Residency · Residency · Ophthalmology

Gonioscopy and Angle Assessment

Purpose and Importance

Gonioscopy is the clinical examination of the iridocorneal angle -- the junction where the peripheral iris meets the cornea and where the trabecular meshwork resides. It is the only definitive method for classifying glaucoma as open-angle or angle-closure, a distinction that fundamentally determines management. Beyond this classification, gonioscopy is required for identifying angle pathology including neovascularization, recession, synechiae, abnormal pigmentation, tumors, and foreign bodies. While anterior segment imaging modalities such as AS-OCT and UBM provide valuable supplementary information, they do not replace gonioscopy. Every new glaucoma patient should undergo gonioscopy, and the examination should be repeated periodically during follow-up.

Optical Principles

The anterior chamber angle cannot be directly visualized because light traveling from the angle toward the corneal surface undergoes total internal reflection (TIR) at the cornea-air interface. The critical angle for TIR at the cornea is approximately 46 degrees, meaning that light from the angle strikes the posterior corneal surface at an angle too oblique to escape. A gonioscopy lens overcomes this problem by replacing the air interface with a contact lens surface that has a refractive index close to that of the cornea, eliminating TIR and allowing the examiner to see into the angle.

Direct Gonioscopy

Technique

Direct gonioscopy uses lenses such as the Koeppe, Barkan, Swan-Jacob, or Richardson. The patient is positioned supine, and the lens is placed on the cornea with a coupling fluid. The examiner views the angle on the same side as the lens, obtaining a direct, unmagnified view of the angle structures. An operating microscope or portable slit lamp provides illumination and magnification.

Advantages

Direct gonioscopy provides an excellent panoramic overview of the angle anatomy. The Koeppe lens allows simultaneous comparison of the angles of both eyes, which is valuable for detecting asymmetry. This technique is particularly useful in the operating room for procedures such as goniotomy in pediatric glaucoma, and it serves as an effective teaching tool for learning angle anatomy.

Disadvantages

The requirement for the patient to be supine makes direct gonioscopy impractical at the slit lamp, which is where most clinical examinations take place. The technique also requires a separate light source and magnification system.

Indirect Gonioscopy

Technique

Indirect gonioscopy is performed at the slit lamp using lenses that contain mirrors to reflect light from the angle to the examiner. Available lenses include the Goldmann (in one-, two-, or three-mirror configurations), Zeiss, Posner, and Sussman. The lens is placed on the cornea while the patient sits at the slit lamp. Because the mirror reflects light from the opposite angle, the examiner views the angle on the side opposite to the mirror being used.

Goldmann Lens

The Goldmann three-mirror lens (or its single-mirror gonioscopy variant) requires a coupling solution such as methylcellulose. Its larger diameter provides stability on the eye but can artificially open the angle by compressing the cornea against the limbus. This compression effect makes the Goldmann lens unsuitable for indentation gonioscopy.

Zeiss/Posner/Sussman Four-Mirror Lens

The four-mirror lenses have a smaller diameter and a flat contact surface, requiring no coupling solution or only minimal fluid. Their key advantage is that they allow indentation (compression) gonioscopy, in which gentle pressure on the central cornea pushes aqueous peripherally, mechanically opening the angle. This maneuver distinguishes appositional closure from synechial closure and makes the four-mirror lens the preferred instrument for dynamic assessment of angle-closure disease.

Indentation (Compression) Gonioscopy

Indentation gonioscopy is a critical technique for distinguishing the two mechanisms of angle closure. When firm pressure is applied to the central cornea, aqueous is forced peripherally, opening any angle that is merely appositionally closed. If the angle opens with indentation, the closure is appositional and may be treatable with laser peripheral iridotomy. If the angle remains closed despite indentation, the iris is structurally adherent to the angle wall as peripheral anterior synechiae, which are not amenable to LPI alone. This technique is best performed with a Zeiss-type four-mirror lens.

Angle Anatomy (Landmarks from Anterior to Posterior)

The gonioscopic view reveals a series of landmarks arranged from anterior to posterior. Schwalbe line marks the termination of Descemet membrane and the transition from the cornea to the trabecular meshwork. When thickened and anteriorly displaced, it is termed posterior embryotoxon and is associated with Axenfeld-Rieger anomaly. The non-pigmented trabecular meshwork lies just posterior to Schwalbe line; it is the anterior, non-functional portion of the meshwork and appears as a pale band. The pigmented trabecular meshwork is the posterior, functional filtration region that overlies Schlemm canal. It is the most pigmented structure in the angle because melanin granules carried in the aqueous are deposited here as fluid drains through the meshwork. The scleral spur appears as a thin whitish-blue line between the trabecular meshwork and the ciliary body band; it serves as the attachment site for the longitudinal fibers of the ciliary muscle. The ciliary body band is a gray-brown band whose width varies with refractive status -- it is wider in myopic eyes and narrower in hyperopic eyes and in eyes at risk for angle closure. The iris root is the most posterior landmark and represents the insertion of the peripheral iris.

Sampaolesi Line

The Sampaolesi line is a deposit of pigment anterior to Schwalbe line, on the corneal side of this landmark. When present, it is pathognomonic for pseudoexfoliation syndrome, though it can also be seen in pigment dispersion syndrome. Its presence should prompt a careful evaluation for pseudoexfoliative material and zonular weakness.

Grading Systems

Shaffer Grading System

Spaeth Grading System (More Detailed)

The Spaeth system provides a more comprehensive and reproducible description of the angle by documenting three components. The first is iris insertion, graded from A (anterior to the trabecular meshwork) through B (behind Schwalbe line), C (at the scleral spur), D (deep, at the ciliary body), to E (extremely deep). The second is angular width, measured in degrees from 0 to 40 or more. The third is iris configuration, described as s (steep or convex), r (regular or flat), or q (queer or concave). For example, D30r describes a wide-open normal angle with deep iris insertion at the ciliary body, a 30-degree angle, and a regular iris configuration, while B10s describes a narrow angle at risk for closure with iris insertion behind Schwalbe line, a 10-degree angle, and a steep convex iris. The Spaeth system is more descriptive than the Shaffer system and allows meaningful tracking of angle changes over time.

Scheie Classification (Historical)

The Scheie classification grades the angle from wide open (Grade 0) to closed (Grade IV) based on the visibility of angle structures. It is less commonly used today, having been largely supplanted by the Shaffer and Spaeth systems.

Pathologic Gonioscopic Findings

Peripheral Anterior Synechiae (PAS)

Peripheral anterior synechiae are adhesions between the peripheral iris and the angle wall, which may attach to the trabecular meshwork, Schwalbe line, or the cornea itself. They develop in the setting of chronic angle closure, uveitis, neovascularization, iridocorneal endothelial (ICE) syndrome, and as a postoperative complication. On gonioscopy, PAS appear as broad-based or tent-shaped iris attachments that do not release with indentation. They reduce the functional outflow area and can lead to elevated IOP.

Angle Neovascularization (NVA)

Angle neovascularization consists of fine, irregular blood vessels that cross the ciliary body band and trabecular meshwork, often growing from the iris root and radiating toward Schwalbe line. The most common underlying causes are proliferative diabetic retinopathy, central retinal vein occlusion, ocular ischemic syndrome, and chronic uveitis. Angle neovascularization is the precursor to neovascular glaucoma. These abnormal vessels can be distinguished from normal iris vessels because they are irregular in caliber and course, cross the scleral spur, and do not follow the natural pattern of iris crypts.

Angle Recession

Angle recession results from blunt ocular trauma that tears the ciliary body between its longitudinal and circular muscle fibers. On gonioscopy, the ciliary body band appears widened, the angle shows irregular deepening, and iris processes are torn. Because the finding is often unilateral, comparison with the fellow eye is essential for detecting the asymmetry. Patients with angle recession are at risk for late-onset glaucoma that may develop months to years after the initial injury. The mechanism involves trabecular meshwork dysfunction from scarring and membrane formation over the meshwork, and these patients require lifelong IOP monitoring.

Pigment Findings

The pattern of pigmentation on gonioscopy provides diagnostic clues. Heavy, homogeneous pigmentation of the trabecular meshwork is characteristic of pigment dispersion syndrome and pigmentary glaucoma. A Sampaolesi line points to pseudoexfoliation. Patchy pigmentation may represent normal variation or post-inflammatory changes. The combination of a dense pigment band at the trabecular meshwork with a Krukenberg spindle on the corneal endothelium is the classic presentation of pigment dispersion.

Pseudoexfoliation Material

Pseudoexfoliation material appears as white, dandruff-like deposits visible at the pupil margin, on the lens capsule, and within the angle. When deposited on the trabecular meshwork, this material causes obstruction and elevated IOP. The Sampaolesi line -- pigment deposited anterior to Schwalbe line -- is the most specific gonioscopic sign of pseudoexfoliation. The condition is clinically important because it is associated with weak zonules and increased risk during cataract surgery.

ICE Syndrome Findings

The iridocorneal endothelial (ICE) syndrome produces characteristic gonioscopic findings. Peripheral anterior synechiae have a distinctive broad-based, smooth configuration. Iris abnormalities include corectopia (displaced pupil), polycoria (multiple pupils), and ectropion uveae (posterior pigment layer visible on the anterior iris surface). The condition is unilateral, non-hereditary, and caused by abnormal corneal endothelium that proliferates and migrates over the angle structures.

Gonioscopy in Special Situations

In pediatric patients, direct gonioscopy is performed under anesthesia using a Koeppe or Swan-Jacob lens and is essential for the workup of congenital glaucoma. After ocular trauma, gonioscopy should specifically evaluate for angle recession, cyclodialysis cleft, iridodialysis, and lens subluxation. In suspected neovascular glaucoma, a gentle technique is critical -- excessive compression of the angle can push the iris against the trabecular meshwork and obscure early neovascularization. For plateau iris, gonioscopy reveals a narrow angle with a flat or slightly convex iris configuration, a pattern that differs from the classic convex iris of pupillary block; the diagnosis is confirmed by UBM demonstrating anteriorly positioned ciliary processes.

<image>Gonioscopic view of a normal open anterior chamber angle showing all anatomical landmarks from anterior to posterior. Labels identify: Schwalbe line (white line at the termination of Descemet membrane), non-pigmented trabecular meshwork (pale band), pigmented trabecular meshwork (brown band overlying Schlemm canal), scleral spur (thin white line), ciliary body band (gray-brown band), and iris root with iris processes bridging to the ciliary body. The angle is Shaffer grade 4 (wide open). An inset diagram shows the cross-sectional anatomy corresponding to each gonioscopic landmark.</image>

<image>Pathologic gonioscopy findings montage — four panels. Panel A: Peripheral anterior synechiae (PAS) — tent-shaped iris adhesions to the trabecular meshwork that do not release with indentation gonioscopy. Panel B: Angle neovascularization — fine, irregular blood vessels crossing the ciliary body band and scleral spur onto the trabecular meshwork (compare with an inset showing normal radial iris vessels that do not cross the scleral spur). Panel C: Angle recession — widened ciliary body band with torn iris processes and irregular angle deepening on one side compared with the normal fellow eye angle shown adjacent. Panel D: Heavy trabecular meshwork pigmentation in pigment dispersion syndrome with a dense, homogeneous dark band at the TM level. Label the key findings in each panel.</image>

<image>Comparison of Shaffer and Spaeth angle grading systems. Left side: Shaffer grading — five cross-sectional diagrams showing the iridocorneal angle at grades 0 through 4, with increasing angular width and progressively more angle structures visible. Right side: Spaeth grading — three diagrams showing the three components: (1) iris insertion site from A (anterior) to E (extremely deep); (2) angular width measurement in degrees; (3) iris configuration: s (steep/convex), r (regular/flat), q (queer/concave). Example Spaeth grades annotated on each diagram (e.g., D35q for a wide-open concave angle, B10s for a narrow convex angle).</image>

Key Clinical Pearls

Gonioscopy is the only definitive method for classifying an angle as open or closed, and it must be performed on every new glaucoma patient. Indentation gonioscopy with a Zeiss-type four-mirror lens is essential for distinguishing appositional closure (which opens with compression and may respond to LPI) from synechial closure (which remains closed and represents structural damage). Both eyes should always be compared: unilateral angle deepening suggests angle recession from prior trauma, while unilateral narrowing suggests a lens- or iris-related mechanism. During the examination, the room should be dark and the slit beam should be thin and directed away from the pupil to prevent pupil constriction and artifactual angle opening. The Sampaolesi line -- pigment deposited anterior to Schwalbe line -- is the most specific gonioscopic sign of pseudoexfoliation. Angle neovascularization discovered in a diabetic or post-CRVO patient warrants urgent panretinal photocoagulation and anti-VEGF therapy; treatment should not be delayed until IOP elevation occurs. Angle recession from blunt trauma may cause glaucoma years to decades after the initial injury, so these patients require lifelong IOP monitoring. When performing gonioscopy, all four quadrants should be documented with notation of iris configuration, angle width, pigmentation, and any pathology identified.

References

• Alward WLM. Color Atlas of Gonioscopy. Foundation of the AAO, 2008.
• Spaeth GL, et al. The Spaeth gonioscopic grading system. In: Glaucoma Surgery. Thieme, 2009.
• Friedman DS, He M. Anterior chamber angle assessment techniques. Surv Ophthalmol. 2008;53(3):250-273.
• AAO BCSC Section 10: Glaucoma. 2023-2024.

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