Angle Assessment Techniques

Angle Anatomy & Gonioscopy Basics - Peeking & Probing

• Angle Structures (Anterior to Posterior): 📌 S-L-T-C

  • Schwalbe's Line (SL): Termination of Descemet's membrane; anterior-most structure.
  • Trabecular Meshwork (TM): Pigmented (functional) & non-pigmented parts; main site of aqueous outflow.
  • Scleral Spur (SS): Whitish band; ciliary body attachment. Key landmark for TM identification.
  • Ciliary Body Band (CBB): Grey/brown band; anterior aspect of ciliary body. Most posterior structure.

• Gonioscopy Principles:

  • Visualizes the iridocorneal angle, overcoming total internal reflection at the air-cornea interface.
  • Direct Gonioscopy: (e.g., Koeppe lens)
    • Patient supine; provides a panoramic, erect view of the angle.
  • Indirect Gonioscopy: (e.g., Goldmann, Zeiss lenses)
    • Uses mirrors at the slit lamp; provides an inverted, virtual image.
    • Goldmann: Single mirror (routine, 62° inclination), 3-mirror.
    • Zeiss: 4 mirrors (good for indentation, 64° inclination).
  • Indentation Gonioscopy: (Dynamic)
    • Differentiates appositional (angle opens) vs. synechial (angle remains closed) angle closure.

⭐ The Scleral Spur (SS) is the most crucial and consistent landmark in gonioscopy, essential for identifying the Trabecular Meshwork (TM) located just anterior to it.

Gonioscopic Techniques & Grading - Sizing Up the Space

• Types of Gonioscopy:

  • Direct: Koeppe lens (patient supine; diagnostic/surgical).
  • Indirect: Goldmann (3-mirror), Zeiss/Posner/Sussman (4-mirror) (patient at slit-lamp).
    • Indentation Gonioscopy (Forbes Test): Differentiates appositional (angle opens with pressure) vs. synechial (angle remains closed/fixed) closure. Crucial for Primary Angle Closure Glaucoma (PACG) assessment.

• Angle Structures (Posterior to Anterior): 📌 "Can't See Till Sunrise"

  • Ciliary Body Band (CBB): Darkest, grey-brown band.
  • Scleral Spur (SS): Whitish, prominent line; attachment for ciliary muscle.
  • Trabecular Meshwork (TM): Pigmented (posterior, functional) & non-pigmented (anterior). Site of aqueous outflow.
  • Schwalbe's Line (SL): Anterior limit of angle; termination of Descemet's membrane.

• Shaffer Grading (Angle Width):

  • Grade 4 (35-45°): CBB visible; Widest, safest.
  • Grade 3 (25-35°): SS visible; Open, no closure risk.
  • Grade 2 (20°): TM visible; Narrow, closure possible.
  • Grade 1 (≤10°): Only SL/part of TM visible; Very narrow, high risk of closure.
  • Grade 0 (0°): Closed; Iris in contact with cornea, no structures visible.

• Spaeth System: More detailed: Records Iris insertion (A-E), Angular width (degrees), Peripheral Iris Contour (f-flat, c-concave, p-plateau, s-steep, b-bowed).

⭐ In Shaffer's grading, an angle of Grade 2 (20°) or less is considered critically narrow (occludable angle) and indicates a significant risk for acute angle closure glaucoma.

Advanced Imaging & Clinical Signs - Tech View & Tell-Tales

• Ultrasound Biomicroscopy (UBM)
  • High resolution (25-50 µm); contact procedure.
  • Visualizes ciliary body, sulcus, posterior chamber (PC).
  • Key for: Plateau iris, cysts, tumors, cyclodialysis clefts, sulcus pathology.
• Anterior Segment OCT (AS-OCT)
  • Non-contact, rapid; light-based imaging.
  • Types: SD-OCT, SS-OCT (deeper penetration, wider field).
  • Measures: Angle Opening Distance (AOD), Trabecular-Iris Space Area (TISA), ACA.
  • Details TM, Schwalbe's line, iris profile; quantifies angle.
• Scheimpflug Imaging (e.g., Pentacam)
  • Non-contact, rotating camera; 3D anterior segment analysis.
  • Measures ACD, ACV, lens parameters. Less angle structure detail.
• Key Clinical Signs (Tell-Tales)
  • PAS (Peripheral Anterior Synechiae): Iris adherent to TM/cornea; chronic angle closure.
  • Sampaolesi's Line: Pigment line anterior to Schwalbe's (PEX, PDS).
  • Blood in Schlemm's Canal: Due to ↑EVP or ocular hypotony.
  • NVA (Angle Neovascularization): Pathognomonic for neovascular glaucoma (NVG).

⭐ UBM remains unparalleled for visualizing structures posterior to the iris, such as the ciliary body, crucial for diagnosing conditions like plateau iris syndrome.

High‑Yield Points - ⚡ Biggest Takeaways

• Gonioscopy remains the gold standard for direct iridocorneal angle visualization.
• Shaffer's grading (Grade 0-closed to 4-widest) is a key clinical classification.
• Angle structures (posterior to anterior): Ciliary Body Band, Scleral Spur, Trabecular Meshwork, Schwalbe's Line.
• Indentation gonioscopy is crucial to differentiate appositional from synechial angle closure.
• Van Herick technique: Slit-lamp estimation; peripheral ACD ≤1/4 corneal thickness suggests occludable angle.
• UBM and AS-OCT offer objective imaging, especially with opaque media or for detailed structure analysis; AS-OCT is non-contact.