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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Achieving Success With Soft Lenses
for Patients With Keratoconus
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Rigid lens options (corneal and scleral) have been the traditional choice for patients with keratoconus when the visual acuity (VA) with spectacles is no longer sufficient. However, soft lenses have increasingly come into sight as a valuable alternative. Manufacturers have put significant effort into developing specialty soft lenses that maintain a regular front surface while on the eye. These lenses have increased centre thickness, and an aspheric front curve is typically used to optimise the VA while the peripheral zone is thinner to increase oxygen supply and improve comfort. This enables these lenses to provide a vision correction equal to that of rigid corneal lenses when the keratoconus is in an early or moderate stage; even in more advanced cases, these lenses can sometimes provide a viable alternative, as demonstrated by two case reports. Case 1 discusses early keratoconus in a 29-year-old male with autism. He expressed concerns about the comfort of contact lenses and noted that he would not wear lenses if they caused any discomfort. The patient found the Kerasoft IC lenses comfortable and was happy with the improvement of his visual acuity. He made the decision to commence wearing contact lenses. Case 2 discusses a 25-year-old male with advanced keratoconus in one eye, while the visual acuity in the other eye is 1.0 without correction. When the patient wears the scleral lens OD, this eye appears to have a bigger lid aperture compared to OS. He asked to be fitted with an alternative. Refitted from a scleral to a soft lens with increased centre thickness (Novakone), the visual acuity remained remarkably the same, while the asymmetric lid aperture problem was resolved. The cases show that these lenses can offer an effective alternative to rigid, hybrid and scleral lenses, providing similar vision correction with greater comfort and other advantages.
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How Important Is the Fit of a Standard
Soft Lens on a Normal Eye?
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It’s an ongoing debate in the (specialty) lens arena: how important is the 'fit' part with soft lenses to prevent dropouts and provide better care? The international community is not always convinced. A recent (excellent) paper by Morgan and Sully focuses on Soft contact lens discontinuations and their dramatic impact on the overall success of the modality. The paper considers the background and underlying evidence for the potential causes of soft lens discontinuation in new wearers, and it presents clinical management strategies to minimize this phenomenon. Lens fit, though, is not a prominent feature in this article. In the 'TFOS International Workshop on Contact Lens Discomfort: Report of the Contact Lens Materials, Design, and Care' paper by Jones et al (open access), 'good lens fit' was one of the few items for which they found clear supportive evidence of a link with comfort. A recent poll by Contact Lenses Today showed that the vast majority of eye care practitioners responding to the survey reported the fit of a standard soft lens on a normal eye to be very important (55%) or moderately important (24%), with only 24% indicating that it was 'not very important.'
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Two posters from Spain at the Global Specialty Lens Symposium focus on the corneo-scleral junction (CSJ) angle and what it may mean for soft lens fitting. Javier Rojas Viñuela's poster (#129) concluded that the mean CSJ angle was 177.5±1.1° but that regional differences were observed. A mean 7.7±3.7° difference was found between the steepest (smallest) and flattest (largest) angle within the same eye, with a large range among individuals (ranging from 3.5° to 17.8°). The CSJ angle was smaller (steeper) in the nasal region than in the remaining sectors. The poster concludes that the CSJ angle influences sagittal height, which is a key parameter for ensuring a successful lens fit, especially in large-diameter lenses. However, to date only a few works have characterized this parameter, the authors state. Javier Sebastián et al (poster #130) compared sagittal height measurements obtained with profilometry and estimated with corneal topography. They found a 5±28μm difference at a 10mm chord and a 47±182μm difference at 15mm in the normal cornea group, compared with a 6±109μm difference between the instruments at 10mm and 122±430μm at 15mm in the irregular cornea group. This means there are statistically significant differences in the sagittal height measured with both devices for the 15mm chord but not for the 10mm chord, and also that the differences in the normal corneal group were much smaller than in the irregular cornea group. This poster won 2nd prize in the research category.
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Understanding Soft Lens Fitting for Keratoconus
in Four Steps
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The most common type of irregular cornea is keratoconus, and the prevalence of this appears to be 5-fold to 10-fold higher than previously reported. In some parts of the world, such as in the middle east, the incidence of keratoconus is considered to be even higher. But the landscape of keratoconus management is changing rapidly. Corneal cross-linking (CXL) is becoming the standard of care for young patients with progressive ectatic corneal disease. It is reported that 25% fewer corneal transplants were performed in the 3-year period in which CXL became available. There are probably not fewer keratoconus patients; supposedly more will be seen, but most likely in the earlier stages of the condition. Topography and wavefront-guided excimer laser treatments can improve corneal contour and improve corneal symmetry. In addition, there have been major developments in the field of corneal transplants for keratoconus. While a penetrating keratoplasty (replacing the entire cornea in its full thickness with donor tissue) not too long ago was standard procedure, now an array of lamellar techniques, in which only a portion of the cornea is replaced by donor tissue, are increasingly used. This can provide many advantages, one being that the corneal irregularities are less prominent, as a part of the patients’ original cornea remains intact. All these developments may impact what management methods we offer and apply; glasses and soft (specialty) lenses may become more common as a first-line method of vision correction. This article in Global Contact explores how. Photo: soft keratoconus lens on the eye. Courtesy Thibaut Syre (France)
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Simple Is Sometimes Better
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See also the poster and free paper by Sydney Krisa et al from Massachusetts Eye & Ear Infirmary (US) presented at the recent GSLS 2023: ‘Your Weapon of Choice in Early Keratoconus and Mild Corneal Scars: Soft Toric Lenses’. If a soft lens provides satisfactory results, that option should not be overlooked. Simple is sometimes better.
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Soft or Rigid Lens for Posterior Microphthalmos?
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Research from Turkey compared a soft silicone hydrogel lens (Toris K) for keratoconus with a rigid corneal lens in 11 patients with posterior microphthalmos (PMs). Patients with this presumably autosomal-recessive entity typically have normal anterior segment dimensions but have shortening of the posterior ocular segment and resultant high hyperopia. Retinal folds and/or pigmentary retinopathy may be seen, and there is a propensity for uveal effusion. A total of 22 eyes were included in the study; the mean axial lengths were 16.01±0.1mm and 15.9±0.2mm in the right and left eyes, respectively. Mean K1 and K2 were 48.6±2.2D and 49.4±2.2D, respectively. Mean logMAR best-corrected visual acuity (BCVA) of the 22 eyes before contact lens fitting was 0.63±0.56 with spectacles. After Toris K and corneal lens fitting, mean logMAR BCVAs were 0.43±0.20 and 0.35±0.25, respectively. Both lenses provided better visual acuity than spectacles. Rigid corneal lenses provided significantly better visual acuity compared to the HydroCone lens, but eight of the 11 patients (73%) experienced ocular discomfort with the rigid lenses. Corneal surfaces are steeper in patients with PMs than in the normal population, and for that reason, their vision should be rehabilitated by special-design keratoconus lenses such as Toris K or rigid corneal lenses. But although vision rehabilitation seems better with the rigid lenses, most patients preferred Toris K because of discomfort with the rigid lenses.
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