COMBINATION LENSES

New Concepts in Combination Lenses

Whether hybrid or piggyback, newer combination lens designs let you offer GP optics with soft lens comfort.

By Robert L. Davis, OD, FAAO; S. Barry Eiden, OD, FAAO; & Mary Anne Murphy, OD

Choosing a contact lens design for a patient can be as easy as selecting a diagnostic lens from your inventory, or it can involve considering multiple variables such as convenience, comfort, vision, lens durability, care solutions, and handling. The quick and easy approach is not always in a patient's best interest. Both soft and GP lenses may provide adequate optical performance, though subtle characteristics often make the difference between a content patient and one who is enthusiastically satisfied. For example, soft toric lenses often perform satisfactorily, providing good vision in many patients—but we have found that when asked, patients frequently say that the vision fluctuates with blinking.

Soft contact lenses, in general, are acceptable for the majority of our patients, but when given an opportunity to compare the optical quality of a soft lens to a GP lens, our patients will generally select the optically superior performance provided by the GP contact lens. Conversely, soft contact lens comfort may overturn a patient's decision for an optically superior modality.

Combination Lens Options

This is where combination lens designs—defined in this article as a combination of GP and soft lens materials—can offer the best of both worlds. For example, the combination of a separate soft and GP lens in a piggyback system helps many of our irregular cornea patients benefit from the comfort of a soft lens and the optics of a GP lens.

Likewise, unlike soft toric lenses, the rotation of a hybrid contact lens (a single lens with a central GP portion combined with a soft skirt) does not cause blurring of vision because of the tear layer between the GP portion of the lens and the central cornea. The soft peripheral skirt provides improved comfort. Lipson (2007) compared hybrids to soft toric contact lenses and found that subjects preferred soft toric lenses 56 percent of the time with regard to comfort, but the hybrid lenses provided significantly better visual acuity. Of the seven previous GP wearers, five (71.4 percent) preferred the hybrid lens technology, suggesting that comfort may be a more important criteria compared to vision. Certain patients will not tolerate traditional GP lens designs because of discomfort, and certain patients demand more optical performance than that delivered by a soft toric design.

The purpose of this article is to provide a working model for fitting patients with newer soft-GP combination lenses and to provide pearls in making this design concept successful for your patients.

Fitting Combination Lenses

As mentioned previously, one combination system is the piggyback approach, which has been around for many years. While a standard, high-Dk soft lens can be used as the base, another approach is to use a customized soft lens that features a carrier that “holds” the GP lens. A new example of this is the Recess Pillow Lens System (RPLS) (Fusion Technologies), in which a GP lens rides on top of a soft lens that has a center recess cut out portion (Figure 1). The RPLS utilizes a hydrophilic base lens with integrated anterior recessed geometry that allows for a customized GP lens to be placed within the recess carrier. The hydrophilic portion creates a new resultant anterior corneal surface curve that is more regular and flatter.

Figure 1. Recess Pillow Lens System.

The thickness of the soft base lens modifies the central corneal curvature, so the GP portion is fit 0.1mm flatter to parallel the resultant central curve. The rigid lens performs only as an optical refractive surface, and the recess pillow lens combination moves as a single unit. The ideal curvature for the RPLS hydrogel component is the same as that for a normal hydrogel lens. Slight movement is necessary for corneal physiology. The cutout portion of the soft lens is 0.3mm larger than the rigid lens component. The RPLS can use any GP material ordered from your GP lens laboratory. The soft portion of the RPLS can be fabricated in any hydrogel material from a customized laboratory.

Also previously mentioned, a second combination lens approach is a hybrid lens design, and one example of this is the SynergEyes lens (SynergEyes), which has a GP lens center bonded to a soft peripheral zone. The SynergEyes Duette is a newer design in which the GP portion is a UV-blocking, 130-Dk material. The low-modulus silicone hydrophilic skirt of the SynergEyes Duette is an 84-Dk lens material.

The goal in fitting these hybrid lenses is to have the GP portion parallel the radius of the cornea, similar to the alignment fitting of traditional GP lenses. To fit with an alignment fitting philosophy, the SynergEyes design must have a minimum of 0.50D of apical clearance between the anterior corneal surface and the posterior GP surface. The tear layer resulting from this apical clearance will protect the cornea from potential friction induced by the cornea and contact lens surfaces rubbing against each other.

In situations in which there is greater than 1.00D of corneal toricity, the simplest approach is to use a mid-K fitting philosophy calculated by using the average of the flat and steep keratometric meridians. This will result in a fitting relationship in which tears can adequately flow beneath the lens, providing nutritional support and a sufficient fluid barrier necessary for proper corneal physiology. Using traditional low-molecular-weight sodium fluorescein to assess the fitting relationship between the cornea and GP portion of the lens will reinforce the fitting relationship that your topographical map has presented. The sodium fluorescein observation is the space that is quantified by the principal meridian curvature identified by your topographer and your base curve lens selection. Once you become comfortable with the fitting process, you can eliminate sodium fluorescein from your fitting procedure to save time. In our clinic (EyeVis LLC), we have performed base curve optimization studies comparing sodium fluorescein patterns and optical coherence tomography (OCT) measurements to analyze the fitting relationship (Figure 2). We've found that selecting the base curve empirically, using the mid-K approach, is as successful as using sodium fluorescein.

Figure 2. An OCT image of a SynergEyes lens.

After selecting the appropriate base curve for the GP portion of the hybrid lens, it is necessary to refine the fit by selecting the ideal soft lens curvature. The role of the hydrogel portion is to provide optimum comfort and lens positioning necessary for a successful outcome. The fitting goals for the hydrogel component are adequate movement equal to a soft lens design, centration for optimal viewing, and corneal coverage with the lens tucked under the upper and lower lids for comfort. If the hydrogel component is too steep, the lens will tighten significantly over time, creating scleral impingement, lens seal-off, and decreased wearing time. This is an important consideration in an effort to avoid acute red eye syndrome (ARES) or contact lens acute red eye (CLARE). The ideal skirt curve for the SynergEyes design is the flattest possible that does not cause skirt curve fluting (Figure 3). The soft portion of the lens in both the SynergEyes A series and the Duette platform may tighten over time. Waiting five to seven minutes after lens application will allow for a more realistic evaluation of the fitting relationship. A skirt that is too steep may result in red eye, lens seal-off, and discomfort at the two-week follow-up visit. Changing to a flatter skirt should address these issues and prevent a potential fitting failure.

Figure 3. Edge fluting from a too-flat hybrid lens skirt.

After selecting the proper base curve and skirt curve, the next step is to apply the hybrid lens onto the eye. Air bubbles, debris under the lens, and poor surface wettability can make the best-fitting lens unsuccessful. When applying the lens, fill the concave bowl of the rigid portion with an artificial tear or rewetting drop. Balance the lens on your index finger or on the supplied inserter. Be sure to hold open the patients' fissure to avoid eyelid interference during application. Apply the lens on the inferior portion of the cornea and push it toward the superior part of the cornea with a single motion. This spreads the wetting agent to allow coverage of the entire anterior surface, forcing any air between the cornea and lens towards the superior cornea and out from beneath the lens. Use a slit lamp or hand-held blue light to observe the lens on the eye, making sure there are no air bubbles or debris beneath the lens. Occasionally, the peripheral soft skirt may roll under the lens, which is usually an application error; reapplication of the lens will resolve this problem.

Creating a successful hybrid fit involves not only selecting the appropriate lens design, but also other factors such as educating potential candidates about this and other lens types as they relate to comfort, convenience, vision, lens replacement schedule, care regimen, and wearing time. The primary goal in selecting the best lens for any patient is to meet the patient's comfort and vision requirements with a lens design that provides uncompromising ocular health. Problem solving, addressing patients' complaints, and observing potential fitting complications will result in successful patient outcomes.

Benefits of Combination Lens Designs

Combination lens designs have been used to solve many problems associated with vision and contact lens complications—and ultimately to reduce dropouts. Contact lens dropouts have contributed to a flat contact lens market. Combination lens designs can address common problems that can lead to dropouts associated with lens awareness, irritation, peripheral corneal 3 o'clock and 9 o'clock staining, dellen, and vascularized limbal keratitis (VLK). A silicone hydrogel skirt or base combined with a silicone-acrylate GP center helps reduce problems associated with oxygen transmissibility. The GP portion addresses any problems with soft lens-related reduced visual acuity and reduces the fluctuation of vision experienced with a soft toric lens design. The combination platform increases lens stability, providing better centration, and reduces lens flexure, enabling you to fit patients who have higher amounts of astigmatism.

In addition, incorporating a UV-blocker into the GP portion (standard in the Duette hybrid and also available in some silicone hydrogel materials for the RPLS) provides an enhanced therapeutic protection for patients at risk for age-related macular degeneration and cataracts.

The reverse geometry design of the Duette lens provides a 0.75mm knee junction supported 360 degrees around the optical zone, which was absent in the original SynergEyes A design. This support counteracts the forces of the lid on the lens to help prevent lens flexure with the blink. The 7.0mm optical zone helps improve lens centering, resulting in less flare and glare from pupillary dilation at night. With the enlarged optical zone and GP center material, the Duette design solves these potential hazardous visual conditions that can occur at night when the pupil is dilated.

A primary advantage of the Duette hybrid lens is ease of fit, with only five base curve selections and three skirt curve designs. Therefore, fitting these lenses can be an efficient use of chair time.

The RPLS can be fabricated in any design configuration including with a toric GP lens correcting for lenticular astigmatism as well as abnormal corneal curvature configurations. The primary advantage of the RPLS is its “Pillow Lens” component. This customizable lens design can be used with any GP configuration while at the same time protecting the cornea from GP lens trauma.

Unlimited Potential Candidates

These combination lens designs have increased the potential contact lens patient base. The combination lens modality has been used both for mainstream contact lens candidates as well as for those who previously experienced challenges with lens wear. They are for patients who have normal corneas—with or without refractive astigmatism—as well as for patients wearing soft spherical or soft toric lenses who desire improved and consistent vision quality. They are for traditional GP wearers who desire improved lens comfort. Patients involved in sports and those who lead active lifestyles are particularly good candidates for these designs. These lenses are more than just problem-solvers; they provide increased fitting options to satisfy the most critical patients who have normal corneal configurations.

Contact lens therapies will continue to be available in a wide array of parameters that include “off the shelf” varieties as well as customized products addressing the specific needs of our patients. The soft-GP combination lens designs are customized products that are designed for our patients' individual fitting characteristics. A successful contact lens practice requires a mix of both therapies to provide the best options for our patients. Partnering with our patients to find an optimal contact lens therapy will lead not only to content patients, but to those who are enthusiastically satisfied. While there is no single lens that can promise success to every patient, taking the time to address patient concerns is a sure-fire way to create a loyal patient. The combination of lens materials might be the answer that our patients are looking for. CLS

For references, please visit www.clspectrum.com/references.asp and click on document #198.