Effect of Dual-Focus Soft Contact Lens Wear on Axial Myopia Progression in Children

Effect of Dual-Focus Soft Contact Lens Wear on Axial Myopia Progression in Children
Nicola S. Anstice, BOptom, PhD; John R. Phillips, MCOptom, PhD
Department of Optometry and Vision Science, New Zealand National Eye Centre, The University of Auckland, New Zealand
Ophthalmology
Volume 118, Issue 6 , Pages 1152-1161, June 2011

In this study, dual focus lenses (center of the lens has the minus prescription surrounded by a concentric zone with a lowered prescription, in this case a reduction of 2 diopters),  slowed the progression of myopia in comparison to the use of single vision lenses (lenses with only the full minus prescription).

From the abstract:

"Participants

Forty children, 11–14 years old, with mean spherical equivalent refraction (SER) of −2.71±1.10 diopters (D).
Methods
Dual-Focus lenses had a central zone that corrected refractive error and concentric treatment zones that created 2.00 D of simultaneous myopic retinal defocus during distance and near viewing. Control was a single vision distance (SVD) lens with the same parameters but without treatment zones. Children wore a DF lens in 1 randomly assigned eye and an SVD lens in the fellow eye for 10 months (period 1). Lens assignment was then swapped between eyes, and lenses were worn for a further 10 months (period 2).
Main Outcome Measures

Primary outcome was change in SER measured by cycloplegic autorefraction over 10 months. Secondary outcome was a change in axial eye length (AXL) measured by partial coherence interferometry over 10 months. Accommodation wearing DF lenses was assessed using an open-field autorefractor.
Results

In period 1, the mean change in SER with DF lenses (−0.44±0.33 D) was less than with SVD lenses (−0.69±0.38 D; P < 0.001); mean increase in AXL was also less with DF lenses (0.11±0.09 mm) than with SVD lenses (0.22±0.10 mm; P < 0.001). In 70% of the children, myopia progression was reduced by 30% or more in the eye wearing the DF lens relative to that wearing the SVD lens. Similar reductions in myopia progression and axial eye elongation were also observed with DF lens wear during period 2. Visual acuity and contrast sensitivity with DF lenses were not significantly different than with SVD lenses. Accommodation to a target at 40 cm was driven through the central distance-correction zone of the DF lens.

Conclusions
Dual-Focus lenses provided normal acuity and contrast sensitivity and allowed accommodation to near targets. Myopia progression and eye elongation were reduced significantly in eyes wearing DF lenses. The data suggest that sustained myopic defocus, even when presented to the retina simultaneously with a clear image, can act to slow myopia progression without compromising visual function."

Link to the abstract:http://www.ophsource.org/periodicals/ophtha/article/S0161-6420(10)01154-1/abstract

Annual Changes in Refractive Errors and Ocular Components before and after the Onset of Myopia in Chinese Children.

Annual Changes in Refractive Errors and Ocular Components before and after the Onset of Myopia in Chinese Children. (2012)
Xiang F, He M, Morgan IG.State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China; ARC Centre of Excellence in Vision Science and Visual Sciences Group, Research School of Biology, College of Medicine, Biology and Environment, Australian National University, Canberra, Australia.Ophthalmology. 2012 May 9

In this study, participants had their eyes examined every year from 2006 to 2010 -- kids who developed myopia were followed.  The question is, why do children develop myopia, especially if there is a low or no genetic predisposition?  Animals generally seem to not develop myopia in their natural environments (but in the lab, they can become myopic under certain conditions); I read an article that   said that dogs can become myopic naturally...  In this study, it is suggested that myopic defocus possibly slows myopic development, though it does not stop it.  According to this theory, becoming myopic and experiencing defocus sends a signal to the eye to slow down axial growth.  In most  infants these visual input is enough to direct the eye towards emmetropic refraction: unaided good vision at near and far.  Why does this process fail in myopic children?
From the text:"Children who were not myopic at the first examination and myopic in at least 1 subsequent examination from 2006 to 2010 were included in the analysis. Annual change in SER increased slowly from 4 years before the first detection of myopia to 2 years before myopia onset (-0.25 to -0.4 diopter [D]). The rate of progression was the highest during the year of onset (-0.92 D). After the first detection of myopia, the rate of progression decreased to -0.71 D in the following year and kept decreasing. Annual change in axial length showed a similar, but inverse, shape to that of SER. Annual change in lens power did not change significantly around the onset of myopia.Before the onset of myopia, axial elongation and progression accelerate. After a myopic refraction is established, axial elongation and progression decrease. We suggest that the increases before myopia may be due to increased intensity of study and decreased time outdoors. In contrast, the rapid slowing after the onset of myopia may represent an inhibitory effect of myopic defocus on eye growth."
Link to abstract:
http://www.ncbi.nlm.nih.gov/pubmed/22578257

The effect of bright light on lens compensation in chicks.

The effect of bright light on lens compensation in chicks.
Ashby RS, Schaeffel F.
Institute for Ophthalmic Research, Section of Neurobiology of the Eye, University of Tübingen, Tübingen, Germany. regan.ashby@anu.edu.au
Invest Ophthalmol Vis Sci. 2010 Oct;51(10):5247-53.

This study looked at how bright light affected the development of refractive error (myopia or hyperopia) induced by optical defocus (caused by plus or minus lenses, +7 or -7).   The chicks with minus lenses that were exposed to 15, 000 lux (brighter than a SAD lamp, much brighter than typical indoor lux levels) for 5 hours per day developed myopia at a slower rate than those exposed to 500 lux (what one might be exposed to typically indoors).    The role of dopamine was found to be important: when the chicks were injected with a dopamine antagonist,  the protective effect of the light against myopia was negated.

From the abstract:
"It has been shown that sunlight or bright indoor light can inhibit the development of deprivation myopia in chicks. It remains unclear whether light merely acts on deprivation myopia or, more generally, modulates the rate of emmetropization and its set point. This study was conducted to test how bright light interacts with compensation for imposed optical defocus. Furthermore, a dopamine antagonist was applied to test whether the protective effect of light is mediated by dopamine.

Exposure to high illuminances (15,000 lux) for 5 hours per day significantly slowed compensation for negative lenses, compared with that seen under 500 lux, although full compensation was still achieved. 


High illuminance also reduced deprivation myopia by roughly 60%, compared with that seen under 500 lux. This protective effect was abolished, however, by the daily injection of spiperone, but was unaffected by the injection of a vehicle solution.

High illuminance levels reduce the rate of compensation for negative lenses and enhance the rate for positive lenses, but do not change the set point of emmetropization (target refraction). The retardation of myopia development by light is partially mediated by dopamine, as the injection of a dopamine antagonist abolishes the protective effect of light, at least in the case of deprivation myopia."


From the full text:
"A possible interaction that should be considered is the change of pupil size in bright light. Schaeffel et al.²⁷ found that the pupil size in chicks is reduced by roughly 50% of its maximum diameter under an illuminance of only 1000 lux. It is clear that a smaller pupil size increases the depth of focus and may therefore diminish the error signal driving emmetropization. However, changes in depth of focus cannot explain why bright light accelerated compensation for positive lenses. Furthermore, the development of deprivation myopia was also significantly suppressed under bright light, even though depth of focus does not play a role under the diffusers. In summary, changes in depth of focus cannot explain the effects of high illuminance on compensation for imposed defocus. Pupil constriction apparently also has no effect on refractive development in the uncovered fellow eyes.

Exposure to high illuminance levels reduces the rate of ocular growth normally seen in response to the fitting of negative lenses or translucent diffusers, and enhances the growth suppression of plus lenses, but does not alter normal ocular development. Further, the protective effect of light against the development of myopia appears to be mediated by dopamine, as the injection of a dopamine D2-specific antagonist abolishes the protective effect of light, at least in the case of deprivation myopia."
Link to the text

http://www.iovs.org/content/51/10/5247.full