Direct and Indirect Gonioscopy
Gonioscopy techniques fall into 2 broad categories: (1) direct and (2) indirect (Fig 4-4). Direct gonioscopy is performed with a binocular microscope, fiber-optic illuminator, or slit-pen light together with a direct goniolens, such as the Koeppe, Swan-Jacob, Barkan, Wurst, or Richardson type. The lens is placed on the eye; and saline solution, methylcellulose, or an ophthalmic viscosurgical device is used to fill the space between the cornea and the lens, acting as an optical coupler between the 2 surfaces. The goniolens provides direct visualization of the anterior chamber angle (ie, light reflected directly from the angle is visualized). With direct gonioscopy, the clinician has an erect view of the angle structures, which is essential when angle surgery (eg, goniotomy or placement of a stent in the Schlemm canal) is performed. Direct gonioscopy is most easily accomplished with the patient in a supine position, and it is commonly used in the operating room for examining the eyes of infants under anesthesia.
Table 4-1 Gonioscopic Examination
Figure 4-2 Gonioscopic appearance of a normal anterior chamber angle. 1, Peripheral iris: a, insertion; b, curvature; c, angular approach. 2, Ciliary body band. 3, Scleral spur. 4, Trabecular meshwork: a, posterior; b, mid; c, anterior. 5, Schwalbe line. Asterisk, Corneal optical wedge (parallelepiped corneal wedge).
Figure 4-3 Normal and narrow angles. A, Normal open angle. Gonioscopic photograph shows trace pigmentation of the posterior trabecular meshwork and normal insertion of the iris into a narrow ciliary body band. The Goldmann lens was used. B, Normal open angle. This gonioscopic view using the Goldmann lens shows mild pigmentation of the posterior trabecular meshwork. A wide ciliary body band with posterior insertion of the iris can also be seen. C, Narrow angle. This gonioscopic view using the Zeiss lens without indentation shows pigment in the inferior angle but poor visualization of angle anatomy. D, Narrow angle. Gonioscopy with a Zeiss lens with indentation shows peripheral anterior synechiae (PAS) in the posterior trabecular meshwork. Pigment deposits on the Schwalbe line can also be seen. This is the same angle as shown in part C.
(Part A courtesy of Angelo P. Tanna, MD, parts B–D courtesy of Elizabeth A. Hodapp, MD.)
Figure 4-4 Direct and indirect gonioscopy. Gonioscopic lenses eliminate the tear–air interface and total internal reflection. With a direct lens, the light ray reflected from the anterior chamber angle is observed directly, whereas with an indirect lens, the light ray is reflected by a mirror within the lens. Posterior pressure with an indirect lens forces open an appositionally closed or narrow anterior chamber angle (dynamic gonioscopy).
(Illustration courtesy of Mark Miller.)
Indirect gonioscopy is more frequently used in the clinician’s office. Light reflected from the angle passes into the indirect gonioscopy lens and is reflected by 1 or more mirrors within the lens. This method may be used with the patient in an upright position, with illumination and magnification provided by a slit-lamp microscope. The indirect goniolens yields an inverted and slightly foreshortened image of the opposite angle. Although the image is inverted, the right–left orientation of a horizontal mirror and the up–down orientation of a vertical mirror remain unchanged. The foreshortening, combined with the upright position of the patient, makes the angle appear somewhat shallower than it does on direct gonioscopy. The Goldmann-type 1- or 3-mirror gonioscopy lens requires a viscous fluid such as methylcellulose for optical coupling with the cornea. Posterior pressure on the lens, especially if it is tilted, indents the sclera and may falsely narrow the angle. Among indirect gonioscopy lenses, these provide the clearest visualization of the anterior chamber angle structures, and they may be modified with antireflective coatings for use during laser procedures.
The Posner, Sussman, and Zeiss 4-mirror gonioscopy lenses allow all 4 quadrants of the anterior chamber angle to be visualized without rotation of the lens during examination. Because these lenses have approximately the same radius of curvature as the cornea, they are optically coupled by the patient’s tears. The posterior diameter of these lenses is smaller than the corneal diameter, and thus posterior pressure can be used to force open a narrow angle by means of a technique called dynamic gonioscopy (also known as compression or indentation gonioscopy). With dynamic gonioscopy, the clinician puts gentle pressure on the cornea with the goniolens, which forces aqueous humor into the angle, causing it to open to a greater degree than its native state in the absence of peripheral anterior synechiae (PAS) (see Fig 4-4). With indirect gonioscopy, the observer can optimize the view of the anterior chamber angle by repositioning the patient’s eye (having the patient look toward the mirror being viewed by the examiner) or by slightly tilting the lens. However, pressure on the cornea will artificially open a truly narrow or closed angle. The examiner can detect this pressure by noting the induced Descemet membrane folds.
When an area of the angle is closed, one cannot initially differentiate between appositional angle closure and angle closure due to PAS. The technique of dynamic gonioscopy is essential for distinguishing iridocorneal apposition from synechial closure. Many clinicians prefer these 4-mirror lenses because of their ease of use and the ability to perform dynamic gonioscopy.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.