The anterior chamber angle is where aqueous humor exits the eye — understanding its four key structures, from anterior to posterior, is essential for gonioscopy and for understanding every form of angle-based glaucoma.
Structures of the angle (anterior to posterior)
- Schwalbe's line — the peripheral termination of Descemet's membrane and the anterior-most landmark of the angle; appears as a thin, glistening line on gonioscopy
- Trabecular meshwork — spans from Schwalbe's line to the scleral spur; the primary site of aqueous outflow resistance and drainage into Schlemm's canal. Often visibly pigmented, especially in its posterior (functional/pigmented) portion — pigment density here is clinically relevant (e.g., pigment dispersion syndrome, pseudoexfoliation)
- Scleral spur — a whitish band posterior to the trabecular meshwork, marking the posterior attachment of the meshwork and the anterior insertion of the ciliary muscle; the most consistent, reliable gonioscopic landmark for angle grading since it doesn't vary in visibility due to pigmentation the way the trabecular meshwork does
- Ciliary body band — visible posterior to the scleral spur as a grey-brown band, representing the anterior face of the ciliary body; its visibility (or lack thereof) is central to angle grading systems (e.g., Shaffer, Spaeth)
Why the scleral spur matters most
When gonioscopic view is poor or pigmentation is minimal (common in younger or lightly pigmented eyes), the scleral spur remains the most reliable structure to identify — it is used as the reference point in every major angle grading system precisely because trabecular meshwork pigmentation is too variable to rely on alone.
Clinical relevance
- Angle closure is defined by iridotrabecular contact — specifically, contact obscuring visualization of the posterior trabecular meshwork on gonioscopy
- Angle recession (a common consequence of blunt trauma) is a tear between the longitudinal and circular fibers of the ciliary muscle, widening the visible ciliary body band asymmetrically compared to the fellow eye — a key finding to actively look for after any blunt ocular trauma, since angle recession glaucoma can present years later