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International Newsletter and Forum on Rigid Gas Permeable Contact Lenses, Corneal Shape, Health and Vision |
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Global warming
It was heart-warming to see so many people from around the globe meet up in Las Vegas (USA) recently for the Global Specialty Lens Symposium and to share their knowledge and ideas. Delegates from 27 countries as well as speakers and poster presenters from New Zealand to Italy and from India to Japan made this a truly global meeting. But most striking was not the nearly 400 attendees and their nationalities, but the good atmosphere and the shared interest in correcting (challenging) corneas with the best contact lens options available in the world. I heard one participant mention "I hardly had time to talk to my wife on the phone - so many interesting presentations to listen to, so many people to meet." Presbyopia, orthokeratology and custom made/lathable soft (silicone hydrogel) materials all were hot topics at the meeting.  But the 'hottest show on the strip" was scleral lenses: scleral lens design, scleral lens fitting and scleral lens shape were prominent in the program and the talk of the day. There is so much to share and so much to learn regarding this topic, and this meeting was the ideal platform to discuss it amongst peers. Although Las Vegas alone may be responsible for at least a small hole in the ozone layer, it wasn't particularly warm outside for the time of year in the entertainment capital of the world. But inside at the meeting the atmosphere was warm and fraternal. Global warm.
Eef van der Worp |
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Music to my tears I
Efficient tear mixing and timely removal of cellular debris, bacteria or unwanted chemical species that accumulate between the lens and cornea during contact lens wear, especially during closed-eye situations, appear necessary for safe lens wear. To measure this, fluorometry can be used to estimate the tear flushing rate. Meng C. Lin and others at the University of California, Berkeley school of optometry looked at tear mixing with different types of contact lenses. In theory, better tear mixing may lead to a significantly lower frequency of several types of adverse clinical events. Compared to soft lenses, (R)GP lenses have very fast tear exchange rates. The optimum tear-mixing time is not known, but the investigators suggest that the tear mixing time ideally should be close to that in daily wear with (R)GP lenses. In (R)GP lens wear the tear mixing time ranges from 5-7 minutes, while in soft daily lens wear it varies between 22 and 35 minutes for a variety of soft lenses. Most probably because of this the corneal epithelial permeability in (R)GP lens wearers recovers quickly (within two hours of awakening), while with soft lenses this continues to worsen (i.e. the permeability of the cornea keeps increasing). Is this perhaps the explanation for the large difference in adverse events between the two modalities? |
| Presbyopia & Contact Lenses |
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Vision-air
Wavefront aberrometry continues to intrigue those in the contact lens industry, and many visionaries keep referring to it as the technology of the future. Because of the transition in index of refraction from air to cornea, most of the aberrations of the human ocular system can be found on the anterior surface. This also means that with a standard (R)GP lens we can correct the bulk of the optical aberrations on the ocular surface (90% - the rest is 'lost' due to the difference in index of refraction between the cornea and the tear film). But the human eye is an interesting phenomenon. A great article in the Journal of Vision (full access) by Pablo Artal and colleagues from Spain shows that some of the internal aberrations of the eye are the opposite of the ones on the front surface, e.g. they compensate for each other. By correcting the optical aberrations on the front surface of the eye with a (R)GP lens, the internal aberrations can be 'activated,' thus working against us. While in the majority of cases (R)GPs can be beneficial to improve vision, this phenomenon should be evaluated carefully. Lens movement and lens centration should also be controlled for, since they can cause negative effects as well. |
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The Story
One of the first quotes in this great contact lens history book written by Timothy Bowden from the United Kingdom is from George Nissel and says, 'I feel that contact lens history is being made before our eyes and it should be recorded somewhere.' Making history before our eyes is exactly what is also happening at this very moment-but luckily, somebody is recording it. This recently introduced book covers everything from the very first reference to contact lenses almost 500 years ago (Leonardo Da Vinci) up to the newest lens modalities available today. Of course a large part is devoted to (R)GP lenses, and one of the most interesting subjects may be the scleral (originally called 'haptic') lens coverage. They were surpassed by newer corneal lenses but are now completely back on the agenda (see the 'GSLS coverage' in this I-site). We can learn from history, indeed. See the book's website and Alan Saks' book review for more information on the book. |
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Music to my tears (and to the cornea) II
A 45-year-old man was referred for contact lens consultation and evaluation of his severely dry eyes and ocular discomfort subsequent to systemic diagnosis of Chronic Graft versus Host Disease 18 months after bone marrow transplant. He had experienced only minor relief from traditional dry eye therapy and presented with severe visual acuity loss and corneal staining. Michael Lipson, assistant professor at the University of Michigan's department of Ophthalmology and Visual Science, fitted him with an 18.2 mm scleral lens. The improvements in visual acuity, slit lamp findings and overall comfort are typical for this type of case. See this month's I(n)-site-the-practice for the full story and outcome. |
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RK in reverse
At the recent Bronstein meeting in Phoenix (USA), a fantastic conference with many highly qualified (R)GP lens experts both on the podium and in the audience, there was general agreement that many of us are currently seeing in our offices a wave of post-radial keratectomy (RK) patients who are unsatisfied with their vision. Needless to say, these are challenging corneas to deal with, especially because some of them are very unstable. Sometimes a reverse geometry lens can actually be a great solution, as in this case. Photo: Tom Quinn, (Ohio, USA) one of the great speakers at the meeting | |
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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-politcal. Its editor Eef van der Worp, optometrist, PhD, FAAO, FBCLA, FIACLE is a lecturer for a varity of industry partners, but is not related to any specific company. Please contact us at: i-site@netherlens.com. | |
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