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International Newsletter and Forum on Rigid Gas Permeable Contact Lenses, Corneal Shape, Health and Vision |
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Nerves
 Every day you walk into a room (five days in a row) and find about 1000 new posters on any eyecare topic. It drives you nuts! Add to that a few hundred presentations and workshops: 7000 titles in total. It really gets on your nerves. This is the ARVO - the Association for Research in Vision and Ophthalmology - meeting. The beauty is: you see science evolving - on the spot. While you talk to the poster presenters showcasing their research on large boards, others provide feedback: so-and-so has done this that way - maybe we should be heading in that direction, etc. This is 'a meeting,' in the most literal sense of the word. And so you come home with a million (or so) new ideas. It takes a lot of adaptation to digest all the information. Neural adaptation, by the way, is just one of the great insights I took home from ARVO this year (see next item). Some more highlights of the meeting regarding (R)GPs and corneal shape can also be found in this newsletter. Eef van der Worp
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Neural Adaptation
 Keratconus is a slow process. And it involves high amounts of lower and higher order aberrations. Aberrations that patients may get used to. And it may be hard for them at first, when they get a new correction method, to adapt to the new way of seeing. And this may potentially explain why the visual acuity in keratoconus patients sometimes regresses where we expect better vision with an (R)GP or scleral lens, for instance. This came from a poster and presentation by Geunyoung Yoon et al (program#1394). They were able to measure the higher order aberrations over a scleral lens and to put the aberration correction on the front surface of the lens. This generally leads to an improvement in vision - but not quite perfect yet. What they did to improve this was to also correct for the decentration of the pupil. They measured the location of the pupil behind the scleral lens and made sure that the higher order aberrations were corrected over that pupil plane. This again improved the vision, but again the theoretical vision thus achieved was greater than the actual visual acuity the patient reported. Yoon et al suggested that neural adaptation may play a role in this, a lesson we all may learn from in clinical practice. See further the I(n)-site-the-practice item in this newsletter. |
Meibomian Gland Dysfunction
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MGD - is it the (R)GP?
 Jason Nichols at ARVO looked at meibomian gland atrophy in contact lens wearers. A report by Arita et al in 2009 suggested a higher rate of meibomian gland dropout in contact lens wearers compared with non-lens wearers, raising the question as to whether meibomian gland dropout was related to modulus of a contact lens and mechanical interaction between the lens and the lid. Nichols et al (program#6301) conducted a clinical trial with low modulus silicone hydrogel daily disposable lenses compared to spectacle wearers, but did not find a trend toward any meibomian gland loss in the lens wearers compared with the spectacle wearers over a year. When they went back to the original Arita et al article, they found that the 'current lens wearers' group in the study by Arita et al included a number of (R)GP lens wearers with meibomian gland dropout. Possibly, the meibomian gland atrophy found in the Arita article may be attributed largely to (R)GP lens wear, they suggest. Future work is needed to confirm this hypothesis. A review article on Meibography by Heiko Pult and Jason Nichols can be found in the May edition of Optometry & Vision Science. |
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Large studies on Large Lenses
 A study by Farid Afshar, Ken Pullum and Linda Fickes (program#4716) reported on a retrospective review of 612 patients managed with scleral contact lenses at Moorfields Eye hospital in the United Kingdom. In the keratoconus group (n=160), the mean unaided visual acuity was 2/60. With scleral lenses, 75% of patients achieved a visual acuity of ≥6/12. In the corneal transplant group (n=700), mean unaided visual acuity was 3/60 with 81.9% of patients achieving a visual acuity of ≥6/12. Muriel Schornack et al (program#4715) reported on the use of scleral lenses in 114 patients with ocular surface disease in an outpatient setting and concluded they can be effective in the management of a variety of conditions that compromise the ocular surface. Although the primary goal of scleral lens wear in these patients is ocular surface protection, they stated, visual acuity also improves with lens wear in the majority. 'When Lightening Strikes Twice' was the title of a poster by Sahar Kohanim et al (program#4708) on seven cases of Stevens-Johnson Syndrome (SJS) and Corneal Ectasia. They used PROSE treatment scleral lenses (prosthetic replacement of the ocular surface ecosystem) to successfully manage these patients. Whether there is a causal relationship between SJS and corneal ectasia is unclear at this point. Picture courtesy of Jason Jedlicka.
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More Nerves
 Helen Swarbrick (program#4731) presented a study that concluded that central corneal sensitivity is reduced after a single overnight wear of orthokeratology lenses. This suggests that the mechanical force exerted by contact lenses may be a key influence on corneal sensitivity, the investigators reported. Edward Lum et al (program#6108) looked at the morphology of the corneal sub-basal nerve plexus in soft and orthokeratology contact lens wearers using laser-scanning confocal microscopy. This study revealed an apparent decrease in central corneal nerve density with orthokeratology lens wear. This suggests that the mechanism underlying refractive change during orthokeratology treatment may also impact the corneal nerve morphology in lens wearers - either temporarily or more permanent. Pauline Kang (program#4713) investigated the time course of the effects of overnight orthokeratology (OK) lens wear on peripheral refraction and corneal topography. The greatest change occurred during the first night of orthokeratology lens wear. Subsequent changes in both peripheral refraction and corneal topography were less dramatic across subsequent days - up to seven days. Vinod Maseedupally et al (program#4714) looked at treatment zone decentration during orthokeratology on eyes with low and moderate amounts of corneal toricity. The treatment zone was decentred in both groups, with greater decentration in the group with low (≤1.50D) compared to the group with moderate (>1.50D) amounts of corneal toricity. This may call for toric orthokeratology lenses.
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Decentered Higher Order Aberration Corrected Sclerals
Higher order aberrations (HOAs) are often the culprit behind sub-optimally corrected keratoconus patients who are wearing either corneal (R)GP lenses or scleral prosthetic devices. Wavefront-guided correction with scleral prosthetic devices has many benefits for patients with keratoconus. The stability of the device ensures proper placement of the optics, once any decentration and rotation are factored into the design. As a result, this case demonstrated a significant reduction in the HOAs with a custom wavefront-guided correction. However, the BCVA with the wavefront-guided correction was significantly poorer than that of normal subjects, even though the optical quality was excellent. This demonstrates that a patient with keratoconus who has long-term neural adaptation with optical blur due to HOAs may not elicit the maximum visual benefit upon optical correction. However, this neural deficit may be overcome given sufficient time to re-adapt with corrected optics, which may eventually improve overall visual performance. Click here for the full report.
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Upcoming Events
- ISCLS congress 2012, September 7-12, Kent UK
- ECLSO congress, September 14-16, Nice FR
- ISCLS congress 2012, September 7-12, Kent UK
- VDCO Contact 2012, October 5-7, Friedrichshafen DE
- AAO, Oct 24-27, Phoenix US
- CCLS Symposium December 1-2, Houston 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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