Optic nerve hypoplasia is a congenital anomaly characterized by a decrease in the number of axons in the structure of the affected nerve. Clinical symptoms are represented by decreased visual acuity, nystagmus, strabismus, increased fatigue. Diagnosis is based on direct ophthalmoscopy, electroretinography, CT of the head, visometry, histological and microscopic examination. Patients are shown electrostimulation of the optic nerve, laser pleoptics, compensation of deprivation, as well as symptomatic therapy of strabismus and nystagmus.
Optic nerve hypoplasia was first described by the British ophthalmologist W. Newman in 1864. The disease is diagnosed in 50% of children diagnosed with fetal alcohol syndrome. According to statistics, at the age of 5 to 15 years, 5.9% of all cases of blindness are due to this anomaly in the development of the eye. About 90% of children with this pathology suffer from strabismus or nystagmus. In 46-53% of patients, in addition to the underdevelopment of optical fibers, agenesis of the corpus callosum and transparent septum is diagnosed. A number of malformations of the central nervous system can be detected in 12-45% of patients. The disease occurs with the same frequency among men and women.
Sometimes, with the underdevelopment of optical fibers, a mutation of the PAX6 gene is detected at the 11p13 locus, which is usually combined with clouding of the lens and aniridia. An autosomal dominant type of inheritance has been established. The triggering factors include:
- The impact of teratogenic factors. It has been experimentally proven that the intake of alcoholic beverages, the consumption of narcotic drugs (cocaine) and smoking during pregnancy significantly increases the likelihood of the disease.
- Metabolic disorders. Pathology is often diagnosed in children born to mothers with type 1 diabetes mellitus, a history of hypothyroidism.
- The effect of medicines. The lesion of optical nerve fibers in the fetus causes the mother to take phenobarbital, antidepressants, quinine during pregnancy.
- Intrauterine infections. The development of the disease often provokes infection of the fetus with cytomegalovirus, a herpetic infection.
The pathogenetic mechanism is directly related to the violation of the division of ganglion cells of the inner lining of the eye at 4-6 weeks of embryogenesis. Amacrine and horizontal cells are not affected. According to another pathogenetic theory, the disease is caused by the phenomenon of axonal regression at 16-31 gestational weeks. When the disease is combined with other abnormalities of brain development, the leading role in the formation of defects is assigned to retrograde degeneration due to the predominance of encephaloclastic processes. Violation of the differentiation of the structures of the hemispheres and optical fibers is often associated with the pathology of regulatory processes. The mechanical theory is based on the compression of the visual pathway by a malignant neoplasm, organized by exudate, blood clots.
Symptoms of optic nerve hypoplasia
In the case of a severe course, the first clinical manifestations are observed by parents already during the newborn period. Children develop strabismus, nystagmus, and disorientation in space early. At an older age, patients complain of double vision, dizziness, difficulties in fixing the gaze, which are manifested by small-scale movements. Symptoms increase with excitement, fatigue, in stressful situations. With prolonged concentration of the gaze, headache, blurred vision, increased fatigue occurs. Visual acuity impairment varies from a slight decrease to complete blindness.
Pathology can be one- or two-sided. With a unilateral or asymmetric form, binocular vision is impaired. When the patient closes the eye, the symptoms disappear. Often children try to limit the participation of the affected eyeball in the act of vision. In order to compensate for visual dysfunction, patients tilt their heads at the angle of the clearest vision. The two-sided form is characterized by deviation of the eye, which is manifested by a constant deviation of the eyeballs in a certain direction. At the same time, it seems that a person is always looking in the same direction. Afferent pupillary defect is detected in most patients. Due to the asymmetrical position of the iris and pupil, difficulties of adaptation in society are often observed.
Optic nerve hypoplasia is often complicated by a pronounced decrease in vision up to amaurosis. Patients with this pathology in the anamnesis are more prone to joining infectious and inflammatory eye diseases (pan- and endophthalmos, scleritis), which is associated with a violation of regional blood supply and trophic. As a rule, secondary involvement in the pathological process of the retina and uveal tract leads to the development of retinitis, anterior and posterior uveitis. With concomitant lesion of the optical tracts, hemianopia occurs. The disease is often combined with malignant neoplasms of the brain (suprasellar tumors, teratoma).
To make a diagnosis, a physical examination and a special ophthalmological examination are used. In the presence of pathology in parents or close relatives, genetic screening is performed at week 16 of intrauterine development. In the postnatal period , diagnosis is based on:
- Electroretinography. With the help of electrophysiological examination, a decrease in the amplitude of the electroretinogram due to trans-synaptic degeneration is determined. Registration of the potentials emanating from the retina makes it possible to assess the degree of visual dysfunction.
- Ophthalmoscopy. The effect of a “double ring” is observed, in which a layer of pigmentocytes is visualized along the periphery of the OND reduced in diameter. Differentiation of foveolar and macular reflexes is sharply difficult. The diameter of the retinal vessels has not been changed, but they have a corkscrew-like course.
- CT of the head. Computed tomography reveals a narrowing of the diameter of the optic nerve channel. With a unilateral form, the difference in the size of the channels on the healthy and affected side exceeds 20%. A thin nerve in the orbital part is visualized.
- Histological examination. There is a decrease in the number of retinal ganglion cells with a normal content of horizontal and amacrine cells.
- Electron microscopy. A decrease in the number of astroblasts, atrophic and degenerative changes in axons are visualized. The presence of fluid between the axolemma and the nerve sheath indicates axonal and periaxonal edema. The pathology of the structure of the myelin sheath is determined by reducing the total number of astrocytes and oligodendrocytes.
- Visometry. The severity of visual dysfunction varies widely, since it depends on the severity of nerve underdevelopment.
Additionally, the calculation of the ratio of the distance between the OND and the macula to the diameter of the disc, which is normally less than 3, is shown. Differential diagnosis is performed with aplasia and atrophy of the optic nerve. Characteristic ophthalmoscopic signs of atrophy are a waxy shade of OND, excavation of its surface, narrowing and reduction of the number of retinal vessels. With aplasia, the complete absence of the optic nerve disc is determined against the background of weakly expressed pigmentation of the inner shell of the eyeball. The macula is not subject to differentiation. Only choroid vessels are visualized.
Treatment of optic nerve hypoplasia
Therapy is effective only with early therapeutic measures. This is due to the fact that in the first year of life, the pre- and postgenicular pathways, the lateral cranial body and cortical centers are at the stage of formation. Treatment includes:
- Percutaneous electrical stimulation of the optic nerve. The effectiveness of the method directly depends on the initial visual acuity. Electrostimulation is prescribed by courses. On average, 3 to 5 courses are conducted.
- Compensation for ocular deprivation. To compensate for this phenomenon, the child is given eyeglass and contact correction of visual acuity. Prevention of the development of amblyopia involves the use of metered occlusion of a better-seeing eye.
- Laser pleoptics. The technique is based on the use of low-intensity laser radiation, which improves microcirculation and metabolic processes in surrounding tissues, increases the activity of DNA, RNA and enzymes, has a beneficial effect on the energy potential of cells and trophic processes.
Symptomatic therapy is based on surgical treatment of nystagmus and strabismus. Operative methods of strabismus correction are used at the age of 5 years. Depending on the type of strabismus, operations are prescribed that weaken or strengthen the functions of the oculomotor muscles. The purpose of treatment for nystagmus is to form a position of relative rest by restoring the physiological position of the muscles. According to individual indications, botox injections are carried out into the orbital cavity to reduce the amplitude of small-scale movements of the eyeballs. Additionally, neuroendocrine disorders (neonatal hypoglycemia, panhypopituitarism, secondary hypothyroidism) are corrected.
Prognosis and prevention
The prognosis is determined by the severity of hypoplasia. A minor defect in the structure of the optic nerve can go unnoticed for a long time. Timely treatment leads to positive results. Specific prevention of this developmental anomaly has not been developed. Non-specific preventive measures are reduced to preventing the effects of teratogenic factors (alcoholic beverages, narcotic drugs, ionizing radiation). With a high risk of the disease, perinatal diagnostics and specific therapy from the newborn period are indicated.