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Myopia is the most common human eye disorder in the world, with prevalence estimated at nearly 50% in the United States and up to 96% in some Asian countries.1,2 Although we traditionally think of myopia as starting in school-age kids, the onset of myopia appears to be getting earlier. In Taiwan and Singapore, for example, the prevalence of myopia among children 6 and 7 years old is estimated to be 20% to 30% and as high as 84% in high school students.3
Apart from the economic burden that it carries, myopia is a significant public health concern. High myopia is associated with many sight-threatening ocular pathologies, including retinal detachment, myopic macular degeneration, and earlier onset of cataract and glaucoma.4
Fortunately, several treatments in multiple clinical trials have been shown to be effective in slowing the progression of myopia, presenting a unique opportunity for practitioners of pediatric optometry and ophthalmology to intervene in the course of this progressive condition. This three-part series, titled Innovations in Myopia Control, will examine these treatment methods and review some of the research that supports their use.
The treatment method that perhaps achieves the most consistent myopia control is the systematic use of orthokeratology (ortho-k) lenses, also known as corneal reshaping. A recent meta-analysis reported that the use of ortho-k lenses can slow axial elongation in myopic children by an average of 41%,5 an effect that is both statistically significant and clinically meaningful. With more children being fit with these lenses for myopia control, it is worthwhile to review some of the basics and special considerations for pediatric patients.
HOW THE LENSES WORK
In overnight ortho-k, the patient wears rigid lenses overnight to temporarily change the curvature of the cornea. Modern ortho-k lenses use breathable rigid gas permeable (RGP) materials and a reverse geometry design to achieve faster and more effective corneal reshaping than was possible with older designs.6
Reverse geometry lenses are characterized by a central base curve that is significantly flatter than the central corneal curvature, and steeper “reverse” curves that allow a smooth transition to the alignment-fitting landing curve in the periphery. This design improves lens centration and allows more efficient distribution of the hydraulic pressure beneath the lenses, leading to faster and more significant central corneal flattening.
HOW THE LENSES ARE THOUGHT TO CONTROL MYOPIA
Ortho-k corrects refractive error centrally while leaving myopic defocus peripherally. This is what is thought to provide a controlling effect for patients with myopia. Myopic defocus has been demonstrated to have a strong inhibitory effect on axial elongation in animal models, even when only limited to the peripheral retina.7 Additionally, it has been shown that refractive development is mediated locally to the extent that defocus applied to one hemisphere causes ocular growth only in the corresponding half of the eye.8 Therefore, optical treatment strategies have shifted, attempting to manipulate the retinal image quality in the peripheral retina and permitting clear central vision while maintaining peripheral myopic defocus (ie, the eye’s growth stop signal)—as is done with ortho-k.
CONSIDERATIONS FOR YOUNG PATIENTS
In the Myopia Control Clinic at the University of California, Berkeley, ortho-k is the most common myopia control treatment option selected by patients. In our experience, ortho-k lenses offer several advantages, particularly for young patients, and they are well-tolerated when the appropriate approach is used.
One of the most significant advantages of ortho-k lens use is being free of contact lenses during the day. In our patient population, this translates to not having to manage contact lens wear and care at school. This also means that parents or guardians can assist with lens insertion, removal, and care if the kids are not ready to take on this responsibility alone.
In our fitting process, the provider initially inserts the lenses and then allows sufficient time (at least 10-15 minutes) for the child to adapt to wearing them. During this time, we recommend that kids get up and take a short walk around the clinic or go outside and get used to wearing the lenses to appreciate their vision without glasses and to take their mind off the initial discomfort.
We rarely use a topical anesthetic agent to help with adaptation in order to present the most realistic initial experience to the patient in the office. We explain to patients and parents that, when we put the lenses on, this should be the most uncomfortable the lenses ever are. It is important for patients to be able to understand what a “normal” level of discomfort is in contrast to when there might be a problem requiring further care.
WHAT ARE THE RISKS?
Although there are many notable advantages of ortho-k lens wear for pediatric patients, it would be irresponsible not to comment on the risks associated with contact lens wear. Corneal staining is fairly common and can be easily managed with artificial tears or discontinuing lens wear for a short time. Microbial keratitis (MK) is the most serious and concerning complication of ortho-k.
A recent review reported only sporadic cases of MK with no significant associations with baseline levels of myopia, sex, or brand of ortho-k lens, and many reported cases originated in East Asia, most notably in mainland China and Taiwan.9 The most significant risk factors were found to be lack of training for practitioners and wearers, improper lens fitting, poor compliance with lens care regimens, and loss to routine follow-up care. Also, the incidence rates of reported infections decreased dramatically after 2002, when regulators in China posted regulations regarding the inspection and registration of ortho-k lenses; the training and certification processes for ortho-k practitioners; and requirements for instrumentation, fitting, and follow-up procedures.
Despite the fact that MK is a rare event, considering its vision-threatening potential, it is important to provide extensive education to both patients and parents regarding rigorous compliance with lens care regimens.
Ortho-k has been demonstrated to be a safe and effective method of vision correction for children, and it has the added advantage of slowing the progression of myopia. When prescribed carefully, ortho-k lenses offer the significant advantage of providing kids with clear vision without glasses or daytime contact lenses.
In upcoming issues of AOC, two additional options for myopia control therapy—multifocal contact lenses and atropine—will be discussed, along with recommendations for selecting the most appropriate treatment for your patient.
1. Vitale S, Sperduto RD, Ferris FL 3rd. Increased prevalence of myopia in the United States between 1971-1972 and 1999-2004. Arch Ophthalmol. 2009;127(12):1632-1639.
2. Pan CW, Dirani M, Cheng CY, Wong TY, Saw SM. The age-specific prevalence of myopia in Asia: a meta-analysis. Optom Vis Sci. 2015;92(3):258-266.
3. Lin LL, Shih YF, Hsiao CK, Chen CJ. Prevalence of myopia in Taiwanese schoolchildren: 1983 to 2000. Ann Acad Med Singapore. 2004;33(1):27-33.
4. Flitcroft DI. The complex interactions of retinal, optical and environmental factors in myopia aetiology. Prog Retin Eye Res. 2012;31(6):622-660.
5. Si JK, Tang K, Bi HS, Guo DD, Guo JG, Wang XR. Orthokeratology for myopia control: a meta-analysis. Optom Vis Sci. 2015;92(3):252-257.
6. Swarbrick HA. Orthokeratology (corneal refractive therapy): what is it and how does it work? Eye Contact Lens. 2004;30(4):181-185.
7. Smith EL 3rd, Hung LF, Huang J. Relative peripheral hyperopic defocus alters central refractive development in infant monkeys. Vision Res. 2009;49(19):2386-2392.
8. Wallman J, Gottlieb MD, Rajaram V, Fugate-Wentzek LA. Local retinal regions control local eye growth and myopia. Science. 1987;237(4810):73-77.
9. Liu YM, Xie, P. The safety of orthokeratology – a systematic review. Eye Contact Lens. 2016;42(1):35-42.
Sarah Kochik, OD, FAAO
• clinical instructor and PhD candidate, University of California, Berkeley, School of Optometry
• financial interest: conference travel support, Paragon Vision Sciences
Maria Liu, OD, PhD, MPH, FAAO
• assistant professor, clinical optometry and vision science, University of California, Berkeley, School of Optometry
• financial interest: consultant, Paragon Vision Sciences