FACTORS WHICH INFLUENCE THE OBJECTIVE VISIBILITY OF OPACITIES IN THE OCULAR MEDIA
Bianca Friedman · Archives of Ophthalmology · 1942
Every ophthalmologist has encountered failure in attempting to discover an opacity in the vitreous which was strikingly manifest to the patient. On the other hand, no difficulty whatever is experienced in visualizing some opacities. A number of simple factors operate in connection with the objective visibility of opaque or semiopaque obstructions to the transparency of the ocular media. The light rays by which an opacity is detected arise from two sources. Firstly, incident light from the examiner's instrument strikes the anterior surface of the opacity and illuminates it directly ; some of the rays are reflected back to the observer, who obtains a more or less bright image of the anterior surface. Secondly, light is reflected from the retina to form a luminous background for the opacity. If the opacity is dense the retroillumination accentuates its outlines sharply by contrast. If the opacity is semiopaque it will become conspicuous by virtue