Hypermetropic astigmatism is a disease in which there is no single focus of light rays on the retina due to the different radius of curvature of the optical systems of the eye. The main symptoms of the disease are decreased visual acuity, discomfort, increased visual fatigue, distortion of the object in question. The diagnostic complex includes visometry, biomicroscopy, duochromic test, pachymetry, keratotopography, a test with Raubicek and Snellen figures, and the study of fusion reserves. Conservative treatment involves the appointment of glasses or contact lenses. Operational tactics are reduced to restoring the curvature of the cornea and lens.
Hypermetropic astigmatism is a congenital or acquired anomaly of clinical refraction, which is most difficult to correct. The disease was first described by the English scientist I. Newton in 1670. The term “astigmatism” was introduced by the Dutch ophthalmologist F. Donders in 1869. According to statistics, about 48-58% of the population have astigmatic visual defects. The hypermetropic form accounts for about 3% of the total number of all ametropias. Over the past 10 years, the prevalence of pathology among children has increased 3.5 times. Male and female individuals get sick with the same frequency.
The congenital form is genetically determined and inherited according to the autosomal dominant type. Less often, defects in the structure of the anterior segment of the eye are caused by the action of the extraocular muscles of the eyeball in childhood with the convergence of the visual axes. The main reasons for the development of the acquired variant of hypermetropic astigmatism are:
- Diseases of the cornea. The appearance of symptoms is caused by diseases in which the border membrane is affected, including an eyesore, ulcer, endothelial dystrophy. The inflammatory process proceeds without such complications, the exception is deep keratitis.
- Pathology of the lens. Refractive errors provoke organic lesions of the lens. The most common etiological factor is cataract. Astigmatic changes in the axis are accompanied by coloboma and pseudoexfoliative syndrome.
- Iatrogenic intervention. The disorder develops in the long-term postoperative period when performing surgical interventions on the cornea or lens. The main trigger factor is considered to be the uneven tension of the seams.
- Injuries to the eyeball. Penetrating eye wounds potentiate the formation of dense scars and synechiae that deform the cornea and lens. Organic defects on the surface of the refractive media of the eye become an obstacle in the way of light rays.
The hypermetropic variant of the disease is based on a violation of the refraction of light rays in the main optical meridians. This is usually due to a change in the radius of curvature of the cornea. The irregular shape of the cornea is a consequence of pathological processes in which the lesion reaches the anterior boundary layer. Bowman’s membrane is incapable of regeneration, therefore all changes affecting it are irreversible, leaving behind traces in the form of scars. Less often there are cases when the leading role in pathogenesis is assigned to the pathology of the structure of the lens.
With astigmatism on the two main meridians located perpendicular to each other, the difference in refractive power reaches its maximum. Light rays cannot concentrate at one point on the inner shell of the eye. The consequence of these changes is the distortion of the image on the retina and a decrease in its clarity. The role of mutations of the PDGFRA, SHH, and VAX2 genes in the development of a congenital variant of pathology has been proven, but these changes concern only the corneal form. The acquired type occurs as a complication with organic lesions of the structures of the eyeball.
There are congenital and acquired forms of the disease. Hypermetropic astigmatism is classified into three degrees. The weak degree corresponds to visual dysfunction up to 3 dptr, medium – from 3 to 6 dptr, high – above 6 diopters. Changes within 0.5 diopters do not play a significant diagnostic role. From a clinical point of view , the following types of astigmatism are distinguished:
- Simple hypermetropic. In this variant, one of the focal lines coincides with the retina, the other is located behind the inner shell of the eyeball. Emmetropic refraction is maintained along one of the leading meridians.
- Complex hypermetropic. In the complex variant, the mesh shell is located in front of the focal lines. The two main meridians are characterized by refraction with the same name, however, their degree of severity is different.
- Mixed. The most complex form. One focal line is localized in front of the inner shell of the eye, and the other behind it. Myopia is observed in one of the main meridians, hypermetropia in the other.
In most cases, the first signs of the disease can be traced at an early age. Pathology is often combined with hyperopia. As a rule, by the time it is possible to exclude physiological hypermetropia, the main defects are already clearly formed. Clinical manifestations of the disease depend on the degree of severity. Congenital astigmatism up to 0.5 dpt is not accompanied by visual discomfort. With a weak degree, symptoms corresponding to hypermetropia prevail in the clinical picture. The use of classical convex or concave glasses for the purpose of correction does not have the desired effect.
The main complaints of patients are deterioration of vision, a feeling of pain and “sand” in the eyes. With increased visual load (reading, watching TV, working at the computer), severe fatigue is noted. Patients often suffer from a headache, which worsens in the evening. Unpleasant sensations are localized in the brow area. With pronounced astigmatism, the image in question has a deformed, blurry appearance. There may be diplopia and pain in the ocular region. Due to the intolerance of glasses, patients are forced to replace them frequently.
Untimely correction of astigmatism potentiates the development of strabismus and asthenopia. In children, astigmatic changes lead to meridional amblyopia, in which visometric disorders are noted only along certain meridians. The severity of hypermetropia increases with age. In severe cases, the progression of visual dysfunction leads to a total decrease in visual acuity. If contact lenses are used incorrectly, point defects are formed in the epithelial layer with further formation of ulceration sites. Patients are at risk of developing xerophthalmia.
The diagnosis is based on anamnestic information, physical examination data and the results of specific diagnostic methods. Before a full examination, an ophthalmologist evaluates the state of binocular vision. Unlike orthophoria in astigmatism, the movements of the eyeballs are clearly traced at the moment of opening the eyelids. When using the four-point Worth test, the patient sees four circles, which indicates stereoscopic vision. Basic research methods:
- Visometry. The definition of visual acuity is carried out monocularly, initially without correction. Next, the nature of visual dysfunction is studied with the use of spectacle lenses or a special ruler of various optical strengths. The latter value is stable, does not depend on external circumstances and the patient’s condition.
- Duochromic test. The technique is based on chromatic aberration. With the hypermetropic type of refraction, the patient sees better in green light. This is due to the fact that rays with a short wavelength (blue-green) are refracted more strongly.
- Inspection with a slit lamp. The purpose of biomicroscopy is to exclude pathological changes in the anterior pole of the eyeball. The detection of scales and crusts at the edge of the eyelids, lesions of the excretory ducts of the meibomian glands serves as a contraindication to further correction by contact method.
- A test with astigmatic figures. The figures of Snellen and Raubicek are used for the study. In the presence of astigmatic defects, the opposite rays have clearer outlines in the case of using a radiant figure. With the help of the Raubicek test, not only the main meridians are determined, but also the degree of the disease.
- Keratotopography. Computer keratotopography is a non-invasive technique that allows you to study the characteristics of the curvature of the anterior and posterior surfaces of the cornea. With corneal astigmatism, a combination of areas with reduced, increased and normal sphericity is revealed.
- Pachymetry. The study is assigned to measure the thickness of the cornea. Optical pachymetry is used in order to choose the right contact lenses. Next, using an ultrasound pachymeter, keratotopographic parameters are measured with a lens put on the eye.
- Research of fusion reserves. For the test, a synoptophore or a metered eye load with prismatic compensators is used. It is possible to consider black lines on a white screen, which patients see as curved curves with varying degrees of deformation.
Treatment of hypermetropic astigmatism
Treatment tactics are determined by the age of the patient and the degree of severity of the changes. Mild to moderate astigmatism in children up to the age of four can be leveled by assigning glasses. With a high degree of eyeglass correction leads to the development of complications, therefore, the use of rigid spherical and toric lenses is shown. They are made for each patient, taking into account individual characteristics. The use of soft toric lenses in children is justified when astigmatism is combined with anisometropia, myopia or hypermetropia of a high degree. Adults and children over the age of 14 can be prescribed both glasses and contact lenses.
Surgical treatment is resorted to with low efficiency of conservative methods of correction of visual dysfunction. The operation is recommended after reaching the age of 18-20, since at this age the visual system is already fully formed. The main types of surgical interventions performed in patients with hypermetropic astigmatism:
- Arched keratotomy. Arc-shaped incisions are made on the opposite side of the pathologically altered meridian. This contributes to the protrusion of the flat and flattening of the raised focal line. The effect of keratotomy is dosed by varying the length, depth and proximity of the incisions to the optical center of the cornea.
- Photorefractive keratotomy. Using an excimer laser, a metered removal of corneal tissue is performed at a predetermined depth. The surrounding structures are not affected. This technique allows to eliminate astigmatism up to 3 diopters.
- Laser keratomylosis. During the operation, a microkeratome forms a thin flap. After processing the bed with a special laser, a separated flap is placed on it. The refractive procedure makes it possible to correct astigmatic changes up to 5 diopters.
- Implantation of a toric intraocular lens (IOL). After extracapsular cataract extraction, viscoelastic is injected into the capsule sac. Next, the IOL is captured by the optical part and immersed. At the end, aspiration of viscoelastic is performed and a seam is applied.
Prognosis and prevention
With timely correction, the prognosis for hypermetropic astigmatism is favorable. Complete restoration of lost functions is possible. With inadequate treatment, pathology can provoke dangerous complications that are accompanied by progressive visual dysfunction. Specific preventive measures have not been developed. Non-specific prevention is aimed at preventing eye injury in industrial conditions (wearing protective glasses), treatment of diseases of the lens and the anterior part of the eyeball, medical examination of persons at risk.