Refractive errors are a group of diseases in ophthalmology in which a decrease in visual acuity is caused by a violation of the focus of the image on the retina. Common symptoms for all pathologies: blurred vision, rapid eye fatigue when performing visual work, discomfort or headache with eye strain. Visometry, refractometry, ophthalmoscopy, eye ultrasound, biomicroscopy, perimetry are used for diagnostics. Therapeutic tactics are reduced to the appointment of glasses or contact methods of optical correction. Modern methods of treatment are represented by refractive or laser surgery.
H52 Refraction and accommodation disorders
Refractive errors are a widespread group of ophthalmic pathologies. According to WHO statistics, about 153 million people in the world suffer from visual dysfunction, the development of which is caused by uncorrected refractive anomalies. Approximately 25-30% of the population are diagnosed with myopia, 35-45% with hypermetropia. The overall prevalence of astigmatism among all violations of the refractive ability of the eyeball is 10%. Senile visual impairment occurs in 25% of the population. Refractive errors are observed everywhere, in all age groups.
There are many reasons for the development of ametropia, but it is not always possible to establish an etiological factor. Hypermetropia may be the result of delayed growth of the eye. Under normal conditions, it is diagnosed during the newborn period. Other forms of refractive ability disorders are polyethological pathologies, the main causes of which are:
- Anatomical features of the eye structure. In people with myopia, the elongated sagittal axis of the eyeball is determined. With farsightedness, the anterior-posterior axis is shortened. Also, a predisposing factor is often a change in the refractive power of optical media.
- Hereditary predisposition. Myopia is a genetically determined pathology. With an autosomal dominant type of inheritance, the disease has a lighter course and occurs later. Autosomal recessive form is associated with early onset and unfavorable prognosis.
- Excessive visual load. Prolonged performance of visual work (reading, watching TV, computer games) leads to a spasm of accommodation. A decrease in the accommodative ability of the eyeballs is one of the risk factors for the development of myopia.
- Infectious diseases. Myopic or hypermetropic variant of clinical refraction often becomes a consequence of past infections (rubella, ophthalmic herpes). Violation of optical functions is often caused by congenital toxoplasmosis.
- Organic changes in the anterior segment of the eyes. Eye injuries, keratitis, scarring and opacities of the cornea lead to a change in the radius of curvature of the cornea and lens. Violation of the trajectory of the light beam acts as a trigger factor for the development of acquired astigmatism.
- Metabolic disorders. Persons with a history of metabolic disorders are at risk of weakening accommodation. The highest probability of pathology is observed in patients with diabetes mellitus. This is due to excessive synthesis of sorbin and a change in the shape of the lens.
This group of pathologies is characterized by a violation of the refractive power of the optical system of the eye, which entails a change in the location of the posterior main focus in relation to the retina. This leads to a violation of the focusing of light rays on the retina. Normally, the fixation point at the optical distance should correspond to the retina. This type of refraction is called emmetropia. At the same time, visual acuity near and far is not changed. All anomalies in which there is no normal focusing of the image are combined under the general name “ametropia”.
In myopia (myopia), the posterior focus is located in front of the retina. This causes visual dysfunction only when looking at objects that are far away. In hypermetropia (hyperopia), the focus point is located behind the inner shell. Vision in the distance remains within the normal range, and near progressively decreases.
With astigmatism, the value of the refractive power on the individual inter-perpendicular axes of the optical media of the eye varies significantly. If the refraction of the right and left eyes does not correspond to each other, this indicates anisometropy. The size of the eyeball and the characteristics of refractive media have a direct impact on the refractometric indicators. Under physiological conditions, clinical refraction undergoes age-related changes.
Refractive anomalies can be of congenital or acquired origin. They can develop in isolation or be combined with other eye pathologies. The systematization of visual dysfunction by individual degrees is based on the results of refractometry. According to the clinical classification in modern ophthalmology , the following types of refractive errors are distinguished:
- Myopia. Nearsighted persons do not have visual acuity impaired up close. Visual dysfunction is observed exclusively when trying to view an image located in the distance. To eliminate the symptoms of myopia, scattering (minus) lenses are used.
- Hypermetropia. Farsightedness is manifested by normal vision when looking into the distance and reduced vision when viewing images located near. You can correct the hypermetropic type with collecting (plus) lenses.
- Astigmatism. The development of the disease is due to the irregular shape of the cornea or lens. Due to the scattering of light rays, a distorted image is formed on the retina.
- Presbyopia. Senile hyperopia is an age–related deterioration of the functions of the optical system. The mechanism of anomaly development is based on sclerotic changes of the lens, which are most pronounced in the central part.
Symptoms of refractive errors
Clinical manifestations of pathology are determined by the type of refractive errors. With myopia, patients complain about the vagueness of a far-away image. When viewed at a short distance, vision is not impaired. To improve perception, patients squint their eyes. Prolonged optical load provokes discomfort in the temporal and frontal areas of the head, pain in the eye socket, photophobia. Myopia creates difficulties when traveling on your own transport, watching a movie at the cinema. Age-related changes in accommodation lead to an improvement in visometric indicators in the fourth decade of life.
Patients with hypermetropia note that vision worsens only when reading, using a smartphone. Viewing objects located in the distance is not accompanied by visual dysfunction. Hypermetropics are characterized by increased fatigue of the eye muscles, migraine when working at a short distance. With 1 degree of farsightedness, compensation mechanisms provide good vision both in the distance and near. A high degree of hyperopia is manifested by total optical dysfunction, regardless of the distance to the object in question. Deterioration of visual acuity with age indicates the development of presbyopia.
The progressive course of myopia leads to carpal degeneration of the inner shell, which is subsequently complicated by retinal detachment. Damage to the vessels of the uveal tract provokes hemorrhages in the vitreous or anterior chamber of the eye. In persons with 3-4 degrees of myopia, the probability of destruction of a jelly-like substance is the highest. In the absence of timely correction of astigmatism, there is a high risk of developing amblyopia and strabismus. Patients with hyperopia often have recurrent conjunctivitis, blepharitis. The most severe complication is blindness.
The diagnosis is based on anamnestic information, the results of instrumental research methods and functional tests. For patients with suspected refractive errors, visometry is performed with the auxiliary use of trial lenses (collecting and scattering) and the use of skiascopy. Specific diagnostics includes carrying out:
- Computer refractometry. This is the main method of studying clinical refraction, which is based on visometry with the additional use of special lenses. If visual acuity is equal to 1.0 dpt, we are talking about emmetropia. With hypermetropia, visual dysfunction is eliminated with the help of a collecting lens, myopia – scattering.
- Visometry. With myopia, the decrease in vision varies widely. When performing visometry according to the standard technique using the Sivtsev-Golovin table, visual dysfunction in hypermetropia cannot be detected.
- Ophthalmoscopy. Examination of the fundus of patients with myopia reveals myopic cones, staphylomas and degenerative-dystrophic changes in the macular area. Multiple rounded or slit-like defects are visualized in the peripheral parts of the retina.
- Ultrasound of the eyes. Ultrasound examination is performed to measure the parameters of the eyes. With myopia, the elongation of the anterior–posterior axis is determined, with hyperopia – its shortening. With the fourth degree of myopia, changes in the consistency of the vitreous body are often detected.
- Perimeters. There is a concentric narrowing of the angular space visible to the eye with a fixed gaze. For patients with astigmatism, the loss of individual areas from the visual field is characteristic. For a more detailed diagnosis of the central part of the visible space, the Amsler test is used.
- Biomicroscopy of the eye. When examining the anterior part of the eyes, single erosive defects on the cornea are revealed. With hypermetropia, it is often possible to visualize the injection of conjunctival vessels.
Treatment of refractive errors
Treatment tactics are determined by the form of refractive anomaly. Patients with myopia are shown eyeglass correction with the help of diffusing lenses. In the first degree of myopia, compensatory mechanisms allow the use of glasses or contact lenses only as needed. With a weak degree of farsightedness, glasses with collecting lenses are assigned only for working at close range. Constant use of glasses is indicated for severe asthenopia. The use of contact lenses has a less pronounced effect, which is associated with the formation of a smaller image on the inner shell of the eye. With myopia up to -15 dpt, laser correction is possible.
For the treatment of presbyopia, in addition to lenses for the correction of ametropia, spherical collecting lenses are prescribed for a small distance. Patients with astigmatism are individually selected glasses in which cylindrical and spherical lenses are combined. Contact correction involves the use of toric lenses. With a low efficiency of eyeglass correction, microsurgical treatment is indicated, which is reduced to applying micro-incisions to the cornea (astigmatomy). Excimer laser correction is possible with the I degree of astigmatism. With a high degree of pathology, implantation of phakic lenses is indicated.
Prognosis and prevention
The prognosis for these diseases is often favorable. Timely correction of optical dysfunction makes it possible to achieve full compensation. Specific methods of prevention have not been developed. Non-specific preventive measures are aimed at preventing spasm of accommodation and progression of pathology. To do this, it is necessary to perform visual gymnastics, take breaks when working at the computer and reading books, monitor the lighting. Middle-aged and elderly patients are recommended to undergo an annual examination by an ophthalmologist with mandatory measurement of intraocular pressure and visometry.