Introduction
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 Nearsightedness , a person has difficulty distinguishing distant objects, but sees well up close; visual fatigue, headache, impaired twilight vision, and progressive deterioration of visual acuity are noted. Diagnostics of myopia includes visometry, skiascopy, refractometry, ophthalmoscopy, biomicroscopy, and ultrasound of the eye. With Nearsightedness , it is necessary to maintain visual hygiene, wear glasses with diverging lenses, contact lenses; perform surgical correction of myopia using surgical methods (lensectomy, implantation of phakic lenses, radial keratotomy, keratoplasty, collagenoplasty) or laser surgery (LASIK, SUPER LASIK, LASEK, PRK, etc.).
General information
Nearsightednessis quite common in the general population: according to WHO, 25-30% of the world’s population suffers from myopia. Most often, it develops in childhood or puberty (from 7 to 15 years) and subsequently either remains at the current level or progresses. With myopia, light rays emanating from distant objects are focused not on the retina, as in a normal eye, but in front of it, as a result of which the image is unclear, blurry, and blurred.
The condition of Nearsightedness stood principal pronounced by Aristotle in the Fourth era BC. In his works, the thinker famous that specific persons are obligatory to lop-sided their eyes to recovering extricate unfriendly objects and named this wonder “myops” (from the Greek – “to squint”). In modern ophthalmology, myopia has another name – myopia.
Causes of Nearsightedness
Normally, with 100% vision, parallel rays from distant objects, having passed through the optical media of the eye, are focused into a point of the image on the retina. In a myopic eye, the image is formed in front of the retina, and only a blurry and fuzzy picture reaches the light-perceiving shell. With Nearsightedness, such a situation occurs only when the eye perceives parallel light rays, i.e., with distant vision. Rays emanating from close objects have a diverging direction and after refraction in the optical medium of the eye are projected strictly onto the retina, forming a clear and distinct image. Therefore, a persistent through myopia understands unwell in the distance as well as up close.
To clearly distinguish distant objects, it is necessary to give parallel rays a diverging direction, which is achieved with the help of special (spectacle or contact) diverging lenses. The refractive influence of the lens performance in could you repeat that it is necessary to weaken the refraction of the myopic eye, is usually expressed in diopters (D) – it is from this point of view that the magnitude of myopia is determined, which is indicated by a negative value.
Myopia stays grounded on the difference amongst the refractive authority of the optical organization of the eye and the measurement of hers axis. Therefore, the mechanism of Nearsightedness, firstly, can be associated with the excessive length of the optical axis of the eyeball with a normal refractive power of the cornea and lens. With myopia, the length of the eye reaches 30 mm or more (with a normal eye length in an adult – 23-24 mm), and its shape becomes elliptical.
When the eye is lengthened by1 mm, the degree of Nearsightedness increases by 3 diopters. Secondly, with myopia, there may be too strong a refractive power of the optical system (over 60 diopters) with a normal length of the optical axis of the eye (24 mm). Sometimes through myopia, a assorted apparatus takes dwelling – a blend of these two blemishes. In both cases, the image of objects cannot be normally focused on the retina, but is formed inside the eye; in this case, only foci from objects located close to the eye are projected onto the retina.
In most cases, it is hereditary. If both parents have myopia, develops in children in 50% of cases; if the parents have normal vision, it occurs in only 8% of children. A common cause of failure to observe vision hygiene requirements: excessive visual loads at close range, insufficient lighting in the workplace, prolonged work at the computer or watching TV, reading in transport, incorrect posture when reading and writing.
Often, the development of true myopia is preceded by false myopia, caused by overload of the ciliary (accommodative) muscle and accommodation spasm . Nearsightedness may be accompanied by other ophthalmopathologies – astigmatism , strabismus , amblyopia , keratoconus , keratoglobus . Infections, hormonal fluctuations, intoxications, birth injuries , TBI , which worsen microcirculation in the membranes of the eye, have an adverse effect on visual function. The progression of myopia is facilitated by a deficiency of such microelements as Mn, Zn, Cr, Cu, etc., and improper correction of already identified myopia.
Classification of Nearsightedness
First of all, a distinction is made between congenital (associated with intrauterine developmental disorders of the eyeball) and acquired (developed under the influence of unfavorable factors) myopia. According to the leading mechanism of myopia development, axial (with an increase in the size of the eyeball) and refractive myopia (with excessive power of the refractive apparatus) are distinguished.
A condition accompanied by progression of myopia by 1 or more diopters per year is considered progressive Nearsightedness . With a constant, significant increase in the degree of myopia, they speak of malignant myopia or myopic disease, which leads to visual disability. Conjunctivitis myopia does not progress and is well corrected with lenses (spectacles or contact lenses).
The so-called transient (temporary) Nearsightedness , lasting 1-2 weeks, develops with swelling of the lens and an increase in its refractive power. This condition occurs during pregnancy, diabetes , taking corticosteroids, sulfonamides, and in the early stages of cataract development.
According to refractometry data and the required correction power in diopters, myopia is classified as mild, moderate and high:
- weak – up to -3 Dptr inclusive
- average – from -3 to -6 Dptrs inclusive
- high – more than -6 diopters
The degree of high Nearsightedness can reach significant values (up to -15 and -30 diopters).
Symptoms of myopia
For a long time, myopia is asymptomatic and is often detected by ophthalmologists during routine examinations. Nearsightedness usually develops or progresses during school years, when children have to deal with intense visual loads during their studies. It should be noted that children begin to see distant objects worse, have trouble seeing lines on the board, try to get closer to the object being examined, look into the distance, and squint. In addition to distant vision, myopia also worsens twilight vision: people with myopia have worse orientation in the dark.
Constant forced eye strain leads to visual fatigue – muscular asthenopia, accompanied by severe headaches , aching eyes, pain in the eye sockets and anophthalmos . Against the background of Nearsightedness, heterophoria, monocular vision and divergent concomitant strabismus may develop .
With progressive myopia, patients are forced to frequently change glasses and lenses to stronger ones, since after some time they no longer correspond to the degree of Nearsightedness and correct vision. Development of myopia arises unpaid to elongating of the eyeball and is often create in adolescence. Elongation of the anterior-posterior axis of the eye with myopia is accompanied by widening of the palpebral fissure, which leads to slight exophthalmos. The sclera after over extended and insipid acquires a bluish tint due to luminous vessels.
The eye vessels are lengthened when the eyeball is stretched, the blood supply to the retina is interrupted, and the visual activity is impaired. The blood vessels may be weak which may cause hemorrhage in the retina and vitreous body. The most serious complication of Nearsightedness can be retinal detachment and the blindness that accompanies it .
Diagnosis of myopia
Analysis of myopia necessitates ophthalmological tests , inspection of eye assemblies, diversion studies , & ultrasound of the eye . Visometry ( visual acuity testing ) is performed according to a table using a set of trial spectacle lenses and is subjective. Therefore, this type of examination for Nearsightedness must be supplemented by objective diagnostics: skiascopy , refractometry , which are performed after cycloplegia and allow determining the true value of the eye’s refraction.
Conducting ophthalmoscopy and biomicroscopy of the eye with a Goldman lens in case of Nearsightedness is necessary to detect changes in the retina (hemorrhages, dystrophy, myopic cone, Fuchs spot), protrusion of the sclera (staphyloma), clouding of the lens, etc. An eye ultrasound is needed to measure the anterior-posterior axis of the eye, Dry eye the lens size, to assess the homogeneity of the vitreous body, and to rule out retinal detachment. The differential diagnostics are performed with true myopia and false one, and transient Nearsightedness.
Treatment of myopia
Correction and treatment of Nearsightedness can be carried out by conservative (drug therapy, glasses or contact correction), surgical or laser methods. Medication courses, carried out 1-2 times a year, help prevent the progression of Nearsightedness. It is recommended to maintain vision hygiene, limit physical activity, take vitamins B and C, use mydriatics to relieve accommodation spasm (phenylephrine), conduct tissue therapy (aloe, intramuscular vitreous body), take nootropic drugs (piracetam, hopantenic acid), physiotherapy ( laser therapy , magnetic therapy , massage of the cervical-collar zone, reflexology ).
In the process of treating myopia, orthoptic methods are used: training of the ciliary muscle using negative lenses, hardware treatment (accommodation training, laser stimulation , color pulse therapy, etc.). To correct Nearsightedness, contact lenses or glasses with diverging (negative) lenses are selected. To maintain the accommodation reserve for Nearsightedness, as a rule, incomplete correction is performed. For v higher than -3 dptr, the use of two pairs of glasses or glasses with bifocal lenses is indicated. For high , glasses are selected taking into account their tolerance. Night lens container used to precise slight to reasonable myopia .
To date, more than twenty methods of refractive and laser surgery for the treatment of myopia have been developed in ophthalmology. Excimer laser correction of Nearsightedness involves correcting vision by changing the shape of the cornea, giving it normal refractive power. Laser correction of myopia is performed for myopia up to -12-15 diopters and is performed on an outpatient basis. Among the methods of laser surgery for Nearsightedness , the most widespread are LASIK , SUPER LASIK , EPILASIK , FemtoLASIK , LASEK , photorefractive keratectomy ( PRK ). These methods differ in the degree of impact and the method of forming the surface of the cornea, but are essentially identical.
Refractive lens replacement ( lensectomy ) is used for high myopia (up to -20 D) and loss of natural eye accommodation. The system involves eradicating the lens and placing an artificial lens with the essential optical power inside the eye. Implantation of phakic lenses , as a method of treating v, is used when natural accommodation is preserved. In this case, the lens is not removed, but a special lens is additionally implanted into the anterior or posterior chamber of the eye. By implanting phakic lenses, very high (up to -25 D) degrees of Nearsightedness are corrected.
The radial keratotomy method is rarely used due to a large number of limitations in modern Nearsightednesssurgery. This process includes making non through circular incisions on the periphery of the cornea when fused change the shape and optical power of the cornea.
Scleroplasty operations for myopia are performed to stop the growth of the eye. During scleroplasty, strips of biological transplants are inserted behind the fibrous membrane of the eyeball, covering the eye and preventing its stretching. Another operation aimed at restraining eye growth is collagenoscleroplasty .
In some cases of Nearsightedness, it is advisable to perform keratoplasty – transplantation of a donor cornea, which is given a certain shape using software modeling. The optimal method of treating myopia can only be determined by a highly qualified ophthalmologist surgeon ( laser surgeon ), taking into account the individual characteristics of the visual impairment.
Prognosis and prevention of Nearsightedness
Through appropriate correction of stationary myopia high visual acuity can be maintained in most cases. In case of progressive or malignant myopia, the prognosis is determined by the presence of complications (amblyopia, scleral staphylomas , retinal or vitreous hemorrhages, retinal dystrophy or detachment). By a high degree of Nearsightedness and changes in the fundus heavy physical labor lifting weights and work associated with prolonged visual strain are contraindicated.
Preventive examinations aimed at identifying in risk groups, medical examination of people with myopia, preventive measures, rational and timely correction play a major role.