MUSCE VOLITANTES is the term applied to ocular spectra, which appear like flies on the wing, or floating black spots before the eyes. There are two kinds of musem voli tantes—the one a perfectly harmless kind, while the other is 'symptomatic of one of the most serious diseases of the eyes, viz., amaurosis.
Whoever will look through a minute pin-hole in a card at the clear sky may see float ing beforelnis sight a number of translucent tubes or fibers, and many little beads, of which some are separate, some attached to the tubes, and some apparently within them. Some of tire tubes or fibers are straight. others looped or twisted, and others again forked. All these objects are bright in the middle, and bounded by fine black lines. beyond and parallel to which may be seen an appearance of colored lines or fringes. The donblings and crossings of the loops or knots in the twisted fibers appear as black points. Though the eye be fixed, these bodies change their position with greater or less rapidity. Now, in ordinary light and vision all these objects are imperceptible, unless the knots or fibers happen to Inc larger than usual, when they constitute the harmless kind of =scan voli tantes. The black blues and fringes are phenomena of the inflexion or diffraction (q v.)
of light., which are never seen except in divergent rays, and all muscse yolirantes having such fringes must be situated at a greater or less distance from the retina; and there are conclusive reasons for believing that they occupy tire vitreous humor, and cannot there fore portend amaurosiss whereas those black spots which have nO• fringes, and which do not move, or which move only with the motions of the eye, are points in the retina which are insensible to light, and are therefore to be dreaded as symptomatic of danger to vision. To decide, then, whether the muscat volitantes are or are not indicative of danger, the patient should fix his eye on a white surface (as a sheet of letter-paper) after a sudden shake of the head; if they sink gently downwards, they are innocent. It should perhaps be added, that though they seem to descend, they must in reality be ascending; floating up in the vitreous humor as for as the cellular partitions formed by the hyaloid membrane will permit. See EYE. For further information on the differ ences between the innocent and the dangerous forms of musex volitautes, the reader is referred to an article by sir David Brewster in the Korth British, Reekw for Nov., 1856.