AAO: Gonioscopy Still Best to Diagnose Primary Angle Closure

Laurie Barclay, MD

September 03, 2013

Anterior segment imaging techniques are helpful to view primary angle closure (PAC) in glaucoma, but visualization of the anterior chamber angle (ACA) is insufficient to substitute for gonioscopy, according to an American Academy of Ophthalmology (AAO) Ophthalmic Technology Assessment published online August 26 in Ophthalmology.

"Assessment of the ACA is critical in distinguishing primary open-angle glaucoma [POAG] from primary angle-closure glaucoma," lead author Scott D. Smith, MD, MPH, chairman, Eye Institute, Cleveland Clinic Abu Dhabi, United Arab Emirates, told Medscape Medical News. "The clinical examination of the ACA by gonioscopy is essential in the evaluation of glaucoma patients, but is a qualitative and subjective assessment that is prone to variability between examiners. Imaging devices [may] provide a more objective assessment of the ACA."

The goal of this comprehensive literature review was to evaluate how imaging aids in PAC diagnosis. A search of PubMed and the Cochrane Library database through July 6, 2011, identified 371 unique citations regarding the association between anterior segment imaging and gonioscopy and assessment of whether such imaging aids in diagnosing PAC.

"POAG is a type of glaucoma associated with a narrow or closed ACA, which is where the fluid aqueous humor exits the eye," AAO Secretary of Quality of Care Anne L. Coleman, MD, PhD, Fran and Ray Stark Professor of Ophthalmology, David Geffen School of Medicine, University of California, Los Angeles (UCLA), told Medscape Medical News. "If the angle is narrowed or closed, the fluid builds up inside the eye, which leads to high [intraocular] pressures that damage the optic nerve and [may cause] loss of vision."

Of 134 articles selected by members of the Ophthalmic Technology Assessment Committee Glaucoma Panel to be of possible clinical significance, 79 studies met inclusion criteria, including 3 providing level I evidence, 70 providing level II evidence, and 6 providing level III evidence.

"This is a very relevant technology assessment by the AAO evaluating the use of anterior segment imaging in the diagnosis and management of glaucoma," Dilraj S. Grewal, MD, Department of Ophthalmology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, told Medscape Medical News when asked for independent comment. "An objective assessment of the anterior segment including ACA measurement would be an invaluable tool, especially in the diagnosis of primary angle closure, and would serve as the ideal screening method."

Pros and Cons of Imaging Modalities

Anterior segment imaging techniques include ultrasound biomicroscopy (UBM), anterior segment optical coherence tomography (OCT), Scheimpflug photography, and scanning peripheral anterior chamber depth analyzer (SPAC). The type of information offered by each imaging technique varied substantially.

"There is good evidence that information obtained through anterior segment imaging by UBM, OCT, and Scheimpflug photography correlates with clinical findings from gonioscopy," Dr. Smith said. "In addition, each of these devices provides quantitative information that can supplement the qualitative assessment provided by gonioscopy. Imaging by UBM provides the greatest range of anatomic information, as it is able to image through tissues that are opaque to light, allowing imaging of the ciliary body and other structures posterior to the iris."

Because OCT images can be obtained in a completely dark environment, this method allows greater sensitivity in identifying eyes with appositional angle closure. For large-scale PAC screening, noncontact imaging with OCT, Scheimpflug photography, and SPAC is preferable to contact imaging using UBM.

"UBM imaging requires contact with the eye, and is thus more time consuming and uncomfortable for the patient than OCT imaging, which also allows direct imaging of the ACA," Dr. Smith said. "Scheimpflug photography cannot image the ACA directly and provides more limited information than the other modalities."

Study Strengths and Limitations

This study was the first comprehensive literature review on ACA assessment in glaucoma, with strengths and limitations reflecting those of the included studies.

"There is very scant level I evidence available as yet on these imaging modalities," Dr. Grewal said. "For instance, there were no studies providing level I evidence for UBM or Scheimpflug imaging, and only 3 for anterior segment OCT imaging."

Dr. Coleman notes an additional limitation in that only English-language publications were included.

"The literature search was performed in 2011 and therefore may not include more recent publications," coauthor Brian A. Francis, MD, MS, Riffenburgh Professor of Glaucoma, director of Glaucoma Services, USC Eye Institute Keck School of Medicine, Los Angeles, California, told Medscape Medical News. "In addition, some new technologies that did meet a minimum level of evidence were excluded."

Gonioscopy Still Required

"These imaging devices should be used to supplement the current clinical exam and gonioscopy but cannot be used to replace gonioscopy at this time, because they do not provide information on abnormal vessels in the angle, trabecular meshwork pigmentation, and peripheral anterior synechiae," said Dr. Coleman, who is also professor of epidemiology, UCLA Fielding School of Public Health. "[However], they do add benefit because they provide quantitative measurements of the angle width and other structures and they provide information on the angle width in different lighting situations."

To fully realize the potential of imaging in PAC diagnosis, Dr. Smith and Dr. Coleman recommend additional research with longitudinal monitoring of patients suspected of having angle closure to prospectively identify anatomic measures predicting future development of disease and response to treatment. Ongoing and recently completed studies may help provide further insight in this area.

"At Northwestern, we routinely use retinal nerve fiber layer imaging for monitoring glaucoma patients, [and] spectral domain anterior segment OCT, Pentacam Scheimpflug imaging, and UBM in select patients with narrow angles," Dr. Grewal added. "Ophthalmologists [must] realize that these instruments, while offering repeatable and reproducible measurements, do have limitations. Until we have reliable data confirming their validity, it is imperative to use these instruments as an adjunct to and not as an alternative for a good gonioscopic examination."

Dr. Grewal noted the need for adequately powered prospective studies with a longer duration of follow-up, and recent interest in newer, high-resolution imaging devices, such as swept source OCT and adaptive optics for anterior segment imaging, which provide higher-resolution images with better visualization of the angle anatomy.

"If [OCT identifies] appositional angle closure or an angle opening of less than 5 degrees, a laser peripheral iridotomy is definitely indicated, [and for] angles of 5 to 10 degrees laser is recommended," Dr. Francis said. "If there is anterior lens vault, and if the patient has significant cataract, then cataract extraction is recommended and may obviate the need for laser. In patients with persistent narrow angle after laser, or a plateau iris configuration, I recommend UBM to analyze the ciliary processes and contact with the peripheral iris."

In these cases, Dr. Francis suggests laser iridoplasty or surgery with lens extraction with or without laser shrinkage of the ciliary processes (endoscopic cilioplasty). He recommends additional research to study the role of the lens and lens extraction in treating PAC.

"Anterior segment imaging does not yet play an essential role in glaucoma diagnosis," Dr. Smith concluded. "However, the ability of anterior segment OCT to image the ACA in complete darkness, without inducing pupil constriction by room or slit-lamp illumination, allows the possibility to detect appositional angle closure with more sensitivity than gonioscopy. It can also be useful in selected patients to verify the widening of the anterior chamber angle after laser iridotomy."

The American Academy of Ophthalmology funded this study without commercial support. One of the study authors is a consultant for iScience. Dr. Francis reported financial disclosures involving the Advanced Imaging for Glaucoma Study, Quantel, Sonomed, and Endooptiks. Dr. Smith, the remaining study authors, Dr. Coleman, and Dr. Grewal have disclosed no relevant financial relationships.

Ophthalmology. 2013;1e13. Abstract

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