|Quarterly newsletter on Soft Specialty Contact Lens |
Research, Developments, Designs and Materials SPRING 2011
WORLD WIDE VISION
Global Specialty Lens Symposium
The global meeting in Las Vegas (USA) drew more than 500 participants including close to 400 eyecare practitioners. It represented a true global audience, with participants from 31 countries. Many practitioners and researchers from all over the world shared their knowledge and experience in specialty lens fitting. The meeting in the past featured primarily gas permeable lens topics, but that seems to be changing. Many lectures at the meeting this time were directly or indirectly related to soft specialty lens options.
Myopia control, also with (customized) soft lenses, was covered as was wavefront correction with soft lenses. Many presentations and breakout sessions concerned the use of custom-made soft contact lenses for the irregular cornea. Boris Severinsky presented a paper on silicone hydrogel mini-scleral lenses for keratoconus: a topic he also covered in our last SoftSpecialEdition Newsletter. Perhaps the biggest news at the meeting for the US market was that a new lathable silicone hydrogel material (Definitive-Contamac) gained United States Food and Drug Administration (FDA) approval. This may be of pivotal importance for the soft specialty lens modality going forward as many labs can work with this material to design lenses for patients who typically can benefit most from higher Dk materials. See link below for full conference coverage regarding soft specialty lenses.
Global Specialty Lens Symposium Paris - Las Vegas (USA)
|IN THE LITERATURE|
Differences in Eye Anatomy & Physiology May Require Customized Fitting
Ethnic Differences & Soft Lenses
Ping Situ, of the University of Waterloo (Canada), covers an interesting topic on post lens tear film thickness in soft lens wear in the February issue of the silicone hydrogels website. She refers to an experiment from Meng Lin et al (Berkeley, USA) which showed that the post lens tear film thickness was decreased with an increase of the BCR. But one of the most valuable findings from this study, Ping Situ reports, may be the effect of different ethnicity on the post-lens tear thickness.
Ping Situ - Feature Review; siliconehydrogels.org Febr 2011
In another editorial on the silicone hydrogel website, Jerome Ozkan of the Brien Holden Vision Institute (Australia) looks at that topic specifically. Several differences exist in Asian eyes compared to other eyes, including differences in tear break-up time, horizontal iris diameter, corneal sensitivity, eyelid anatomy and even corneal epithelial barrier function. He concludes that the future range of contact lens designs and materials must take into account the existence of ethnic differences in ocular anatomy and physiology that directly relate to the success of contact lens fitting. Better understanding of these ethnic differences in ocular characteristics may be helpful for practitioners' clinical decision-making process in achieving a more successful fitting outcome.
Jerome Ozkan - Editorial; siliconehydrogels.org Febr 2011
|IN THE LITERATURE|
Power Profiles & Visual Acuity
Wavefront Technology to Aid in Soft Lens Evalluation
Evaluating the optical performance of soft lenses is unfortunately hard to do in clinical practice. Alexis Vogt et al looked at the power profiles in different multifocal lens designs using a Hartmann-Shack wavefront sensing tool to shed some light on the optical performance of aspheric lenses.
Alexis Vogt et al - Contact Lens Spectrum Jan 2011
From a more clinical standpoint: Craig Norman, also in Contact Lens Spectrum, mentioned using over-corneal topography in multifocal soft lens evaluation to locate the central optical zone of the lens on-eye and to see if this reasonably matches the pupil. If decentered significantly, he reports, this can be a clue as to why the patient is having poor reading performance and/or haloes with distance vision.
Craig Norman - Contact Lens Spectrum Jan 2011
An article in Contact Lens & Anterior Eye looks at spherical aberration in relation to visual performance in contact lens wear. The conclusion of this study is that non-custom-made spherical aberration-control soft lenses have little effect on visual quality, although this does not mean that some patients with, for instance, large pupils or larger than average amounts of spherical aberrations could not benefit from non-customized spherical aberration-controlled lenses.
Lindsoog Petterson et al - Contact Lens & Anterior Eye Febr 2011
The Importance of Edge Design in Soft Lens Wear
Teresa Hübner et al from the University of Applied Sciences in Jena (Germany) looked at fitting characteristics of soft contact lenses with different edge designs. Using an optimized cutting technique, the edge profiles of 27 commercially available disposable contact lenses (hydrogel and silicone hydrogel lenses) produced by 10 different manufacturers were analyzed. Hübner et al found that lens edge design can be categorized into four different groups, and these edge-groups were consequently evaluated in a clinical experiment. The fitting behavior and comfort of the soft lens is influenced by edge design they concluded. Two-sided profiles and round edges should be given preference over other edge designs, particularly if lenses with higher modulus are used according to the investigators. Reasons why this may be the case are discussed. See full coverage of the paper via the link below.
Soft Lens Edge Design
Determining the Base Curve in
Custom Soft Contact Lens Design
Matt Lampa & Mark André
In addition to the overall diameter, the base curve is the other essential parameter that defines the sagittal depth of a contact lens. In determining our starting base curve for a custom soft contact lens, we need to take this into account. A long established nomogram that we call the "fit factor" assists us in this process. The starting base curve of the contact lens is determined by a simple three-step process. Click here for more about base curve selection in custom soft lenses.
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