Refractive Lens Surgery

Fig. 10.6. Anterior
movement of the
Crystalens with pilocarpine
as compared
to cyclopentolate. The
mean movement of
0.84 mm when applied
in a weighted fashion
to the various IOL
powers actually
implanted yields
a mean monocular
accommodative
change of +1.79
diopters
challenges associated with obtaining valid
power change maps with wavefront aberrometry.
High-resolution ultrasound studies have
also been performed, which demonstrate anterior
movement of the Crystalens optic upon
accommodation (Fig. 10.5). Additionally,
in a study using immersion A-scan ultrasonography
to examine the anterior chamber
depth (ACD) in Crystalens patients upon
paralysis of accommodation with a cycloplegic
as compared to stimulation of accommodation
with a miotic, the ACD decreased
significantly [10]. Average forward movement
of 0.84 mm was demonstrated in this
study, which translated into 1.79 diopters of
average monocular accommodation with the
Crystalens (Fig. 10.6).
10.3 Clinical Considerations
With an implant available that provides accommodation,
what factors influence the decision
to use the Crystalens in any given patient?
One concern regarding the Crystalens,
particularly in young patients, is the possibility
that the lens could experience material fatigue,
resulting in failure of the hinge over
time. The lens has been subjected to biomechanical
testing, which simulates the
Chapter 10 The Eyeonics Crystalens 91
many accommodative cycles likely to occur
throughout the lifespan of a patient. In fact,
the testing performed subjected the lens to
much more vigorous movement than would
ever be encountered physiologically. This
testing indicates that the lens material will
last without deterioration. Unlike acrylic,
which has a tendency to crack under repeated
stress, the flexibility of silicone is well suited
to a moving hinge.
Another consideration relates to the use of
the Crystalens in patients with very large
pupils. While excellent scotopic results were
achieved in the clinical trial, these patients
had an average age of approximately 70 years.
How will the lens perform in much younger
patients with larger pupils? My own clinical
impression is that Crystalens patients have no
greater incidence of dysphotopsia than those
with any other IOL, but I tend to proceed cautiously
in patients with very large pupils. As
we gain more experience with this lens, we
will understand this issue more thoroughly.
Patients with diseased maculae and limited
visual potential after lens surgery will
probably not obtain sufficient benefit from
the Crystalens to justify its use. Similarly, patients
in whom the use of a silicone IOL is
contraindicated are not candidates. FDA labeling
of the Crystalens states that it should
not be used in the presence of a posterior cap-