contact
lens case reports
Interpreting
Piggyback Fluorescein Patterns
BY PATRICK J. CAROLINE, FAAO,
& MARK P. ANDRé, FAAO
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Figure
1. Patient JB with advanced keratoconus OD and early keratoconus OS.
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Patient JB has advanced keratoconus in the right
eye and mild keratoconus in the left. Simulated K readings were OD 55.12 @ 55/70.00
@ 145 with an apical radius of curvature of 63.25D (3.90mm), OS 45.75 @ 158/47.87 @ 68 (Figure 1). After numerous failures with GP contact
lenses, JB came to us for a custom soft contact lens to serve as the base for an
eventual piggyback fitting.
Fortunately for him, JB first saw one of our forth year optometry
students who naively fit him with a standard Acuvue Oasys (Vistakon) lens with an
8.4mm base curve. To our surprise, it fit perfectly (Figure 2). We have subsequently
used the Oasys lens for patients who have even more advanced keratoconus with great
success. It appears that the low modulus of the senofilcon A material (water content
38 percent, Dk 103) allows it to accommodate a wide range of corneal shapes.
Fitting the GP Lens
We performed corneal mapping over the surface of the soft lens
to establish the new corneal shape, then diagnostically fit the patient with the
new aspheric I-Kone lens design (Valley Contax). Figure 3 shows how we use fluorescein
to better visualize the fitting relationship of the GP to the underlying soft
lens. It's clear to see when the appropriate lens-to-lens fit has been established.
Today,
JB wears his piggyback lenses 14 hours a day with excellent comfort and a VA of
20/25. Most importantly, he enjoys the return of his binocular vision.
Take-away Pearls
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Figure
2. Corneal mapping without (top left) and with (lower left) the Oasys soft lens;
(right) fluorescein stained Oasys lens OD. |
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Figure
3. Fluorescein patterns of three different I-Kone contact lenses over the surface
of the soft contact lens. |
This case demonstrates two important piggyback fitting pearls.
First, the Acuvue Oasys lenses appear to have a low enough modulus to accommodate
a wide range of corneal shapes, making it ideal as a piggyback soft lens. Second,
you can successfully use standard fluorescein to evaluate the fitting relationship
of a GP to the surface of a planned replacement silicone hydrogel lens in a piggyback
system.
Patrick Caroline is an associate
professor of optometry at Pacific University and is an assistant professor of ophthalmology
at the Oregon Health Sciences University. He is also a consultant to Paragon Vision
Sciences and SynergEyes, Inc. Mark André is an associate professor of optometry
at Pacific University. He is also a consultant for Alcon Labs, CooperVision and
SynergEyes, Inc.
Contact Lens Spectrum, Issue: June 2006