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a disturbance of vision consisting in the doubling of seen objects. Most often diplopia occurs when there is weakening (paresis) or paralysis of one of the oculomotor muscles, when coordinated, harmonious movements of the eyeballs are disrupted, as a result of which the image of the observed object falls on noncorresponding (located at various distances from the macula lutea) points of the retinas of both eyes. In diplopia binocular vision is always disturbed. Diplopia disappears when one eye is closed. Rarely (for example, after trauma, when there is detachment of the root of the iris and two so-called pupils are formed, and when there is subluxation of the crystalline lens), monocular diplopia—when the same object yields two images in one eye—may occur. When the other eye is closed the doubling does not cease. Investigation of diplopia is valuable in identifying paralyses of the oculomotor muscles, which occur frequently even with some constitutional diseases (encephalitides and cerebral hemorrhages, for example).
L. A. KATSNEL’SON