The evaluation of the drainage angle of the anterior segment is one of the most critical skills for any eye physician. There is no skill with such a high payoff when it comes to providing excellent care for patients with glaucoma. Consider that in China, as of 2001, there was an estimated 28 million people with occludable angles on gonioscopy and that 91% of the glaucoma-related blindness in China is caused by angle closure1. Similarly, one would be hard-pressed to find a less expensive but more powerful tool than the gonioprism for detecting any kind of vision threatening disease. While recent advances in anterior segment imaging have made it possible to image the iridocorneal angle and indeed even the ciliary body with ultrasound and optical coherence tomography (Figure 1), these tools cannot come close to matching the pure efficiency of gonioscopy.
For the record, gonioscopy should be performed at baseline in any patient with glaucoma or suspected glaucoma or with the appearance of anterior chamber shallowing or peripheral iridocorneal narrowing. Gonioscopy should then be repeated periodically in phakic patients (every 1 to 5 years) after the baseline evaluation, at the discretion of the physician. We should keep in mind that age and hyperopia (axial length) are two risk factors for angle closure and that we should repeat gonioscopy more frequently in patients with those risk factors. Additionally, approximately 18% of patients with exfoliation glaucoma will develop angle closure as well, and we should watch the angle carefully in those patients. Gonioscopy should also be repeated in a patient with a change in intraocular pressure profile, and in any patient after a procedure that affects the angle has been performed.
Gonioscopy is not without its limitations. For one, an objective technique for documenting gonioscopic findings has not quite become available, and it can be difficult to communicate these findings to patients. Most clinicians would agree that optical coherence tomography and even ultrasound biomicroscopy may have as much value as a patient education tools as they do for diagnostics. Another limitation of gonioscopy is that it is a subjective art rather than a quantitative assessment, and this by nature leads to test retest variability as well as limited inter-observer agreement.
More so than ever, the skill set acquired by performing routine gonioscopy has an increasing utility. Consider that the emerging field of minimally invasive or micro incisional glaucoma surgery (MIGS) depends upon intraoperative gonioscopy to place a number of glaucoma implants into Schlemm's canal, the sub conjunctival space or the supra-ciliary space from an ab Interno approach.
In summary, gonioscopy is here to stay, and its role in glaucoma management will only expand as we develop new therapies to treat the drainage angle.
Figure 1. An anterior segment high definition optical coherence tomography image of the drainage angle. The image demonstrates
angle closure with iridocorneal touch. The high-resolution image also demonstrates a slight amount of corneal endothelial edema
in the region of angle closure.
1. Foster PJ, Johnson GJ. Glaucoma in China: how big is the problem? Br J Ophthalmol. 2001;85:1277-82.
2. Wishart PK, Spaeth GL, Poryzees EM. Anterior chamber angle in the exfoliation syndrome. Br J Ophthalmol. 1985;69:103-107.
Nathan Radcliffe, MD, a glaucoma specialist, is an assistant professor of ophthalmology and director of the Glaucoma Service at Weill Cornell Medical College and New York-Presbyterian Hospital in New York.