SoftSpecialEdition is a quarterly newsletter FOR HEALTH CARE PROVIDERS that gives independent updates from the international literature on soft specialty lens-related topics. View as Webpage
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Understanding Lens Optics May Increase Success
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When I first started in practice, I would prescribe a multifocal contact lens to one patient that optically performed great, but when prescribing that same lens to another patient it might fail miserably. At the time, although I immediately moved on to prescribe something else, I remember feeling frustrated with this lack of predictability and with the lack of information to make educated decisions on lens selection to best treat my patients. Fortunately, in the last 10 to 20 years, technology has changed remarkably so that practitioners now have the necessary details to take much of the guesswork out of successfully prescribing contact lenses for our patients. Knowledge about optics and aberrations is key in this process. What factors play a role? Age is one of the more important ones and is better known, but the optics of each eye also vary with accommodation, tear film, pupil size to name a few. What ultimately matters for all patients and their vision, is how the optics of their lens combine with the optics of their eyes. The issues that impact contact lens optics are now of increasing importance as companies aim to develop and manufacture complex lens designs to better correct the presbyope (without inducing aberration) or to slow myopic eye growth in children. Let’s continue to urge manufacturers and researchers to help clinicians understand the detailed knowledge of the optics of every lens so that when practitioners prescribe a lens, they can make educated decisions on why it should work and what to do next if it does not work as intended. It is important to give contact lens optics more thought; let’s give them the place they deserve within our industry and profession. This will help us each time that we prescribe a lens to maximize the likelihood of successfully for every patient. Take the guesswork out of contact lens optics. See link below for more.
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Take the Guesswork out of Soft Lens Fitting
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Stephanie Ramdass in her 'Custom Soft Corner' looks at the use of contact lens sagittal height values or CL-SAG, a metric that is not included on the foil packaging or labeling for commercially available soft contact lenses, in practice. She noted that during a Global Specialty Lens Symposium panel titled “What’s Special About Specialty Soft Contact Lenses,” Matt Lampa from Pacific University shed light on the importance of understanding the CL-SAG of lenses used in everyday practice. Central keratometric readings of the cornea (approximately 4mm worth of data) are often used to determine the initial soft diagnostic contact lens, but this is limited. When the same manufacturer offers two different base curves for the same lens type, it is tempting to fit the flatter lens option on flatter eyes and vice versa. However, the actual difference in CL-SAG of these two theoretical lens options is minimal, and thus, the lenses may fit nearly identically on the eye (assuming that they have the same diameters). With the created CL-SAG chart, it is evident that there is a range in the CL-SAG values of existing soft contact lens. There is renewed interest in putting the science back into soft lens fitting. With the aid of technology, it is easy to see that there is quite a variation in off-the-shelf lenses and that they are not one-size-fits-all. Further research will support this discussion and allow practitioners to look at their diagnostic soft lens trays with a fresh perspective. See this link for the CL-SAG charts available and the link below for the full article.
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Myopia Management - One Child at a Time
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A new book on myopia management based on 'The Montreal Experience' was just launched. It covers in detail all intervention methods, but it surely also digs into soft lens options. In particular, the book reinforces the fact that myopia management must be customized according to the patient, as different devices may lead to different outcomes. Some devices that are effective for a given patient may lead to progressing myopia or to an increase in axial length in another patient who has similar refractive error. The Montreal Experience implies that the design of contact lenses must take into account the physiological parameters of the patient, including measurement of the pupil area, as well as the importance of dose–response, including with optical intervention. There are two ways to increase the dose of myopic defocus on the retina and to influence its response. First, a larger area of myopic defocus causes a slowing of myopia progression, and second, it is possible to increase the signal strength by increasing the power of the addition. Both can be applied in a controlled manner potentially with custom-made soft lenses. Choroidal volume analysis is a new and promising means to evaluate the ocular response to any of these visual stimulations; it may be a convenient means to test, in the short term, the individual response and to determine the best strategy for a given patient, according to the authors.
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Global Specialty Lens Symposium
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Poster Session Highlights on Soft Lens Fitting
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Jason Marsack et al (GSLS poster #150) reported on key challenges for fitting and manufacturing wavefront-guided soft contact lenses. The process starts with the fitting of a standard spherical soft lens, after which they used the NextWave aberrometer (Wavefront Dynamics) to quantify wavefront error and spherical lens rotation and translation. The results showed that wavefront-guided lenses can be made in a soft lens material and that they are capable of reducing higher-order aberration - but alignment of the wavefront patch with regard to the underlying pupil is crucial and challenging.
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Mari Fujimoto et al evaluated the relationship between corneoscleral profile and sagittal depth in soft contact lens fitting (poster #34). Clinical implications of this case series included that with significant temporal lens decentration, selecting a lens of a greater sagittal depth (CL-SAG) may improve lens centration. Also, patients who have steep central Ks, a low corneal eccentricity, and a high corneal angle will likely require a lens from the right-hand side of the chart to provide an adequate lens fit. And if patients exceed the deepest CL-SAG available on the market, they will likely be best served with a custom soft lens.
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Both rhegmatogenous retinal detachments and scleral buckles may produce significant changes in shape of the eye, with modifications to the conjunctival and scleral anatomy. Amanda Dieu looked at this (poster #123) and found globe shape alterations after buckling to be potentially irreversible. As a result, fitting soft contact lenses on these post-surgical eyes may be a challenge. Due to the irregular scleral contour, conventional soft contact lenses may decenter, causing optical aberrations. Topography scans over the soft contact lenses may provide clinicians with additional information regarding lens centration and optical quality. Because post-scleral-buckling eyes are typically highly myopic, even small amounts of lens decentration may cause visual blur.
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Eric Yoshinaga described Lyme disease as the most common tick-borne infection and noted that it presents with a variety of ocular manifestations such as keratitis, iridocyclitis, vitritis, multifocal choroiditis, and panophthalmitis. It can lead to severe vision loss and permanent damage that is noticeable long after the active infection has been treated. Dense corneal scarring can have a significant impact on a patient’s vision, self-image, and psychological well-being. A prosthetic contact lens can play an important role in improving self-confidence and social relationships, and with the availability of fitting sets, it should be considered whenever indicated.
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More on specialty & custom soft lens related topics @ GSLS 2023 Las Vegas (US)
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Soft Specialty Lens Resources
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