Gonioscopic Angle Landmarks & Grading Systems

The Angle Landmarks, Anterior to Posterior

On gonioscopy of a normal, open angle, four landmarks appear in a fixed order as the examiner scans from anterior (corneal side) to posterior (iris side). The most anterior is Schwalbe's line: a fine white ring or ridge marking where Descemet's membrane terminates, and functionally the anterior limit of the trabecular meshwork. An anteriorly displaced Schwalbe's line, prominent enough to see without a goniolens, is called posterior embryotoxon. This finding is classically associated with Axenfeld-Rieger syndrome.

Moving posteriorly, the next structure is the trabecular meshwork, conventionally split into an anterior non-pigmented segment and a posterior pigmented segment. Most functional aqueous outflow occurs through the posterior, pigmented portion. Behind that lies the scleral spur, the most posterior white landmark visible in a normal angle. It is the attachment point of the longitudinal (meridional) fibers of the ciliary muscle. When the ciliary muscle contracts, it pulls the scleral spur posteriorly, widening the intertrabecular spaces and increasing conventional outflow: this is the mechanism behind pilocarpine's IOP-lowering effect. The most posterior structure visible in a wide-open angle is the ciliary body band, a grayish-brown strip immediately anterior to the iris root.

The Shaffer Grading System

The Shaffer system grades the anterior chamber angle from 0 to 4, based on the most posterior structure visible and the angular width between the iris root and the trabecular meshwork:

• Grade 4 (35–45°): the ciliary body band is visible, wide open, no risk of closure.
• Grade 3: the scleral spur is visible.
• Grade 2: only the posterior trabecular meshwork is visible.
• Grade 1: only the anterior trabecular meshwork is visible, an angle this narrow at meaningful risk of closure.
• Grade 0: no angle structures are visible at all; the angle is closed.

Shaffer grading is fast and reproducible, which is why routine clinical documentation defaults to it.

The Spaeth Grading System

The Spaeth system is more detailed than Shaffer. Rather than a single composite number, it records three separate parameters: angular width (in degrees, similar to Shaffer), the iris insertion point relative to the angle landmarks, and peripheral iris contour. Insertion is graded A through E: A is anterior to the trabecular meshwork, B is behind Schwalbe's line at the meshwork, C is at the scleral spur, D is posterior to the scleral spur, and E is within the ciliary body. Contour is recorded separately, as flat, convex (bowed), or concave (plateau-like). Because width, insertion, and contour are captured independently, Spaeth grading gives a more complete description, useful for tracking angle changes over time or communicating findings precisely between examiners.

Van Herick: Estimating the Angle Without a Goniolens

The Van Herick technique is not a gonioscopic grading system. It is a slit-lamp method for estimating anterior chamber depth, and by extension angle closure risk, without ever placing a lens on the eye. A narrow slit beam is directed at roughly 60° near the temporal limbus; the width of the dark, aqueous-filled space between the corneal light section and the anterior iris surface is then compared to the thickness of the adjacent corneal section. A peripheral chamber depth under a quarter of corneal thickness suggests a narrow angle at risk of closure and warrants a formal gonioscopic exam. Van Herick is fast and useful as a screening estimate, but it remains an indirect proxy. Actual gonioscopy is what grades the angle definitively, with Shaffer or Spaeth.

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