Gonioscopic Assessment and Documentation
In performing both direct and indirect gonioscopy, the clinician must recognize the landmarks of the anterior chamber angle. It is important to perform gonioscopy with dim room lighting and a thin, short light beam in order to minimize the amount of light entering the pupil. An excessive amount of light can cause increased pupillary constriction that could falsely open the angle, changing the peripheral angle appearance and potentially preventing the identification of a narrow or occluded angle. The scleral spur and the Schwalbe line, 2 important angle landmarks, are most consistently identified. A convenient gonioscopic technique to determine the exact position of the Schwalbe line is the parallelepiped, or corneal wedge, technique (see www.aao.org/basic-skills/corneal-wedge-introduction and Fig 2-4). This technique allows the observer to determine the exact junction of the cornea and the trabecular meshwork. Using a narrow slit beam and sharp focus, the examiner sees 2 curvilinear reflections, 1 from the external surface of the cornea and its junction with the sclera and the other from the internal surface of the cornea. The 2 reflections meet at the Schwalbe line (see Fig 2-4). The scleral spur is a thin, pale stripe between the ciliary body face and the pigmented zone of the trabecular meshwork. The inferior portion of the angle is generally wider and is the easiest place in which to locate the landmarks. After verifying the landmarks, the clinician should examine the entire angle in an orderly manner (see Table 4-1).
Proper management of glaucoma requires the clinician to determine not only whether the angle is open or closed but also whether other pathologic findings, such as angle recession or PAS, are present. In angle closure, the peripheral iris obstructs the trabecular meshwork—that is, the meshwork is not visible on gonioscopy. The width of the angle is determined by the site of insertion of the iris on the ciliary face, the convexity of the iris, and the prominence of the peripheral iris roll. In many cases, the angle appears to be open but very narrow. It is often difficult to distinguish a narrow but open angle from an angle with partial closure; dynamic gonioscopy is useful in this situation (see Figs 4-3 and 4-4).
The best method for describing the angle is to use a standardized grading system or to draw the iris contour, the location of the iris insertion, and the angle between the iris and the trabecular meshwork. Various gonioscopic grading systems have been developed, all of which facilitate standardized description of angle structures and abbreviate that description. However, the clinician should keep in mind that some details about the angle structure will be eliminated with the use of abbreviated descriptions. The most commonly used gonioscopic grading systems are the Shaffer and Spaeth systems. A quadrant-by-quadrant narrative description of the chamber angle noting localized findings such as neovascular tufts, angle recession, or PAS may also be used to document serial gonioscopic findings. If a grading system is used, the clinician should specify which one.
The Shaffer system describes the angle between the trabecular meshwork and the iris as follows:
Grade 4: The angle between the iris and the surface of the trabecular meshwork is 45°.
Grade 3: The angle between the iris and the surface of the trabecular meshwork is greater than 20° but less than 45°.
Grade 2: The angle between the iris and the surface of the trabecular meshwork is 20°. Angle closure is possible.
Grade 1: The angle between the iris and the surface of the trabecular meshwork is 10°. Angle closure is probable over time.
Slit: The angle between the iris and the surface of the trabecular meshwork is less than 10°. Angle closure is very likely.
Grade 0: The iris is against the trabecular meshwork. Angle closure is present.
The Spaeth gonioscopic grading system expands on this schema to include a description of the peripheral iris contour, the insertion of the iris root, and the effects of dynamic gonioscopy on the angle configuration (Fig 5-4).
Blood and vessels
Ordinarily, the Schlemm canal cannot be seen on gonioscopy; however, it can easily be visualized if blood enters the canal. This can occur when episcleral venous pressure exceeds IOP, most commonly because of compression of the episcleral veins by the lip of the goniolens (Fig 6-4). Pathologic causes of blood in the canal include hypotony and elevated episcleral venous pressure, as in carotid-cavernous fistula or Sturge-Weber syndrome.
Figure 4-5 The Spaeth gonioscopic classification of the anterior chamber angle, based on 3 variables: A, site of iris attachment to the inner surface of the cornea, sclera, or ciliary body; B, angular width of the angle recess; C, configuration of the peripheral iris.
(Illustration courtesy of Mark Miller.)
Figure 4-6 Goniophotograph showing blood in the Schlemm canal, visible through the semiopaque trabecular meshwork. Elevated episcleral venous pressure resulted in blood reflux into the canal.
(Courtesy of G.A. Cioffi, MD.)
Normal blood vessels in the angle include radial iris vessels, portions of the arterial circle of the ciliary body, and vertical branches of the anterior ciliary arteries. Normal vessels are oriented either radially along the iris or circumferentially (in a serpentine manner) in the ciliary body face. Vessels that cross the scleral spur to reach the trabecular meshwork are usually abnormal (Fig 7-4). The vessels seen in Fuchs uveitis syndrome are fine, branching, unsheathed, and meandering. Patients with neovascular glaucoma have vessels crossing the ciliary body and scleral spur and arborizing over the trabecular meshwork. Contraction of the myofibroblasts accompanying these vessels leads to PAS formation.
Iris processes and PAS
It is important to distinguish PAS from iris processes, which are open and lacy and follow the normal curve of the angle. The angle structures are visible in the open spaces between the iris processes. Synechiae are more solid or sheetlike (Fig 8-4). They are composed of iris stroma and obliterate the angle recess.
Pigmentation of the trabecular meshwork increases with age and tends to be more marked in individuals with darkly pigmented irides. Pigmentation can be segmental and is usually most marked in the inferior angle. The pigmentation pattern of an individual angle is dynamic over time, especially in conditions such as pigment dispersion syndrome. Heavy pigmentation of the trabecular meshwork should suggest pigment dispersion or pseudoexfoliation syndrome. In pigment dispersion syndrome, over time, pigment may no longer be actively liberated, and the trabecular meshwork pigmentation dissipates. This occurs most rapidly in the inferior angle, resulting in relatively heavier pigmentation of the superior angle—sometimes the only remaining sign of previous pigment dispersion syndrome.
Figure 4-7 Goniophotographs showing neovascularization of the angle. A, Anatomically open angle. B, Closed angle.
(Part A courtesy of Keith Barton, MD; part B courtesy of Ronald L. Gross, MD.)
Figure 4-8 Goniophotograph showing both an area of sheetlike PAS (arrow) and an open angle (right).
(Courtesy of Louis B. Cantor, MD.)
Pseudoexfoliation syndrome may be associated with pigment granules on the anterior surface of the iris and increased pigmentation in the anterior chamber angle, as iridolenticular friction in the peripupillary region is thought to cause pigment liberation from the iris epithelium and peripupillary transillumination defects. In addition, a line of pigment deposition, known as the Sampaolesi line, anterior to the Schwalbe line is often present in pseudoexfoliation syndrome. Other conditions that cause increased anterior chamber angle pigmentation include uveal melanoma, trauma, surgery, inflammation, angle closure, and hyphema.
Effects of trauma
Posttraumatic angle recession may be associated with monocular open-angle glaucoma. The gonioscopic criteria for diagnosing angle recession include
an abnormally wide ciliary body band (Fig 9-4)
increased prominence of the scleral spur
torn iris processes
marked variation of ciliary face width and angle depth in different quadrants of the same eye
Figure 4-9 Goniophotograph showing angle recession. Note the widening of the ciliary body band.
(Reprinted with permission from Wright KW, ed. Textbook of Ophthalmology. Williams & Wilkins; 1997.)
Figure 4-10 Forms of anterior chamber angle injury associated with blunt trauma, showing cross-sectional and corresponding gonioscopic appearance. A, Angle recession (tear between longitudinal and circular muscles of ciliary body). B, Cyclodialysis (separation of ciliary body from scleral spur) with widening of suprachoroidal space. C, Iridodialysis (tear in root of iris). D, Trabecular damage (tear in anterior portion of meshwork, creating a flap that is hinged at the scleral spur).
(Reproduced with permission from Shields MB. Textbook of Glaucoma. 3rd ed. Williams & Wilkins; 1992.)
In evaluating for angle recession, the clinician may find it helpful to compare one part of the angle to other areas in the same eye or to the same area in the fellow eye. Figure 4-10 illustrates a variety of gonioscopic findings caused by blunt trauma. If the ciliary body separates from the scleral spur (cyclodialysis), it will appear gonioscopically as a deep angle recess with a gap between the scleral spur and the ciliary body. Detection of a very small cleft may require ultrasound biomicroscopy.
Various other findings that may be visible by gonioscopy include
anteriorly rotated ciliary processes (sometimes visible after dilation)
goniotomy or trabeculotomy cleft
inflammatory angle precipitates (analogous to KPs)
intraocular lens haptics
iris or ciliary body tumors or cysts
hyphema or hypopyon
surgical devices such as aqueous drainage tubes and stents
peripheral lens abnormalities such as severe zonular dehiscence (sometimes visible after dilation)
retained anterior chamber foreign body or crystalline lens material
sclerostomy site for trabeculectomy
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.