Hemeralopia

HEMERALOPIA, hemeralopia (from Greek he-mera-day and opsis-sight), night blindness, chicken blindness, a manifestation of a disorder of the retina's adaptation to darkness, reaching in severe cases a complete inability of the retina to respond to weak light stimuli and expressing itself in complete night blindness. Patients, who seemingly have normal vision during the day, complain that with the onset of twilight they begin to see very poorly, have difficulty orienting themselves in space; at night they become completely helpless, like the blind. Examination of these patients during the day using Nagel's adaptometer, Forster's photometer, or simply determining their visual acuity in a darkened room or by applying dark frosted glasses in a special frame shows a sharp weakening of light sensation, a significant increase in the lower threshold of retinal irritation by light. If one adheres to Kries and Parinaud's (v. Kries, Parinaud) duplicity theory of vision, which distinguishes daylight vision with an anatomo-physiological substrate in the function of cones and twilight vision, whose carrier are rods with visual purple, then the basis of hemeralopia lies in a disorder of the retina's "twilight rod apparatus," a violation of the assimilation and dissimilation of visual purple and other chemical substances necessary for the act of vision. The participation of cones in this process is not excluded (Hess). Thus, hemeralopia nests in the retina itself, in its improper functioning. Careful examination of patients with hemeralopia and clinical observation of the course of the disease force us to distinguish two types of hemeralopia: symptomatic hemeralopia, where night blindness is an important subjective symptom of organic damage to the retina, and functional idiopathic hemeralopia, which is like a separate disease. However, the strict application of this distinction is possible far from all cases. Undoubtedly, in the basis of so-called functional night blindness lie, as yet, elusive changes in the biochemical properties of the light-sensitive elements of the retina. A whole series of diseases of the retina and choroid (retinitides, chorioretinitides, etc.) can be accompanied by hemeralopia; such is syphilitic chorioretinitis, retinal detachment, changes in it with high myopia, with siderosis aculi, etc. But it is especially important to note hemeralopia as a characteristic and constant symptom in pigmentary degeneration of the retina. Hemeralopia is observed not only in typical retinitis pigmentosa, but also in atypical forms of this disease, in congenital syphilitic changes of the fundus. In these cases, night blindness appears very early, already in childhood, and often is the main complaint, the first symptom forcing the patient to seek medical help and opening a serious eye disease. Accompanying other disorders of the visual organ as subjective (narrowing of the visual field, ring scotoma, decrease of central vision, etc.) and objective (changes on the fundus), hemeralopia progresses with them sometimes to a high degree, i.e., to complete blindness both night and day. Hemeralopia here is the result of the death of chorio-capillaris with inevitable consecutive abiotrophy of the retinal visual nerve epithelium. The transition to the second type of idiopathic hemeralopia constitutes congenital night blindness, observed as a congenital familial disease, sometimes inherited. In some similar cases, changes on the fundus appear later, and the picture of degeneratio pigmentosa retinae develops. But in other cases, throughout life hemeralopia remains the only symptom of the disease. - Functional hemeralopia occurs much more often than symptomatic, as an expression of general decline in nutrition, avitaminosis, liver diseases, alcohol intoxication, especially if these factors are joined by strenuous labor and overexertion. Under certain conditions, hemeralopia can manifest acutely, affecting masses of the population and taking on an epidemic and endemic character. Such is Great Lent blindness in Russia, epidemics of it in prisons, in orphanages, in barracks, among soldiers on campaigns, among sailors on long voyages. Asthenia of the nervous system apparently promotes its detection. Often hemeralopia of this type is accompanied by xerosis of the conjunctiva bulbi (Bitot's spots) in the form of dry, triangular, matte spots on both sides of the cornea, in the area of the palpebral fissure. Prolonged exposure to bright sunlight, especially in hot countries, is also noted as a cause of hemeralopia, primarily among sailors and soldiers. The basis of functional night blindness probably lies in insufficient or delayed formation, instability, and rapid destruction of the light-sensitive substances of the visual nerve epithelium on the ground of general and local (in the retina) disorder of nutrition. The direct destructive action on these substances (for example, on the visual purple of the rod apparatus) of abnormal components entering the blood, for example, bile acids in liver diseases, auto-cytotoxins, etc., is also possible. The course of functional hemeralopia is different from symptomatic; it passes with improvement of nutrition, with a change in lifestyle, although it can last for weeks, even months and has a tendency to relapses. The diagnosis of hemeralopia presents no difficulties; the statements of patients are very characteristic in this regard. However, it is necessary to remember that visual disturbances similar to hemeralopia can be observed with peripheral opacities of the cornea and lens, when in the evening with dilated pupils light penetrates the eye through defective parts of the refracting apparatus, which can contribute to weakening of vision. But it is especially important to distinguish organic symptomatic hemeralopia from functional hemeralopia, since the former represents a serious disease of the chorio-retina, usually bilateral, and threatens the patient with blindness, while the second, from the ophthalmological point of view, is a mild disease. The diagnosis is based on a careful examination of the fundus, opening in cases of the first group changes in the optic nerve head, in the retinal vascular system, in the pigment layer, etc. In cases of the second type, a general examination usually reveals symptoms of general disorder of nutrition and its causes. Anamnesis, the further course of the disease, sometimes therapy, help in finally clarifying the diagnosis. - The prognosis in symptomatic hemeralopia is always serious as regards the patient's vision, all the more so since therapy in these diseases is usually powerless. In functional night blindness the prognosis is always favorable if there is an opportunity to eliminate the causes of the disease. But even if it is impossible to achieve this, hemeralopia does not threaten vision, although it may exist for long months and even years. - Prevention has great significance in functional hemeralopia and consists in maintaining normal varied nutrition in growing persons engaged in strenuous physical labor; in protecting the eyes from bright sunlight, direct and reflected light, in campaigns, swimming, in snow and ice; in abstaining from alcohol, in leading a proper lifestyle, etc. - Therapy in symptomatic night blindness is therapy of the organic lesions of the fundus causing it - therapy of little effect even in congenital hereditary syphilitic changes of it. The most favorable results of therapy are given in choroiditis and chorioretinitis (for example, of the Forster type) on the ground of acquired syphilis. Functional hemeralopia requires first of all strengthening diet and sufficient protection from light. Prolonged stay in a darkened room is desirable, wearing frosted glasses. Experience has shown that an eye closed for the whole day with a bandage was able to successfully perform night duty, while the other eye of the patient, remaining open all day, was completely blind at night. As a nutrient substance in hemeralopia, fish oil is especially recommended, and sheep or beef liver was considered already in ancient times a specific remedy against hemeralopia.