Comparing short sighted refraction profiles created by two different designs of an orthokeratology contact lens

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Myopia (short sightedness) is a refractive condition where the distance from the front to the back of the eye is too long for the refractive strength of the eye, leading to light being focussed in front of the retina (light sensitive layer on the inside back of the eye) and subsequently causing blurred vision. Myopia typically develops in childhood while the eye is growing and is believed to be accelerated by correcting the myopia with glasses. When myopia first presents the child complains of poor distance vision which is corrected by glasses. Unfortunately, myopia continues to progress requiring the child to return at regular intervals to get ever stronger glasses, until they reach adulthood. Orthokeratology (OK) lenses are specialised contact lenses that are worn during sleep to reshape the front surface of the eye to temporarily correct myopia. Recent research has shown that OK lenses are effective at slowing progression of myopia by 50%. These encouraging results have led contact lens manufacturers to develop OK lens designs with greater effectivity in slowing progression of myopia. While these ‘Myopia Control’ OK lenses are now being supplied to optometry practices and marketed as being more effective in slowing progression of myopia compared to standard OK lens designs, there is no scientific evidence to support that they are any more effective than standard OK designs. The aim of this project is to increase understanding on how myopia control OK lens designs will affect known stimuluses for myopia progression compared to standard OK lens designs. The scientific literature reveals that OK causes peripheral light rays to be focussed further towards the front of the eye than central light rays, which is termed peripheral myopic defocus. Peripheral myopic defocus has been shown to slow progression of myopia in animal models, and this same mechanism is believed to be the reason why OK lenses slow progression of myopia. The manufacturers of myopia control OK lens designs claim that they are more effective at slowing progression of myopia compared to standard OK lens designs because they create a greater amount of peripheral myopic defocus. We are going to investigate the potential for greater slowing of myopia progression with myopia control OK lens designs, by measuring the effect that the different OK designs have on myopic defocus in young adults over 1 week of wear, which is the reported shortest duration of time for the full refractive effect to be achieved. This study is important as optometrists need to know the true effect that OK lenses marketed to slow myopia progression have on refractive mechanisms that have been shown to retard progression of myopia, if they are to be effective in managing myopia in their child patients. Outcomes will also assist the design of future longitudinal studies using standard and myopia control OK lens designs.

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