This section is from the book "The London Medical Dictionary", by Bartholomew Parr. Also available from Amazon: London Medical Dictionary.
A dimness of sight, (from darkness or cloudiness). It also signifies a small scar or mark over the pupil, of a light blue colour. It is usually synonymous with caligo cornet, or blindness from opacity of the cornea. See Cullen's Nosology. It is the Leucoma nephelium of Salvages, and is described as a speck of the cornea, somewhat pellucid, which occasions objects to appear as if seen through smoke, or a cloud. By inspection obliquely it is discovered to be different from the opacity of the aqueous humour, accompanying some diseases of the eye. This disease consists in an obstruction of the lymphatic arteries of the cornea, and is often the consequence of more active inflammation. Any powder, mild and soluble, thrown into the eye; a drop or two of emetic vine, or of tincture of opium, will remove it; but in children it vanishes spontaneously.
A very complicated ointment is recommended by Mr. Bell for this complaint, and for diseases of the eyelids, copied from Pellier. We shall not transcribe it, since, from frequent experience, we have found equal parts of unguentum mercuriale and saturninum as effectual. In fact, it is only a combination of mercury, zinc, and lead, though operose and inelegant; the balsam. Peruv. adding nothing to its efficacy. The ointment of M. de Gravers has no lead, but the zinc supplies its place, and the efficacy is increased by the ad-dition of one-fifth of the compound tincture of benzoin. See Albugo oculorum, and also Wallis's Nosologia Methodica Oculorum.