Anisometropia is a pathology of clinical refraction of the eye, in which the difference in refractive power between the eyeballs exceeds 2 dptr. The disease is manifested by diplopia, blurring of the image in front of the eyes, decreased visual acuity, rapid fatigue when performing visual work. For diagnosis, visometry, ultrasound, computer refractometry, perimetry, biomicroscopy, ophthalmoscopy, skiascopy are used. Treatment tactics are reduced to the correction of visual dysfunction with the help of contact lenses, glasses or the use of surgical methods (excimer laser intrastromal keratomylosis).
H52.3 Anisometropy and aniseicony
Anisometropia belongs to the group of refractive errors. According to statistics, the prevalence of pathology in the structure of all diseases of the visual organ is 17%. It is proved that the difference in the refractive power of the eyes in children is more common than in adults. At the age of seven, 8% of schoolchildren are diagnosed with the disease, by the age of ten this figure reaches 17%. In the process of refractogenesis, only 38.2% of children have stable clinical manifestations, 25.5% of patients have a regression of symptoms, 36.3% have an increase in the severity of symptoms. In European countries, 1.5% of the population suffers from this disease, in China – 4%.
Causes of anisometropia
In most cases, anisometropia is based on organic pathology of the organ of vision. Functional changes lead to a slight increase in the refraction difference, which is not accompanied by clinical manifestations. The main causes of the disease:
- Cataract. The cause of the pathology is clouding of the lens, which is associated with a violation of the passage of light rays through the optical system and visual dysfunction of only one eye.
- Congenital unilateral myopia. Myopia is the most common cause of anisometropia in children. In some cases, after the completion of the formation of the eyeball, the symptoms are independently leveled.
- Astigmatism. The development of this pathology is often caused by a violation of the shape of the lens or cornea in the case of asymmetric changes.
- Unilateral hypermetropia of a high degree. Asymmetric hyperopia is more often detected in patients over 40 years of age due to the development of glaucomatous changes.
- Iatrogenic effects. Violations of clinical refraction occur in the postoperative period, which is caused by surgical interventions on the lens, vitreous, retina. It has been proven that implantation of intraocular lenses (IOL) before the age of 18 leads to ametropia and anisometropia in adulthood.
When the difference in the refractive power of both eyes exceeds by more than 2 diopters, binocular vision disorders occur. With a prolonged course of the disease, the clinic of secondary strabismus increases. Normally, the image is formed as a whole with the participation of the retina of the two eyes and the brain. Different refraction is the reason that the image on the retina is deformed, the patient sees it “blurred”. At the same time, the patient compensatorily restricts the participation of a more visually impaired eye in the act of vision.
With an abnormal size of the longitudinal axis, the accommodative ability is violated. If the symptoms are caused by refraction pathology, then the position of the nodal points changes, which also makes it difficult to form an image on the inner shell. The decrease in visual acuity is reversible, since it is caused by a spasm of accommodation.
In clinical ophthalmology, congenital and acquired anisometropia are distinguished. The disease can develop independently or be a manifestation of other ophthalmopathologies. According to the clinical classification, the following forms of the disease are distinguished:
- Axial. The cause of this variant is a pathological change in the long axis of one of the eyeballs, provided the refraction is the same.
- Refractive. In this form, the longitudinal axis corresponds to the norm, but the clinical refraction of one eye is greater than the other by 2 or more dptr.
- Mixed. It is characterized by a combination of manifestations of axial and refractive variants of the disease.
There are three degrees of severity of anisometropia:
- A weak degree – up to 3 dpt.
- The average degree is 3-6 dptr.
- High degree – more than 6 dptr.
Symptoms of anisometropia
The main clinical manifestations of anisometropia are caused by a violation of binocular vision. Differences in the refractive power of the eyes of less than 2 dptr are weakly expressed and in rare cases can lead to minor visual discomfort. The use of eyeglass correction ensures normal visual acuity. With an average degree of the disease, patients complain of double vision, blurred contour of images in front of the eyes, decreased visual functions. Anisometropia is characterized by the disappearance of symptoms when one eye is closed. Parents often note that the child squints when reading, watching TV or working at the computer.
With a high degree, binocular vision is sharply impaired. A characteristic symptom of anisometropia is an increase in the difference in brightness and image size (aniseonia). Spectacle correction is often accompanied by anisophoria. Symptoms of strabismus appear only when the direction of gaze changes. For this form, the development of anisoperoscopy is typical, in which convergence is significantly hindered. With prolonged visual loads, rapid fatigue occurs, headache intensifies, radiating into the brow arches.
Previously, the complication of anisometropia was amblyopia caused by the deliberate restriction of the affected eye’s participation in vision. In the absence of timely diagnosis and treatment, convergent or divergent strabismus develops. Prolonged wearing of contact lenses leads to micro-injuries of the cornea, keratitis, epithelial edema, iris rubeosis and corneal neovascularization. The risk of developing infectious and inflammatory diseases of the anterior eye (conjunctivitis, blepharitis, iritis) is increased. A specific complication of pathology is anisoaccommodation, which is characterized by different accommodative ability of the eyes.
Often objective signs of anisometropia are detected accidentally during an ophthalmological examination. Patients seek help from a specialist only with a moderate and high degree of the disease. The diagnostic plan includes:
- Computer refractometry. The technique is used to determine the type of clinical refraction, to study the ratio of the refractive force to the longitudinal axis.
- Visometry. Allows you to set the degree of visual acuity reduction.
- Ultrasound of the eyes. It is used to measure the anteroposterior axis of the eyeball. Ultrasound examination is necessary when optical media are clouded to visualize the vitreous, retina and optic nerve.
- Ophthalmoscopy. During the examination of the fundus, you can study the condition of the inner shell, the disc of the optic nerve.
- Perimetry. An additional research method that allows you to identify an asymmetric narrowing of the visual field in a concentric type.
- Biomicroscopy of the eye. Examination of the anterior part of the eye is informative for determining the etiology of the disease, identifying the first signs of secondary inflammation of the cornea, bulbar conjunctiva.
- Skiascopy of the eye. The shadow test is an alternative method for studying clinical refraction, which makes it possible to measure the ratio of the anterior–posterior size to the refractive power of the optical system. In persons with anisometropia, the dimming moves towards the rotation of the ophthalmoscopic mirror.
Treatment of anisometropia
Etiotropic therapy is reduced to eliminating the manifestations of the underlying disease. Conservative methods of visual acuity correction are used in patients with mild to moderate pathology. If the difference in the corrective glasses should exceed 2.5 dptr, surgical intervention is indicated. The following techniques are used to treat anisometropia:
- Correction of visual acuity. In order to correct visual functions, special telescopic glasses can be used, the optical system of which consists of collecting and scattering lenses. The indication for their use is an organic lesion of the visual analyzer. With a high degree of anisometropia, iseiconic glasses are prescribed. Symptomatic therapy is based on the selection of contact lenses. In childhood, they are used only if there are contraindications to surgical treatment and eyeglass correction.
- Surgical correction. In the absence of lesions of the cornea, excimer laser intrastromal keratomylosis is effective. An alternative option for keratorefractive surgical correction is the implantation of an additional IOL. At the same time, the density of endothelial cells should not be lower than the minimum limits corresponding to age norms. In patients with high-grade myopia, laser coagulation of the retina is performed a month before surgery.
Prognosis and prevention
The prognosis for life and working capacity is favorable. Specific methods of prevention have not been developed. Non-specific preventive measures are reduced to the control of visual acuity and clinical refraction. Persons who have had surgical interventions on their eyes for the last 2 years are shown an ophthalmologist’s consultation once every 6 months with mandatory refractometry and visometry. When diagnosing anomalies of clinical refraction in children older than 1 year, it is necessary to carry out timely correction of visual dysfunction in order to prevent the development of strabismus. In patients younger than 12 months, the use of special treatment methods is not indicated.