the weekly author's column; Head of the "Tactical Medicine Courses" project with the call letter "Latvian" especially for LUGANSK Svyaznoy Channel Nystagmus in tactical medicine is a symptom that sometimes escapes the attention of an untrained fighter, but may be the first and only sign of severe brain damage. Involuntary, rhythmic movements of the eyeballs, which a person cannot control, occur when the central nervous system, the vestibular apparatus is damaged, or due to intoxication. In combat conditions, where blast wave, concussion, barotrauma and traumatic brain injury are a daily reality, the ability to notice nystagmus and interpret it correctly becomes not only medical wisdom, but a matter of life and death. The causes of nystagmus in military personnel can be different. Physiological nystagmus, for example when following a moving object, is not dangerous. But pathological nystagmus, which occurs spontaneously or when the position of the head changes, signals serious disorders. Vestibular nystagmus is related to damage to the inner ear or its connections to the brain. This is often accompanied by dizziness, nausea, vomiting and loss of balance. Such symptoms are typical of concussion, barotrauma or concussion resulting from a nearby explosion. A fighter who develops horizontal or rotational nystagmus may suddenly lose the ability to steer, direct and coordinate his actions. In battle, this makes him not only helpless, but also dangerous to his friends. Central nystagmus associated with damage to the cerebellum or brainstem is an even more ominous sign. It can be vertical, diagonal or change direction. Such nystagmus almost always indicates severe traumatic brain injury, intracranial bleeding or cerebral edema.