Astigmatism is a violation of refraction caused by an irregular, non-spherical shape of the cornea or lens, which leads to the scattering of light rays and the formation of a distorted image on the retina. Disease over 1 dpt is manifested by visual impairment, blurry blurry vision of objects, headache, rapid fatigue with visual loads, discomfort in the brow area. Diagnosis includes consultation with an ophthalmologist, visual acuity testing, refraction examination (sciascopy, refractometry), biomicroscopy, ophthalmometry, ophthalmoscopy, ultrasound of the eye, computer keratotopography. Treatment is carried out with the help of glasses and contact correction, laser correction using the LASIK technique, astigmotomy, implantation of phakic lenses.
Astigmatism, along with nearsightedness and farsightedness, refers in ophthalmology to the so–called ametropia – conditions characterized by a change in the refractive power of optical media and distortion of the back focus of the eye. Among all types of ametropia, astigmatism occurs in 10% of cases. Early correction is the key to successful prevention of amblyopia and strabismus.
With astigmatism, as a result of a violation of the uniform curvature (sphericity) of the cornea or lens, their surface has unequal refractive power in different meridians, so the beam of rays does not converge at one point of the retina, as it normally happens. In some cases, the image focuses on the retina, but in the form of a segment, a blurred ellipse or a “figure of eight”; in others – behind or in front of the retina. The image seen by a person becomes distorted, blurry, and indistinct.
Causes of astigmatism
The cause of astigmatism is a violation of the configuration of the optical system of the eye – an uneven curvature of the cornea or an irregular shape of the lens. In most cases, disease is an inherited pathology of vision, often associated with congenital uneven pressure of the eyelids, oculomotor muscles and bones of the orbit on the membranes of the eye. Therefore, if one of the parents in the family suffers from astigmatism, the child should be examined by an ophthalmologist as early as possible.
Acquired astigmatism can develop in adults due to scarring of the cornea resulting from eye injuries, ophthalmological operations, dystrophic processes (keratoconus), corneal opacity, inflammation (keratitis).
Types of astigmatism
Depending on the refraction of the main meridians (perpendicular planes of the eye), there are direct astigmatism (with the greatest refractive power of the vertical meridian), reverse astigmatism (with the greatest refractive power of the horizontal meridian) and astigmatism with oblique axes.
By type, correct and incorrect astigmatism are distinguished. With the right astigmatism, the two main meridians are mutually perpendicular; with the wrong one, they are located obliquely. Correct disease is divided into simple, in which there is normal refraction in one of the meridians – emmetropia; complex, characterized by the same refraction (myopia or hypermetropia) in both meridians; mixed – with different types of refraction in the meridians. When combined with nearsightedness, they talk about myopic astigmatism, with farsightedness – about hypermetropic astigmatism.
According to the time of occurrence, congenital (correct) and acquired (incorrect) astigmatism are distinguished. Congenital astigmatism in the range of 0.5-0.75 dpt is considered physiological – in this case, it does not affect visual acuity and does not need correction. Acquired astigmatism is always pathological.
The direction of the meridians characterizes the axis and is expressed in degrees. The difference in refraction of the weakest and strongest meridians reflects the magnitude of astigmatism, measured in diopters. According to the latter feature, a weak degree (up to 3 dptr), an average degree (3-6 dptr) and a high degree (above 6 dptr) of astigmatism are distinguished.
With an incorrect refractive ability of the cornea, they speak of corneal astigmatism, with a defect in the refraction of the lens – about the lens.
Symptoms of astigmatism
As a rule, astigmatism manifests itself in preschool or early school age. A child with astigmatism may confuse similar letters or change their places in words, complain of poor eyesight, distortion and blurred vision of objects, frequent headaches, unpleasant sensations in the brow area. Disease is characterized by asthenopia, which manifests itself in rapid visual fatigue, a feeling of “sand” in the eyes; intolerance to wearing glasses, which requires their frequent replacement.
The symptoms are not very specific; in the early stages, the disease is often manifested by a slight lack of focus of vision, therefore it is often mistaken for eye fatigue. Alarming signs that may indicate astigmatism are loss of visual clarity when objects are seen uneven, deformed, blurry; pain, redness, burning in the eyes; double vision with increased visual load (when reading, working at a computer), difficulty in visually determining the distance to objects, etc.
Consultation of an ophthalmologist in case of suspected astigmatism includes a comprehensive assessment of the state of visual function, examination of eye structures, refraction study, indirect imaging research methods.
Visual acuity testing (visometry) is performed without correction and with correction. In the latter case, the patient is put on a trial frame in which one eye is closed with an opaque screen, and cylindrical lenses of different refractive powers are placed in front of the other, achieving maximum visual acuity.
The degree of refraction is determined by skiascopy (shadow test) with spherical lenses and cylindrical (astigmatic) lenses (cylindroskiascopy). More complete information about the violation of refraction is provided by refractometry performed in the state of mydriasis (pupil dilation).
In order to find out the probable causes of astigmatism (inflammatory or degenerative diseases of the cornea), biomicroscopy of the eye is performed; ophthalmoscopy is performed to exclude pathology of the fundus and vitreous. The anterior-posterior segment of the eye is examined using ophthalmometry and ultrasound of the eye.
The presence and degree of corneal astigmatism, as well as the detection of keratoconus is carried out by computer keratotopography.
Treatment of astigmatism
In order to treat astigmatism, glasses, contact, laser and microsurgical correction are used. Ophthalmological correction is indicated for astigmatism of more than 1 dpt, progressive decrease in visual acuity, symptoms of asthenopia, an increase in the degree of hyperopia or myopia.
Eyeglass correction is provided by an individual selection of glasses (most often complex), in which spherical and cylindrical lenses are combined. Spherical lenses are selected according to the rules of correction of hypermetropia or myopia, the refractive power of a cylindrical lens should coincide with the degree of astigmatism. With a high degree of astigmatism, wearing complex glasses can be accompanied by dizziness, pain in the eyes, visual discomfort.
An alternative to the eyeglass correction can be the use of toric (astigmatic) contact lenses. The advantage of contact correction is the fact that the lens, unlike glasses, forms a single optical system with the eye and does not cause spatial distortion. With a slight degree of astigmatism, orthokeratological (night) lenses can be used. In order to adjust glasses and contact lenses, periodic repeated consultations with an ophthalmologist are necessary. However, both glasses and lenses are only able to correct vision defects for a while, but they cannot completely get rid of astigmatism.
With myopic or mixed astigmatism, intolerance to eyeglass correction, the impossibility of laser correction and various refraction in the meridians, astigmotomy (keratotomy) is indicated – a procedure for applying micro-incisions to the cornea, which allows to weaken a strong meridian along the periphery. With hypermetropic astigmatism, laser or thermokeratocoagulation can be performed – cauterization of the periphery of the cornea, increasing its convexity and refractive power.
In recent years, excimer laser correction according to the LASIK technique has played a leading role in the treatment of astigmatism. It is indicated for astigmatism up to ± 3-4 dpt. The procedure of laser correction is performed on an outpatient basis using local drip anesthesia. During the correction process, the surface layer of the cornea with a thickness of 130-150 microns is separated using a special microkeratome device, then a part of the cornea is vaporized to a certain depth with a laser in well-defined areas, after which the detached flap is returned to its place. Suturing with this method of correction is not performed, since the epithelium along the edge of the flap is restored independently. Vision improvement after excimer laser correction is noted already 1-2 hours after the end of the procedure, and the final recovery occurs within a week.
In the postoperative period, it is recommended to limit physical and visual loads, protect the eyes from injury, exclude thermal procedures (sauna visits, taking hot baths). It is prescribed to instill drops into the eyes (with dexamethasone, an antibacterial and moisturizing component), a second examination by an ophthalmologist. In the future, it may be recommended to undergo hardware treatment (laser stimulation, video computer training), taking special vitamin preparations for the eyes, taking courses of eye gymnastics, massage of the neck-collar zone, hydro procedures, etc.
If excimer laser correction of astigmatism or its high degree is impossible, phakic lenses are implanted.
Prognosis and prevention
With untimely or inadequate treatment, a sharp decrease in visual acuity, amblyopia, strabismus may develop. The criteria for the qualitative correction of astigmatism is to improve the quality of binocular vision.
Prevention consists in the rational distribution of visual loads, their alternation with special exercises for the eyes and physical activity, prevention of injuries and inflammation of the cornea. To detect congenital astigmatism, it is necessary to conduct a medical examination of children in accordance with the age schedule. Prevention of secondary complications requires timely optical correction of astigmatism.