Gonioscopy is a contact examination for direct observation of the anterior chamber angle. It provides essential information for diagnosing glaucoma subtypes, determining treatment strategies, and postoperative evaluation by observing the angle, which is the aqueous humor outflow pathway 3). Many diseases other than glaucoma also present with abnormal findings in the angle, making it one of the basic ophthalmic examinations.
The normal angle structures, from the corneal side to the iris side, are arranged in the following order 3).
Schwalbe’s line: Corresponds to the posterior end of Descemet’s membrane and appears as a white linear elevation protruding into the anterior chamber. In exfoliation glaucoma, wavy pigmentation (Sampaolesi’s line) may be seen anterior to Schwalbe’s line 3).
Trabecular meshwork: Located between Schwalbe’s line and the scleral spur. The area from the center to the scleral spur corresponds to the functional trabecular meshwork and is observed as a pigmented band. In exfoliation glaucoma and pigmentary glaucoma, it shows marked pigmentation 3).
Scleral spur: Observed as a white line between the ciliary body band and the trabecular meshwork. Iris processes may be seen on its surface. In pediatric glaucoma, the iris may attach anterior to the scleral spur, making it unobservable 3).
Ciliary body band: Corresponds to the anterior surface of the ciliary body and is observed as a gray-black band. In traumatic angle recession, the width of the ciliary body band increases 3).
Angle vessels: Physiologically, ciliary vessels may be observed, showing concentric or radial regular patterns. Pathological neovascularization presents with irregular, tortuous courses and numerous branches 3). They may be missed when blood flow is interrupted under high intraocular pressure.
QWhy is gonioscopy necessary in all glaucoma evaluations?
A
Gonioscopy is essential for classifying glaucoma and is extremely important for determining treatment strategies. Conditions such as plateau irisglaucoma exist where the central anterior chamber depth is nearly normal but narrow angles or angle closure are present, so assessment of anterior chamber depth alone is insufficient. Angle examination should be performed in all cases to check for pseudoexfoliation material, pigment dispersion, neovascularization, inflammatory deposits, angle recession, and peripheral anterior synechiae, which can cause secondary glaucoma.
Gonioscopy should be performed in all patients undergoing evaluation for glaucoma2).
Evaluation of Primary Glaucoma
Diagnosis of primary open-angle glaucoma: Careful evaluation of the anterior chamber angle is necessary to rule out angle-closure glaucoma and secondary causes of elevated intraocular pressure4).
Evaluation of primary angle-closure disease: In patients suspected of primary angle-closure disease, bilateral gonioscopy is mandatory to assess the presence of iridocorneal contact (ITC), peripheral anterior synechiae, and plateau iris configuration 5).
Ocular hypertension: Essential for excluding secondary causes of elevated intraocular pressure6).
Postoperative evaluation: Important for assessing the status of aqueous outflow pathways after MIGS or trabeculectomy, and for evaluating blood clots, iris incarceration, and formation of peripheral anterior synechiae.
Others: Also indicated for evaluation of anterior chamber tumors, intraocular foreign bodies, and post-traumatic assessment.
Gonioscopy includes direct method using a direct gonioscope and indirect method using an indirect gonioscope3).
Direct gonioscopes include Koeppe, Barkan, Swan-Jacob, and Hill lenses. The patient is placed in a supine position, the lens is placed on the cornea, and observation is performed with a handheld slit lamp microscope. They are mainly used in children and during surgery3).
Indirect gonioscopes include the Goldmann gonioscope and the Zeiss four-mirror lens. They can be used with the patient seated and a slit lamp microscope, and are the most commonly used in daily practice3). Note that the image is a mirror image. The Goldmann single-mirror lens has a high mirror height and a large angle, making it suitable for observing the angle recess in narrow angles. The four-mirror lens allows observation of the entire circumference without rotation and can also be used for indentation gonioscopy.
For accurate diagnosis of angle closure, it is desirable to perform both static and dynamic gonioscopy3).
Static gonioscopy: In a dark room, reduce the slit lamp light intensity as much as possible, avoid directing light into the pupil, and do not press the eye with the gonioscope. Evaluate the angle opening in the primary position under natural mydriasis3). Non-organic and organic closure cannot be differentiated.
Dynamic gonioscopy: Increase the slit lamp light intensity to induce miosis, tilt the gonioscope or eye position, and apply mild pressure to open the angle3). Diagnose the presence and extent of organic closure, nodules, and neovascularization.
Indentation gonioscopy: Compress the central cornea to deform it, allowing aqueous humor to push the peripheral iris posteriorly, thereby observing the angle recess3). This is the only method to differentiate functional closure (relative pupillary block) from organic closure (PAS). In plateau iris configuration, the iris root does not move due to anteriorly rotated ciliary processes, presenting a characteristic S-shaped (double hump sign).
Shaffer classification: Based on the angle between the trabecular meshwork and the peripheral iris, it classifies the angle into 5 grades from Grade 4 (20–45°, wide angle) to Grade 0 (0°, complete closure)3).
Scheie classification: Classifies based on visible structures. Grade 0 shows all structures, while Grade IV is the narrowest state where even Schwalbe’s line is not visible3). In Japan, it is commonly used together with the Shaffer classification.
Spaeth classification: Describes the angle morphology using three elements: iris insertion site, iris insertion angle, and peripheral iris shape (concave q, flat r, convex s). A high correlation with ultrasound biomicroscopy has been reported4).
van Herick method: A screening method that estimates the width of the angle by comparing corneal thickness and peripheral anterior chamber depth3). Grade 2 or lower (anterior chamber depth ≤ 1/4 of corneal thickness) suggests possible angle closure, requiring gonioscopy. It is non-contact and easy to perform, but does not replace gonioscopy.
QWhen is compression gonioscopy necessary?
A
It is performed when the angle is extremely narrow and it is difficult to differentiate non-organic from organic closure by routine dynamic gonioscopy. A gonioscope with a small contact area is used to compress the central cornea, moving aqueous humor and pushing the peripheral iris posteriorly to observe the angle recess. In areas with peripheral anterior synechiae, the iris is not pushed down, and the trabecular meshwork or angle recess cannot be observed. Excessive compression may cause Descemet’s membrane folds, reducing visibility, and may distort the angle, leading to misdiagnosis as organic closure.
4. Representative Abnormal Findings and Clinical Significance
In gonioscopy, it is important not to overlook the following abnormal findings. Observe the entire circumference carefully under sufficient magnification.
Peripheral anterior synechiae (PAS): Adhesions between the angle and peripheral iris, with various shapes such as tent-like, trapezoidal, or broad planar forms 3). They occur in primary angle closure, as well as in neovascular glaucoma, uveitis, ICE syndrome, after blunt trauma, and following laser or intraocular surgery.
Pathological neovascularization: Secondary to ocular ischemic disease, arising from the iris root and forming fine branches 3). Once the open-angle phase transitions to the closed-angle phase, intraocular pressure control becomes difficult. Under high intraocular pressure, they are easily missed due to blood flow cessation.
Pigmentation: In exfoliation glaucoma, a pigment band extending beyond Schwalbe’s line (Sampaolesi line) is characteristic; in pigmentary glaucoma, uniform heavy pigmentation of the entire trabecular meshwork is typical 3).
Angle recession: Seen after blunt trauma, characterized by widening of the ciliary body band 3). The extent and width vary depending on the severity of trauma.
Angle dysgenesis: In developmental glaucoma, high iris insertion is present. In Axenfeld-Rieger syndrome, persistent uveal strands and thickening of Schwalbe’s line (posterior embryotoxon) are observed.
Postoperative findings: Gonioscopy is essential for differentiating blood clot adhesion, synechiae, peripheral anterior synechiae formation after MIGS, and blood clots or iris incarceration at the surgical site after trabeculectomy.
Advantages: Allows non-contact observation of the angle with less patient burden. Resolution is superior to UBM, and it offers excellent quantifiability and reproducibility. Wide-range tomographic images can be obtained 1).
Limitations: Evaluation of peripheral anterior synechiae is difficult, and pigmentation or fine abnormal findings cannot be captured. In some cases, identification of the scleral spur is difficult 1). It detects more iridocorneal contact than gonioscopy, which may lead to false positives 1).
Role: Useful as an adjunct to gonioscopy, but not a replacement 2). It is useful for identifying iris configuration in narrow angles and assessing the influence of the lens 2).
Ultrasound Biomicroscopy (UBM)
Advantages: Allows cross-sectional observation of fine structures of the anterior segment including the angle, iris, and part of the ciliary body3). Excellent for visualizing the ciliary body, and observation in complete darkness is possible. Angle assessment is possible even with corneal opacity.
Limitations: Contact method, causing greater patient burden. Resolution is inferior to OCT. Only provides a single tomographic image at an arbitrary location, limiting evaluation to a planar view.
Role: Useful for evaluating the ciliary body and elucidating the mechanism of plateau iris. Used as an adjunctive tool in cases where gonioscopic evaluation is difficult.
Gonioscopy allows evaluation of color tone, dynamic assessment via indentation gonioscopy, and direct confirmation of peripheral anterior synechiae, which cannot be replaced by imaging diagnostics 2). On the other hand, imaging diagnostics excel in quantitative and objective documentation and are suitable for longitudinal comparison. It is important to use both complementarily.
QCan anterior segment OCT completely replace gonioscopy?
A
It cannot replace gonioscopy. Anterior segment OCT is non-contact, has excellent quantifiability and reproducibility, and imposes less burden on patients, but evaluation of peripheral anterior synechiae, pigmentation, and fine abnormal findings (such as neovascularization or nodules) is difficult. Moreover, it detects more iridocorneal contact than gonioscopy, which may lead to false positives. The EGS (European Glaucoma Society) guidelines also state that anterior segment imaging should not replace gonioscopy.
Nidek’s GS-1 is a stationary contact-type gonio camera that uses a 16-mirror goniolens to capture and stitch together 360-degree angle photographs. By capturing images at multiple focal points, focus adjustment for different angle structures can be performed post hoc.
GonioPen is a handheld gonioscopy device developed in Singapore that provides high-resolution images of the iridocorneal angle. It is compact and can be used by technicians with minimal training.
Smartphone cameras with slit-lamp adapters can capture gonioscopic photographs and videos. Additionally, direct smartphone imaging without a slit lamp has been reported. This is expected to be useful in areas with limited medical resources.
Conventional direct surgical gonioscopes require tilting the patient’s head or the microscope. In contrast, the double-mirror gonioscope uses two built-in mirrors to provide an upright view of the angle, allowing observation and manipulation of the entire circumference without tilting. With the advancement of MIGS, such surgical gonioscopes continue to evolve.
