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C CLINICAL RESEARCH

GONIOSCOPY
Evaluation of the anterior chamber angle is one of the most important components in the examination of
patients with, or suspected of having glaucoma. Unfortunately, gonioscopy remains a procedure commonly
omitted from the glaucoma examination by both optometrists and ophthalmologists. 127,128 Just as objective im-
aging of the optic nerve head complements but does not replace ophthalmoscopy, anterior segment ultrasound
biomicroscopy and optical coherence tomography of the anterior segment supplement but do not replace go-
nioscopy. Gonioscopy remains the only method to fully visualize the anterior chamber angle and trabecular
129
meshwork.
Van Herick’s method, an indirect biomicroscopic assessment of anterior chamber depth, is a common compo-
nent of a comprehensive examination. A narrow slit beam is directed at the peripheral cornea at an angle
130
of approximately 60 , and the width of the space between the posterior cornea and anterior iris is compared
°
to the peripheral corneal thickness. Due to the increased risk of angle closure, gonioscopy is indicated if the
width of that space is one-quarter or less of the corneal thickness when measured at the limbus. This is a more
common presentation in women, and in those individuals who are hyperopic, of Asian ethnicity, or developing
nuclear cataracts. 24
Additionally, gonioscopy is indicated at the baseline examination for anyone with or identified as being at risk for
POAG, and ideally annually post-diagnosis. Despite being relatively common, POAG is a diagnosis of exclusion
made after ruling out angle closure and the presence of any secondary etiology. The latter includes pigment dis-
persion and exfoliation, and conditions that are typically unilateral including angle recession, anterior segment
inflammation, neovascularization, and angle dysgenesis such as in irido-corneal-endothelial (ICE) syndrome. 25,131-134
Gonioscopy is only contraindicated in the presence of suspected globe perforation, hyphema, orbital fracture, or
severe corneal compromise. Appendix 1 serves as a review of the gonioscopy procedure.
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Clinical Recommendation for gonioscopy:
• Although POAG may be the most common form of the disease in North America, it remains a diagnosis of
exclusion requiring confirmation of an open and unobstructed anterior chamber angle through gonioscopy.

Under normal circumstances, the principle of total internal reflection precludes visualization of the angle. This optical
limitation can be overcome through the use of lenses or prisms in performing direct or indirect gonioscopy. Direct go-
nioscopy utilizing a high-plus Koeppe-type contact lens is rarely used in routine clinical practice, but may be employed
in the operating room where patients are supine and sedated for procedures including goniotomy (surgically opening
the canal of Schlemm). This technique provides a panoramic view with minimal distortion, allows simultaneous com-
parison of the two angles, and unlike indirect visualization, provides an upright non-inverted image. 135
Indirect gonisoscopy is the technique most commonly performed by optometrists using the magnification of
the biomicroscope and a mirrored lens. These lenses provide a reversed image of the angle opposite to the
mirror being used, and with practice can become a convenient and expedient means of angle evaluation. Two
lens types are available: a large diameter (12 to 15mm), steeply curved (7.4mm) Goldmann one-, two-, or three-
mirror lens requiring a more viscous coupling medium (‘scleral’ lenses); and a smaller diameter (9mm) and
flatter (7.85mm) Zeiss, Sussman, or Posner four- or six-mirror lens using the patient’s tear layer as the coupling
medium can be employed (‘corneal’ lenses). The smaller contact area of the corneal lenses allows for indenta-
tion gonioscopy to differentiate appositional from synechial angle closure and identify plateau iris, a rare ana-
tomic configuration in which an anteriorly positioned ciliary body forces the peripheral iris into appositional
closure. The corollary is that the use of a smaller lens requires gentle pressure to avoid artificially deepening
the angle: corneal striae are a sign of excessive pressure. Given that some corneal compression is unavoidable,
tonometry should be performed in advance of gonioscopy, as the latter may temporarily reduce intraocular
pressure. 136,137

Interpretation of Gonioscopic Results
A number of grading systems have been proposed to correlate the gonioscopic appearance of the angle with
the risk of angle closure: the Shaffer system assigns a numerical grade, estimated angular width, and anatomic
description, while the more complex Spaeth system includes a description of angular approach, peripheral iris

18 CANADIAN JOURNAL of OPTOMETRY | REVUE CANADIENNE D’OPTOMÉTRIE VOL. 79 SUPPLEMENT 1, 2017