Myopia is a refractive error in which the eyeball is too long for the refraction of the different ocular refraction components.
At birth there is almost no incidence of myopia. Only 2-3% of newborns have it. The condition prevalent at this age is hyperopia, above three diopters (D), in which the opposite situation occurs1. The eyeball is too short for the refractive power of the eye.
In the first few years of life, a process called emmetropization2takes place, in which the eye grows and, therefore, hyperopia is reduced and eliminated. At six years old, the majority of children show signs of emmetropia. The existence of so-called physiologic hyperopia is understood to be around 0.75 diopters. Starting at this time, and although the eye continues to grow until about age 20, it grows into such a shape that refractive changes caused by the greater axial length are compensated by other ocular changes such as a loss of the crystalline lens power.
If that axial growth is not compensated for as stated above, simple myopia will appear. If myopia is present at birth, or in the first few years of emmetropization, it is very likely that the eye has or will reach an axial length over 26 mm. That myopia is then considered a true eye disorder and it is called pathological myopia. This myopia entails implicit problems at the fundus of the eye that may cause significant reductions to visual acuity in adulthood.
It should be highlighted that simple myopia, a priori a refractive error and not a pathology, may turn into a pathology depending on the diopters and/or axial length it reaches. Above 5-6 diopters, or LAX > 26 mm, may induce a significant iatrogenesis such as, among other things, macular degeneration, retinal detachment, or cataracts3. The risk of such complications increases for low (>-2 D), moderate (<-2D – >-5D), and high (<-5D) myopia as shown in Table I.
Prevalence and Etiology
The global presence of myopia is increasing significantly. In 2016 a Holden et al.4 study indicated that in 2010 myopia affected 1.9 billion people in the world: 28% of the global population. By 2050 myopia is expected to affect 5 billion people: in other words 50% of the population. The study also reported that in 2010 high myopia affected 3% of the population while in 2050 it would reach 10%, posing a risk of significantly low vision and blindness. The past, present, and future based on region of the world can be seen in Table II and gives this article its title.
Our research group (Vision Research Group [GIV]) recently published research regarding the prevalence of refractive errors in children ages 5 to 7 in Spain, finding, as shown in Figure 1, an increase with age of near-sighted children to the detriment of myopic and hypermetropic children5.
With regard to its etiology, it was always considered and has recently been demonstrated that there is a significant genetic factor. Therefore, the risk of being near-sighted is tripled and sextupled, respectively, by having one or two near-sighted parents6. In myopia appearing before age six, the genetic component is considered to be predominant. Nevertheless, genetics does not explain the huge changes to the error’s current and future prevalence. It is believed that miopic-genetic factors exist that act on the child starting at age six, such as close work and reading, that may increase existing myopia or cause it to appear starting at that age. Therefore, today myopia is often considered a problem of interaction between genetics, environment, and development7.
Sunlight has been found to prevent against myopia8. Spending more than 2.7 hours per day outdoors, not necessarily engaging in sports, is the right amount, while spending less than 1.5 hours per day increases one’s probability of developing myopia9.
Moreover, race also has an influence on the risk of the appearance of myopia, with Asian people most at risk and Black people the least.
Many of the risk factors for the appearance and rapid progression of myopia are understood and shown in Table III.
Compensation and Addressing Myopia
Compensation for myopia is often done with glasses. Their lenses are called negative and are spherical or aspheric. With these lenses, patients go back to having visual acuity in distance vision. However, they do not have any benefit on the progress of the refractive error. In some cases it even seems that the reasons for which myopia appears or progresses increase. According to the latest theories this is due to the existence of a hyperopia in the periphery of the retina and/or a delay in the accommodative function that allows us to focus during close vision (technically accommodative lag).
It has been proven that there will be progression when myopia first appears, and the most attention must be paid to myopia appearing before 10 years of age (between 6 and 10). In these cases and in those in which myopia appears after 10 years of age with above average progression (>0.75 D per year), attempts must be made to control the progression of myopia so that when the patient is an adult their myopia does not surpass 5 or 6 diopters.
Today there are different techniques that have proven to be effective, to a greater or lesser extent, in slowing the progression of simple myopia. They are10:
- Ophthalmic lenses for glasses
- bifocal or multifocal lenses, or
- special lenses to control myopia called prismatic bifocals
- Contact lenses
- Overnight orthokeratology
- Soft multifocal and prismatic bifocal lenses
- Pharmacological treatment:
- Super-diluted atropine (0.01% concentration)
Table IV details the average control results that may be achieved with each of these techniques.
The GIV recently published the results of a clinical trial (MiSight Assessment Study Spain [MASS]) that it conducted with MiSight® contact lenses, lenses designed and approved for controlling myopia in children and adolescents, compared to a control group using glasses, in children age 8 to 12. Myopic progression in diopters was found to slow with the contact lenses by 39.2% compared to the control group11.
Additionally, optical techniques have begun to be combined with pharmacological techniques in order to increase their effectiveness12.
Each of the above-mentioned options has its own specific advantages and disadvantages and a vision professional, ophthalmologist, optician, or optometrist should be the one to prescribe the best option in each individual case.
In conclusion, in all cases in which simple myopia appears, the Universidad Europea Vision Research Group recommends following the algorithm37 developed by Canadian optometrist Langis Michaud, which is more or less accepted by the vision professional community and shown in Figure 2. Lifestyle, genetic background, and age of appearance are the fundamental pillars when defining a strategy to follow.
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