Case History: The Piggy-back Solution

Jennifer Smythe

Jennifer Smythe is an Associate Professor of Optometry and the Coordinator of the Cornea and Contact Lens Residency at the Pacific University College of Optometry in the USA. Dr. Smythe, a 1993 graduate of the Pacific University College of Optometry, completed a residency in contact lenses at that same institution in 1994, and her Master's of Science in Clinical Optometry in 2000. She team teaches the contact lens curriculum at the college and is in private practice in Beaverton, Oregon. Dr. Smythe is a member of the Primary Care Optometry News editorial board, a contributing editor for Contact Lens Spectrum, a Fellow in the American Academy of Optometry, and a Diplomate in the Section on Cornea and Contact Lenses.

The benefits of silicone hydrogel contact lenses for the normal cornea have been well established. Most notably, complications related to hypoxia have been virtually eliminated. The physiological response (or lack thereof) has paved the way for more advanced applications of these high-Dk materials. This includes utilization of the lenses for therapeutic benefit. Silicone hydrogel lenses have quickly become a welcome breakthrough in the specialty contact lens practice.

Until recently an underutilized modality of contact lens correction was the "piggy-back" fit. With current material and design advancements, this system of a rigid contact lens worn over a soft lens on same eye is a viable option for problem solving lens decentration, maintaining corneal epithelial integrity and, enhancing patient comfort.

A fifty-four year old healthy woman (NU) was referred to the office by a local refractive surgeon for a contact lens fitting OD. NU had Lasik OU in December 1998 and two enhancements OD in 3/99 and 6/00. This very active patient reported that she was happy with her vision in the left eye however, she was constantly aware of blur OD, especially during her daily golf game. Prior to having Lasik, NU wore rigid contact lenses for thirty years which, she discontinued one month before surgery. She reported hypersensitivity to Benadryl otherwise, her medical history was unremarkable. Uncorrected visual acuity was 20/200 OD, 20/20-1 OS and some improvement was achieved with the following manifest refraction:

OD -1.75-1.75 X 080 20/40-2

OS -0.50 -0.25 X 088 20/20

Videokeratoscopy was performed and the corneal map displayed significant inferior ectasia OD and a fairly normal and well centered ablation zone OS (Figures 1 and 2).

Figure 1: OD, Post Lasik and 2 enhancements - click to enlarge	Figure 2: OS, Post-Lasik - click to enlarge

Further inspection of the topography OD revealed over a 20D difference between the apex (steepest point inferiorly) and the superior mid-peripheral cornea. Several GP corneal designs with various optic zone diameters and base curves were diagnostically trialed however, every attempt to either clear or limit the amount of bearing on the inferior cornea caused excessive impingement of the contact lens on the superior cornea. Subsequently each lens decentered significantly inferiorly. Diagnostic fitting with GP scleral lenses (both fenestrated and non-fenestrated designs) also failed due to bubble entrapment secondary to the severe disparity between the superior and inferior corneal curvature. The decision was finally made to attempt a piggy-back fitting.

Figure 3: OD, Over 8.6/+0.75 FND - click to enlarge	Figure 4: Piggy Back System - click to enlarge

A Focus Night and Day (Ciba Vision) 8.6 / 13.8 +0.75 D was inserted and video-keratoscopy was performed over the top of the silicone hydrogel contact lens (Figure 3). The base curve of an appropriate GP lens was selected based on the radius of curvature 3 mm temporal from center on the corneal map. A 43.00 D / 9.5 / -3.00 CAD (Valley Contax) GP lens was placed on top of the silicone hydrogel. The lens positioned slightly low and a bubble was trapped between the two contact lenses in the mid-periphery which could potentially encroach upon into the papillary zone in dim illumination. A smaller OAD/OZ diameter lens in the same base curve and design was then trialed and it centered well without any bubble entrapment (Figure 4). The Nafl pattern displayed slight apical touch of the rigid lens and no edge fluting of the soft contact lens. Both lenses moved freely with the blink without excessive decentration, the patient reported that comfort was excellent and through a spherical over-refraction visual acuity was 20/25.

NU has been successfully wearing Focus Night and Day 8.6 / 138 / +0.75 with a CAD HDS 100 43.00 D / 9.0 / -4.00 OD for over 5-months and performs nightly disinfection and storage in AoSept ClearCare (Ciba Vision). Acuity with the lenses has been a stable 20/25+1 and she is thrilled with the comfort and clarity of vision that the system provides. She was re-evaluated at one week, one-month and three months post-dispense and no physiological compromise has been observed.

There are a multitude of indications for the piggy-back technique for both the regular and irregular cornea. Although the most common condition that may warrant a piggyback modality is keratoconus, as observed in the case of NU, post-surgical ectasia can mimic the corneal topography of this degeneration. As the asymmetry between the superior and inferior cornea increases, maintaining centration and limiting impingement or bubble entrapment of a rigid contact lens is often a significant challenge. A piggyback system worn full-time, or even for part of the day, can increase maximum wear time of the rigid contact lens and ultimately have a positive impact on the patient's quality of life.