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International Newsletter and Forum on Corneal & Scleral Rigid Gas Permeable Contact Lenses, Corneal Shape, Health and Vision
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I-site newsletter is a global newsletter which is purely educational in nature and launched in 2009, that monthly provides independent updates from the international literature on specialty (R)GP lenses and related topics. To unsubscribe at any time, click the link 'SafeUnsubscribe' at the bottom of this newsletter.
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Cloudy with a Chance of Fogging
Maybe one of the finest examples of the evolution of scleral lenses is not the increase in the number of peer-reviewed publications on this topic as reported on earlier - well, that too actually - but the way we look at 'midday fogging' or cloudiness, as it has been called by various investigators. Two things are quite interesting about this: first is the fact that midday fogging was considered an unavoidable nuisance for a long time. As long as patients could wear their scleral lenses for a reasonable number of hours per day, they basically shouldn't complain about taking the lens out during the day once. Or twice. Now, that has changed with the evolution of the modality over the last decade. Or, as Mile Brujic and Dave Kading said it in Contact Lens Spectrum: 'if post-lens fogging is the new norm, we don't want to be normal.' No worries about the latter part, boys. But the thing is, we don't accept 'nuisances' like this anymore within the scleral lens modality. This proves to me that the future for this modality does not look cloudy at all - literally. The forecast looks pretty bright and sunny if you ask me.
Eef van der Worp
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Optics is basically the root of our profession - and we should be careful not to deviate from it too much. Therefore, the January 2020 special edition of Clinical & Experimental Optometry deserves extra attention, and credits.
Stephen Vincent and
Scott Read host a special 'visual optics - looking beyond 2020' issue. It features interesting articles on spectacle and low vision optics, but certainly contact lenses get their share. Amit Jinabhai from the University of Manchester (UK) looks at customised aberration-controlling corrections for keratoconic patients using contact lenses, while Augustine Nti and David Berntsen from the University of Houston (US) cover optical changes and visual performance with orthokeratology.
They state that overnight orthokeratology can temporarily reduce myopia, hyperopia, and astigmatism, which leads to improvements in uncorrected high- and low-contrast visual acuity with very little regression throughout the day; but, it also increases higher-order aberrations and can improve accommodative accuracy. Specifically, myopic orthokeratology increases positive spherical aberration. In line with that, from Hong Kong (CH) Jason Lau et al report on the influence of orthokeratology compression factor on ocular higher-order aberrations.
Rohan Hughes et al from Brisbane (AU) wrote a nice review article: higher order aberrations, refractive error development and myopia control.
A number of other papers also dig into myopia, its development and the aberrations involved.
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If you say that people or things are in limbo, you mean that they are in a situation in which they seem to be caught between two stages (Collins Dictionary)
and it is unclear what will happen next. Hypoxia is such a topic in the scleral lens arena. However, we may have had shed new light on this. First, Stephen Vincent at the Global Specialty Lens Symposium 2020 reported on post-lens fluid reservoir (PLFR) thickness, showing that indeed there is a significant reduction in oxygen transmissibility, and therefore an increase in corneal edema, if the PLFR thickness increases. However, new calculations show that beyond the 400 micron mark (where previous studies stopped measuring), the effect tapers off and even levels out between 400 and 800 microns of PLFR thickness. In addition, Clayton Radke from the University of California, Berkeley (US) showed that the limbus may have a previously unaccounted-for effect. The hypoxia measurements done so far always looked at central clearance and central swelling. However, this did not take into account external sources of oxygen, such as the blood supply in the limbal area. The calculations he presented at the
scleral lens forum
in Las Vegas show that hypoxic conditions decrease substantially from center to periphery.
Both of these findings may explain, at least in part, the
discrepancy between theory and practice
as previously described by Bergmanson, Ezekiel and Van der Worp in an editorial in Contact Lens & Anterior Eye in 2015.
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Can We Accelerate the Orthokeratology Effect?
Steven Turpin is an optometrist working at different practices in the state of Washington (US). He graduated from Pacific University College of Optometry, followed by a residency specialising in Cornea and Contact Lenses. He sees patients on a daily basis now and seeks answers in the literature to the questions he encounters there. Even better, Steven shares those issues and the scientific backing with us in his weekly blog -
Practically Abstract
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During a recent orthokeratology consult, for instance, he was asked by the mother of a young patient how long it generally takes for the lenses to work. One night? One week? One month? He gave her the standard party line that it depends on a variety of factors including Rx, corneal rigidity, etc., but full correction with consistent vision is achieved by the two-week mark in almost 100% of patients. She then asked whether there was any way to increase the rate of treatment. This ties in with an article that he links to by Wan et al 'Does increasing compression factor accelerate orthokeratology effect?' Based on that piece of research, Steven looks at the effect of increased compression factor, which has been shown to increase spherical aberration as well. The latter could play a role in the myopia controlling effects of orthokeratology too. For the full blog, paper summary and Steve's remarks, see link below.
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Upcoming Events
- NCC 2020, 15-16 March, Veldhoven (NL)
- EFCLIN, 23- 25 April, Berlin (DE)
- EAOO, 15-17 May, Helsinki (FI)
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- Orthokeratolgy Society of Oceania, 5-7 June, Gold Coast (AU)
- Int Congress of Scleral Contacts, 24-25 July, Ft Lauderdale (US)
- The Summit 2020, 4-6 Sept, Rome (IT)
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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:
[email protected].
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