Short-sightedness or myopia is an ametropia in which the person (then called a myope) cannot see sharp objects far away, but nearby objects. Hence the name (close) myopia. Therefore, an object with a 0 vergence will not be sharply perceived and as the object approaches, the vergence will drop to a negative number. As soon as this number equals the degree of ametropia, the object will be observed sharply.
The word myopia comes from the Greek μυωψ (muoops) nearsighted, short-sighted.
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- General
- Causes
- Tools
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General
Myopia is not a disease, but a refraction error, a refractive error, in the optical system of the eye. If we look into the distance, the image of the object we are looking at should be projected onto the retina. To be precise, the image is projected on a special spot, the fovea. An eye that is too long, or an eye with a curved (too convex) lens system, projects the image in front of the retina, i.e. in front of the fovea, so that an image is blurred on the retina.
The anomaly usually begins to develop from 8 to 12 years of age and in the teens it gradually increases as the eye grows and thus the eye length increases. The focal point within the eye will then move further in front of the retina. When maturity is reached, the refraction error usually remains stable.
The classification of eye abnormalities – such as nearsighted and farsighted – and their explanation and correction, was elaborated by the Dutch ophthalmologist Franciscus Cornelis Donders. The magnitude of the refractive error is measured by an optician, orthoptist, optometrist or ophthalmologist. It is expressed in the diopter of the necessary lenses. The higher the dioptric myopia, the closer the subject will have to be to be sharply perceived.
Causes
The causes of myopia are probably diverse. The enormous increase in myopia in the last half century suggests, according to some, that excessive use of the eyes at a short distance (computer use, reading) often leads to myopia.
In 2018, it emerged that a result of the Generation R study shows that frequent and long-term viewing of smartphones and / or tablets in children increases the risk of myopia.
Myopia is hereditary. CREAM (Consortium for Refractive Error and Myopia), a collaboration between all myopia studies worldwide, identified 26 genes for myopia and refraction abnormalities. These genes have different functions, such as transmission of signals in the brain to the eyes, building of the connective tissue in the eyes and development of the eye. Carriers of several of these genes have a 10 times higher risk of myopia.
In addition to genetic factors, environmental factors also play an important role. Reading a lot or the extent to which someone played outside as a child causes or worsens the complaints in people who are already hereditary. We also see that people with a higher education level (such as a university) are more likely to have short-sightedness.
Tools
Glasses or contact lenses with concave lenses (called negative strength, often referred to as “min-strength”) cause the rays to diverge so that they converge on the retina.
This can also be achieved by laser reshaping the cornea to make it less convex. Two of the most commonly used methods are the LASEK and LASIK treatment
When the refraction error is large, the usual corrective means can be a problem. Lenses then become very thick on the outside edge and contact lenses are not tolerated by everyone. The laser treatment is therefore no longer possible because too much tissue has to be removed from the cornea to achieve the desired effect. Then there are even more surgical options.
In a PIOL operation, an extra intraocular lens can be surgically used for the own eye lens and thereby make the glasses or contact lens unnecessary.
In an “early” cataract operation, a so-called CLEAR operation (where CLEAR stands for Clear Lens Extraction And Replacement), the lens is replaced by an artificial lens. This does lead to a loss of accommodation capacity, so that a correction tool for close viewing (reading glasses) remains necessary. In most cases this is done with reading glasses or if a far-sight correction is still required with progressive glasses. Usually, a CLEAR operation is recommended for people whose own accommodation capacity is less (older than 45-50 years) and the PIOL operation for people whose accommodation capacity is still OK.
Related articles
Farsightedness (hyperopia)
Long-sightedness (presbyopia)
Human eye
Bates method
Glasses
