As the prevalence of myopia increases worldwide, optometrists need to be informed about methods for myopia control and be prepared to discuss the options with concerned parents, according to Jeff Walline, OD, PhD.
Based on available research, treatment with atropine drops that block muscarinic receptors in the retina appear to be the most effective method for slowing progressive myopia. The use of this nonselective muscarinic antagonist, however, is limited by side effects including mydriasis and cycloplegia arising from blockade of muscarinic receptors found in the iris and ciliary body.
Alternatively, contact lenses (CLs), including corneal reshaping lenses and soft bifocal lenses with a distance center design, show promise for controlling progressive myopia and may be worth recommending. More data are needed, however, to confirm initial positive results and to establish the permanency of the benefit once lens wear is stopped.
Further research is also needed to better understand the mechanism by which myopia progression is slowed, as that might help to guide parameters for lens design that would lead to better outcomes, said Dr. Walline, assistant professor, Ohio State University (OSU) College of Optometry, Columbus.
"Currently, [CLs] seem to be the best option to consider when parents are concerned about a child's progressing near-sightedness. Contrary to the belief held by many parents, children can become proficient with lens care to maintain safety if they receive appropriate guidance from the eye-care practitioner and parental reminders," he said.
Based on their wearing schedule—with insertion at bedtime and removal in the morning—orthokeratology lenses have advantages as a method for myopia control. With these lenses, children can enjoy clear vision all day without glasses or CLs. Also eliminated is any need for lens handling at school, Dr. Walline said. Currently, there are no randomized controlled studies investigating the efficacy of orthokeratology, but available evidence shows that while it does not prevent progression, it may slow the growth of the eye by about 50% and minimize change in refraction, he said.
Findings from a study conducted by Dr. Walline's OSU colleague, Mark A. Bullimore, MCOptom, PhD, FAAO, suggest orthokeratology is relatively safe in terms of the risk of microbial keratitis. Based on calculation of a 95% confidence interval using adverse event data collected from prescribing practitioners, the maximum risk of microbial keratitis was about 24 per 10,000 years of wear, which is comparable to the risk of overnight wear conventional or silicone hydrogel soft CLs. [Optom Vis Sci 2009;86:E-abstract 90583).
"These data suggest that flattening the cornea does not add any additional risk for infection. Nevertheless, the risk is higher than with daily wear [CLs], so patients and their families must be counseled about lens care and to come in immediately if there is any pain, redness, or decreased vision," Dr. Walline said.
The mechanism by which orthokeratology is thought to control myopia involves an optical effect on the cornea. It is believed that the lens reshapes the central cornea so that the child can see clearly, but leaves the peripheral cornea untreated. As a result, light focusing in front of the retina in the periphery may act as a cue to slow myopic eye growth.
This theory is the basis for soft bifocal CLs with a distance center design as a method for myopia control, and there has been growing interest in this modality among researchers and in industry. Three studies evaluating distance-center soft bifocal CLs reported efficacy in slowing myopia progression, but the rate ranged from 26% to 79%, and only one of the studies, which had a short duration, was published in a peer-reviewed journal. [Ophthalmol June 2011;118:1152-1161)
"Clearly, there is a lot more research that is needed in this area, but it is an interesting approach to myopia control and something that practitioners should follow closely," Dr. Walline said.
Soft bifocal CLs might especially be considered for children who are already out of the range for orthokeratology CLs. Currently, CooperVision and Vistakon have soft bifocal lenses with a distance center design that may potentially be used to slow eye growth, but they have not received FDA approval specifically for myopia control.
Dr. Walline is a consultant for Johnson & Johnson Vision Care and Bausch + Lomb. He has received previous research funding from Johnson & Johnson Vision Care, Paragon Vision Sciences, and is currently performing research sponsored by CooperVision, and Alcon.