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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World Wide Vision XXXXVIII
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At a Junction in Soft Lens Fitting
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We are at a junction. Quite literally: an important parameter to consider in soft lens fitting is the corneo-scleral junction. After a preliminary evaluation, many eyecare practitioners may switch their “scan” to advanced mode to search for corneal parameters that do not meet the standard. If the corneal parameters are outside the norm, then the “navigation system” may suggest you take the extended parameter/custom path. If this is the case, this is where your “navigation system” needs an update: an extended function is needed to track the limbus and anterior sclera and obtain overall ocular sagittal height (OC-SAG) measurements beyond the cornea. Sometimes, an eye with out-of-the-norm corneal parameters may have not so out-of-the-norm OC-SAG values at chord diameters between 14mm and 15mm. In such cases, another standard or “one-sized” soft lens can still work - or the other way around. The sagittal height values of soft contact lenses available on the market are published, and adjusting the sagittal height of the lens accordingly is a good strategy in these cases. But while “the junction” may play an important role in soft lens fitting, many other variables are involved in how a soft lens behaves on-eye, such as lens material and design, lens flexure, lid interaction, etc. Therefore, isolating ocular surface shape parameters from the other variables to analyze soft lens fitting may be too simple. Thus, the way forward - and a more philosophical “junction” - should be to move away from the traditional deductive method (building theories from experimental findings) to macro data analysis. This means not only analyzing a large number of fittings but also integrating all the multiple variables involved in soft lens fitting in a comprehensive approach. This implies developing an algorithm that goes a step further than merely identifying out-of-the-norm ocular parameters; it should correlate them with successful/unsuccessful soft lens fittings and find patterns that can guide (or navigate) us in the right direction, rather than relying on inflexible theoretical models.
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Therapeutic Soft Lens Use
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Managing Chronic Discomfort and
Chronic Epithelial Dysfunction
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The BCLA CLEAR paper by Jacobs et al (open access until March 2023) classifies soft lenses for therapeutic use into two categories. The first is bandage contact lenses, which are lenses that are used for the treatment of ocular discomfort or to support the cornea during healing after surgery or when the cornea is being treated for an underlying disease state or to protect the cornea from the environment or mechanical interaction with the lids. The second is rehabilitative soft contact lenses; these lenses are prescribed for conditions that prevent a patient from achieving adequate visual function with spectacles because of high, irregular, or asymmetric refractive error. Partially or completely occlusive lenses that improve function or cosmesis after trauma, surgery, or stroke also fall into this category. A recent contribution by Stephanie Ramdass in Contact Lens Spectrum focuses on managing chronic discomfort and managing chronic epithelial dysfunction. She urges to approach this on a case-by-case basis, as there is no single fitting philosophy when it comes to therapeutic soft contact lenses. She refers, as an example, to eyes that have undergone multiple keratoplasty procedures, in which a highly irregular corneal surface with variable elevation patterns across the entire cornea is common. Fitting an off-the-shelf lens will most likely not suffice. Combining the flat central keratometric readings with larger-than-average corneal diameters can yield inadequate lens fits that can add to discomfort with lens wear. These eyes often suffer from chronic ocular surface pain and a constant “raw” feeling. In the open-eye state during the day, every blink can be debilitating, even though there are no obvious signs of mechanical trauma to the corneal surface. Multiple factors need to be taken into consideration when fitting therapeutic lenses. If the ultimate goal is corneal pain alleviation and corneal protection, use your arsenal of custom soft lens options to provide the best option for your patient and manage accordingly. Photo by Towfiqu barbhuiya on Unsplash
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Silicone Hydrogels - Four Decades
of New Chemistry in Soft Contact Lenses
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A recent article by Ralph Stone explores research and development of four decades of soft contact lens materials up to today’s more than 20 silicone-hydrogel-material lens options on the market. In 1984, Holden and Mertz reported that hydrogel polymers relying solely on water to transport oxygen were insufficient to avoid corneal edema with overnight wear. Their study reported that with daily wear, a contact lens with an oxygen transmissibility (Dk/t) of 24.1 did not cause corneal edema. Lessons learned from the first 20 years of hydrogel lens wear included that oxygen transmission to the cornea is critical for successful overnight wear and that relying on water transport alone may not be sufficient to prevent corneal edema. Further, the use of charged molecules to increase water content can lead to higher levels of deposit formation and interaction with tear components (FDA Group IV). With regard to safety, the care of contact lenses is important, and testing standards are crucial. The continued use of hydrogen peroxide, and the development of other key disinfecting compounds, could provide alternative safe approaches to reusing lenses. Overnight wear continues to be a risk factor for infection, and wearing lenses during sleep periods and while swimming and showering are risk factors for infections. The critical problem in the development of silicone hydrogels was the fact that silicone polymers are inherently hydrophobic and thus incompatible with the ocular environment. Simply co-mixing them with hydrophilic polymers such as HEMA or methacrylic acid often fails to produce a clear polymer. The earliest approaches to this problem were founded in the late 1970s. It took another 10 years from these first patents to launch an acceptable silicone hydrogel contact lens in the U.S. market. Silicone hydrogels have addressed the need for oxygen in maintaining corneal health, while there is continued research regarding issues of infection, compatibility of lenses with care systems, and other contact lens-related issues. Photo by Chromatograph on Unsplash
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D.I.M.S., H.A.L.T., S.T.O.P.
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Myopia management with optical intervention, beyond the traditional ortho-k method, continues to gain much attention. In addition to spectacle lenses such as the DIMS (Defocus Incorporated Multiple Segments) and HALT (Highly Aspherical Lenslet Target) lens designs, new soft lens innovations are surfacing as well. A poster presentation at the upcoming Global Specialty Lens Symposium (Montani et al) will explain that many lenses are available, but with a few basic designs. In short, first is the traditional center-distance bifocal designs, then a number of extended-depth-of-focus designs (with some minor and some larger individual differences), the concentric ring design such as what the MiSight lens uses and finally the new 'torus' design that has recently been introduced in some regions (with a very high-plus add in the center over a very small area of 1mm). All in all, soft lens optics are roaring and expanding, and there seems room for growth and optimization in the myopia management arena. The new Spatio Temporal Optical Phase (STOP) technology is available both in spectacle and soft lens form. The paper linked below evaluates the design in a soft contact lens modality against MiSight to compare the visual performance and binocular/accommodative function when worn by young myopic adults.
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Preoperative Angle Alpha and Kappa Contact Lens Test in Patients Undergoing Multifocal IOL Surgery
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The purpose of this study was to assess the preoperative objective angle alpha and angle kappa measurements of patients considering multifocal intraocular lens (IOL) surgery and to perform a multifocal contact lens test. Alpha and kappa angles were measured using the iTrace aberrometer. Two hundred seventeen eyes (111 patients) were included. A standard center-near multifocal lens (Alcon AirOptix plus HydraGlyde Multifocal 8.6/14.0) was fitted, or when there was >0.75D astigmatism, a toric multifocal (Saphir RX Multifocal Toric, MarkEnnovy), with the center-distance design for the dominant eye and the center-near design for the non-dominant eye, was fitted. On day 7, patients were asked whether they wanted to go ahead with surgery based on their visual experience with the contact lenses. Subjective factors related to contact lens wear such as comfort or dryness were excluded from the decision-making. Patients with a positive multifocal lens test typically had small angle alpha and kappa sizes. In this study, many patients refrained from surgery due to a negative contact lens test. The authors state that in counseling patients for multifocal IOLs, the use of contact lenses prior to refractive lens exchange is a useful instrument. Its role can be seen as an alternative or add-on preoperative examination in addition to angle alpha and kappa measurements. He advises to look at custom soft lens fitting, at lens fit independent of lens material first - almost like a corneal or scleral lens. It all starts with understanding the ocular surface shape first.
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Last fall, Matthew Lampa presented a webinar 'Custom Soft Lens Update' on the gpli.info platform, in which he separated out different categories of soft specialty lenses. First, there are the abnormal ocular surface shapes: either large or small eyes or atypical overall surface shapes. Secondly, there are the refractive error and irregular astigmatism candidates; this includes keratoconic eyes, but also post-refractive surgery candidates. And then there are specific subgroups covered, such as aphakia, glaucoma, etc. When opening up into customised soft lens fitting, Lampa further explains, a list of at least seven parameters emerge that can each be individually modfied, such as: base curve radius and diameter but also material, center thickness, design, optical zone and of course, power. That may look overwhelming, but Matt explains in a simple and practical way how to deal with these. He further covers over-topography (over the lens) and what this can do to further enhance specialty soft lens fittings, including for multifocal lens designs and in cases of decentered multifocal lens optics.
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Global Specialty Lens Symposium - live - 2023
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