Orthokeratology Contact Lenses for the Treatment of Myopia in a Group of Danish Children
Orthokeratology Contact Lenses for the Treatment of Myopia in a Group of Danish Children
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. High myopia is associated with an increasing risk of sight threatening complications such as retinal detachment, glaucoma, macular choroidal degeneration and myopic choroidal neovascularization. In myopia the eye is elongated compared to an emmetropic eye. If the elongation of the eye can be controlled the progression of myopia can be controlled. Asian studies have shown reduction in axial length growth by 36-46% in children using orthokeratology contact lenses (OKL). OKL are custom fit, form stable lenses. During sleep the cornea is reshaped creating an emmetropic vision during the day, so no glasses or contact lenses are needed. Twin and family studies have shown a high heritability for the development of myopia, and more than 40 genetic loci have been identified indicating that the effect of OKL in Asian children might not be the same in North European children which is why we want to execute a similar study on North European children.
Purpose:
Method:
A randomized controlled 18 months prospective 1:1 study of a group of Danish children. 60 children will be included; 30 in each group. The participants will undergo several measurements reflecting the anatomy and function of the eye at baseline, 6, 12 and 18 month to evaluate the effect.
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 temporal 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 the 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.
A clear-cut reduction in axial length growth in Asian children using OKL compared to single-vision spectacles (SVS) has been proofed in several studies. In these studies, which are very heterogeneous regarding design, reductions of 36-46% in axial length growth were found compared to a matched control group. Two European prospective cohort studies have investigated the effect of OKL compared to SVS in Spanish children. A reduction in axial growth of 32 % and 38% respectively was found. Side effects of OKL have been evaluated; in a meta-analysis from 2015, including 8 Asian and one of the European studies. Odds Ratio for side effects were 8.87 for the OK group compared to the control group, however all side effects were mild and disappeared after termination of the treatment.
Thus, a reduction in childhood myopia using OKL has been proofed in Asian children; however, weather similar result can be achieved in a group of children from Northern Europe is unknown. The influence of OKL on quality of life impact of refractive correction has never been investigated in a randomized trail. How OKL reduce the axial growth of the eye is unknown. The lenses induce multifocality and higher order aberrations in the cornea, which might change the peripheral defocus. A change in defocus has been suggested as a mechanism for controlling axial length growth.
Primary goals:
In a randomized 18 months prospective 1:1 study of a group of Danish children to:
Hypothesis:
Design:
A 18-month randomized prospective 1:1 study of progression of myopia in a group of Danish children wearing OKL nightly (n=30) compared to a control group wearing SVS (n=30).
Children randomized to OKL will be examined at BL and day 3 and 7 as well as month 1, 3, 6, 9, 12, 15, and 18 after the start of treatment with OKL (T0).
Children randomized to SVS will be examined at BL and month 6, 12 and 18 after receiving new glasses with optimal prescription (T0).
Examination:
Inclusion Criteria:
Exclusion Criteria: