Clinical Study Of Nearsightedness, TReatment With Orthokeratology Lenses 2

Myopia is a common disease of the eye with increasing prevalence in the Western World as well as in South East Asia where 60-90% of the children are affected. A Danish study found that early debut of myopia is associated with a higher degree of myopia later on in life. Myopia may be corrected with spectacles, contact lenses or surgically, but despite this socio-economic burden, high myopia is associated with an increasing risk of sight threatening complications such as retinal detachment, glaucoma, macular choroidal degeneration and myopic choroidal neovascularization.

Myopia is a complex disease with a multi-factorial etiology. Twin studies and family studies have shown a high heritability for development of myopia, and more than 40 genetic loci have been identified. Outdoor activity seems to reduce the myopia progression. The shape of the eye may be of importance; axial growth makes the eye ellipsoidal which increase the peripheral defocus on the retina. Peripheral defocus has been suggested to induce further axial growth of the eyeball.

Accommodation is a significant covariant of near work and reading. A cross section study has shown a reduced precision in accommodation (A) on a near object combined with increased convergence (C) in myopic eyes. This increased AC/A ratio (dynamic) may be a predictor for myopia progression.

Interventions for reducing myopia progression have been many. The effects of progressive additional lenses, multifocal lenses and bifocal lenses have been limited. Anticholinergic eyedrops (Atropin 0.01%) significantly reduce the progression of myopia in Asian children by approximately 50% over a period of two years with limited side effects. Almost similar results have been found in Asian children using orthokeratology contact lenses (OKL) for reducing myopia progression.

OKL are custom fit, form stable lenses used during sleep. The lenses induce a temporary flattening of the cornea, which modify or eliminate refractive errors, leaving no need for glasses or contact lenses during daytime. OKL were introduced in the 1960 ́s, but with limited success due to lens material (PMMA) which was not gas-permeable. Decentration was also a problem making the effect variable and unpredictable. With new gas permeable lens materials and computer assisted topographic measurements of the cornea, fitting of the lenses has been improved significantly, so that nightly wear is now standard treatment.