Anatomy of the anterior chamber angle and gonioscopic appearance (20-mark style)

1) Why gonioscopy is needed

2) Angle anatomy in order (anterior to posterior) and how each looks on gonioscopy

1. Schwalbe line (SL)
   • Most anterior landmark
   • Appears as a thin whitish line, sometimes pigmented
   • Can be highlighted with the corneal wedge technique
   • Prominent pigment at/just anterior to SL is a Sampaolesi line
2. Trabecular meshwork (TM)
   • From SL to scleral spur
   • Anterior TM: pale, relatively nonfunctional
   • Posterior TM: more pigmented, functional outflow portion
   • Pigmentation generally increases with age, often greatest inferiorly
3. Schlemm canal
   • Sometimes visible as a darker line deep to posterior TM
   • Blood may be seen in canal physiologically or with raised episcleral venous pressure
4. Scleral spur (SS)
   • White/yellow-white narrow band just posterior to TM
   • Key landmark separating TM from ciliary body band
5. Ciliary body band (CBB)
   • Dull brown/grey band posterior to SS
   • Width varies with iris insertion/refractive status
   • Often broader in myopes, narrower in hyperopes
6. Angle recess / iris root
   • Posterior dip of peripheral iris insertion
   • May be less visible in physiologically anterior insertion

3) Normal additional findings

• Iris processes: fine lacy strands from peripheral iris toward SS/CBB, common normal variant (especially young/brown irides)
• Radial vessels in angle recess can be normal

4) Abnormal gonioscopic findings (high yield)

• Peripheral anterior synechiae (PAS): broad adhesions of iris to angle structures; unlike fine iris processes
• Neovascularization of angle (NVA): abnormal vessels crossing SS onto TM
• Excessive pigmentation: pigment dispersion, pseudoexfoliation, prior inflammation/trauma
• Angle recession / cyclodialysis / trabecular dialysis in trauma
• Blood in Schlemm canal in venous congestion states

5) Methods of gonioscopy

• Indirect gonioscopy (most clinic use): mirror lenses at slit lamp (e.g., Goldmann/4-mirror)
• Direct gonioscopy: usually supine, often in OR (e.g., Koeppe), useful in infants/surgery
• Indentation (dynamic) gonioscopy:
  • Distinguishes appositional closure (angle opens with indentation)
  • From synechial closure (does not open)

6) Grading of angle width (Shaffer)

• Grade 4 (35-45°): wide open, CBB visible
• Grade 3 (25-35°): open, SS visible
• Grade 2 (~20°): TM visible, SS not seen (narrower)
• Grade 1 (~10°): only SL ± upper TM visible, high closure risk
• Slit: no clear iridocorneal contact but no identifiable angle structures
• Grade 0 (0°): closed (iridocorneal contact)

Key diagrams

Exam-ready short conclusion

Anatomy of angle and gonioscopic appearance (20 marks)

1. Introduction

2. Applied anatomy of the angle (anterior to posterior)

1. Schwalbe’s line
   • Peripheral termination of Descemet membrane
   • Most anterior gonioscopic landmark
   • Appears as a thin glistening line, sometimes pigmented
   • Pigment anterior to it may form a Sampaolesi line
2. Trabecular meshwork
   • Extends from Schwalbe’s line to scleral spur
   • Anterior non-pigmented TM: less functional
   • Posterior pigmented TM: principal aqueous outflow zone, usually more pigmented
3. Schlemm’s canal
   • External to juxtacanalicular trabeculum
   • May appear as a dark line; occasional blood reflux may be seen
4. Scleral spur
   • White band posterior to TM
   • Important landmark separating TM from ciliary body band
5. Ciliary body band
   • Brown/gray band posterior to scleral spur
   • Width depends on iris insertion and ciliary body position
6. Angle recess and iris root
   • Deepest posterior part where peripheral iris inserts

3. Normal gonioscopic appearance

• Open angle shows sequential visibility of landmarks from Schwalbe line to ciliary body band
• Physiologic trabecular pigmentation increases with age and is often maximal inferiorly
• Iris processes: fine lacy strands from iris root to trabeculum/scleral spur, normal variant
• Fine radial vessels at iris root may be normal

4. Technique points (high-yield)

• Perform in dim illumination with narrow slit beam to avoid artificial angle widening
• Use minimal lens pressure during static assessment
• Examine all 4 quadrants
• Use corneal wedge to identify Schwalbe line
• Indentation gonioscopy differentiates:
  • Appositional closure: opens with indentation
  • Synechial closure (PAS): does not open

5. Grading of angle width (Shaffer)

• Grade 4 (35-45°): wide open, closure impossible
• Grade 3 (25-35°): open, closure unlikely
• Grade 2 (~20°): narrow, closure possible
• Grade 1 (~10°): very narrow, closure probable
• Grade 0 (0°): closed

6. Abnormal gonioscopic findings

1. Peripheral anterior synechiae (PAS)
   Broad iris adhesions to angle structures, unlike fine iris processes
2. Increased trabecular pigmentation
   Pigment dispersion syndrome, pseudoexfoliation, post-inflammatory causes
3. Neovascularization of angle (NVA)
   Abnormal vessels crossing scleral spur onto trabeculum, may progress to synechial closure
4. Angle recession/traumatic signs
   Widened ciliary body band, irregular angle after blunt trauma
5. Blood in Schlemm canal
   Seen with raised episcleral venous pressure or vascular anomalies

7. Clinical relevance

8. Conclusion