Use of spectacles, contact lenses, or medications does not inhibit the progression of myopia for any length of time, as seen in in large major studies in children.
Dr. Young discussed the importance of myopia studies, the prevailing mechanisms of myopia, and described human myopia intervention studies, specifically the Correction of Myopia Evaluation Trial (COMET), Contact Lens and Myopia Progression (CLAMP) study, and the Atropine for the Treatment of Myopia (ATOM) study as well as their outcomes.
"Myopia is the most common human ophthalmic disorder," said Dr. Young, director, Pediatric Ophthalmic Genetics Program, professor in ophthalmology, pediatrics, and medicine, Duke University Eye Center and the Duke Center for Human Genetics, Durham, NC, and professor of neuroscience, Duke-National University of Singapore Graduate Medical School. "High degrees of myopia predispose patients to retinal detachment, glaucoma, and premature cataract development.
Mechanisms of myopia
One theory suggests myopia might develop as a result of excessive accommodation and uncoordinated ocular growth mediated by retinal signals in response to prolonged near work, she noted.
"It has been suggested that bifocal lenses might reduce defective accommodative effort and improve the retinal image quality in patients with high accommodative lag," she said. A second theory is that the wearing of rigid gas-permeable contact lenses in a technique called orthokeratology might flatten the cornea and impede axial growth.
A third theory is that atropine, a muscarinic antagonist, reduces myopia in humans and in experimentally induced myopia in animals by a non-accommodative mechanism.
Other hypotheses of myopia development are related to environmental/gene interactions and that beta blockers might reduce the IOP and therefore reduce the mechanical stretching of the scleral wall.
The rationale behind the COMET study, according to Dr. Young, is that patients with myopia have reduced accommodation to near targets and that they have extended periods of defocus that might cause the axial length to elongate. That theory has been demonstrated in animal models of myopia. The thought is that if progressive addition lenses (PALs) are provided, patients would have clear vision as a result of the decreased defocus during near visual tasks, and thus, the progression of myopia would slow.
The COMET study was a multicenter, doublemasked, clinical evaluation of the different rates by which myopia progressed in children who wore PALs (i.e., a Varilux Comfort lens, Essilor International) with +2-D addition, compared with children who wore single-vision lenses (SVLs). The children, who had from –1.25 to –4 D of myopia, were evaluated by cycloplegic autorefraction. The axial lengths were measured by A-scan ultrasonography.
Of the 469 children enrolled, 462 completed the evaluation at the 3-year time point. The study found that the increase in myopia was similar in the two patient groups; the children with the PALs had an increase of –1.28 D of myopia compared with an increase of –1.46 D in the group of children who wore SVLs. Dr. Young noted that the treatment effect was seen during the first year. Some increases in the axial length were seen in both groups.
"The main finding of the study was that the small magnitude of effect does not warrant a change in clinical practice," Dr. Young said.