MUSCÆ VOLITANTES.

New Zealand Graphic, Volume XV, Issue XVII, 26 October 1895, Page 534

MUSCÆ VOLITANTES.

Mnw volitantes, literally ‘flitting flies,’ is a term applied to appearances which sometimes seem like such objects within the eye. Oftener they resemble beaded threads moving across the field of vision. They were once looked on as premonitions of amaurosis, a form of blindness more generally partial, though sometimes total—a form to which excessive smoking often leads. Even now they often cause much alarm, though really they are of not the slightest importance. The fact is, most studious persons see them when their eyes are fatigued or when they are suffering from indigestion. Most persons may see them by looking steadily, say, at a white wall, and any one may do so by looking at a bright surface through a minute perforation in a piece of metal. These facts prove that they have nothing to do with any diseased condition of the eye. The cause of mtrsco' volitantes may be of scientific interest, or at least a matter of cnrions inquiry Doctor Williams, of Boston, author of a celebrated work on the eye, says of them : — • As the eye looks from one side of the page to another, they rise to descend slowly, if the eye is kept in position. They doubtless depend to some extent on changes in the vitreous capable of throwing shadows on the retina, but these changes are not discoverable by ophthalmoscopic examination. . . . They have no important significance.’ According to Quain, • They are caused by the filamentous (thread-like) framework of the vitreous, and by the cellnuclei, or other irregularities on the filaments.’ The •vitreous’ is the transparent jelly-like fluid which fills the entire globe between the lens and the retina. He continues : * These bodies do not differ much in transparency from the vitreous substance, but they differ enough to throw a shadow on the retina behind them.’ In this way they are projected into space. The shadows are much larger than the particles that cause them, and the farther the particles are from the retina, the larger they appear. Hence, short sighted people are more troubled than others in this respect, since their eye-balls are deeper from front to back.