SPECIALTY LENSES
Rigid Optics with Soft Lens Comfort
A look at how the technology behind SynergEyes
lenses benefits both patients and practitioners.
By Brian
Chou, OD, FAAO
The
development of SynergEyes (SynergEyes Inc., Carlsbad, CA) exemplifies how technological
advances in several areas — material science, manufacturing, lens design and
prescribing method — combine such that their sum effect is greater than adding
the individual parts, making the trade name appropriately resonate the meaning of
"synergy."
My
office was one of the 23 sites that participated in the initial FDA clinical studies
of SynergEyes lenses. Currently, more than 50 patients in my practice
are successfully
wearing SynergEyes lenses.
In
this article I'll share some of the relevant information about SynergEyes, giving
a technological perspective on what differentiates this contact lens from its commodity
counterparts.
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Figure
1. A SynergEyes hybrid lens.
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Material Science
Previous hybrid lenses had a Dk of about 14 and
the firm center and soft skirt separated relatively easily. Even though some GP
materials now exist with Dk values exceeding 150, until now, no manufacturer successfully
developed a high-Dk hybrid contact lens because of the difficulty in bonding hydrophilic
skirts to high-Dk rigid materials.
The breakthrough in material science is the
proprietary Hyperbond technology that allows a strong link between a hydrophilic
skirt and a highly oxygen permeable rigid center. The polymer chemists at SynergEyes
developed a method to protect the GP material from alteration by the hydrophilic
monomers while providing a strong bond. The technology produces intermediate layers
that preserve the gas permeability, mechanical properties and index of refraction
while producing a multi-zone interface. Each chemically different layer is nanometers
thick. The SynergEyes rigid center has a Dk of 145 with a bond to the soft skirt
that is substantially stronger than anything before, approximately 10 times stronger
than previous hybrid lenses, according to company data.
Manufacturing
Today, contact lens manufacturers frequently use
low-cost cast molding to make lenses. Diamond turning lathes and automation also
produce precision lenses at a reasonable cost.
SynergEyes lenses are manufactured with no-polish
lathing. The process utilizes vibration-free computer-numerical-controlled lathes
driven by proprietary Pro80 design software. Jim Schwiegerling, PhD, Associate Professor
of Ophthalmology at the University of Arizona, developed this software to provide
versatility for the hybrid platform extending beyond standard lathe mini-files.
Spherical, toric, multifocal and rotationally non-symmetrical optical and structural
designs are generated for the hybrid platform.
These methods will produce a family
of lenses targeted to manage the full continuum of refractive errors. The software-driven
polish-free lathed optics are ideal for a platinum standard multifocal, higher-order
aberration correcting lenses and lenses for patent-pending Myopia Progression Control.
The manufacturing efficiency drives the production cost of the SynergEyes lens to
about one-half that of previous hybrid lenses.
Design
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TABLE 1 |
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SynergEyes
A Diagnostic Set Parameters |
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GP Base
Curve |
Flatter
Skirt Curve |
Steeper
Skirt Curve |
7.1 (47.50)
7.2 (46.87)7.3 (46.25) 7.4
(45.62)7.5 (45.00)7.6 (44.37) 7.7
(43.87) 7.8 (43.25)
7.9 (42.75) 8.0 (42.25)8.1 (41.62)8.2
(41.12) |
8.40
8.50
8.60
8.70
8.80
8.90
9.00
9.10
9.20
9.30
9.40
9.50 |
8.10
8.20
8.30
8.40
8.50
8.60
8.70
8.80
8.90
9.00
9.10
9.20 |
Previous attempts at hybrid lenses experienced
limitations besides just hypoxia-related corneal neovascularization and frequent
separation at the rigid-soft skirt border. The first hybrid lenses were launched
nearly 25 years ago. A second-generation hybrid, SoftPerm (CIBA Vision) is still
commercially available. These predecessor lenses have one skirt radius for each
base curve.
The clinical research team at SynergEyes discovered
a clear relationship between corneal curvature, corneal diameter and the required
base curve and skirt radius needed for a successful lens fit. A plurality of skirt
radii for a given base curve radius is necessary to accommodate the geometric diversity
from the full range of corneal diameters. The SynergEyes lenses have the patent-pending
feature of a series of available skirt radii for each rigid center's base curve.
The SynergEyes A and M designs are
indicated for correcting hyperopia, myopia, astigmatism and presbyopia, in aphakic
and non aphakic eyes free of disease. They are approved for daily wear for correcting
up to +20.00D and –20.00D in eyes with astigmatism up to 6.00D; for presbyopia
with add requirements from +1.00D to +4.00D. Each design has two available core
skirt radii and two available extended range skirt radii.
SynergEyes KC for keratoconus patients
and SynergEyes PS for post-surgical patients have three skirt radii for each equivalent
base curve. These lenses feature an aspheric base curve that is more forgiving on
eyes that have high degrees of circumferential and radial irregularity.
The plurality of skirt radii, the
aspheric base curves and the non-rotational platform are all novel for hybrid lenses,
allowing the use of front-surface cylinders and de-centered multifocal optics to
center the simultaneous vision features over the visual axis.
Methods of Prescribing
Low-cost cast molding yields a host of one-size-fits-all
products that require little to no clinical measurement to predict their lens fit.
This reduces the amount of needed practitioner expertise and chair time, saving
the patients from the associated costs.
The parallel arm of contact lens evolution
is toward technology-driven measurements for reducing chair time. This is analogous
to the difference between over-the-counter reading glasses and professionally fit
progressive addition lenses (PALs). Measurements of monocular pupillary distances
with pupillometers and segment heights improve the fitting and success of PALs.
Prescribing for SynergEyes parallels
that used for PALs. Corneal diameter is a major contributing variable for the fit
of contact lenses, yet most clinicians don't routinely measure it. Using the horizontal
visible iris diameter (HVID) allows you to empirically prescribe the SynergEyes
lens with a high degree of success. Many corneal topographers and slit lamp eyepiece
reticules allow for this measurement. SynergEyes has a patent-pending device, the
M-Scan, that is useful for measuring corneal diameter with an accompanying lens
calculator that determines the empirically recommended SynergEyes hybrid lens from
keratometry, manifest refraction and HVID.
The M-Scan also measures pupil size,
which enhances the success of the SynergEyes M multifocal contact lens. The SynergEyes
multifocal has a center add that uses pupil diameter to determine the anterior add
diameter. The device also captures the registration marks on diagnostic lenses to
determine whether any optical decentration is required to center the multifocal
over the pupil.
Conclusion
SynergEyes lenses are polar opposites to the one-size-fits all,
mass-merchandised contact lenses. By embodying advances in material science, manufacturing,
design and prescribing methods, SynergEyes lenses are directed toward practitioners
who appreciate the intellect and expertise behind prescribing.
Dr. Chou is in private group practice in San
Diego. He is also a consultant for the California Board of Optometry and a clinical
investigator and consultant to CooperVision, SynergEyes and Ophthonix.
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Lens Solves GP Instability |
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Lens Solves GP Instability
34-year-old male who has keratoconus complained that
his rigid lenses would eject and decenter, and that his comfortable lens wearing
time had decreased. Visual acuity with habitual GP lenses was 20/40+1
OD and 20/30-3 OS. Manifest
refraction gave –6.50 –4.00 x133 and –5.50 –3.75 x129. Best-spectacle
corrected visual acuity was 20/70-
OD and 20/50- OS. Manual
keratometry gave 46.50 @ 055/52.50 @ 135 (3+distortion) OD and 42.50 @ 045/47.75
@ 135 (3+distortion) OS. Slit-lamp examination showed Vogt's striae and Fleischer's
ring OU.
The hybrid SynergEyes KC contact lenses were prescribed with the
following parameters:
OD 5.70 BC / –6.00D / skirt radius 8.50
OS 5.80 BC / –5.50D / skirt radius 8.60
Resulting visual acuity was 20/30 OD and 20/30 OS. The SynergEyes
lenses demonstrated substantially improved stability on the eye. The patient also
reported reduced lens awareness with the SynergEyes lenses than with his habitual
rigid lenses.
Discussion
The SynergEyes lens combines a high-Dk rigid gas permeable center
optic with a soft hydrophilic skirt. Unlike the lower-Dk SoftPerm (CIBA Vision),
SynergEyes is not prone to junctional separation.
SynergEyes also provides a soft skirt with a specifiable radius
to accommodate a wider variety of eyes. While it's common for keratoconus patients
who are wearing standard rigid lenses to end up viewing through the peripheral optics
of a decentered lens, the soft skirt of SynergEyes positions the rigid optic so
that vision correction is stable even in various fields of gaze. The SynergEyes
soft skirt also minimizes discomfort related to GP lid-lens hypersensitivity.
— Brian Chou, OD, FAAO |
Contact Lens Spectrum, Issue: July 2006