Muscæ Volitantes

Muscæ 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 muscæ volitantes—the one a perfectly harmless kind, while the other is symptomatic of serious disease of the eyes. Whoever will look through a minute pin-hole in a card at the clear sky may see floating before his sight a number of translucent tubes or fibres, and many little beads, of which some are separate, some attached to the tubes, and some apparently within them. Some of the tubes or fibres 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 coloured lines or fringes. The doublings and crossings of the loops or knots in the twisted fibres appear as black points. Though the eye be fixed, these bodies change their position with greater or less rapidity. These appearances are produced by the shadows of minute corpuscles and fibres present in the vitreous humour. They are not generally noticed under ordinary conditions; but some persons, especially those who have small pupils or who are shortsighted, readily see them, especially on looking at a bright surface, such as a white cloud or a brightly-illuminated sheet of paper. If attended to and watched they become more prominent, and may cause a good deal of annoyance. When they become visible and troublesome under ordinary conditions they generally indicate some defective state of health, particularly of the digestive organs. The appearance of dark spots before the eyes not answering to the above description generally points to the existence of a diseased condition of the deeper parts of the eye, vitreous humour, retina or choroid: and as these, or the morbid conditions causing them, are almost always visible with the ophthalmoscope, the eyes should be thoroughly examined in any doubtful case (see EYE, OPHTHALMOSCOPE). For further information on the differences between the innocent and the dangerous forms of muscæ volitantes, the reader is referred to an article by Sir David Brewster in the North British Review for November 1856.