Evidence of the benefits of new types of optical corrections for myopia prevention?

Abstract

Over the past few decades, the prevalence of myopia has significantly increased, especially in East and Southeast Asian countries, where the prevalence of myopia in school leavers is now around 80%. The risk of myopia related complications such as myopic macular degeneration, retinal detachment, cataract, glaucoma, visual impairment and blindness, all increase with increased severity of myopia without any safe threshold of myopia for any of its known ocular complications.

Various specially designed contact lenses and spectacle lenses has been developed to prevent myopic progression. The Orto-K treatment contact lenses are worn during the night to decrease the corneal refractive power so that during the day you can see far without optical correction. Peripheral hyperopic refraction is assumed to increase the progression of myopia. To correct the relative peripheral hyperopic refraction various contact lenses and glasses have been developed so that the central myopic refractive error is fully corrected and the peripheral refraction corrected to the direction of hyperopia in relation to the central correction.

The main aims this presentation is to highlight the chalenges, related to conducting and reporting these studies, and with a few examples show differences between statistically significant and in practice significant treatment benefits.

There is a large individual variation in the progression of myopia. Progression of myopia in two same aged myopics with the same myopia can significantly differ from each other. Myopia progresses generally more in the early stages. The most significant factors causing variation in myopia progression are parental myopia, time and intensity spent on near work, time spent outdoors, age of myopia onset, and change in refraction prior to the myopia examination point. Especially the wide range range in baseline refraction and age at the beginning of the research intervention makes reliable randomization challenging. Comparability would be improved if the randomisation to the treatment and control group could be carried out for example half or one year before beginning the treatment intervention. In this way, the potential effects of the natural progression of myopia in study groups could be taken into account.

The the difference between treatment and control groups are often reported as percentage benefit, which actually does mean much. For example 50% benefit of treatment can be received from refraction canges 0.1 D vs 0.2 D, which is practicaly nothing or 1.0 D vs. 2.0. It is also important to report in what period of time the benefit of treatment occurs and when the treatment is no longer beneficial, instead of reporting about sustained benefit, when the changes between the groups do not change.

Before new therapies are generally introduced, several independent studies on the benefits and potential harms and complications of treatments shuld be conducted with sufficiently large datasets.

The presentation discusses, with some practical examples, in more detail about these and other factors potentially affecting on the reliability of clinical studies about myopia treatment.