Toric contact lenses fitting - Optometry Today

Toric contact lenses fitting
The changing dynamics of soft CL technology
Susan Resnick OD, FAAO
The past two decades have brought remarkable advances and innovation in
soft contact lens technology. The vastly superior hydrogel lenses that we
prescribe today came about as a result of gradual yet significant
improvements in lens design, materials and manufacturing capabilities.
Eyecare practitioners now enjoy an everincreasing
array of contact lens options with
which to satisfy patients’ needs and
expectations for comfort, convenience and
visual satisfaction. Undoubtedly, however,
most of us in the trenches recognise that
there is still room for improvement in certain
aspects of soft lens design and fabrication.
One such area is the toric hydrogel lens
category.
We have certainly come a long way from
the time when fitting soft toric contact
lenses was largely relegated to the ‘contact
lens specialist’. Throughout the last decade
in particular, with the advent of improved
lathing techniques and the development
and introduction of moulded contact lenses,
we have witnessed a quantum leap in lens
quality and reproducibility. The subsequent
availability of toric designs in a planned
replacement modality, along with significant
expansions in parameter ranges, have
further served to ‘mainstream’ soft
astigmatic contact lens fitting. Yet concerns
related to patient and practitioner satisfaction
have continued to plague this niche
market.
If we compare our clinical experiences
with spherical lens wearers to those with
our astigmatic patients, it is apparent that
the expectations of the latter group are still
not fully met. Our toric lens patients invariably
do not attain the levels of overall vision
quality that spherical lenses provide. These
patients often report inferior visual acuity
compared to what they achieve with their
spectacles. While a consistent level of mildly
reduced visual quality may be a compromise,
some patients are willing to accept
this. Problems related to rotational instability
and variability of vision remain obstacles
to satisfying the visual needs of many.
Likewise, patient satisfaction with the
physical comfort of soft toric lens designs
About the author
Dr Susan Resnick is a principal in a
specialty contact lens practice in New
York City and Roslyn, NY. She serves
on new product advisory panels and
as a media liaison for Vistakon. She
has no financial interest in the
product mentioned in this article
has historically lagged behind that of spherical
lens wearers. While newer, thinner
lenses incorporating enhanced edge profiles
greatly diminish overall lens awareness as
compared to previous designs, a considerable
percentage of patients still do not
achieve the level of comfort they desire. This
is most apparent in those who require an
astigmatic lens on one eye only, or those
who are marginally tolerant or are more
highly sensitive individuals.
Practitioner satisfaction is inextricably
linked to patient satisfaction, for this is how
we gauge our success. We desire and
expect rapid, predictable and stable lens
positioning. These are the requisite
functional attributes of lens design that will
provide our patients with the clarity and
consistency of vision they require and
deserve. We also strive to offer our
astigmatic patients parity in the same level
of comfort afforded to our spherical lenswearing
patients. More than 40% of the
vision corrected population requires
astigmatic corrections for levels of 0.75D or
more. Estimates place practitioner satisfaction
levels with current technology at a low
14% 1 . Thus, it is important that manufacturers
continue to devote energy and
resources to research and development in
this vital area of contact lens care.
Thirty years and few innovations
Two principal methods of toric lens design
have been used throughout the past 30
years in an attempt to achieve the goal of
lens stabilisation – prism ballast and dual
thin zones. These conventional soft toric
designs, while conceptually sound, are
limited by conventional fabrication methods
– lathing or grinding of lenticulated or offaxis
zones. When manufacturers try to fit
their current lens designs within the
framework of their current manufacturing
capabilities, the number of degrees of
freedom available to the lens designer is
reduced. The obvious main result, as seen
over the past few years, is a series of
products showing only incremental
improvements over their predecessors
within the same family of designs.
In a clinical setting, practitioners witness
the varying degrees of influence that lid
configuration (such as lid angles and lid
tightness) and ocular surface anatomy (such
CLINICAL
Astigmatic contact lens fitting
Zone of thickness
➛
Figure 1
The Accelerated Stabilisation Design (ASD)
of ACUVUE ® ADVANCE ® Brand Contact
Lenses for Astigmatism provides a new
level of stabilisation (for illustration purposes only)
as conjunctival elevations) have on the
effectiveness and feasibility of each of these
conventional designs. Other factors shown
to affect the orientation position of toric
soft lenses include the degree of myopia
and palpebral aperture size 2 .
While we may observe general trends
with a given design or brand, we have not
been able to accurately predict soft lens
orientation with any consistency based
upon anatomical factors. In an attempt to
improve consistency and rapidity in lens
orientation, refinements have been made
along the way in the form of periballasting
and eccentric lenticulation. However, no
new advancements in design have been
made.
Improvements in toric lens design
Prism ballast and conventional dual thin
zones designs are based on the same
‘watermelon seed’ principle, which teaches
that a wedge will orient itself in such a way
as to decrease the pressure on its thick side.
While this design concept is sound and has
been shown to be effective in orienting
lenses, it has not been optimised to take
into account the fact that the principle
applies regardless of the lens orientation
because the lid forces repeat themselves
blink after blink. As a result, the same lid
forces that tend to orient a misoriented lens
will also tend to dislodge a properly aligned
lens. The effect of these forces is to reduce
lens stability, which leads to unstable vision
over time.
Improved understanding of eye dynamics
and the application of advanced manufacturing
techniques has provided the
engineering synergism responsible for the
next generation of soft toric lenses. One
such design that uses the forces of the blink
is the Accelerated Stabilisation Design (ASD)
of ACUVUE ® ADVANCE ® Brand Contact
Lenses for Astigmatism. Much like the ‘on
demand’ four-wheel drive feature now
available in many motor vehicles, this design
features multiple ‘active zones’ that permit
the lid to interact with the lens in a positive
39 | May 5 | 2006 OT

CLINICAL
Astigmatic contact lens fitting
way, but only when required (Figure 1). The
lens is designed in such a way that the
watermelon seed principle is maximised
when the lens is misoriented, and
minimised when the lens is correctly
aligned. The result is a lens that rotates
quickly to its desired position and remains
stable when properly aligned.
Revolutionary advancements
Factors influencing corneal physiology and,
ultimately, patient comfort in toric lens
designs do not differ from those we
encounter with spherical lenses, but they
are often more clinically significant. Chronic
hypoxia of the peripheral cornea (often
inferiorly in ballasted designs and nasotemporally
in traditional thin zone designs) may
be evident in the form of unacceptable
levels of localised peripheral or circumlimbal
neovascularisation 3 . Symptoms may include
reduced wearing time and red eyes. Lens
surface drying, whether attributable to
reduced tear volume or unstable tear film,
have been associated with blurry and
changeable vision 4 . This may further
diminish the marginal visual quality or
inconsistency in acuity that our current toric
lens wearers suffer. Post-blink movement
and lens tightness have been correlated
with lens orientation 2 .
Fortunately, silicone hydrogel technology
has eliminated or substantially reduced
many of these adverse and undesirable
hypoxia-related issues. Many patients report
fewer dry eye symptoms, perhaps because
of the lower water content of these materials
or from reduced surface dehydration 5,6 .
Having experienced the clinical advantages
of these materials as spherical lens designs
over the past few years, we have been
looking forward to being able to offer these
same improvements to our toric lens
patients.
The availability of a toric lens made in a
material using Hydraclear technology may
be a compelling enough reason to embrace
the new toric product by Johnson &
Johnson Vision Care – but I believe that
ACUVUE ADVANCE Brand Contact Lenses
for Astigmatism truly raises the bar for toric
lens performance. Many patients are
impressed with the lens’ extraordinary
comfort upon application. In one large
scale, masked independent clinical study,
92% of lenses oriented within 10˚ of the
zero position at settling time (Figure 2), and
96% of lenses remained within 5˚ of the
settled position after three minutes (Figure
3) 7 . In fact, the lens consistently orients
within a minute or two of application and
exhibits minimal rotation and virtually no
variability of axis position. The same study
found that 87% of lenses oriented within
one minute at 5˚ (Figure 2), and 85% of
lenses remained within five degrees of
settled position within one minute (Figure
3). No extended settling period, multiple
rechecks or multiple diagnostic lenses were
required, so chair time is therefore greatly
100
80
60
40
20
0
87
66
47
One minute
87
reduced, and patients report excellent endof-day
comfort with less redness 7 .
So begins an exciting era in the evolution
of toric lens technology. ACUVUE
ADVANCE Brand Contact Lenses for
Astigmatism will help us to turn the page
on accepting vision that is only good
enough, on our reluctance to fit toric lenses
because of the time and effort involved, and
on the frustrations of unsatisfactory fitting
outcomes. New toric lens wearers will now
have a better chance than ever at success
with the first lenses they try.
Current wearers will enjoy more stable
vision and better comfort in environments
or during activities that previously may have
been problematic. No longer should we feel
compelled to avoid fitting our low-cylinder
patients because we believe that it’s not
worth it. This new lens should rekindle our
enthusiasm and refuel our confidence in
delivering results that satisfy the highest
expectations of our toric patients and that,
in turn, boost our professional satisfaction.
71
59
Three minutes
References
92
76
66
Traditional setting
Figure 2
Ninety-two percent of lenses oriented within 10˚ at settling time, and 87%
of lenses oriented within 5˚ within one minute
100
80
60
40
20
ACUVUE ® ADVANCE for Astigmatism (n=366 eyes/lenses)
Traditional Prism Ballast Benchmark (n=352 eyes/lenses)
Traditional Dual Thin Zone benchmark (n=152 eyes/lenses)
85
76
65
Orientation within 5˚
Rotational stability within 5˚
96
0
One minute
Three minutes
Figure 3
Ninety-six percent of lenses remained within 5˚ after three minutes, and 85%
remained within 5˚ within one minute
86
76
1. Data on file, Vistakon, a division of
Johnson & Johnson.
2. Young G, Hunt C and Covey M (2002)
Clinical factors influencing toric soft
contact lens fit. Optom. Vis. Sci. 79 (8):
11-19.
3. Bergenske P (2005) Prescribing soft toric
contact lenses. Contact Lens Spectrum
20 (2): 34-9.
4. Begley CG, Caffery B, Nichols KK and
Chalmers R (2000) Responses of
contact lens wearers to a dry eye survey.
Optom. Vis. Sci. 77 (1): 40-6.
5. Snyder C (2004) A primer on contact
lens materials. Contact Lens Spectrum
19 (2): 34-9.
6. Jones L (2002) Modern contact lens
materials: a clinical update.
Contact Lens Spectrum 17 (9): 24-35.
7. Data on file, Vistakon, a division of
Johnson & Johnson
Acknowledgement
Originally published by Review of Cornea & Contact Lenses, May 5©2005 Jobson Publishing.
40 | May 5 | 2006 OT