Gets Makeover with Advanced Materials
JOHN MARK JACKSON, OD, MS, FAAO
I'm always amazed at how advancing technologies
can breathe new life into old ideas. A perfect example is the increasing popularity
of prescribing piggyback contact lens systems (Figure 1).
Figure 1. High-Dk materials are
piggyback lens systems.
the case of an irregular cornea such as keratoconus, if clinicians can't achieve
an acceptable fit with a GP lens, they'll sometimes use a GP lens directly on top
of a hydrogel lens. This fitting approach often provides better comfort and centration
than using the GP alone and may be the only way to fit the patient.
has one definite drawback: Because oxygen must pass through two lenses, it decreases
the supply to the cornea. However, today's silicone hydrogels and high-Dk GPs minimize
Figure 2. Patient's post-RK topography.
A Post-RK Case
Our 51-year-old patient underwent RK surgery in 1990. She reported
that her surgery was initially successful, but over the years her vision worsened.
Her entrance acuities were 20/70 OD, 20/400 OS while wearing soft spherical lenses
prescribed elsewhere that she'd worn for three years. She also noted monocular diplopia
in each eye while wearing the soft lenses. Subjective refraction was +9.50 –2.25
x 045 20/50 OD and +8.25 –1.25 x 140 20/25 OS. Her corneas had prominent RK
scars with about 0.25mm of vascularization into the scars 360 degrees; otherwise
her ocular health was unremarkable. Figure 2 shows her corneal topography.
fit her with GP lenses in an attempt to eliminate the diplopia and improve her visual
acuity. We tried reverse-geometry lenses because of her oblate cornea. The lenses
improved her vision substantially, eliminating the diplopia and providing acuity
of 20/20 in each eye. However, the lenses we tried would decenter or eject from
the eye, or they would adhere.
A Winning Combination
We decided to try a piggyback lens system with a high-Dk spherical
GP lens on top of a silicone hydrogel lens. We first fit the soft lens and
took K readings over the lens. We used this reading to select the base curve for
the GP lens. Piggyback systems usually use a low-powered soft lens with the main
correction in the GP lens. We achieved an acceptable result with +0.50D soft lenses
and spherical GP lenses with parameters of 7.50mm base curve, 9.6mm overall diameter
and +7.00D power. The patient was successful with this combination and pleased with
Although today's specialty lens designs (such as reverse geometry
lenses) are better than ever, sometimes they just won't cooperate. Using an old
friend like the piggyback system combined with today's advanced materials can be
a winning combination for you and your patients. CLS
Dr. Jackson is an assistant
professor at Southern College of Optometry where he works in the Advanced Contact
Lens Service, teaches courses in contact lenses and performs clinical research.
Contact Lens Spectrum, Issue: December 2005