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International Newsletter and Forum on Rigid Gas Permeable Contact Lenses, Corneal Shape, Health and Vision |
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Specialty Academy
The America Academy of Optometry (AAO) is already gearing up for its meeting later this year in October in New Orleans (US) - without question, it's one of the more important meetings in our field. Looking at the contact lens track on the 2015 program, something stands out: Of the 20 lectures provided in general on contact lenses, the bulk are (R)GP- and certainly specialty lens-related. Eight of the 20 lectures have the word 'scleral' in their title. That must be an all-time record. Four more CE courses are on corneal reshaping/myopia control. Two additional lectures are on multifocal lenses, one covers (R)GP torics, one is on tinted contact lenses and two are on corneal disease (including keratoconus). Of the two remaining lectures, one is on 'dry eye and contact lenses,' and just one lecture is on a non-specialty topic: 'daily disposables.' This seems to emphasize the importance - and need - for good specialty lens education. This I-site will cover a number of these topics as well - hopefully adding to the general knowledge on specialty (R)GP) lens fitting.
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Optical Coherence Tomography (OCT)
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Imag(in)e (R)GP Lens Fit Evaluation with OCT
 VanNasdale et al at ARVO 2015, presented a poster on using spectral domain OCT to image (R)GP lenses (poster # 4125). The physical characteristics of (R)GP lenses could be extracted in their experiment from cross sectional OCT data. Optical properties of (R)GPs could also be assessed, according the investigators, using optical path length differences induced by (R)GP lens thickness and index of refraction changes.
Piotrowiak et al used spectral OCT to assess lens-to-cornea fit of (R)GP lenses as a potential alternative to fluorescein pattern evaluation. BCR steepening of 0.1 mm or more led to measurable changes in lens-to-cornea fits: BCR changes of the lens in the order of 0.1mm, 0.2mm and 0.3mm of radius resulted in average apical clearances of 12.38 (SD=9.9), 28.79 (SD=15.4) and 33.25 (SD=10.6) microns, respectively. But although this OCT technique represents a potential new method of assessing lens-to-cornea fit, apical clearance detection with current commercial OCT technology showed lower sensitivity compared to the fluorescein pattern assessment, according to the investigators. |
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A Quasi-Inflammatory Disease?
Keratoconus has been traditionally classified as a noninflammatory disease. According to McMonnies in Optometry & Vision Science, an analogy can be drawn between keratoconus and osteoarthritis, which also involves significant inflammatory processes but, like keratoconus, does not meet all of the classic criteria for an inflammatory disease. Classifying keratoconus as quasi-inflammatory (inflammatory-related) rather than a noninflammatory disease appears to be more appropriate and may help shift the management focus toward developing effective anti-inflammatory therapies, according to the author (see link below).
Ghosh et al (poster # 6104) at ARVO 2015 presented a study looking at the changes in corneal cell morphology with baseline observation in keratoconus patients wearing different types of (R)GP lenses. Specially designed (R)GP lenses resulted in fewer changes in corneal morphology compared to regular (R)GP lenses: after six months of lens wear, the mean anterior (845) and posterior (678) stromal keratocyte density were significantly less compared to baseline observation (891 & 714 respectively). A larger sample size may further assist in understanding the cellular changes in keratoconus, in addition to the use of mini-sclerals for keratoconus.
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ARVO 2015 Update
Kang et al presented a poster at ARVO (poster # 6090) using OCT to look at the OK effect in-vivo. They demonstrated that central corneal thinning is primarily epithelial in nature and that the increase in mid-peripheral corneal thickness after OK is a combination of epithelial and stromal tissue change. Application of Munnerlyn's formula indicates that changes in corneal thickness account substantially for the central refraction change measured after OK.
Maseedupally et al (poster # 6089) looked at the outcome of three OK lens designs worn overnight for 2 weeks. Although significant differences were found in corneal refractive power change between some lenses, the differences were not clinically significant. The authors conclude that the three lens designs used in this study induce similar corneal refractive effects. They did not find a 1:1 relationship between central reduction and para-central increase in refractive power as has been reported by others.
Peripheral refractive error degrades the quality of retinal images and has been hypothesized as a potential factor in stimulating the development of refractive error. Various contact lens designs are based on this hypothesis. The aim of a study by Yoo et al (poster # 2175) was to evaluate the impact of OK treatment on the peripheral wavefront aberration in myopic eyes. They found OK treatment to be effective in reducing the degree of peripheral hyperopic defocus in myopic eyes.
Yuan et al (poster # 6003) looked at the role of accommodative response in OK and found that dynamic accommodation was improved in myopic children after OK. The anterior eye morphology seemed to be more "accommodative" at relax status. This may suggest that improvement of accommodation is a key factor for myopia control using OK.
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A 43-year-old Caucasian female underwent a penetrating keratoplasty. The patient complained about shadow (double) vision and some discomfort with her current reverse curve (R)GPs. Fluorescein pattern evaluation showed adequate peripheral landing of the contact lens OS, but heavy bearing on the temporal part of the graft. In contrast, the nasal graft pattern showed a large pooling area. While observing the Pentacam (Scheimpflug) cross-section measurements, the reason for the asymmetric fitting became obvious: the whole graft was tilted and displaced. The same reverse curve design was chosen, but with tilted optics to mimic the unique geometry of the tilted graft. Although challenging, it is fascinating and satisfying to restore vision in such patients, and this is more than worth going the extra mile.
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Upcoming Events
- EurOK, July 10-12, Budapest (HU)
- ISCLS, Aug 29-Sept 3, St. Gallen (CH)
- Myopie Kongress, 12-13 Sept, Keulen (DE)
- AAO, 7-10 Oct, New Orleans (US)
- ECLSO, 16-17 Oct, Izmir (TU)
- CLMA, 28-31 Oct, Miami (US)
- Cornea CL & Cont Vision Care Symposium, 5-6 Dec, 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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