This short US paper reviews the evidence of clinical trials conducted to date where short-sighted children have undergone Overnight Vision Correction (OVC) treatment and tries to draw conclusions on the effectiveness of the treatment in slowing down or halting the further development of short-sightedness as well as in terms of the safety risks - if any - associated with OVC. Referencing the LORIC Study from Hong Kong and the CRAYON Study from the US, the author highlights that these different trials both produced evidence that the further progression of short-sightedness could be slowed or halted by children wearing overnight ortho-k corrective contact lenses. However, the author believes that more studies are required to provide a stronger body of evidence for this theory and to provide further assurance on the safety of OVC.
EXTRACT
Early evidence indicates that corneal reshaping GP contact lenses, or modern orthokeratology lenses, may slow myopia progression in children. But are the risks worth the benefits? This review will highlight results of the studies examining orthokeratology and myopia control in children performed to date as well as the questions that remain unanswered.
Risks and Benefits
The control of myopia has been the quest of many researchers for decades. In the United States alone, 100 million people are myopic, and most became myopic during childhood. In countries such as Hong Kong, China, Singapore, and Taiwan, the prevalence of myopia is even higher.
Because myopic progression occurs through axial eye growth, the control of myopia-hence reduced eye growth-has the potential to decrease ocular morbidity secondary to complications such as retinal detachment, glaucoma, and chorioretinal degeneration. In addition, patients who have lower myopia have better spectacle cosmesis and more predictable refractive surgery results compared to patients who have high myopia.
Various interventions have been attempted to control myopia progression. However, treatments such as alignment fitted GPs, multifocal spectacles, and candidate pharmaceutical agents have had little to no clinical effect in the ability to slow eye growth or myopia progression.
Overnight orthokeratology has demonstrated effectiveness in reducing myopia in adults and adolescents. Note that reduction refers to a decrease in existing myopia, and control refers to less progression of myopia compared to a control group.
However, there are known risks to overnight use of orthokeratology lenses. As in overnight use of soft lenses, sleeping in contact lenses increases the risk of microbial keratitis. In a summary of microbial keratitis related to overnight orthokeratology, Watt et al (2007) reported that about 50 percent of those affected were children younger than 16 years old, and about 75 percent were in East Asia. Therefore, if orthokeratology is effective in controlling myopia in children, then its benefit must well exceed the risk associated with this mode of lens wear in this age group.
Children and Myopia Control
Because of the previously unknown risk-to-benefit ratio, there are no reports in the literature of completed randomized, controlled clinical trials of orthokeratology versus a conventional method of myopia correction to slow myopia progression in children. However, there is anecdotal evidence that orthokeratology lenses slow the progression of myopia in children, and two small pilot studies utilizing historical controls that confirm the effect.
The first study was performed by Reim et al and published in 2003. They used changes in refractive error and base curve of corneal reshaping lenses to monitor myopia progression after three years of therapy in 164 eyes of adolescents. There was no control group. They reported that myopia increased by -0.37D after three years, which appears substantially less that reported for single vision spectacle wearers (about -0.50D to -0.78D per year in their comparisons).
January 2010 Contact Lens Spectrum, LORETTA B. SZCZOTKA-FLYNN, OD, PHD, MS, FAAO
Read Full article at: Contact Lens Spectrum
