Astigmatism – the violation of a refraction caused by the irregular, asheric shape of a cornea or a crystalline lens that leads to dispersion of light beams and formation of the distorted image on a retina. The astigmatism of over 1 is shown by sight violation, indistinct indistinct vision of objects, a headache, bystry fatigue at visual loadings, discomfort in nadbrovny area. Diagnostics of an astigmatism includes consultation of the ophthalmologist, visual acuity check, a refraction research (a skiaskopiya, refractometry), biomicroscopy, ophthalmometry, an oftalmoskopiya, ultrasonography of an eye, a computer keratotopografiya. Treatment of an astigmatism is carried out by means of-point and contact correction, laser correction by a technique of LASIK, an astigmotomiya, implantation of fakichny lenses.
The astigmatism, along with short-sightedness and far-sightedness, belongs in ophthalmology to, so-called, to ametropiya – the states which are characterized by change of the refracting ability of optical environments and distortion of back focus of an eye. The ametropy astigmatism occurs among all types in 10% of cases. Early correction of an astigmatism is the key to successful prevention of an ambliopiya and squint.
At an astigmatism as a result of violation of uniform curvature (sphericity) of a cornea or a crystalline lens their surface has the unequal refracting force in various meridians therefore the bunch of beams does not meet in one point of a retina as it occurs normal. In one cases the image is focused on a retina, but in the form of a piece, an indistinct ellipse or "eight"; in others - for or before a retina. The image seen by the person with an astigmatism becomes distorted, indistinct, indistinct.
Violation of a configuration of optical system of an eye – uneven curvature of a cornea or irregular shape of a crystalline lens is the reason of an astigmatism. In most cases the astigmatism is the inherited pathology of sight which is often connected by congenital uneven pressure a century, glazodvigatelny muscles and bones of an eye-socket on eye covers. Therefore if in a family someone from parents suffers from an astigmatism, the child has to be examined at the ophthalmologist as soon as possible.
The acquired astigmatism can develop at adults owing to the cicatricial changes of a cornea which resulted from injuries of an eye, ophthalmologic operations, dystrophic processes (keratokonus), turbidity of a cornea, inflammations (keratit).
Types of an astigmatism
Depending on a refraction main a meridian (the perpendicular planes of an eye) distinguish a direct astigmatism (with the largest refracting force of a vertical meridian), the return astigmatism (with the largest refracting force of a horizontal meridian) and an astigmatism with slanting axes.
By the form allocate the correct and wrong astigmatism. At the correct astigmatism two main meridians are mutually perpendicular; at wrong - are located slantwise. The correct astigmatism is subdivided into idle time at which in one of meridians there is a normal refraction – an emmetropiya; difficult, characterized by the same refraction (a miopiya or a gipermetropiya) in both meridians; mixed – with different types of a refraction in meridians. At a combination to short-sightedness speak about a miopichesky astigmatism, with far-sightedness – about a gipermetropichesky astigmatism.
On time of emergence distinguish the congenital (correct) and acquired (wrong) astigmatism. The congenital astigmatism within 0,5-0,75 is considered physiological – in this case it does not affect visual acuity and does not need correction. The acquired astigmatism always is pathological.
The direction of meridians characterizes an axis of an astigmatism and is expressed in degrees. The difference of refraction of the weakest and strongest meridians reflects the astigmatism size which is measured in dioptries. On the last sign allocate weak degree (to 3 ), average degree (3-6 ) and high degree (higher than 6 ) an astigmatism.
At the wrong refracting ability of a cornea speak about a corneal astigmatism, at defect of refraction of a crystalline lens – about lenticular.
As a rule, the astigmatism, is shown at preschool or early school age. The child can confuse similar letters to an astigmatism or interchange the position of them in words, complain of poor eyesight, distortion and an illegibility of vision of objects, frequent headaches, unpleasant feelings in nadbrovny area. The asthenopia which is shown in bystry visual fatigue, feeling of "sand" in eyes is characteristic of an astigmatism; intolerance of glasses wearing that demands their frequent replacement.
Malospetsifichna astigmatism symptoms; at early stages the disease is often shown by a small rasfokusirovannost of sight therefore often is accepted to fatigue of eyes. As the guarding signs which can indicate an astigmatism serve loss of clearness of sight when objects seem uneven, deformed, indistinct; pains, reddening, burning in eyes; doubling in eyes at the raised visual loading (during the reading, work at the computer), difficulty in visual determination of distance to objects, etc.
Diagnostics of an astigmatism
Consultation of the ophthalmologist at suspicion on an astigmatism includes complex assessment of a condition of visual function, survey of structures of an eye, a refraction research, the indirect visualizing research methods.
Check of visual acuity (vizometriya) at an astigmatism is made without correction and with correction. In the latter case to the patient put on a trial frame in which one eye is closed by the opaque screen, and before another place cylindrical lenses of the different refracting force, trying to obtain the maximum visual acuity.
Degree of a refraction is defined by a skiaskopiya (shadow test) with spherical lenses and cylindrical (astigmatic) lenses (tsilindroskiaskopiya). Fuller information on violation of a refraction is supplied by refractometry which is carried out in a condition of a midriaz (expansion of a pupil).
For the purpose of clarification of probable causes of an astigmatism (inflammatory or degenerate diseases of a cornea) the eye biomicroscopy is carried out; for an exception of pathology of an eye bottom and a vitreous body the oftalmoskopiya is carried out. The front-back piece of an eye is investigated by means of ophthalmometry and ultrasonography of an eye.
Existence and degree of a corneal astigmatism, and also identification of a keratokonus is carried out by means of a computer keratotopografiya.
Treatment of an astigmatism
For the purpose of treatment of an astigmatism use-point, contact, laser and microsurgical correction. Ophthalmologic correction is shown at an astigmatism more than 1 , the progressing decrease in visual acuity, asthenopia symptoms, increase in degree of far-sightedness or short-sightedness.
-Point correction is provided with individual selection of points (most often difficult) in which spherical and cylindrical lenses are combined. Spherical lenses select according to rules of correction of a gipermetropiya or miopiya, the refracting force of a cylindrical lens has to coincide with astigmatism degree. At high degree of an astigmatism wearing difficult glasses can be followed by dizziness, gripes in eyes, visual discomfort.
Use of torichesky (astigmatic) contact lenses can serve as an alternative of-point correction of an astigmatism. As the advantage of contact correction serves the fact that the lens, unlike points, forms uniform optical system with an eye and does not cause spatial distortions. At insignificant degree of an astigmatism ortokeratologichesky (night) lenses can be used. For the purpose of correction of points and contact lenses periodic repeated consultations of the ophthalmologist are necessary. However both points, and lenses, are capable only of time to correct visual impairments, but cannot save from an astigmatism completely.
At the miopichesky or mixed astigmatism, carrying out an astigmotomiya (keratotomy) – the procedure of drawing micronotches on a cornea allowing to weaken a strong meridian on the periphery is shown to intolerance of-point correction, impossibility of carrying out laser correction and various refraction in meridians. At a gipermetropichesky astigmatism it can be executed laser or a termokeratokoagulyation – the cauterization of the periphery of a cornea increasing its camber and force of refraction.
In recent years in treatment of an astigmatism the leading role is occupied by eksimer-laser correction by LASIK technique. It is shown at an astigmatism to ±3-4 . The procedure of laser correction of an astigmatism is carried out on an outpatient basis with use of local drop anesthesia. In the course of correction by means of the special device a microkeratoma separate a blanket of a cornea 130-150 microns thick, then the laser in accurately certain sites evaporate a part of a cornea on a certain depth then the otsloyenny rag is returned into place. Suture at this way of correction of an astigmatism is not made as the epithelium on edge of a rag is restored independently. Improvement of sight after eksimer-laser correction is noted already 1-2 hours later after the end of a procedure, and final restoration happens within a week.
In the postoperative period restriction of physical and visual activities, protection of eyes against traumatizing, an exception of thermal procedures (visit of a sauna, acceptance of hot bathtubs) is recommended. The instillation in eyes of drops (with dexamethasone, the antibacterial and moistening component), repeated survey of the ophthalmologist is appointed. Further passing of hardware treatment (a lazerstimulyation, video computer trainings), reception of special vitamin medicines for eyes, passing of courses of eye gymnastics, massage cervical zones, hydroprocedures etc. can be recommended.
At impossibility of carrying out eksimer-laser correction of an astigmatism or its high degree implantation of fakichny lenses is carried out.
Forecast and prevention of an astigmatism
At untimely or inadequate treatment of an astigmatism sharp decrease in visual acuity, an ambliopiya, squint can develop. As criteria of qualitatively carried out correction of an astigmatism serves improvement of quality of binocular sight.
Prevention of an astigmatism consists in rational distribution of visual loadings, their alternation with special exercises for eyes and physical activity, prevention of injuries and inflammations of a cornea. Identification of a congenital astigmatism requires carrying out medical examination of children according to the age scheduled plan. The prevention of secondary complications demands timely optical correction of an astigmatism.