Night blindness: causes, symptoms, diagnosis, treatment

Congenital stationary night blindness, or nyctalopia (lack of night vision) is a non-progressive disease caused by dysfunction of the rod system. Histological examination does not reveal structural changes in the photoreceptors. The results of electrophysiological studies confirm the presence of a primary defect in the outer plexiform (synaptic) layer, since the normal rod signal does not reach the bipolar cells. There are different types of stationary night blindness, which are differentiated by ERG.

Congenital stationary night blindness with a normal fundus is characterized by different types of inheritance: autosomal dominant, autosomal recessive and X-linked.

Normal fundus

1. Autosomal dominant congenital nyctalopia (Nugare type): minor abnormality in cone electroretinogram and subnormal rod electroretinogram.
2. Autosomal dominant stationary nyctalopia without myopia (Riggs type): normal cone electroretinogram.
3. Autosomal recessive or X-linked nyctalopia with myopia (Schubert-Bornschein type).

Congenital stationary night blindness with fundus changes. This form of the disease includes Ogushi disease, a disease with an autosomal recessive type of inheritance, which differs from stationary congenital night blindness by changes in the fundus, manifested by a yellowish metallic luster, more pronounced in the posterior pole. The macular area and vessels look prominent against this background. After 3 hours of dark adaptation, the fundus becomes normal (Mitsuo phenomenon). After light adaptation, the fundus slowly regains its metallic luster. When studying dark adaptation, a noticeable lengthening of the rod threshold is revealed with normal cone adaptation. The concentration and kinetics of rhodopsin are normal.

With changes in the fundus

1. Ogushi disease is an autosomal recessive disorder characterized by an extension of the dark adaptation period to 2-12 hours to achieve normal rod thresholds. The color of the fundus changes from golden-brown during light adaptation to normal in the state of tempo adaptation (Mizuo phenomenon).
2. "White-dotted" fundus is an autosomal recessive disorder characterized by multiple small white-yellow dots at the posterior pole with intact fovea and peripheral extension. Blood vessels, optic disc, peripheral fields, and visual acuity remain normal, electroretinogram and electrooculogram may be abnormal during routine examination and normal during prolonged tempo adaptation.

The fundus albi punctatus is compared to the starry sky at night, since myriads of whitish small delicate spots are regularly located on the middle periphery of the fundus and in the macular area. The disease has an autosomal recessive type of inheritance. FAG reveals focal areas of hyperfluorescence not associated with white spots, which are not visible on angiograms.

Unlike other forms of stationary night blindness, in the white-dotted fundus, a slowdown in the regeneration of visual pigment is noted in both rods and cones. The amplitude of photopic and scotopic a- and b-waves of the ERG is reduced under standard recording conditions. After several hours of dark adaptation, the scotopic ERG response slowly returns to normal.

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