Quarterly newsletter on Soft Specialty Contact Lens
Research, Developments, Designs and Materials WINTER 2013
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Sagittal Height and Soft Lens Fitting
Is the Peripheral Corneal Angle a Good Predictor?
It is well established that insights into the sagittal height of the anterior eye can be helpful in fitting both custom soft and scleral RGP lens designs. In a study of 55 normal eyes at Pacific University, we showed that, at a chord of 15.0 mm, the average sagittal height of the eye was 3,681 microns, with a range of 3,310 to 4,080 microns measured over the horizontal meridian using OCT (optical coherence tomography). While corneal central radius of curvature, corneal eccentricity and even diameter have proven to be poor indicators of overall sagittal height of the eye, another indicator may prove to be a better predictor. In this second part of the trilogy on soft lens fitting and ocular surface shape, the role of the peripheral corneal angle is evaluated as a possible predictor of overall sagittal height. Our studies indicate that perhaps the best predictor of sagittal height, as an alternative to OCT, is the corneal angle that begins at 10.0 mm and extends out to the limbus. The cornea is curved throughout its 10.0 mm chord; however, from 10.0 to approximately 12.0 mm, the corneal shape is more appropriately described as an angle. The higher this angle, the greater the sagittal depth of the eye, and the lower the angle, the lower the sagittal height. Click here for full report.
Patrick Caroline and Randy Kojima
Portland (OR) USA
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IN THE LITERATURE
Myopia Control - the Soft Revolution
Soft Lens Design, Multifocal Soft Lenses, Peripheral Refraction
Slowly but surely, a soft revolution is taking place in our contact lens practices. As opposed to managing the symptoms of myopia, as we have been doing for centuries, the focus now is on treating myopia - partially at least, it seems. As an illustration of the interest in this, one of the leading journals in our field, Optometry & Vision Science, published a special issue on the topic hosting over 20 articles. Several articles cover axial length changes and peripheral hyperopic defocus. Two articles in particular focus on soft lens options for myopia control: Jeff Walline et al from the Ohio State University (OH USA) reported a 50% reduction in the progression of myopia and a 29% reduction in axial length elongation during a 2-year period in children aged 8-11 wearing soft multifocal contact lenses compared to a historical control group. David Berntsen and Carl Kramer from the University of Houston (TX USA) try to explain what is happening optically with these center-distance multifocal lenses in their paper; in other words, what is happening to the peripheral defocus while wearing multifocal soft lenses? When looking at distance, these lenses create a peripheral myopic defocus whereas the spherical lenses create a peripheral hyperopic defocus. At near, the multifocal lens resulted in relatively more myopic (less hyperopic) peripheral defocus than the spherical lens used in this study. The study also shows that variation exists among different locations on the retina and that variations among individuals are present. This could in theory mean that custom-made soft myopia control lenses are desired in the future to optimize the myopia controlling effect. See also the 'education' item later in this newsletter.
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IN THE LITERATURE
High-Plus Soft Lenses as an Alternative to Patching?
Optical Penalization, Children, Unilateral Aphakia, Occlusion Therapy
Ten patients with unilateral aphakia after congenital cataract extraction underwent treatment with a high-plus contact lens in their sound eye after a period of failure with traditional occlusive patching. The effectiveness of the treatment was investigated. After an average 15-month delay between the end of occlusive patching and the start of optical penalization with high-plus contact lenses, 6 of 10 patients achieved good compliance with high-plus contact lens therapy. The authors conclude that using a high-plus contact lens to optically penalize the sound eye of a unilaterally aphakic child seems to have potential as an effective alternative to occlusive patching for those with compliance issues. A prospective study is warranted to assess long-term safety and efficacy in visual outcome, they state.
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IN THE LITERATURE
Contribution of Soft Lenses of Various Powers to Piggyback Optics
Soft Lens Carrier, Piggyback, Contact Lens Optics
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Photo: Patrick Caroline
Pacific University
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Investigators at the University of Montreal (Canada) looked at using three different powered soft lens carriers and their in-vivo contribution in power to a piggyback system. The -6.00D and +6.00D carriers used in this study provided 21% of their marked power to the system, the +0.50D lens did not contribute any power. The plus-powered soft lens enhanced centration of the RGP lens, and the authors conclude that plus-powered carriers are recommended for use in piggyback systems from a fitting standpoint rather than using minus-powered carrier lenses.
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IN THE LITERATURE
OCT to Image Soft Lenses In-Vivo
Post-lens Tear Film Thickness, Soft Lens Fit Assessment
 In the series of 'classical papers' regarding soft lens fitting, this (full access) paper by Wang et al from 2011 is a 'must-see.' With ultra-high-resolution optical coherence tomography (OCT), the investigators were able to image the cornea, the soft lens - and the post-lens tear film. Also, the changes over time in the post-lens tear film, inserted with a drop of artificial tears in this study, can be imaged. The investigators also considered the possibility of using OCT to evaluate soft contact lens fitting. Both lens movement and lens centration can be monitored with micron-precise accuracy.
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| CASE REPORTS
Therapeutic Silicone Hydrogel Lenses
Bandage Contact Lens, Extended Wear, Silicone Hydrogel
A number of reports featuring silicone hydrogel bandage lenses have appeared in contact lens journals in recent months. Tamar Shafran et al reported on 43 cases of therapeutic silicone hydrogel lens use. Of these 43, 26 were fit for pain relief; 81% were judged to be effective and 8% partially effective. Improvement in corneal integrity was the treatment goal in 25 cases; this was fully effective in 64% of cases and partially effective in 24%. The silicone hydrogel lens used therefore proved to be successful in the majority of cases, the authors concluded. Nilufer Yesilirmak and Dilek Altınors report an unusual case with a bandage silicone hydrogel lens after 7 years of continuous wear that was applied over cyanoacrylate glue treatment for corneal perforation. After the initial cyanoacrylate adhesive application, a bandage silicone hydrogel contact lens was placed on the eye. After 7 years with the same silicone hydrogel lens on her eye, the patient complained of permanent redness in her left eye. Based on this state of the eye and this report, the authors state that 'silicone hydrogel contact lenses exhibit good efficacy and safety when utilized as a continuous wear therapeutic lens with antibiotics.'
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EDUCATION
Corneal Topography in Myopia Control Matt Lampa & Mark André
In recent years, the global eye care community has learned an immense amount concerning myopia, its development and how to attempt to control its progression courtesy of fantastic research from around the world. The corneal topographer is useful in gaining an understanding of what is needed in optical profile centrally versus peripherally:
the most minus correction (flattest) is concentrated centrally, with a smooth transition toward the periphery to increasing plus power (steepening). This optical profile also occurs in a center distance multifocal aspheric contact lens - as can be seen by the topographic map taken over a lens of such add power. By utilizing a custom aspheric center distance multifocal, the practitioner can vary not only the add power, but also the zone size, which is dedicated to center distance and the surrounding near zone. Again, the corneal topographer's difference display is useful in determining these zone sizes in an attempt to mimic the post-orthokeratology profile and optimize the effect of controlling myopia.
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| CONFERENCE
'Soft Focus Las Vegas'
Soft Lens Fitting, Sagittal Height, Custom-Made Lenses
The renewed interest in specialty soft contact lenses will also be in focus at the annual Global Specialty Lens Symposium in Las Vegas. More than ever, the upcoming edition features information on soft lens fitting - in all of its aspects. Lee Hall from the United Kingdom has some fascinating results to present on limbal ocular shape and its relationship to the characteristics of soft lens behavior on-eye. Also, sagittal height information and its potential role in soft lens fitting is highlighted by Eef van der Worp from Amsterdam, the Netherlands, in this year's session on topography and lens fitting. Mark André and Randy Kojima, both from Pacific University in Oregon (USA), report on custom-made soft lenses and the role that corneal topography can play in fitting them. Boris Severinsky from Israel will host a panel on soft specialty lens case reports, with Mark André, Jennifer McMahon (UK), and Greg DeNaeyer (USA). This and more - like the influence of power and lens design on the zonal oxygen transmissibility of silicone hydrogel soft toric contact lenses by Tony Hough (UK) - will be the focus of GSLS 2014 within the soft lens modality.
Global Specialty Lens Symposium 2014
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