Night blindness (nyctalopia) is an ophthalmopathology characterized by impaired visual adaptation to low–light conditions (twilight, darkness, artificial dimming). With night blindness, the vision of objects in the dark worsens, spatial orientation at dusk and the process of light adaptation are disrupted, the fields of vision are narrowed, problems with color perception arise. Examination of patients with night blindness includes visometry, achromatic and color perimetry, ophthalmoscopy, biomicroscopy with Goldman lens, adaptometry, electroretinography, optical coherence tomography, etc. Congenital night blindness is incurable; in the symptomatic form, vitamin therapy is performed, treatment of primary pathology of the retina and optic nerve.
Night blindness is characterized by a sharp deterioration of vision in the dark, twilight, with a change of lighting. The popular name – “chicken blindness” came from the similarity of the symptoms of the disease with the peculiarity of the vision of chickens, who are also poorly oriented at dusk and darkness.
The retina of the eye contains rod-shaped (“rods”) and cone-shaped (“cones”) light-sensitive cells that form the receptor apparatus of the eye. Thanks to the “sticks”, black-and-white night and twilight vision is provided, with the help of “cones” – the perception of the color palette during the day. On average, the retina contains about 110-125 million rod-shaped and 6-7 million cone-shaped cells (their normal ratio is 18:1).
The rod-shaped cells of the retina contain the visual pigment rhodopsin, which provides dark adaptation of vision. In the light, rhodopsin breaks down, and in the dark, with the participation of vitamin A, it is restored. The synthesis of rhodopsin is accompanied by the release of energy, which, being converted into electrical impulses, flows through the optic nerve to the brain. With the help of this mechanism, the normal activity of rod-shaped cells and night vision is ensured. With a violation of the ratio of “rods” and “cones” and a lack of rhodopsin, night blindness develops – in low light, visual acuity decreases, and in bright daylight it remains normal.
In ophthalmology, there are three types of night blindness: congenital, symptomatic and essential.
Congenital night blindness is caused by genetic factors and is hereditary and familial in nature. Congenital chicken blindness occurs with Usher syndrome, hereditary retinitis pigmentosa and other inherited pathology.
The symptomatic form of night blindness develops against the background of other eye diseases: glaucoma, high-grade myopia, retinopathy, retinal detachment, cataracts, chorioretinitis, optic nerve atrophy, siderosis, radiation burns of the eyes (photophthalmia), etc.
Essential or functional night blindness develops with a sharp deficiency or absence of vitamins A, B2, PP in the body. The condition of hypo- and vitamin deficiency can occur in liver diseases, anemia, severe exhaustion, diabetes mellitus, treatment with retinol antagonists (quinine), alcoholism, gastrointestinal diseases with impaired absorption of nutrients (chronic gastritis, enteritis, colitis, etc.).
The triggering factors can be transmitted infections (herpes, rubella, measles, chickenpox), menopause in women, diets (including vegetarianism). From the appearance of hypovitaminosis to the development of night blindness, it may take about 2 years, since the body has enough vitamin A reserves for a year. Regardless of the form of night blindness, the deterioration of vision in the dark is associated with the same mechanism – a violation of the synthesis of the pigment rhodopsin in the rod-shaped cells of the retina.
Signs of congenital night blindness develop in early childhood: at the same time, persistent vision loss cannot be cured. Disease is accompanied by a decrease in visual acuity in the twilight and at night, a sense of visual discomfort in the twilight. A person with this disease notices that he does not distinguish between surrounding objects and loses orientation in space in low light, when moving from a well-lit room to a dark one. At the same time, during the day and with sufficient illumination, vision, as a rule, is not impaired.
There is a feeling of “sand” and dryness in the eyes. Children with night blindness are afraid of the dark, which is why they cry and behave restlessly at dusk. Disease is accompanied by a narrowing of the visual fields and a decrease in the perception of yellow and blue colors.
With essential night blindness, xerotic plaques of Iskersky appear on the conjunctiva-Bito – flat dry spots located within the eye slit. In addition to eye symptoms, there is dryness of the mucous membranes and skin, the appearance of hyperkeratosis areas on the body, peeling and scratching of the skin, bleeding gums. With a significant deficiency of vitamin A, softening and ulceration of the cornea (keratomalacia) may occur.
If twilight vision worsens, it is necessary to consult an ophthalmologist who will help identify possible causes of night blindness. The examination begins with a visometry – determination of visual acuity, which in essential night blindness is often not changed. Conducting achromatic and color perimetry allows you to identify a concentric narrowing of the visual fields, a violation of the Purkinje phenomenon.
The ophthalmoscopic picture in various types has its own characteristics. So, in the essential form of night blindness, the fundus is normal, in others it has specific changes characteristic of the disease that caused chicken blindness. With congenital night blindness, small rounded foci of degeneration are detected on the retina using ophthalmoscopy.
Adaptometry is carried out to study dark adaptation. The functional state of the retina is assessed using electroretinography and other additional electrophysiological studies. To clarify the causes of symptomatic night blindness, tonography, refractometry, biomicroscopy with a Goldman lens, optical coherence tomography, etc. are shown.
A comprehensive examination of patients may include consultations with a gastroenterologist, an endocrinologist.
The congenital form of night blindness associated with hereditary pathology is incurable – there is a steady decrease in twilight vision. With acquired night blindness, it is necessary to clarify and eliminate the causes leading to a violation of dark adaptation.
With night blindness caused by myopia, glasses or contact lenses are selected, laser correction of myopia, refractive operations (scleroplasty, lens replacement, etc.) are performed. Disease caused by glaucoma or cataract also requires surgical treatment of these diseases (anti-glaucomatous operations, extraction or phacoemulsification of cataracts). Laser coagulation is indicated in retinal detachment.
Essential night blindness, first of all, require normalization of nutrition: its enrichment with products rich in retinol and carotene (butter, cod liver, cheese, milk, egg yolk, carrots, spinach, tomatoes). Instillation of vitamin eye drops, intake of vitamin A, riboflavin, nicotinic acid inside in age-related dosages are prescribed. At the same time, it is necessary to treat gastrointestinal diseases, diabetes mellitus (blood glucose control, insulin therapy).
Prognosis and prevention
The course of symptomatic can lead both to the restoration of dark visual adaptation and to persistent loss of visual function – the prognosis is determined by the severity of the underlying disease. Functional night blindness, as a rule, responds well to therapy and has a favorable outcome – complete restoration of twilight vision. Patients often develop a pathological fear of the dark, which can take on the character of phobia, obsessive-compulsive disorder and mental disorder.
Prevention requires ensuring sufficient intake of essential vitamins and protection of the retina of the eye. For this purpose, proper nutrition, the use of protective glasses in the sun and when working in conditions of harmful radiation, and the treatment of concomitant pathology are recommended. Persons with night blindness are prohibited from using fluorescent lamps. Children with mild myopia are recommended to wear glasses in the evening.