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The
Five Myths of Masking Astigmatism: Myth #2
Myth #1 – Visual acuity with low cylinder
toric lenses is not significantly
better than with single vision spherical lens correction
Myth #2 – The risk of variable vision with toric lenses is too much
of a trade-off
relative to the assurance of stable spherical vision
Myth #3 – Toric lenses aren’t as comfortable as spherical lenses
Myth #4 – Significantly more chair time is required to fit toric lenses
Myth #5 – The higher cost to patients of toric lenses is a barrier
relative to
spherical lenses |
In our last article, we
dispelled the myth that: “Visual acuity with low cylinder toric lenses is not
significantly better than with a spherical lens correction.” In this edition we
will discuss whether the presumed risk of variable vision with toric lenses is
an expected trade-off relative to spherical lens correction.
Because the power in a toric lens is not equal in all meridians, rotational
stability is a critical factor in visual acuity. Some of the earlier toric
designs have not always optimized stability - sometimes they resulted in
variable vision. Some of today’s newer toric lens design technologies have been
refined to provide very stable, exceptionally clear vision.
Consider a lens like the Bausch & Lomb PureVision® Toric lens. The patented
Lo-Torque® design provides exceptional rotational stability, and a balanced
vertical thickness profile adds axis stability. In a 2006 Independent study,
this newer design was preferred by eye care professionals across a variety of
metrics when compared to an alternative toric lens designs, such as the dual
thin zone design.1
A well-designed toric lens will also achieve full centration which
provides better optical quality. Centration is the main determinant of high
contrast vision performance. Centration plays an important role in aligning the
lens optics with the visual axis enhancing optical quality. (see Figure 2).
In a study of 107 patients,
only 78% achieved full centration with Acuvue Advance for Astigmatism lenses,
but once refit into PureVision toric lenses over 90% achieved full centration.2
The Bausch & Lomb PureVision Toric lens is also designed to help reduce the
amount of positive spherical aberration among the general population by
adjusting the shape factor of the anterior surface across the range of powers.
The aspheric optics combined with all of the other sophisticated design
characteristics help PureVision Toric lenses deliver improved vision quality in
a variety of settings.
The examples above show how design features of toric contact lenses can deliver
exceptional vision to astigmatic patients even versus spherical lenses.
Specifically, in a clinical evaluation of astigmatic patients conducted
comparing the PureVision Toric lens to wearers’ previous lenses, 89% of the
patients achieved 20/20 vision or better when wearing the PureVision Toric lens.3
Only 35% had achieved 20/20 with spherical lenses. (Figure 3)
Don’t allow patients to settle for a less than optimal vision correction and for
astigmatic patients that means giving them a toric lens. Educate your patients
and offer them a proven toric lens design – PureVision Toric. They’ll be glad
you did.
Look for our next edition of EyeMatters as we address the misperception that
toric lenses are not as comfortable as spherical lenses. And, if you miss any
editions of the EyeMatters series, you can go to our news archives at
http://www.eyematters.com/archive.asp.
Sincerely,
Mike Pier, OD
Director, Professional Relations – Practitioner Education
1. Results from an independent 2006 survey of 95 eye
care professionals performed by Directive Analytics. Participation was limited
to eye care professionals who had fitting experience with all brands of silicone
hydrogel toric lenses available at the time of the survey.
2. A total of 18 eye care professionals evaluated 107 patients wearing ACUVUE
Advance for Astigmatism for fit/orientation and visual acuity at initial visit.
These patients were then fitted with PureVision Toric lenses and equivalent
assessments were made at the initial fitting and after two weeks of wear.
3. Results from a clinical evaluation conducted at 117 sites in 8 countries in
which 900 astigmatic patients wearing spectacles (n=119), spherical contact
lenses, or toric contact lenses (n=629) were fitted with PureVision Toric
lenses. After using the PureVision Toric lenses for 1 month, patients completed
a forced choice questionnaire in which they chose product preferences for
specific attributes. Practitioners provided lens fit, slit lamp evaluations and
product performance rating information at each visit.
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denote trademarks of Bausch & Lomb Incorporated. © Bausch & Lomb Incorporated.
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