Orthokeratology (or ortho-k) is the use of specially designed gas permeable contact lenses that are worn during sleep to temporarily correct nearsightedness and other vision problems so glasses and contact lenses aren't needed during waking hours.
Ortho-k also seems to be effective in decreasing the progression of myopia in children. Evidence suggests nearsighted kids who undergo several years of orthokeratology may end up with less myopia as adults, compared with children who wear eyeglasses or regular contact lenses during the peak years for myopia progression. The reason for this is best explained by the Peripheral Hyperopic Defocus Theory below.
Peripheral Hyperopic Defocus Theory is the focussing of the peripheral light rays seen in Figures 1 & 2 behind the retina stimulating the eye to continually grow resulting in higher degrees of myopia. Figure 3 illustrates the effect on the central and peripheral light rays a result of orthokeratology and multifocal contact lenses. The theory is that with the light rays focussed in front of the retina in Figure 3 instead of behind in Figures 1 & 2 there is less stimulus for the eye to progressively grow longer. Studies have demonstrated a significant decrease in the progression of myopia as a result of these treatments.
In 2012, researchers from Hong Kong, Pauline Cho and Sin-Wan Cheung published the results of the Retardation of Myopia in Orthokeratology (ROMIO) Study: A two year randomized clinical trial that found a 43% reduction in axial elongation (growth of the eye associated with progression of myopia) compared to that of subjects wearing single vision glasses. It was concluded that younger children tended to have faster axial elongation and may benefit from early ortho-k treatment.
Furthermore, as myopia control expert Dr. Jeffry J. Walline, O.D., PhD, from the Ohio State University College of Optometry pointed out in his analysis of the study published in the same issue of Investigative Ophthalmology and Visual Science, the benefit of slowed myopia progression from wearing the corneal reshaping lenes extended beyond the first year of myopia treatment.
In March 2014, researchers in Taiwan published results of a study that compared the use of ortho-k lenses with atropine eye drops for the control of myopia in children age 7 to 17. Participants had myopia ranging from -1.50 to -7.50 (with up to -2.75 D of astigmatism) at the beginning of the three year study period. The two myopia control treatments produced comparable results: children wearing the ortho-k lenses experienced myopia progression of -0.28 D per year, and those who wore eyeglasses and applied 0.125% atropine eye drops nightly had an average myopia progression of -0.34 D per year. Although this study did not include a control group that received no treatment, the study authors mentioned that in similar studies the progression of nearsightedness among children wearing ortho-k lenses for myopia control was roughly half of what those who received no myopia control treatment over a two year period.