Sarah Guthrie, PhD is a research scientist at the Centre for Contact Lens Research, University of Waterloo School of Optometry, Canada.As the prevalence of myopia in the world increases, interest in finding ways to control it has grown accordingly. Not only does myopia impart a large financial burden related to optical correction, it is also a leading cause of blindness due to increased risk of retinal detachment, glaucoma, and cataracts. Many different approaches to slowing the progression of childhood myopia are currently under investigation, including the use of pharmacological agents, orthokeratology and bifocal or specially designed contact lenses. The recently published “Dual-focus inhibition of myopia evaluation in New Zealand (DIMENZ)” study illuminates one such approach, investigating the use of an experimental dual-focus soft contact lens for its efficacy in controlling the progression of myopia.
Anstice NS, Phillips JR. Effect of dual-focus soft contact lens wear on axial myopia progression in children. Ophthalmology 2011;118(6):1152-1161.
Forty children aged 11-14 years wore a dual focus lens in a randomly assigned eye and a single vision distance (SVD) lens in the other eye for 10 months (Phase 1), and then lens assignment was crossed over between eyes for another 10 months (Phase 2). All children enrolled had a spherical equivalent refraction of between -1.25 and -4.50D in the least myopic eye, had myopia progression of ≥ 0.50D in the previous 12 months and were prepared to wear contact lenses for at least eight hours per day.
The dual focus soft contact lenses, lathe cut in hioxiflicon A (45% water, 8.5-mm base curve, 14.2-mm diameter), were made up of a central zone to correct refractive error, surrounded by a series of “treatment” and “correction” zones. Participant refractive error was corrected via the correction zones, while the treatment zones produced 2.00D of simultaneous myopic retinal defocus. Pupil size was carefully taken into account, and the central correction zone was made as large as possible to ensure that accommodation was stimulated and clear vision provided, whilst also having myopic retinal defocus present for distance and near viewing. SVD lenses were manufactured with identical parameters as the test lenses, without the treatment zones.
Once the study was completed, it was noted that overall there was less myopia progression in Phase 2 compared to Phase 1. This was likely due to the fact that participants’ eyes had experienced different rates of myopia progression in Phase 1 and were slightly anisometropic going into Phase 2. This led the authors to focus mainly on the results of Phase 1 when reporting their findings.
The overall results show that for the 34 children completing the study, myopia progression and eye elongation were reduced significantly in eyes wearing dual focus lenses compared to single vision distance lenses. In Phase 1, myopia progression was reduced by an average of 0.25D (37%) in the eye wearing the dual focus lens relative to that wearing the single vision distance lens. Similarly, eye elongation was reduced by an average of 0.11mm (49%). In Phase 2, myopia progression was reduced by an average of 0.20D (54%) and eye elongation was reduced by an average of 0.12mm (80%). At the same time, the dual focus lenses provided normal acuity and contrast sensitivity and allowed accommodation to near targets.
This study shows clearly that it is possible to affect myopia progression in children without reducing their in vision. The authors conclude that “sustained myopic defocus, even when presented to the retina simultaneously with a clear image, can act to slow myopia progression”.
