Refractive Lens Surgery

Fig. 10.3. Under
binocular conditions,
84% of Crystalens
patients in the FDA
trial achieved DCNVA
of J2 or better
material is a third-generation silicone with an
integrated chromophore. The plate-haptic
configuration was originally selected for this
lens design because of the tendency for platehaptic
IOLs to position themselves very far
posteriorly in the capsular bag [4, 5]. This
maximum posterior positioning allows for the
greatest potential anterior movement upon
ciliary body contraction. For an average power
IOL, approximately 1 mm of anterior movement
is required to achieve 2 diopters of accommodative
effect. The relatively small optic
was selected as a result of studies by Kammann
demonstrating that plate lenses with
smaller optics tended to position themselves
even further posteriorly than lenses with larger
optics, despite the same overall IOL length
[4].While the optic is unusually small, its position
near the nodal point of the eye, where
light rays cross, theoretically allows the lens to
achieve the optical functionality of an implant
with a larger optic. The placement of hinges at
the optic-plate junctions is designed to maximize
anterior movement of the optic.
Thus, the proposed mechanism of action
of the Crystalens involves constriction of the
ciliary muscle,with redistribution of its mass.
This in turn exerts pressure on the vitreous
base, which increases pressure in the vitreous
cavity and pushes the highly flexible, posteriorly
vaulted optic anteriorly. With accommodative
effort, transient myopia results, and
the patient is able to function well at near.
Chapter 10 The Eyeonics Crystalens 89
10.2 FDA Clinical Trial Results
The US FDA clinical trial examined the use of
the Crystalens in cataract surgery. The trial
was completed in November 2001, with a total
of 497 implantations performed. The trial results
showed that the Crystalens offered visual
performance at distance comparable to any
standard IOL, with excellent uncorrected and
corrected distance acuities. Accommodative
visual performance was measured by testing
the near vision through the distance correction.
This measurement is referred to as the
distance-corrected near visual acuity (DCN-
VA). Monocular testing of Crystalens patients
demonstrated that 91% of eyes were able to
achieve DCNVA of J3 or better, and binocular
testing showed that 100% of patients
achieved DCNVA of J3 or better, with 84%
achieving DCNVA of J2 or better (Fig. 10.3).
This level of near acuity is significantly better
than that typically achieved with standard
IOLs [6, 7]. Vision at the intermediate distance
was very impressive as well. Testing
binocularly through the distance correction,
100% of these patients could see J1 or better
at 32 inches, and 98% could see J1+. From a
clinical standpoint, these patients were largely
spectacle independent, with 74% reporting
that they either did not wear spectacles,
or wore them almost none of the time
(Fig. 10.4).