With all of the recent emphasis on newer GP modalities—such as scleral lenses and hybrid designs—it is easy to forget about more traditional, yet still valid, methods of irregular cornea contact lens correction. Piggyback soft/GP lens fits have a reputation for being a last resort for practitioners, not to mention laborious and expensive for patients. However, this modality should be given more consideration, as the benefits in many cases outweigh any disadvantages.
Pros and Considerations
Comfort When GP lenses are needed to obtain the best possible visual acuity but difficulties arise with centration or patient comfort, piggybacking the GP lens over a soft lens should be considered. Pediatric patients in particular can struggle with GP lens adaptation and comfort, and adding a soft lens under the GP lens can alleviate some of the difficulties in getting these patients accustomed to GP wear.
Hypoxia Oxygen permeability is a concern with a double-lens system. Therefore, it is advisable to use GPs with hyper-Dk values and high-Dk silicone hydrogel soft lenses to avoid any hypoxic complications.
Cost Some argue that the cost of the multiple lenses and care systems required for piggyback fitting is prohibitive. However, when compared to other specialty modalities, the difference is actually quite minimal. A pair of scleral lenses alone can exceed the cost of both a set of GPs and an annual supply of a silicone hydrogel soft lens. Using a daily disposable soft lens can lessen the burden of multiple care systems, and with today’s soft contact lens options, this is readily achievable. Use of hydrogen peroxide care systems for the GP lenses is convenient and affordable in most cases and is preferred when tandem soft lens wear is needed.
Choosing the Right Lens
Selecting the soft lens power does not need to be difficult; starting with a plano soft lens is reasonable unless specific fit or power effects are desired. Because keratoconic GP lenses often have higher-minus powers, it may be possible to shift some of the power to the soft lens to decrease the GP power required (Romero-Jimenez et al, 2015). This could help lessen GP lens edge thickness and possibly improve the eyelid/lens fitting relationship. Using a minus-power soft lens may also provide a flatter anterior surface that could be useful when fitting the GP lens on top (Romero-Jimenez et al, 2013).
A plus-powered soft lens is a better option for improving centration of the GP lens in situations in which a more convex central shape would be potentially beneficial. Regardless, it is important to note that the transfer of power is not exact or easily predictable; the soft lens generally contributes no more than approximately 20% of its labeled power to the overall optics of the piggyback system (Michaud et al, 2013). To obtain notable power contributions and/or fit effects, it is necessary to use moderately high soft lens powers (i.e., > ±3.00D).
When improved GP lens comfort or a better GP lens fit is desired, piggyback systems can be effective, affordable, and surprisingly easy for practitioners to add to their collection of problem-solving GP lens fitting tools. CLS
For references, please visit www.clspectrum.com/references and click on document #277.