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International Newsletter and Forum on Rigid Gas Permeable Contact Lenses, Corneal Shape, Health and Vision |
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Going Backstage with Scleral Lenses
Soft lens fitting and scleral lens fitting have a thing or two in common. Actually, they are more in line with each other than with corneal GP fitting in many ways. The topographical changes that occur behind the lens are another thing they have in common. The Contact Lens and Visual Optics Laboratory at the School of Optometry and Vision Science in Brisbane (AU) has done some of the best clinical specialty lens research in our field over the last decade or so. A new paper from this group, by Stephen Vincent, David Alonso-Caneiro and Michael Collins, focuses on the corneal curvature and optics changes that occur under scleral lenses. Modern mini-scleral contact lenses land entirely on the sclera and overlying tissues, leaving the cornea clear from mechanical pressure by the lens. However, as reported previously by Soeters et al, corneal topographical changes do occur with scleral lens wear. In the study by Vincent et al too, although corneal clearance was maintained throughout the 8-hour lens wear period, significant corneal flattening (up to 0.08 mm ± 0.04 mm) was observed, primarily in the superior mid-peripheral cornea, which resulted in a slight increase in against-the-rule corneal astigmatism. Higher-order aberrations - in terms of horizontal coma, vertical coma and spherical aberration - all underwent significant changes. East Asian participants displayed a significantly greater reduction in corneal clearance and greater superior-nasal corneal flattening compared to Caucasians. In conclusion: practitioners should be aware that corneal measurements obtained following mini-scleral lens removal may mask underlying corneal steepening. There is - still - a lot to learn about what is happening backstage with scleral lens wear.
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Signs, Symptoms & Sclerals
Dry eye has always been somewhat underutilized as a major indication for scleral lenses - the irregular cornea and vision-related factors have always prevailed in that regard. But it has become clear over the last decade or so that scleral lenses can be a major help in dry eye management. To evaluate dry eye signs and symptoms in scleral lens wear, 26 keratoconus patients (with intrastromal corneal rings, and a group without these rings) were evaluated. The patients wore the scleral lenses from 6 to 9 hours. The mean scleral lens sag for all patients was 4310 microns, ranging from 4200 microns to 4800 microns. The Ocular Surface Disease Index scores were statistically lower after wearing scleral lenses for both groups of patients. Also, both groups exhibited a significantly lower osmolarity and a significant rise of MMP-9 concentration after wearing scleral lenses. In conclusion: the authors state that short-term scleral lens wear improves the symptomatology and some of the signs of dry eye, such as osmolarity and Ap4A concentration. The increased MMP-9 concentration could be caused by tear film stagnation and use of preserved saline.
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Adaptation & Prediction
Neophyte rigid gas permeable corneal contact lens wearers were evaluated over a 1-month period. Twenty-two young healthy subjects were enrolled in the study and fitted with (R)GPs. Six subjects dropped out due to discomfort from the study before 1 month (a 27% discontinuation rate). Successful RGP wearers (16 participants) achieved high levels of subjective vision and high comfort scores between 10 and 15 days of wear. Conversely, unsuccessful wearers discontinued wearing the lenses after the first 10 to 15 days, showing comfort scores and wearing time that were significantly lower compared with the first day of wear. Schirmer's test showed a significant increase at 10 days, and the BUT trends decreased after the first week of wear in the unsuccessful group. This, the authors state as a summary of the results, may indicate that symptomatology related with dryness and discomfort detected during the first 10 days of the adaptation phase may help the clinician to predict those participants who will potentially fail to adapt to (R)GP lenses. Photo: Jan Pauwels UZA
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Central Corneal Thickness Change
 Following up on last month's edition, with lots of coverage of orthokeratology: the January 2016 edition of Eye & Contact Lens is a special edition devoted to myopia control, with a primary role for orthokeratology. In addition, an interesting paper was published in Eye & Contact Lens: a meta-analysis of central corneal thickness changes with overnight orthokeratology. A total of 10 studies containing 239 patients in total (339 eyes) from clinical studies were included in this analysis. Central corneal thickness reduced significantly from 1 day to 1 week by 5.73 microns, and a significant mean reduction of 5.89 microns also occurred from 1 day to 1 month. No significant reduction was found between 1 week and 1 month. Although further research seems indicated to find the precise change, this meta-analysis for now demonstrates that most of the reduction in central corneal thickness occurred during the first week and remained thinner for 1 month.
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Recurrence or Re-emergence after Keratoplasty?
Keratoconus may recur following penetrating or lamellar keratoplasty, but latency is considerably longer in the penetrating version. Since keratoplasty involves only partial excision of the cornea, and recent research strongly indicates the presence of the pathology in the peripheral host cornea, the reappearance of the pathology after a latency period is most likely due to migration of the disease from host to donor cornea. This notion is further corroborated by the shorter latency period in partial thickness keratoplasty, in which more of the diseased host cornea remains in place. Other proposed causes for the recurrence of keratoconus, such as eye rubbing and contact lens wear, were reportedly not associated with a significant number of cases and, therefore, are not the primary factor. Based on existing literature, it is concluded that in post-keratoplasty keratoconus, the etiology stems from re-emergence of the disease rather than recurrence. Keratoconus patients in need of keratoplasty should be counselled on the possibility of the disease re-emerging.
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Refractive Improvements after Refractive Surgery
 Refractive surgery does not always result in an optimal visual outcome. In some cases, overnight orthokeratology can improve the optics in these eyes, especially in reducing higher-order aberration and by increasing the optical zone diameter of the eye. In this case, orthokeratology was used as a treatment after a photorefractive keratectomy (PRK) procedure. A 39-year-old male Caucasian had undergone PRK in 1991. The patient complained of increasing vision problems, especially at nighttime or during low light conditions. He received a -0.5D/-0.75D spectacle correction for driving from his ophthalmologist, but he was still not satisfied with the visual outcome. Overnight orthokeratology was selected as treatment for this patient. After 4 months of wearing these lenses, his VAsc was 1.25, and the patient had noticed a dramatic reduction in halos and shadows. Topography showed a 64% increase in optical zone diameter to 4.25mm. Orthokeratology is an excellent alternative treatment post-refractive surgery, and this option should be more often considered as a valuable treatment option for patients suffering from reduced visual outcomes after refractive surgery, in the authors' opinion. The quality of vision can in some cases be restored, while still having the freedom from spectacles and contact lenses during daytime hours.
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Upcoming Events
- Vision by Design, April 6-11, Phoenix USA
- EFCLIN, 28-30 April, Valencia (ES)
- ARVO, 1-5 May, Seattle (US)
- ECLSO, 30 Sept-1 Oct, Paris (FR)
- European Ophthalmology Conference, Sept 21-23, Amsterdam (NL)
- AAO, 9-12 Nov, Anaheim (US)
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I-site is an educational newsletter that is distributed on a monthly basis and provides an update on rigid gas permeable related topics (scientific research, case reports and other publications worldwide). I-site is objective and non-political. Its editor Eef van der Worp, optometrist, PhD, FAAO, FBCLA, FIACLE, FSLS is a lecturer for a variety of industry partners, but is not related to any specific company. Please contact us at: i-site@netherlens.com.
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