Sclerotic scatter

Abstract

Sclerotic scatter involves the scattering of incident light by the timbal sclera followed by entry of part of the scattered light into the cornea, where some of the light travels through total internal reflection to the other side, where it scatters a second time in the timbal sclera. It is then visible in the form of a timbal scleral arc of light. Sclerotic scatter has been used for decades to spot and delineate corneal opacities, which disrupt and scatter the light travelling through total internal reflection. To implement the technique, the slit beam and the binoculars of the slit lamp should be dissociated so that the timbal sclera is illuminated, while the binoculars are centered on the cornea. The technique does not provide any information as to the depth of corneal opacities and therefore needs to be complemented by direct illumination. The second sclerotic scatter may also be used clinically, for instance for diode cycloablation, the posterior part of the arc of light projecting 0.5 mm behind the scleral spur. This article aims to describe the phenomenon of sclerotic scatter, explaining how the slit-lamp should be set to use this technique, describing its clinical applications (in the opacified cornea and in the normal sclera), showing that the timbal scleral arc of light of sclerotic scatter may be seen under certain circumstances in daily life with the naked eye and, finally, explaining how the arc of light differs from peripheral light focusing ("Coroneo effect"). (C) 2017 Elsevier Masson SAS. All rights reserved.