contact lens materials
A Second Look at a Second Lens
BY NEIL PENCE, OD, FAAO
Though it was many years ago, memories of the first few patients I fitted in a piggyback contact lens system remain fresh. They were all keratoconus patients who had suffered increasing discomfort and wearing time problems with their GP contact lenses. When a soft hydrogel lens was fit and the GP lens placed on top, all three commented on the improved comfort compared to their GP lenses alone.
What makes these keratoconus patients particularly memorable is that within six months of being fit, two of the three patients suffered corneal hydrops. This definitely tempered some of my initial enthusiasm about piggyback fits. I had to question whether the piggyback lenses had contributed to their hydrops events.
When a short time later Dr. Barry Weissman mentioned in a conversation that lack of oxygen likely played little role in hydrops, I was relieved. Piggyback lenses had been pretty much a last resort for these patients who had significantly advanced keratoconus, which is also the group most at risk for hydrops.
Concerns remained, however, about the oxygen reduction caused by piggyback fits with hydrogel material lenses. Even if hydrops was not a significant concern, oxygen deprivation in the peripheral and midperipheral cornea could encourage vessel encroachment. Among other concerns, corneal neovascularization might complicate any future corneal transplant.
I relegated piggyback lens fitting to basically a tool of last resort to help keep keratoconus patients in lenses longer.
Silicone Hydrogel Success
With the advent of silicone hydrogel materials, oxygen concerns with piggybacking have greatly lessened. Weissman and Ye (2006) have shown that the oxygen transmission of a system using both high-Dk GP lenses and silicone hydrogel lenses is only slightly less than that of silicone hydrogels alone. It's an improvement over the GP lenses alone of a decade ago.
The system using both high-Dk GP lenses and silicone hydrogel lenses also offers significantly more oxygen transmission than custom hydrogel toric lenses or available hybrid lenses — other options you might consider to provide a similar comfort and fitting benefit.
If we can fit patients, particularly keratoconus patients but others as well, in a more comfortable lens system that is also safe, that should warrant a serious reconsideration of its use. For patients experiencing increasing 3 o'clock and 9 o'clock staining or dryness problems, comfort problems and decreased wearing time with their GP lenses, piggyback fitting can be a definite improvement. It might also be warranted in patients with increased conjunctival and limbal hyperemia in their GP or hybrid lenses.
While slightly inconvenient with two lenses and care systems per eye, patients have responded very positively to piggyback contact lenses due to the comfort and wearing time benefits.
A Beneficial Role
Piggyback contact lenses can play a beneficial role for patients who experience comfort or wetting problems, yet need the optical properties of a GP lens. We may question whether it's an under utilized option, considering its benefits. At the least, the ability to use high-oxygen transmissible lens materials makes piggyback lens fitting a technique certainly worthy of a second look. CLS
To obtain references for this article, please visit http://www.clspectrum.com/references.asp and click on document #158.
Dr. Pence is director of the Contact Lens Research Clinic, Indiana University School of Optometry in Bloomington, Indiana. He is a consultant or advisor to B&L, CIBA Vision and Vistakon, and has received research funding from AMO.