contact lens case reports

Consider Piggyback Lens Systems for Irregular Corneas

contact lens case reports
Consider Piggyback Lens Systems for Irregular Corneas

Figure 1. Corneal map of the patient's right eye.

Piggyback lens systems (a GP lens on top of a soft lens) date back as far the mid-1970s. Today, they remain the most overlooked and underutilized modality for improving the physical fit and/or comfort of a GP lens. Past attempts with low Dk, dual lens systems frequently resulted in signs and symptoms of corneal edema. However, with high Dk silicone hydrogel lenses and stable high Dk GP materials, the modality has evolved into a viable alternative to more traditional fitting techniques.

Patient SE is a 28-year-old male with a six-year history of bilateral keratoconus. The patient had historically been a good GP wearer until approximately six months ago when he began to experience discomfort and a loss of wearing time with the right eye only (Figure 1). Slit lamp examination revealed that both lenses were moving well with a slightly low resting position OU (Figure 2). We made a number of attempts to optimize the fit of the right lens, but all failed to resolve the patient's lens awareness symptoms. We eventually fit the patient with a piggyback lens system that consisted of a Focus Night & Day (CIBA) soft lens and a Paragon HDS 100 GP lens.

Figure 2. GP lens on the patient's right eye.

Fitting Procedure

First we diagnostically fit the soft lens to optimize lens movement and position. It is best to select a lens with low plus or near plano power so that the anterior surface of the soft lens better emulates the prolate shape of the normal cornea. Follow this with keratometry or videokeratography over the anterior surface of the soft lens to determine the radii of the "new" corneal surface. Select a GP lens with a base curve equal to the flat K and a diameter of approximately 9.0mm to 9.5mm.

We adjusted the base curve until an appropriate fit was established (Figure 3). An over-refraction helped determine the GP lens power, which can be manufactured in a traditional design with standard peripheral curves and a standard edge profile.

Figure 3. Piggyback system on the patient's right eye.

We have found piggyback lenses to be a simple yet effective technique for addressing comfort, vision and lens positioning problems associated with GP lenses on atypical corneas. Conditions in which piggyback lenses may be beneficial include post keratoplasty, post corneal trauma, post refractive surgery, corneal dystrophies and degenerations and a wide range of diseased-induced corneal scars.

Patrick Caroline is an associate professor of optometry at Pacific University and an assistant professor of ophthalmology at the Oregon Health Sciences University.

Mark André is director of contact lens services at the Oregon Health Sciences University and an adjunct assistant professor of optometry at Pacific University.