Nearsightedness, or myopia, is one of the most common refractive eye defects. Over a billion people live with it in the world, and less than half of them heal it. What is this disadvantage? Is it possible to correct it effectively?
Nearsightednessis a visual defect in which both genetic and environmental factors contribute to its development, and the role of the latter grows more and more over the years. Under physiological conditions, the image is ideally created on the retina thanks to the eye's refractive system. Nearsightedness occurs when the image is not formed on the retina, but in front of it. This can be caused by the cornea or lens refracting light too much, or when the eyeball is too long (which is the most common cause).
Myopia - causes
Nearsightedness can be inherited in many ways, but as the number of myopia cases has increased significantly and systematically since the 1950s, it is believed that environmental factors are the main factor in its formation.
Close-up visual work, such as reading, writing and computer work, is considered to be the main cause of the disease, when as a result of excessive "overstraining" the eyes, compensatory lengthening of the eyeball occurs.
Myopia - symptoms
People suffering from myopia will see well up close, but distant objects will be blurry, blurry for them. The more advanced the disease, the more clearly the distance at which patients' vision decreases.
The nearsighted eyes often blink when looking into the distance, making the image on the retina less distracted, thereby increasing its sharpness. Apart from visual disturbances, there may also be headaches as well as a feeling of tension and fatigue in the eyeballs.
Types of myopia depending on the cause
Depending on the cause, we can distinguish several types of myopia:
- axial myopia- the most common type, associated with excessive length of the eyeball; usually develops during puberty;
- curvature myopia- appears when the elements in the refractive system of the eye are too convex and the length of the eyeball is within the normal length; these may be disorderscongenital, but more often occurs as a transient condition associated with an accommodative spasm (excessive contraction of the ciliary muscle) that occurs spontaneously or with certain topical medications, such as pilocarpine
- refractive myopiaarises when the structure of the optical system is correct, but its refractive force increases; most often it concerns the lens, which may become cloudy as a result of various disease processes, sometimes in the course of advanced diabetes
Types of myopia depending on the severity
Short-sightedness is divided according to the degree of advancement. The degrees are determined by the strength of the scattering lens needed to correct the defect in question, measured in diopters. Therefore, we can distinguish three types of myopia:
- Low myopia , the so-called school - usually appears in childhood, gradually increases in adolescence, and reaches its maximum level in women between 15 and 17 years of age , and in men a little later - between 18 and 20 years of age. This degree does not exceed the level of -3.0 D.
- Average myopiaranges from about -4.0 D to -6.0 D, maximum -8.0 D.
- High myopiausually appears in very early childhood or even infancy, and develops to such an extent that it sometimes reaches a value well over -8.0 D .
High and very high myopia is a defect most often of genetic origin, usually accompanied by a significant elongation of the eyeball and progressive degenerative changes.
The eyeball, which under physiological conditions is similar to a sphere, becomes almost cylindrical here. Therefore, very advanced retinal, choroidal and vitreous atrophic changes often occur at the posterior pole of the eyeball.
The risk of retinal detachment increases significantly, and there is a large decrease in visual acuity, often leading to blindness. In Marfan syndrome, myopia often reaches a dozen or even several dozen diopters, of course with the "-" sign.
Myopia - diagnosis
Patients frequently report to an ophthalmologist themselves quickly when they experience deterioration of their eyesight. The bigger problem is in young children who do not report visual impairment themselves, all responsibility then rests with the parents who should react quickly.
Sometimes myopia coexists with a genetic disease, then the diagnosis is made veryearly, together with other disorders that may accompany the disease on this basis.
An ophthalmological examination is necessary to diagnose myopia. There is a subjective method of examining the refractive error which is based on the Donders rule. During this examination, the patient's eyesight is corrected while looking into the distance with distracting lenses, starting with the weakest ones, gradually increasing their strength. The weakest distracting lens that allows sharp vision is a measure of myopia.
The Donders method, however, can be wrong in the case of accommodation spasm and in children and young adults who are physiologically more accommodating than usual. In this case, with farsightedness, strong accommodation will create apparent myopia, which will result in incorrect treatment.
Another method that allows you to avoid such mistakes is skiascopy (also known as retinoscopy), which is an objective examination. In order to perform this examination correctly, the accommodation in the examined eye must be abolished, it is the so-called pharmacological paralysis of accommodation, i.e. cycloplegia.
Cycloplegia is performed most often with the use of tropicamide, atropine and cyclopentolate (mainly in children). During the skiascopy, the doctor projects a beam of light onto the patient's eye, and then, while the machine is moving, he observes the direction of movement of the red light from the fundus, which can be seen in the pupil. In myopia, these directions are opposite to each other.
After such an examination, pupil dilation may cause a short-term decrease in visual acuity or photophobia.
Myopia - treatment
Glasses
Myopia is treated with concave diffusing lenses. The oldest and most popular method is the spectacle method. Lenses placed in front of the eye in this case reduce the image according to their power.
In adults, glasses with a power difference of more than 2.0 D between the lenses cannot be used, because the size of the image formed on the retina should be the same or very similar in both eyes. What then to do in such a situation? Correct the eye that "sees better" completely and as best as possible, and in the second one use the strongest possible lenses, but just enough to stick to the above rule.
The glasses should be separated from the center of the cornea by 12 millimeters. In children, light glasses that do not break should be used. You also need to pay a lot of attention to the selection of appropriate frames.
The nose and the back of the child are not fully developed yet, therefore the frames should be used,which have soft and flexible temples to keep the lenses from the cornea constant.
Lenses
Contact lenses are more and more often used by patients who most often choose them for aesthetic reasons. For high myopia, lenses are the preferred treatment option as they have little effect on resizing the image that forms on the retina. Additionally, contact lenses, unlike glasses, do not narrow the field of view.
This method, however, has its drawbacks. Some patients develop conjunctival or corneal complications, such as conjunctivitis, mechanical abrasions to the cornea, damage from prolonged lens wear, and sometimes even corneal ulceration. Therefore, proper hygiene and care of lenses and the eyes themselves are very important in this method.
Myopia can be treated with orthokeratology. It consists in flattening the curvature of the central part of the cornea with special lenses worn at night. The flattening obtained lasts all day after removing the lenses. This method can be used in both children and adults.
Operation
There are also different surgical methods that differ depending on the center in terms of advancement and innovation. These are largely laser surgeries that aim to modify the shape of the cornea, such as keratotomy, refractive photokeratectomy, LASEK or LASIK. However, not everyone can submit to such a therapeutic method.
Laser refractive surgery is contraindicated in such situations as:
- keratoconus
- age under 18 (except for special indications)
- low corneal thickness (most often<500 um)
- recurrent conjunctivitis and keratitis
- autoimmune systemic diseases
- severe dry eye syndrome
- Glasses and contact lenses - vision correction
- Eye diseases and sight defects - symptoms, causes and treatment
- Farsightedness (hyperopia): causes, symptoms, treatment
- Color blindness: a visual impairment caused by an abnormal structure of the retina
- Tunnel vision: causes, symptoms, treatment
Is it possible to avoid short-sightedness?
Short-sightedness is the scourge of our time. It should be remembered that introducing a few rules into our lives, which we will systematically follow, may protect us from this disease (this does not apply, of course, to genetic myopia, which cannot beavoid).
Good visual hygiene is essential. You have to keep a proper distance from your book or computer to your eyes, take care of proper lighting, and also not to read while lying down.
It is very helpful to perform relaxation exercises several times a day, such as staring at some distant point for a few minutes, relaxed.
Short-sighted people must remember to visit an ophthalmologist regularly, as poorly treated or neglected myopia can cause headaches, lacrimation, eyelid margin inflammation, dry conjunctiva, and consequently progression of the disease.
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