Angle Assessment Techniques

Angle Assessment Techniques

Angle Assessment Techniques

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Angle Anatomy & Gonioscopy Basics - Peeking & Probing

Anterior chamber angle anatomy

  • 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. Gonioscopy vs. OCT: Pros and Cons
  • 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.

Practice Questions: Angle Assessment Techniques

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A child presents with unilateral white reflex (leukocoria) and raised intraocular pressure, raising suspicion of retinoblastoma. Which of the following investigations is the most appropriate to perform?

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Flashcards: Angle Assessment Techniques

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Gonioscopy in glaucomatocyclitic crisis shows a(n) _____-angle.

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Gonioscopy in glaucomatocyclitic crisis shows a(n) _____-angle.

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