Gonioscopy is an essential diagnostic technique for examining the structures of the anterior chamber angle (Table 4-1). Unfortunately, this procedure is underutilized in clinical practice, potentially leading to incorrect diagnosis and management. Gonioscopy is necessary to visualize the anatomy of the angle because, under normal conditions, light reflected from the angle structures undergoes total internal reflection at the tear–air interface. At that interface, the critical angle (approximately 46°) is reached, and light is totally reflected back into the corneal stroma, which prevents direct visualization of the angle structures. During gonioscopy, the examiner eliminates the tear–air interface by placing a plastic or glass lens surface against the cornea. The small space between the lens and cornea is filled by the patient’s tears, saline solution, or a clear viscous substance. Figures 4-2 and 4-3 show schematic and clinical views of the angle as seen with gonioscopy.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.