Contact Lens Design & Materials
Piggybacking: Two New Takes on an Old Concept
By Ronald K. Watanabe, OD, FAAO
When a patient needs a piggyback design, most practitioners would probably grab a silicone hydrogel frequent replacement lens and use it as the base for the GP lens. It is easy, quick, good for oxygen transmission, and it usually works. However, there are times when this easy solution does not work for various reasons. Perhaps the soft lens does not drape very well or decenters excessively. The GP may still not center well or it may be unstable.
In these cases, a more specialized soft lens design may be needed. Two new piggyback soft lens carriers are now available: one uses a new material, while the other is a new design.
Proven Design, New Material
Though the Flexlens Piggyback (X-Cel Contacts) lens has been available for quite some time, it is now available in the Definitive (Contamac) silicone hydrogel material (as are all Flexlens designs). The Flexlens Piggyback lens is designed with an anterior-surface circular cutout that recesses the GP contact lens within the soft lens. When designed properly, the GP contact lens stays within the soft lens carrier, decreasing awareness of the GP lens edge. In addition, the GP lens attains excellent centration and stability, important for many patients who have irregular corneas.
The Flexlens Piggyback lens is available in a wide range of base curves (5.0mm to 11.0mm in 0.1mm steps), diameters (8.0mm to 16.0mm in 0.1mm steps), and anterior cutout diameters (6.5mm to 12.5mm in 0.1mm steps), making it a versatile option for a wide range of corneal contours. The lens should center and move much like any other soft lens. The GP lens should typically be designed 1mm smaller than the cutout diameter to allow some movement and tear exchange.
Though the new material has a Dk of 60, a high-Dk GP material is also recommended for maximum oxygen transmission. The Flexlens Piggyback in Definitive material is currently recommended to be replaced every three months.
A New Soft Lens Carrier
A new design option for piggyback carriers is the Recess Pillow Lens System (RPLS) by Fusion Contact Lens, Inc. This lens is a new take on the piggyback carrier concept in which the GP lens is held within a recess featuring angled edges that “bury” the GP lens within the soft “pillow” (Figure 1). This creates a smooth anterior lens surface that interacts minimally with the lids. The resultant combination moves as a unit and maintains good centration and stability. This is especially useful for specialty GP lenses that cannot maintain good positioning on their own, such as for keratoconus and post-surgical corneas as well as for bitorics, bifocals, reverse geometry lenses, and even spherical designs.
Figure 1. The Recess Pillow Lens System
The Pillow Lens can be manufactured in a variety of hydrogel materials in a wide range of base curves, diameters, and thicknesses to modulate lens fitting characteristics. The recessed zone can also be made in any diameter and should generally be made 0.3mm larger than the GP lens.
Consider for Problem Solving
Both options are great problem solvers when a GP lens alone becomes problematic and “off-the-shelf” soft lens piggybacking is unsuccessful. CLS
Dr. Watanabe is an associate professor of optometry at the New England College of Optometry. He is a Diplomate in the American Academy of Optometry's Section on Cornea and Contact Lenses and Refractive Technologies and is in private practice in Andover, Mass. You can reach him at email@example.com.