I-site April 2010

International Newsletter and Forum on Rigid Gas Permeable Contact Lenses, Corneal Shape, Health and Vision

April 2010

In This Issue

Column

Corneal Hysteresis

Corneal Atlas

Keratoconus viewpoints

I(n)site-the-practice

(R)GP art

Agenda

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Column

Wooden Shoes

Allow me for once to comment on my home country, the Netherlands: our biannual contact lens meeting NCC 2010 last month attracted 1600+ practitioners, which was a surprise even for those of us who organized the meeting. This is roughly 90% of all practitioners in the country, we estimate. The other striking thing is that according to a national survey that came out last month, 29.9% of contact lens wearers in the Netherlands wear (R)GP lenses. Why is that? The joke always has been that if you can wear a wooden shoe, you can wear a (R)GP lens. But 24% of new fits in the Netherlands are with (R)GPs, according to the yearly Eurolens Research survey, and 0% of Dutch people are wearing wooden shoes these days. Lens fitters' interest seems to be a key point in this. In the Netherlands, optometrists are a minority in the contact lens field and ophthalmologists don't fit lenses at all. Most lenses are fitted by contact lens specialists (opticians with a contact lens qualification). All they are interested in is...fitting contact lenses. And that includes fitting (R)GPs. Even if you take out all (R)GP lenses in the Dutch market, we still have more lens wearers than most other European markets. What this means to me is two things: don't underestimate the power of the fitter, and the discussion on lens modality shouldn't be (R)GPs OR soft lenses. (R)GP lenses are a wonderful addition to the contact lens industry, in all its aspects.

Eef van der Worp

Corneal Biomechanics

Hysterical about Hysteresis?

Many researchers get pretty excited, if not hysterical about the cornea's hysteresis (corneal rigidity/ elasticity). The biomechanical properties of a tissue determine how it will respond and deform when placed under stress. Evidence suggests that the biomechanical properties of the cornea and also the sclera are altered in glaucomatous eyes, and elasticity is altered in keratoconic corneas. Until now, assessing the biomechanical properties of corneal tissue has not been possible, confining practitioners and researchers to measuring purely geometrical aspects of the cornea such as thickness and topography. A method of measuring biomechanical properties is the ocular response analyzer. This technique uses a rapid air pulse and an electro-optical system to record two applanation pressure measurements - one while the cornea is moving inward, and the other as the cornea returns. Due to its biomechanical properties, the cornea resists the dynamic air puff causing delays in the inward and outward applanation events. The difference between these two pressure values is corneal hysteresis (CH). Differences in CH between normal and compromised corneas seem highly evident and have lead some experts to theorize that normal eyes exhibiting significantly lower than average CH may be at risk of developing corneal disorders. Hopefully CH information will also translate to more clinical, such as understanding diurnal corneal variations, collagen distribution and restance to intra-ocular pressure in the normal cornea, and understanding and managing corneal ectasia both in the post-refractive surgery eye and in the keratoconic eye.

Corneal Atlas

The Cornea Reviewed

The Corneal Atlas 2010, a supplement to Review of Optometry, is available now for download (PDF). The 22 page booklet with up-to-date information is logically divided into chapters covering different types of corneal infections, dystrophies by corneal layer, corneal degenerations and mechanical plus toxic influences on the cornea followed by inflammatory responses. Put together by Ernest Bowling, Gregg Eric Russell, Joseph P. Shovlin and Christine W. Sindt, this atlas is a very useful clinical guide for every contact lens practice.

YouTube

Keratoconus: viewpoints

In an article in Optometric Management called Four Strategies for Keratoconus, Greg DeNaeyer reviews the main contact lens options for keratoconus: specialty soft lenses, bi-aspheric (R)GPs, piggyback and scleral lenses. But what if the patient asks about surgical options? Youtube actually features a wide variety of short videos showing everything from intra-corneal rings and corneal cross-linking to lamellar keratoplasty and penetrating keratoplasty. It is at least good to know what patients 'know' about their options when they are in your chair, since many of them must have checked these out prior to visiting us.

I(n)-site-the-practice

At War Against Corneal Warpage

Corneal warpage is considered a potential negative 'complication' of contact lens wear. Although more prevalent in (R)GP lens wear, it should not be underestimated in soft lens wear as well. Frank Weinstock, a professor of ophthalmology from Canton, Ohio (USA), looks at the importance of screening for corneal warpage, of removing lenses at the time of each annual exam and the importance of evaluating the eye at dispensing of the lens before the patient leaves the office. See

this month's I(n)-site-the-practice for full coverage of corneal warpage, clinical experience and practice management tips. 'In our practice we insist, and always have, that no corneal deformity should be tolerated' - Frank Weinstock, MD.

(R)GP-ART

Glow in the Dark

An orthokeratology lens fit on a post-RK cornea - often a good option because the central cornea is typically flatter compared to the periphery in such cases. This pattern may also be seen post-PRK, post-LASEK, post-LASIK and even in post-penetrating keratoplasty eyes. An orthokeratology lens - called nachtlens ('night-lens') in the Netherlands - provides the desired shape in those cases. Although this lens most likely will be worn during waking hours only, it can be a sparkle in the night for these patients. Photo: Hans Luijben, the Netherlands (NCC2010 photo competition contender).

International Agenda

Upcoming Meetings 2010

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.