YEAR
2015

ISSUE
No. 2

Quarterly newsletter on Soft Specialty Contact Lens Research, Developments, Designs and Materials
WORLD WIDE VISION

MYOPIA CONTROL WITH SOFT CONTACT LENSES, WHAT IS POSSIBLE?


In the last few decades, the prevalence of myopia has increased rapidly, not only in East Asian countries but also in North America. Importantly, sufferers of high levels of myopia are at a higher risk of potentially blinding pathologies. Preliminary results now indicate that myopia may be controlled successfully by the application of special optical designs using soft contact lenses. Myopia progression in children between the ages of 11-14 years old was reduced by 37%, and axial length by 49%, in eyes wearing a dual-focus soft lens over 10 months in a study. A similar trend was reported in another study with wear of a distance-centre design multifocal soft contact lens when compared to a matched historical control group of 8-11 year olds wearing single vision soft contact lenses: a 50% reduction in myopia progression and a 29% reduction in axial length elongation after 2 years were found for the multifocal wearing group. There is a strong need for larger and longer randomized clinical trials to determine the effect of these designs on myopia control and to determine the mechanism behind the treatment effect. Additionally, the longevity of these effects and methods that can be used to maximize these benefits for each child are key factors that need to be determined to offer the best myopia control with soft contact lenses. While these research activities are underway, few options are currently available in the market that may provide some level of myopia control to some patients with soft contact lenses. 
Percy Lazon de la Jara PhD, BOptom FIACLE FAAO
Head of Clinical Research, Brien Holden Vision Institute, Sydney Australia
SAGs Appeal?
Sagittal Height Differences in Silicone Hydrogel Lenses

 

As there is a weak correlation between K-readings and soft lens fitting characteristics on-eye, eye care practitioners (ECPs) have limited tools for choosing the first trial soft lens. Instruments are available now to measure the sagittal height of the ocular surface over a large area. However, information about the sagittal height of soft lenses (CL-SAG) is currently unavailable to ECPs. A paper in Contact Lens & Anterior Eye measured the sagittal height differences among a selection of commercially available monthly or two-weekly replacement silicone hydrogel soft lenses using the SHSOphthalmic omniSpect by Optocraft. The CL-SAG of all minus lenses ranged from 3454 to 3765 microns-an inter CL-SAG difference of 311 microns. In other words - this is the range of tools that are available if we want to fit monthly or two-weekly replacement silicone hydrogel lenses. Different lenses with the same package base curve value had marked differences in CL-SAG, with potential clinical significance on-eye in terms of lens behavior. 

 

Van der Worp, Mertz, Contact Lens & Anterior Eye - Febr 2015

Epithelial Thickness Changes
Nonuniform Changes to the Corneal Epithelium in Long-term Soft Lens Wear 

The corneal epithelial thickness in long-term soft lens wearers in vivo was measured with Fourier-domain optical coherence tomography. Forty eyes from 40 normal subjects who had never worn soft contact lenses (SCLs) and 40 eyes from 40 SCL wearers who had worn lenses for more than 2 years were enrolled in this cross-sectional observational study. Epithelial thicknesses of the central 2-mm, paracentral 2- to 5-mm and midperipheral 5- to 6-mm zones were obtained. The average epithelial thickness respectively was 54.4 1.1 μm, 53.2 2.2 μm, and 52.3 2.0 μm in normal eyes for these zones, and 49.2 1.9 μm, 48.8 2.2 μm, and 48.7 2.8 μm in soft lens wearing eyes. Compared with normal control subjects, eyes with long-term SCL wear had significantly thinner epithelial thickness in all three zones (p < 0.05). The finding of nonuniformity of the paracentral and midperipheral corneal epithelium thicknesses may be useful for detecting early changes in corneal epithelial thickness caused by long-term soft contact lens wear, the authors conclude. Image: Pacific University OR USA

Jiaxu et al, Optometry & Vision Science - Dec 2014

Predicting Tight or Loose Soft Lens Fits?
Calculated Lens Edge Strain as a Predictor of Soft Lens Tightness

A spreadsheet-based computer model used a novel ellipto-conical corneal model coupled with population data on corneoscleral topography obtained in a previous clinical study to calculate lens edge strain (circumferential elongation) as a predictor of lens tightness. For an eye with average ocular parameters wearing a typical soft lens design (BC, 8.60 mm; diameter, 14.2 mm), the model calculated an edge strain of 2.7%. For the same lens, the tightest fit (8.5% strain) was found with the eye showing the combination of smallest, flattest, most aspheric cornea. Conversely, the loosest fitting (−2.6%) was found with the eye showing the combination of largest, steepest, least aspheric cornea. A change in base curve of 0.4 mm typically resulted in changes in edge strain of less than 2.5%, whereas a change in diameter of 0.5 mm resulted in a change of less than 2%. Using the typical soft lens design and average corneal model, wide variations in corneoscleral junction angle did not critically affect lens fit. More extreme combinations of soft lenses and ocular parameters resulted in edge strain likely to result in a tight (>6%) or loose (<0%) fit.

Young, Optometry & Vision Science - Jul 2014

Conjunctival Indentation Artifact in Soft Lens Wear
Optical Edge Effects Create Conjunctival Indentation with OCT

Researchers from the University of Waterloo (CA) concluded that optical edge effects create conjunctival indentation thickness artifacts when using optical coherence tomography (OCT). An optical displacement artifact was observed when imaging a contact lens on two rigid continuous surfaces with OCT in which compression or indentation of the surface could not have been a factor. Contact lenses imaged in situ also exhibited displacement at the intersection of the contact lens edge and the conjunctiva, likely a manifestation of both the artifact and compression of the conjunctiva. Edge artifacts were observed in a selection of marketed silicone hydrogel and hydrogel lenses. The observed optical displacement ranged between 5.39 μm with Acuvue Advance and 11.99 μm with Air Optix Night & Day when the lens was imaged on the glass reference sphere. Displacement was also observed when the lenses were imaged on the human conjunctiva, ranging from 6.49 μm for the 1-day Acuvue Moist to 17.4 μm for the Pure Vision contact lens. Practitioners should be aware of this effect when observing soft lenses in situ.Image: Pacific University OR USA

 

Sorbara et al, Ophthalmic and Physiological Optics - Febr 2015

Bandage
Comparison of the Use of Bandage Lenses after PRK

Taylor et al from Texas (USA) evaluated the relative pain with three bandage soft contact lenses applied after photorefractive keratectomy (PRK). Patients undergoing PRK were randomized to a senofilcon A (Acuvue Oasys), balafilcon A (Purevision), or lotrafilcon A (Air Optix) bandage SCL in each eye postoperatively and were followed for up to four days postoperatively. The study involved 54 patients, who completed a survey rating on absolute pain in each eye on a visual analog scale. Statistically and clinically significant differences in post-PRK pain among the 3 bandage contact lenses were found in this study.

Choosing The Right Lens
'The best decision is the next right decision'

David Kading in Contact Lens Spectrum refers to a study by Nichols et al (2005), which states that as many as 52% of patients encounter dry eye symptoms with their lens wear. He continues: 'Surprisingly, it seems that these statistics have remained unchanged since I graduated from optometry school. That being said, I still think that the quest for the holy grail of contact lens materials continues, even though we are light years ahead of where we were 10 years ago.' Kading urges us to not overlook ocular surface issues. Independent of contact lens materials and care solutions, he states, the ocular surface is in a constant state of change. From decreased blink rate and quality with computer use, to the change of the seasons, to hormonal shifts, our patients' eyes change with time, and so should our dry eye treatments and contact lens approach. He states in a comment, emphasizing the above: 'My mom always told me that the best decision is the next right decision. I am constantly telling my patients that the perfect contact lens has not been invented yet, but the lens that we are placing them in today is the best lens for them now. Ensure that you can say that with confidence to your patients daily.'

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