[Diacaustic examination of the iridocorneal angle : Video article].

Background: Several methods are available for the examination of the iridocorneal angle: gonioscopy and imaging techniques, such as ultrasound biomicroscopy, optical coherence tomography and Scheimpflug photography play an important role in the diagnostics of glaucoma. There is, however, a need for simple, easily applicable methods for screening of the narrow iridocorneal angle in routine ophthalmological practice.

Purpose: To apply the diacaustic phenomenon in the examination of the iridocorneal angle, to describe the method and give its basic principles.

Material And Methods: This article provides a review of the literature and clinical observations with photographic and video documentation. The technique is demonstrated in detail with the help of a video and which is available online.

Results: The formation and movement of the diacaustic phenomenon in the anterior chamber are observed and documented by photography or video when a light source is moved laterally from front to back. The movement of the diacaustic line on the anterior surface of the iris and the structures of the iridocorneal angle are analyzed in relation to other optical phenomena, such as the Purkinje images 1 and 2, iris shadowing by tangential illumination at the level of the frill and the limbal crescent of light. The diacaustic test can be used to determine the depth of the anterior chamber and the width of the iridocorneal angle. The problems are briefly represented from the perspective of anatomical, physical and medical history aspects and 4 variants of the diacaustic line and 3 phases of the movement of the diacaustic light spot are described.

Conclusion: The diacaustic test is simple, quick and non-contact. It has potential as a screening examination of the narrow iridocorneal angle before medicinal pupil dilation. It can be integrated into the diagnostics of glaucoma for the assessment of the iridocorneal angle.