Quarterly newsletter on Soft Specialty Contact Lens
Research, Developments, Designs and Materials SUMMER 2014
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Soft Lens Decentration
Scleral Shape & Soft Lens Centration On-Eye
 The fitting properties of contact lenses that extend beyond the limbus such as soft and scleral lens designs are dramatically influenced by the underlying shape of the peripheral cornea, the limbus and the sclera. Studies at Pacific University in the United States indicate that intra- and inter-ocular asymmetries in scleral shape exist between the nasal and temporal quadrants of each eye. The cumulative impact of this appears to significantly influence the on-eye positioning of soft contact lenses and, ultimately, the placement of lens optics over the pupil and line-of-sight. In clinical practice, subtle anomalies in the positioning (centration) of soft contact lenses are easily overlooked, and generally there is little optical consequence when single vision optics are used. However, when fitting more complex optics, lens centration takes on greater importance. For instance, these collective findings are of particular significance for optimal delivery of multifocal optics for aging patients with presbyopia and for children in need of myopia control. Click here for full report.
Maria Walker and Patrick Caroline
Portland (OR) USA
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IN THE LITERATURE
Custom Soft Torics Can Fill the Gap
Conventional Toric Soft Lenses, Hospital Based Contact Lens Practice
Frequent replacement toric lenses are restricted to cylindrical powers of -2.75D to -3.50D in hydrogel materials and only up to -2.25D in silicone hydrogel materials. Out of a large group of soft contact lens fits in their practice, Rajni Rajan and Rajeswari Mahadevan retrospectively looked at the use of toric soft lenses. Though the design, material, and power range of marketed toric lenses have improved, the contact lens industry should strive to expand the powers and axes of frequent replacement soft toric lenses, the authors state. John Mark Jackson also looks at toric lenses in his article 'Tune Up Your Toric Fits.' One of the items of interest that he describes is that the amount of residual astigmatism induced by axis misalignment varies with the cylinder power of the lens. For a 0.75D lens cylinder, 10° of axis misalignment results in only 0.25D residual astigmatism, but in a 2.75D lens cylinder the residual astigmatism is 0.92D, which is surely clinically significant.
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IN THE LITERATURE
Multifocal Lenses: Beyond Presbyopia
Myopia, Children, Peripheral Plus Power, Orthokeratology
In Contact Lens Spectrum, two columns report on soft lenses for myopia control: Jeff Walline describes his experience with fitting kids with these lenses as well as what multifocal lenses are currently commercially suitable for myopia control. He mentions the importance of educating the potential lens wearer and the parents about the modality. . David Berntsen looks at the literature in this regard, and at the amount of reduction that can be gained: currently it varies on average between 25% and 50%. Based on information from podiums at different conferences, it appears that 'high plus' in the periphery is needed to obtain a good result. A -1.00D myope can gain +1.00D of power in the periphery with orthokeratology - which may not be enough. For that reason, in these early stages, soft lenses may be preferred over orthokeratology, with a choice of (high) peripheral plus power. See also www.myopiaprevention.org for more on this topic.
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IN THE LITERATURE
Silicone Hydrogel Mini-Scleral Lenses
Corneal Collagen Cross-Linking, Keratoconus
Boris Severinsky and colleagues evaluated the performance of a novel silicone hydrogel mini-scleral contact lens for optical correction of keratoconus in the early stages after corneal collagen cross-linking. The fit with these lenses was performed 2.1±0.97 months after collagen cross-linking, and the mean follow up was after 10.9±4.41 months. Nine eyes were successfully fitted (90 percent) and able to wear the lenses for 10 hours per day or longer at that point (the mean wearing time was 11.7 hours, range 6 to 14 hours). No corneal neovascularization or papillary reaction was found. It was concluded that silicone hydrogel mini-scleral contact lenses can provide successful visual rehabilitation shortly after corneal collagen cross-linking. This new soft contact lens design with scleral fixation and minimal apical touch was demonstrated to be safe shortly after collagen cross-linking, as avoiding contact with the treated zone minimizes contact lens influence on corneal recovery. Photo: Boris Severinsky
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IN THE LITERATURE
Corneal Reshaping with Soft Lenses
Corneal Warpage, Ring Pattern, Orthokeratology Effect
Whether we like it or not, the shape of the ocular surface
is changed and/or reshaped with soft lenses - despite the apparently limited mechanical forces involved. A paper in Global Contact (see link below for downloadable PDF) in two parts looks at a series of cases of silicone hydrogel lens wear, the topographical changes and why this may occur. Corneal topography was performed in neophyte lens wearers before and six to nine months after lens fit. The authors observed that corneal topographical changes do occur, irrespective of lens power, lens design and replacement frequency. Even daily disposable lenses showed unwanted corneal changes, sometimes in a typical circular (almost orthokeratology-like) fashion. Only silicone hydrogel lenses were tested. In theory, the effect of corneal changes may be higher with these lenses than with conventional hydrogel lenses. Patrick Caroline and Mark André also report a report a case of corneal reshaping using an everted 8.4mm base curve, −10.00D, 13.8mm diameter silicone hydrogel lens. The lenses were dispensed for overnight wear, and maximum corneal flattening was achieved within three days. Follow-up topography revealed well-centered treatment zones with −1.75D of corneal flattening OD and −1.25D OS. This case illustrates that while still unpredictable, soft lenses may still have future potential for controlled alteration of corneal shape.
Van der Worp, Molkenboer, Global Contact 2/2014
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| CONFERENCE
ARVO 2014 - ORLANDO
Lens Design, Driving, Astigmatism, Myopia Control, Drug Delivery, Diplopia
ARVO (The Association for Research in Vision and Ophthalmology), this year held in Orlando (FL, USA), is arguably the single most important vision related conference in the world. Quite diverse soft specialty lens topics were covered, such as: Does driving safety improve when correcting astigmatism with toric contact lenses? Pilot data from this study by Cox et al does suggest that correcting astigmatism may have larger than anticipated implications for driving safety (poster #189). Intractable diplopia - do patients like occlusive contact lenses? This small study by Chia et al (poster #2567) indicates that occlusive contact lenses can be an effective and safe treatment in the majority of patients issued with such lenses. Intractable binocular diplopia is a distressing symptom not amenable to conventional management of diplopia. Another poster looked at the development of a Soft Contact Lens for Drug Delivery using a new material. The drug delivery system was described as a useful device - ensuring the vision correction desired and sustained drug release (Matsunaga et al, poster #6050). Kara and Ross (Poster #6057) developed a mathematical model to characterize the suction pressure under the contact lens. The system of ordinary differential equations captures the basic physics and the elastic tension needed to begin to understand a "working" contact lens. Therefore, they claim to be able to create better "rules of thumb" for new contact lens design.
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IN PRACTICE
Challenging Cases Albinism, Keratasia, Microphthalmus, Trichiasis and More
A number of publications in Contact Lens Spectrum focus on using soft lenses in special cases. Patrick Caroline and Mark André cover a case of fitting a 5-year-old child with an opaque tinted soft lens for albinism. The child tolerated the lenses extremely well, and within one week she was able to wear the lenses all-day. The parents reported an immediate improvement in the child's social and developmental behavior. Her indoor and outdoor photophobia had dramatically lessened, and while her visual acuity remained limited, the parents and teachers reported much improved functional acuity both at home and at school. Barry Eiden, Clark Chang, Robert Davis and Shana Brafman cover contact lens options for managing keratoconus and keratectasias. Their paper includes a table on available custom keratoconus soft lens designs. John Laurent and Yin Li look at 'Optimizing Lens Wear in Cases of Pre-Existing Ocular Conditions.' They present nine case reports, some involving soft specialty lenses. This includes a case of a post-LASIK fitting, one on microphthalmus and a case of ocular cicatricial pemphigoid and trichiasis. 'Make a Difference' they conclude in their paper: 'Many of these cases provide us an opportunity to make a significant difference in someone's life, which can be very rewarding.' Also, they state 'Establishing a reputation for fitting patients who have unique or difficult conditions can be a great practice-builder: welcome these patients into your practice.'
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This Newletter is Kindly
supported by:
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