Myopia is an anomaly of the refractive power of the eye (refraction), characterized by focusing the image of objects not on the retina of the eye, but in front of it. With myopia, a person does not distinguish distant objects well, but sees well up close; there is visual fatigue, headache, impaired twilight vision, progressive deterioration of visual acuity. Diagnosis includes visometry, skiascopy, refractometry, ophthalmoscopy, biomicroscopy, ultrasound of the eye. When nearsightedness requires hygiene of vision, wearing glasses with diffusing lenses, contact lenses; surgical correction by surgical methods (lensectomy, implantation of phakic lenses, radial keratotomy, keratoplasty, collagenoplasty) or by laser surgery (LASIK, SUPER LASIK, LASEK, FRK, etc.).
Myopia in the general population is quite common: according to WHO, 25-30% of the world’s population suffers from myopia. Most often, myopia develops in childhood or puberty (from 7 to 15 years) and in the future either persists at the existing level or progresses. With myopia, light rays emanating from distant objects gather into focus not on the retina, as in a normal eye, but in front of it, as a result of which the image turns out to be fuzzy, blurry, blurred.
The condition was first described by Aristotle in the IV century BC. In his writings, the philosopher noted that some people are forced to squint their eyes to better distinguish distant objects and called this phenomenon “myops” (from Greek – “squint”).
Normally, with 100% vision, parallel rays from distant objects, passing through the optical media of the eye, focus to the image point on the retina. In the myopic eye, the image is formed in front of the retina, and only a blurry and blurry picture reaches the light-perceiving shell. With myopia, such a situation occurs only when the eye perceives parallel light rays, i.e. with distant vision. Rays emanating from close objects have a divergent direction and after refraction in the optical medium of the eye are projected strictly onto the retina, forming a clear and clear image. Therefore, a patient with myopia sees poorly in the distance and well up close.
To clearly distinguish distant objects, it is necessary to give parallel rays a divergent direction, which is achieved with the help of special (eyeglass or contact) scattering lenses. The refractive power of the lens, indicating how much it is necessary to weaken the refraction of the myopic eye, is usually expressed in diopters (dptr) – it is from this point of view that the value is determined, which is indicated by a negative value.
Disease is based on the discrepancy between the refractive power of the optical system of the eye and the length of its axis. Therefore, the mechanism of myopia, firstly, may be associated with the excessive length of the optical axis of the eyeball with the normal refractive power of the cornea and lens. With myopia, the length of the eye reaches 30 mm or more (with normal eye length in an adult – 23-24 mm), and its shape becomes elliptical. When the eye is lengthened by 1 mm, the degree increases by 3 dptr. Secondly, with myopia, there may be too strong refractive power of the optical system (over 60 dptr) at the normal length of the optical axis of the eye (24 mm). Sometimes with myopia there is a mixed mechanism – a combination of these two defects. In both cases, the image of objects cannot focus normally on the retina, but is formed inside the eye; at the same time, only foci from objects located close to the eye are projected onto the retina.
In most cases, this disease is hereditary. In the presence in both parents, myopia in children develops in 50% of cases; with normal vision of parents, only 8% of children. A common cause contributing to the development is non-compliance with the requirements of visual hygiene: excessive visual loads at close range, insufficient illumination of the workplace, prolonged work at the computer or watching TV, reading in transport, incorrect landing when reading and writing.
Often, the development of true myopia is preceded by false myopia caused by overload of the ciliary (accommodation) muscle and spasm of accommodation. Disease may be accompanied by other ophthalmopathology – astigmatism, strabismus, amblyopia, keratoconus, keratoglobus. An adverse effect on visual function is caused by infections, hormonal fluctuations, intoxication, birth trauma, TBI, which worsen microcirculation in the membranes of the eye. The progression is facilitated by the deficiency of trace elements such as Mn, Zn, Cr, Cu, etc., incorrect correction of already identified myopia.
First of all, there is a distinction between congenital (associated with intrauterine disorders of the development of the eyeball) and acquired (developed under the influence of adverse factors) myopia. According to the leading mechanism of the development of myopia, axial (with an increase in the size of the eyeball) and refractive myopia (with excessive force of the refractive apparatus) are distinguished.
A condition accompanied by the progression by 1 or more dptr per year is regarded as progressive myopia. With a constant, significant increase in the degree, they talk about malignant myopia or myopic disease, which leads to visual disability. Stationary myopia does not progress and is well corrected with the help of lenses (glasses or contact lenses).
The so-called transient (temporary) myopia, lasting 1-2 weeks, develops with edema of the lens and an increase in its refractive power. This condition occurs during pregnancy, diabetes mellitus, taking corticosteroids, sulfonamides, in the initial stage of cataract development.
According to the data of refractometry and the strength of the necessary correction in diopters, myopia of weak, medium and high degrees is distinguished:
- weak – up to -3 dpt inclusive
- average – from -3 to -6 dpt inclusive
- high – more than -6 dpt
The degree of high myopia can reach significant values (up to -15 and -30 dpt).
For a long time, myopia is asymptomatic and is often detected by ophthalmologists during professional examinations. Myopia usually develops or progresses during school years, when in the process of studying children have to face intense visual loads. It should be noted that children begin to distinguish distant objects worse, it is bad to see the lines on the board, try to get closer to the object in question, looking into the distance, squint their eyes. In addition to long-range vision, twilight vision also worsens with myopia: people with myopia are less oriented in the dark.
Constant eye strain leads to visual fatigue – muscular asthenopia, accompanied by severe headaches, aching eyes, pain in the eye sockets. Against the background of myopia, heterophoria, monocular vision and divergent friendly strabismus may develop.
With progressive myopia, patients are often forced to change glasses and lenses to stronger ones, because after a while they cease to correspond to the degree and correct vision. The progression occurs due to stretching of the eyeball and is often found in adolescence. The elongation of the anterior-posterior axis of the eye in myopia is accompanied by an expansion of the ocular slit, which leads to a slight bulge. The sclera, when stretched and thinned, acquires a bluish tint due to translucent vessels. The destruction of the vitreous body can be manifested by “flying flies”, the feeling of “skeins of wool”, “threads” in front of the eyes.
When the eyeball is stretched, there is an elongation of the eye vessels, a violation of the blood supply to the retina, a decrease in visual acuity. Fragility of blood vessels can lead to hemorrhages in the retina and vitreous. The most formidable complication can be retinal detachment and accompanying blindness.
The diagnosis of myopia requires ophthalmological tests, examination of eye structures, refraction studies, and ultrasound of the eye. Visometry (visual acuity test) is carried out according to the table using a set of trial eyeglass lenses and is subjective in nature. Therefore, this type of examination must be supplemented with objective diagnostics: sciascopy, refractometry, which are carried out after cycloplegia and allow you to determine the true value of refraction of the eye.
Ophthalmoscopy and biomicroscopy of the eye with a Goldman lens in myopia is necessary to detect changes in the retina (hemorrhages, dystrophy, myopic cone, Fuchs spots), protrusion of the sclera (staphyloma), clouding of the lens, etc. To measure the anterior-posterior axis of the eye and the size of the lens, to assess the homogeneity of the vitreous body, to exclude retinal detachment, an ultrasound of the eye is indicated. Differential diagnosis is carried out between true myopia and false, as well as transient myopia.
Correction and treatment of myopia can be carried out by conservative (drug therapy, eyeglass or contact correction), surgical or laser methods. Medication courses conducted 1-2 times a year can prevent the progression of myopia. It is recommended to observe eye hygiene, limit physical activity, take vitamins of group B and C, use mydriatics to relieve spasm of accommodation (phenylephrine), tissue therapy (aloe, vitreous intramuscularly), taking nootropic drugs (piracetam, hopanthenic acid), physiotherapy (laser therapy, magnetotherapy, massage of the cervical-collar zone, reflexology).
In the process of treating myopia, orthoptic techniques are used: training of the ciliary muscle using negative lenses, hardware treatment (accommodation training, laser stimulation, color pulse therapy, etc.).
To correct myopia, contact lenses or glasses with scattering (negative) lenses are selected. To preserve the reserve of accommodation for myopia, as a rule, incomplete correction is carried out. With nearsightedness above -3 dpt, the use of two pairs of glasses or glasses with bifocal lenses is indicated. With high-grade myopia, glasses are selected taking into account their portability. Orthokeratological (night) lenses can be used to correct mild to moderate myopia.
To date, ophthalmology has developed more than twenty methods of refractive and laser surgery for the treatment of myopia. Excimer laser correction involves correcting vision by changing the shape of the cornea, giving it a normal refractive power. Laser correction of myopia is carried out with myopia up to -12-15 dptr and is performed on an outpatient basis. Among the methods of laser surgery for myopia, LASIK, SUPER LASIK, EPILASIK, FemtoLASIK, LASEK, photorefractive keratectomy (PRK) have become the most widespread. These methods differ in the degree of exposure and the way the corneal surface is formed, however, they are essentially identical. Complications of laser treatment of myopia can be hypo- or hypercorrection, the development of corneal astigmatism, keratitis, conjunctivitis, dry eye syndrome.
Refractive lens replacement (lensectomy) is resorted to with high degree of myopia (up to -20 dpt) and loss of natural accommodation of the eye. The method consists in removing the lens and placing an intraocular lens (artificial lens) inside the eye that has the necessary optical power. Implantation of phakic lenses, as a method of treating myopia, is used with preserved natural accommodation. In this case, the lens is not removed, but additionally, a special lens is implanted into the front or rear camera of the eye. By implantation of phakic lenses, correction of very high (up to -25 dpt) degrees is carried out.
The method of radial keratotomy due to the large number of limitations in modern myopia surgery is rarely used. This method involves applying non-penetrating radial incisions to the periphery of the cornea, which, when fused, change the shape and optical strength of the cornea.
Scleroplastic operations for myopia are performed in order to stop the growth of the eye. In the process of scleroplasty, strips of biological grafts are inserted behind the fibrous membrane of the eyeball, covering the eye and preventing its stretching. Another operation, collagenoscleroplasty, is also aimed at restraining the growth of the eye.
In some cases, with myopia, it is advisable to carry out keratoplasty – transplantation of the donor cornea, which is given a certain shape using software modeling. The optimal method of treating myopia can be determined only by a highly qualified ophthalmologist (laser surgeon), taking into account the individual characteristics of visual impairment.
Prognosis and prevention
With appropriate correction of stationary myopia, in most cases it is possible to maintain high visual acuity. With progressive or malignant myopia, the prognosis is determined by the presence of complications (amblyopia, sclera staphyloma, retinal or vitreous hemorrhages, retinal dystrophy or detachment). With a high degree and changes in the fundus, heavy physical labor, lifting weights, work associated with prolonged visual tension is contraindicated.
Prevention of myopia, especially in children and adolescents, requires the development of visual hygiene skills, special exercises for the eyes and restorative measures. Preventive examinations aimed at detecting myopia in risk groups, medical examination of persons with myopia, preventive measures, rational and timely correction play an important role.