Angle grading and anterior-segment imaging

4. Standardized Gonioscopic Grading Systems

Accurate documentation requires standardized nomenclature. The two universally recognized frameworks are the Shaffer system and the Spaeth system.

The Shaffer Classification System

The Shaffer system grades the angular width of the angle recess formed between the trabecular meshwork and the peripheral iris surface, correlating angular approach with angle-closure risk:

The Spaeth Classification System

The Spaeth system provides a comprehensive, reproducible description of angle configuration by incorporating three independent variables:

1. Level of Iris Insertion (Letters A through E):
   • A = Anterior to Schwalbe's line (pathological contact)
   • B = Behind Schwalbe's line (anterior to scleral spur; on trabecular meshwork)
   • C = Scleral spur visible (at scleral spur)
   • D = Deep (ciliary body band visible)
   • E = Extremely deep (exceptionally wide ciliary body band, $> 1.0\text{ mm}$)
   • Convention: The apparent insertion prior to indentation is recorded in parentheses, followed by the true insertion revealed after indentation: e.g., (B) D indicates an angle that appears inserted on the trabecular meshwork at rest, but deepens to a ciliary body insertion upon indentation.
2. Angular Width in Degrees:
   • The estimated angle formed between a tangent to the inner trabecular wall and a tangent to the anterior peripheral iris surface (e.g., $10^\circ, 20^\circ, 30^\circ, 40^\circ$).
3. Peripheral Iris Configuration (Letters r, s, q):
   • r (regular): Flat peripheral iris configuration with minimal curvature; characteristic of normal open angles or plateau iris after iridotomy.
   • s (steep): Prominent convex anterior bowing of the peripheral iris; classic marker of pupillary block.
   • q (queer): Markedly concave posterior bowing of the peripheral iris; characteristic of pigment dispersion syndrome (reverse pupillary block).

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5. Pathological Angle Signs

Careful biomicroscopy of the angle recess frequently reveals characteristic signs that establish specific secondary glaucoma etiologies:

1. Sampaolesi Line

• Appearance: A prominent, wavy, scalloped or continuous line of dense brown-black melanin pigment deposited on or anterior to Schwalbe's line.
• Etiological Differential:
  • Pseudoexfoliation Syndrome (PEX): Pigment deposition is typically patchy, uneven, and accompanied by dandruff-like fibrillar white fibrillar extracellular material on the pupillary ruff, anterior lens capsule, and trabecular meshwork.
  • Pigment Dispersion Syndrome (PDS): Pigment deposition forms an intensely dense, uniform, homogeneous $360^\circ$ dark chocolate-brown band over the posterior meshwork and Schwalbe's line, accompanied by vertical corneal endothelial pigment deposition (Krukenberg spindle) and mid-peripheral radial iris transillumination defects.
  • Chronic anterior uveitis, previous ocular trauma, and anterior segment melanoma.

2. Neovascularisation of the Angle (NVA)

• Biomicroscopic Features: Delicate, fine, arborizing capillary networks that cross the scleral spur to proliferate across the functional trabecular meshwork.
• Critical Differentiation from Normal Angle Vessels:
  • Normal Ciliary Vessels: Large, radial or circumferential branches of the major arterial circle of the iris that run strictly within the ciliary body band or deep iris stroma. They never cross the scleral spur onto the trabecular meshwork.
  • Pathological NVA: Fragile, disorganized, fine capillary loops that cross the scleral spur, arborizing over the functional trabecular meshwork. An invisible myofibroblastic membrane accompanies these vessels; as this membrane contracts, it unzips peripheral anterior synechiae from posterior to anterior, culminating in complete $360^\circ$ synechial angle-closure and intractable neovascular glaucoma (NVG).

3. Angle Recession

• Pathogenesis: Traumatic cleavage or tearing between the circular and longitudinal muscle fibers of the ciliary body following blunt ocular contusion.
• Gonioscopic Triad:
  1. Pathological, irregular widening of the ciliary body band in the affected sector.
  2. Abnormally deepened angle recess compared to the fellow unaffected eye.
  3. Torn, frayed iris processes and a starkly exposed, bare white scleral face.
• Angle recession glaucoma: Associated trabecular injury and later scarring can cause glaucoma months to decades after blunt injury. Greater recession extent increases concern but does not yield one universal lifetime percentage. Record baseline pressure, nerve and fields and arrange long-term surveillance.

4. Cyclodialysis Cleft

• Pathogenesis: Complete disinsertion and separation of the longitudinal ciliary muscle from its anatomical anchor at the scleral spur, caused by blunt ocular trauma or iatrogenic surgical misdirection.
• Pathophysiology: Creates an uncontrolled, direct, pressure-independent drainage fistula between the anterior chamber and the suprachoroidal space.
• Clinical Sequelae: Profound chronic ocular hypotony ($\text{IOP} < 6\text{ mmHg}$), shallow anterior chamber, and hypotony maculopathy (chorioretinal folds radiating from the fovea, optic disc swelling, tortuous vessels, and severe vision loss).
• Gonioscopy: Visualizes a distinct, dark, recessed gap situated directly behind the scleral spur leading into the black suprachoroidal space.

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6. Anterior Segment Imaging: AS-OCT vs. Ultrasound Biomicroscopy (UBM)

Anterior segment diagnostic imaging provides non-invasive, objective, high-resolution cross-sectional tomograms of the anterior chamber angle, complementing subjective clinical gonioscopy.

Plateau Iris Syndrome & The Crucial Role of UBM

• Plateau Iris Configuration: A narrow angle caused by abnormal, large, or anteriorly rotated ciliary processes that mechanically push the peripheral iris root forward, crowding the trabecular meshwork, while the central anterior chamber depth remains normal and flat.
• Plateau Iris Syndrome: Persistent appositional or synechial angle closure in an eye with plateau iris configuration despite a patent laser peripheral iridotomy (LPI).
• Diagnostic Differentiation: Persistent closure after a patent LPI raises concern for non-pupillary mechanisms. UBM can show anteriorly positioned ciliary processes and a reduced ciliary sulcus supporting plateau iris. AS-OCT cannot directly image behind the iris. Interpret imaging with gonioscopy and exclude lens-related and other secondary mechanisms; one image does not prove the diagnosis.