Can we slow down myopia?
Myopia is an optical defect that affects about 30% of the European population and American, and 90% of the population of some countries in Southeast Asia. Prevent nearsightedness, slow or stop the evolution is a major public health issue. Indeed, the ocular complications of nearsightedness are many: retinal detachment, cataracts, glaucoma...
Slow the progression of myopia could benefit many children, and various strategies have been proposed and studied, with variable success: under correct myopia, permeable rigid lenses meet the gas for the correction of day, or night (Orthokeratology), bifocal soft lenses, equip the corrective glasses with progressive lenses, prescribe the eyedrops contains atropine or the pirenzepine... This page is devoted to the results obtained for these various strategies. Before you study them more in detail, it is important to emphasize that the main criterion considered to enjoy the speed of evolution of the short-sightedness is the degree of myopic correction (in power), and not the rate of increase of the length of the eyeball (axial length). Myopia is a condition that the associated morbidity is induced by the lengthening of the eyeball, and not the degree of correction. It is important to not to overinterpret the findings of some studies. There is no way to stop the development of myopia in children or adolescents, but some may slow its progression.
(1) whether under correct nearsightedness?
The sous-correction of myopia to the eye to less to seek accommodation for near vision. Or, as some theories attribute to a lack of accommodation the progression of myopia, it could be interesting to allow, thanks to a correction, to restore a more effective accommodation (with the formation of the image of the targets of the vision in terms of the retina, and not backward). Unfortunately, the sous-correction of myopia is ineffective in this context, and has no effect (1), and even accentuates the evolution of myopia (2). Do not err myopic children.
(2) what's the point of adapting rigid lenses?
Rumor misleadingly brought rigid lenses the day an effect of slowing myopia is unfounded, as evidenced by several recent studies (3,4). The effects reported by some studies were biased by the transitional effect print rigid lenses to the cornea (the rigid lenses induce central flattening, which is used as a method of correction of low myopia in Orthokeratology). In reality, if a slowdown in the progression of myopia (appreciated in terms of lens correction in diopters) is observed, it must be necessarily associated with a lower elongation of the eyeball. Indeed, it should be noted that the excessive and continuous eyeball lengthening is the main mechanism involved in the development of myopia.
No study has shown that wear lenses hard to correct the myopia of children or adolescents slowed the elongation of the eyeball to a control group (for example, children or adolescents myopic corrected in glasses).
(3) whether prescribing progressive lenses or glasses to bifocals?
As the sous-correction of myopia, the prescription of corrective lenses, bifocal or progressive aims compensate for the inadequacy of the supposed accommodation of young myopic. The lower portion of these special glasses of bezel is equipped with an additional power for near vision. Some studies have shown that this type of glass could slow the progression of myopia, but insignificantly clinically (5,6).
The interest of progressive lenses is not enough to be considered as an effective strategy for slowing the progression of myopia.
(4) is the Orthokeratology effective to slow myopia?
The Orthokeratology is a technique of medical correction of myopia, which is to wear rigid lenses at night, to induce a temporary correction of myopia, whose expected duration covers the next day. Unlike the rigid lenses prescribed to be worn overnight, and whose geometry is dictated by the rules of geometrical optics, used for the Orthokeratology lenses are intended to induce a change in shape of the cornea (central Flattening). The effectiveness of the Orthokeratology is limited to low myopia, as it is not possible to flatten the center of the cornea beyond a certain limit. This can be interesting in children or adolescents, because they present a beginner myopia so low, but that is progressive, and for whom refractive surgery is against specified.
Several studies have highlighted a slowing effect significant on the growth of the eyeball of the Orthokeratology to other techniques of correction like rigid lenses (7), glasses; or still monofocal soft lenses (8-10).
The mechanism of this effect retarder could be linked to positive spherical aberration, which is induced by the contour aspherical oblate of the cornea. Flattening the lens at the center of the cornea-induced is necessarily accompanied by a camber in a peripheral ring, under the law on the conservation of the domes curvature undergoing deformation without modification of their surface. Camber induced in the periphery causes a local relative excess of refractive power of the cornea, to its central portion. The rays of light refracted by the corneal periphery converge in front of the retina. However, this "myopic peripheral defocus" seems to be a signal whose effect is to slow eye growth.
(5) interest of bifocal lenses on the development of myopia
The main indication of bifocal contact lenses is the correction of myopia and presbyopia in the elderly for 40 years. In the context of the slowdown in myopia, the potential interest of these lenses naturally oriented lenses optical design with a central portion intended for correction of distance vision, and peripheral portion for the correction of nearly.
This optical profile resembles that which is induced by the central corneal flattening and the peripheral arch produced by nocturnal wear rigid lenses prescribed in Orthokeratology. The positive spherical aberration is a myopisation of light refracted by the periphery of the cornea. Logically, from far away central vision bifocal lenses seem to slow the progression of myopia in half, as the techniques of Orthokeratology
(6) eye drops to slow myopia
Some pharmaceutical agents applied in eye drops have demonstrated an indisputable suppression effect on the development of myopia. The involved molecules have anti-muscarinic so-called effects, characterised by the combination of an expansion of the pupil and of paralysis or part of the accommodation. Atropine and pirenzepine the are two agents with the beneficial effects have been demonstrated in clinical practice (11-20). They cause a paralysis of accommodation and a dilation of the pupil (more marked with atropine). In atropine eye drops is also often prescribed for children to paralyze the accommodation and allow a measure objective refraction more reliable.
The exact mechanism of action of these agents muscarinic to explain the slow-down of myopia is unknown. These drops are not prescribed routine because they generate some side effects sometimes pronounced as photosensitivity (pupillary dilation, or Mydriasis, leads to an excessive illumination of the retina), and the loss of NET vision closely (due to the reduction of cristallinienne accommodation). To reduce these effects and find the optimal concentration of the eyedrops of atropine, several concentrations were tested: 0.5%, 0.1% and 0.01%. Eye drops was administered at night in each eye.
Not surprisingly, the lower concentration (0.01%) was the better tolerated clinically, because it allowed 94% of children read without optical reading addition, whereas they were about 70% to require such assistance for other concentrations. Despite this low concentration, the effect of retarder on the evolution of myopia with the eyedrops of atropine to 0.01% is substantially identical to the higher levels.
A more recent study suggests even that the concentration to 0.01% is more effective for slowing myopia (20); After stopping the eye drops, children who received eye drops dosed at 0.01% showed a recovery progression of myopia less frequent and less intense than those of the groups receiving higher concentrations.
This concentration to 0.01% seemed to reduce the progression of myopia of half to one data collected in control groups receiving a placebo. However, as for other studies, the effect of reduction in the progression of myopia about the power prescribed for correction, effects on the increase of the axial length of the eyeball are not truly demonstrated, but suggested. In the group whose concentration is 0.01%, the increase in axial length over time tends to be lower than in most dose groups. However, the absence of control group (group receiving a placebo eyedrops) in this study does not conclude in a more assertive manner to atropine eye drops to slow the progression of myopia in the long term.
It cannot be formally excluded that atropine reduces the progression of myopia due to a change in the geometry of the lens. This is important, because the anatomical complications of nearsightedness stem elongation of the eyeball, not the power of corrective lenses prescribed to correct a certain degree of myopia.
(7) spend time outdoors in childhood
The practice of sports or outdoor activities has been identified as a factor of prevention of the incidence of myopia (21)... but spend time outside once installed myopia does not slow down the evolution of it (22).
Recent studies suggest that the Orthokeratology, wear bifocal lenses and the administration of eye drops to atropine (0.01%) could slow down myopia, i.e. slow down its evolution in terms of prescribed correction. The Orthokeratology exposed to infectious risks similar to other indications of night wear contact lenses (23) and constraints. Atropine to 0.01% causes significant adverse effects. The effects of these strategies on the lengthening of the eyeball, real public health issue, remain uncertain in the medium term and must be the subject of further studies.
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