Beyond gonioscopy: Angle asessment

Article

Rapid image acquisition and quantitative analysis are possible

Dynamic indentation gonioscopy remains the current reference standard for assessing the anterior chamber angle, but a variety of recently introduced objective imaging techniques may become useful adjuncts in clinical care, said Dr Tin Aung, PhD.

"After all, we use a variety of imaging methods in [the care of patients with] glaucoma... for assessing the optic disc, retinal nerve fibre layer, and corneal thickness," he added. "Perhaps we should also include angle assessments among our imaging techniques in glaucoma."

Newer methods of angle imaging include the use of several types of OCT devices: anterior segment OCT (ASOCT), highdefinition OCT (HDOCT), and sweptsource OCT.

AS-OCT

AS-OCT (Visante, Carl Zeiss Meditec) provides highresolution (10 to 20 µm), cross-sectional images of the anterior segment and angles and offers a number of practical advantages in that it is a noncontact technique performed rapidly with the patient sitting up. The image can be subjectively graded in terms of whether the angle is open or closed, and software is also available for quantitative analysis of various angle parameters, including the angle opening distance, the angle recess area, and the trabeculoiris space area.

"However, the problem with using ASOCT for diagnosing angle closure is that one has to identify contact between the iris and the trabecular meshwork, but the trabecular meshwork is not visible in most images," Dr Aung said. "Therefore, one must use the scleral spur, which lies behind the trabecular meshwork, as a landmark in both qualitative and quantitative assessments. Angle closure is determined by identifying contact between the iris and angle wall anterior to the sclera spur."

A study performed by Dr Aung and colleagues comparing ASOCT and gonioscopy for diagnosing angle closure demonstrated that the imaging technology had high sensitivity (98%) but lower specificity (54.4%) because its use resulted in diagnosis of angle closure in some patients who were considered to have an open angle on gonioscopy.

"Possible reasons accounting for the discrepancy between gonioscopic and ASOCT diagnosis include differences in the lighting conditions used for the two examinations, distortion of the angle configuration when performing gonioscopy, and use of different landmarks for the two methods," Dr Aung said.

In addition to its inability to visualize the trabecular meshwork in most cases, other disadvantages of ASOCT include the fact that scleral spur definition is difficult in up to 30% of images overall, and according to a study by Dr Aung and colleagues, at an even higher rate when assessing the inferior and superior quadrants. In addition, it is usually difficult to visualize the ciliary body or to look for peripheral anterior synechiae (PAS) when using ASOCT, the angle assessment software has limitations and the device is costly.

Related Videos
Ramin Tadayoni, MD, speaks with Sheryl Stevenson
Jennifer I. Lim, MD, FARVO, FASRS, Director of Retina Service, University of Illinois at Chicago
Anat Loewenstein, MD, Professor and Director, Department of Ophthalmology, Tel Aviv Medical Center
Carl D. Regillo, MD, FACS, FASRS, Chief of Retina Service, Wills Eye Hospital, Philadelphia, PA
Arshad Khanani, MD, MA FASRS, on a virtual call
At this year's ESCRS meeting, we asked presenters and attendees, 'What do yoou wish you'd known earlier in your ophthalmology career?'
Diana Do, MD, Professor of Ophthalmology, Byers Eye Institute, Stanford University, discusses the PHOTON study results as presented AAO
Penny A Asbell, MD, FACS speaks at the 2023 AAO meeting
© 2024 MJH Life Sciences

All rights reserved.