maintains an internal rigidity because the polymer cannot absorb water into the interior of the lens, but it can hydrate externally similar to a soft silicone hydrogel. This lens provides a Dk of 56, a low wetting angle of 7.2 degrees and you can order it in all parameters and lens designs including torics and bifocals. The manufacturer recommends Lobob Optimum solutions for cleaning and disinfection.
Menicon Z (tisilfocon A, Menicon, Ltd.) Although silicone hydrogel materials have greatly expanded the continuous wear soft lens market, only one GP lens exists that provides the hyper Dk/t necessary to support this modality: Menicon Z, which currently is the only GP lens that has FDA approval for 30 days of continuous wear. Aspheric and spherical powers are available from 25.00D to +25.00D for daily wear and 25.00 to +8.00D for extended wear. It can correct up to 5.00D of astigmatism and up to +3.00D add powers are available. Menicon recommends the Claris (Menicon, Advanced Medical Optics) lens care system for all its products.
Optimum (roflufocon A, C, D, & E, Contamac Inc.) In some situations, a lens material may meet visual demands but fail to meet a patient's physiologic demands (such as high-Dk lenses that aren't wetting properly). To solve this situation, Contamac, Inc. has recently developed the Optimum family of GP materials for use with all GP lens designs and across the full spectrum of wearing modalities. Optimum lenses provide a comprehensive range of lens materials that include: Optimum Classic (roflufocon A), Optimum Comfort (roflufocon C), Optimum Extra (roflufocon D) and Optimum Extreme (roflufocon E), with Dk values (ISO method) from 26 to 125 (mm Hg). According to the manufacturer, this family of GP lenses is designed to deliver high levels of stability, advanced comfort and enhanced wettability.
Show What You Know
The challenge of selecting the appropriate contact lens for the individual needs of each patient remains the clinician's responsibility. Furthermore, educating your patients regarding the rationale behind the lens selection process is integral to their appreciation for the benefits they may experience with a particular lens material or design. Communicating this information to each contact lens patient not only helps to validate your expertise in using newer technology lenses, but it also reinforces to patients that their primary eyecare physician is working to meet their visual demands while preserving their overall ocular health.
The authors acknowledge Charlie Conner, OD, PhD, professor of Optometry at the Southern College of Optometry, for his help with this article.
|Dr. Landers is a faculty member at the Southern College of Optometry. He's enrolled in the Integrated Program of Biomedical Sciences at the University of Tennessee Health Science Center in Memphis, TN where his research emphasis involves biomaterials and biocompatibility.|
|Dr. Rixon is a clinical instructor at the Southern College of Optometry. He's a 2003 graduate of the Pennsylvania College of Optometry and completed a Family Practice Residency at West Tennessee Eye in Millington, TN.|