Gonioscopy
Principles, Methods & Classification of the Anterior Chamber Angle
Examination question · ~800 words
What is gonioscopy? Discuss its optical principles, instruments and techniques, grading systems for the anterior chamber angle, and clinical and surgical applications.
Try to outline your answer mentally before expanding sections below.
Gonioscopy is the gold-standard clinical technique for direct visualisation of the iridocorneal angle — a region inaccessible to direct observation due to total internal reflection at the corneal surface. It is indispensable in glaucoma diagnosis and management, providing anatomical grading, pathological characterisation, and laser/surgical planning. A thorough understanding of its optical principles, instrument types, grading systems, and clinical applications is essential for the PG ophthalmology candidate.
The angle structures cannot be seen directly because of total internal reflection (TIR) at the air–cornea interface.
- Critical angle of the cornea ≈ 46° (Snell's law: n₁ sin θc = n₂).
- Light from the angle reaches the cornea at > 46°, undergoes TIR, and is internally reflected back — angle is invisible.
- Gonioscopy eliminates the air–cornea interface either by placing an index-matched contact lens directly on the cornea (direct gonioscopy) or by using a mirror to redirect the internally reflected beam (indirect gonioscopy).
- Contact lenses use coupling fluid (saline / methylcellulose) with RI ≈ 1.336, eliminating the interface.
Analogy: Total internal reflection is like a one-way mirror from beneath a swimming pool. Gonioscopy is like using a periscope or eliminating the water–air surface to look sideways at the pool wall.
A. Direct Gonioscopy
| Feature | Direct Gonioscopy |
|---|---|
| Principle | Eliminates TIR — direct view of angle |
| Instrument examples | Koeppe, Barkan, Wurst, Richardson-Shaffer |
| Magnification source | Operating microscope / loupe / slit-lamp (indirect) |
| Position | Supine (usually) |
| Image orientation | Upright, non-reversed — true anatomical view |
| Lens FOV | One quadrant at a time (monocular); panoramic (binocular) |
| Best for | Paediatric exam under GA, surgical gonioscopy (goniotomy), research |
| Limitation | Requires supine position, coupling fluid pool, cumbersome in clinic |
B. Indirect Gonioscopy
Uses a mirror or prism to redirect TIR light out through a different portion of the cornea, allowing slit-lamp examination in the sitting patient. Image is laterally reversed.
| Feature | Single Mirror (e.g. Goldmann 1-mirror) | 3-Mirror (Goldmann) | 4-Mirror (Zeiss / Posner / Sussman) |
|---|---|---|---|
| Mirrors | 1 | 3 (+ central lens) | 4 |
| Angle view | One quadrant per position | One quadrant per position | All 4 quadrants (sequential) |
| Coupling fluid | Required | Required | NOT required |
| Indentation possible | No | No | YES (narrow lens) |
| FOV angle | ~62° | ~59° (mirror) | ~64° |
| Lens contact area | Large | Large | Small |
| Best use | Laser trabeculoplasty | Peripheral retinal exam + angle | Indentation gonioscopy, quick 4Q screen |
| Image orientation | Reversed | Reversed | Reversed |
Koeppe Lens
- Classic direct goniolens; dome-shaped; RI = 1.49 (glass).
- Available in multiple sizes: infant (16 mm), small adult (17 mm), adult (18 mm).
- Placed on supine patient's cornea with saline pool.
- Binocular use with operating microscope → panoramic simultaneous view of all quadrants.
- Preferred for goniotomy (Barkan membrane incision) — binocular stereoscopic view during surgery.
Goldmann 3-Mirror Lens
- Central convex lens for posterior pole; 3 mirrors angled at 59°, 66° (often taught as 67°), and 73° for angle/near-ora fundus, peripheral retina/ora serrata, and equatorial or mid-peripheral retina.
- 59° mirror (smallest, semicircular) = gonioscopy / iridocorneal angle view; it can also show the vitreous and fundus near the ora serrata.
- Requires coupling fluid (methylcellulose / sodium hyaluronate).
- Large contact lens → cannot perform indentation → cannot distinguish appositional from synechial closure.
Zeiss 4-Mirror Lens (Posner / Sussman variants)
- 4 mirrors at 64° each, arranged at 90° intervals → all 4 quadrants sequenced without rotation.
- Small contact area → does NOT require coupling fluid → easy to use, quick.
- Indentation gonioscopy possible due to small lens diameter (9 mm) — key clinical advantage.
- Posner = slightly larger with handle; Sussman = smaller, handheld.
For indentation gonioscopy (differentiating appositional vs synechial closure), always use the Zeiss / Posner / Sussman 4-mirror lens. The large Goldmann lens cannot be indented.
From anterior → posterior (Schwalbe's line to ciliary body band):
| Structure | Appearance | Clinical Significance |
|---|---|---|
| Schwalbe's Line (SL) | Thin white / glistening ridge = termination of Descemet's membrane | Anteriormost landmark; PAS extend to SL in early PACG |
| Trabecular Meshwork (TM) | Anterior (non-pigmented) + Posterior (pigmented) bands | Pigmented TM = zone of Schlemm's canal; pigmentation variable |
| Scleral Spur (SS) | Bright white band; most reliable landmark | Posterior attachment of TM; ciliary body attaches here |
| Ciliary Body Band (CBB) | Grey-brown band posterior to SS | Widened in myopia, trauma, angle recession |
| Iris Root | Last visible structure | Insertion site relative to SS determines angle width |
| Sampaolesi's Line | Pigment anterior to SL on cornea | Exfoliation glaucoma hallmark; also seen in PDS |
| Blood vessels | Radial / circumferential at CBB | Abnormal NV vessels = NVG; normal = no anastomosis on spur |
A. Shaffer Grading System (Most Widely Used)
Based on angular width of the angle recess (degrees between TM and iris surface). Uses the posterior TM as one reference point.
| Grade | Angle Width | Structures Visible | Clinical Interpretation |
|---|---|---|---|
| 4 | 35–45° | Ciliary body band wide | Wide open; closure impossible |
| 3 | 25–35° | Scleral spur visible | Open; closure improbable |
| 2 | 20° | TM visible; SS not seen | Moderately narrow; closure possible |
| 1 | ≤10° | Only SL / upper TM visible | Very narrow; closure very likely |
| 0 (S) | 0° | No structures / iris contacts TM | Closed angle |
B. Scheie Classification (Older)
| Grade | Description |
|---|---|
| Wide open | All structures visible |
| Grade I | Difficult to see over iris root; CBB partially seen |
| Grade II | Ciliary body not visible |
| Grade III | Posterior TM not visible |
| Grade IV | Only SL visible |
Memory tip — Scheie vs Shaffer: Scheie uses Grade I–IV with Grade IV being the MOST closed (narrow) — opposite direction to Shaffer (Grade 4 = most open). This is a classic exam trap!
C. Spaeth Classification (Most Detailed)
Describes three parameters independently — most comprehensive for clinical documentation:
- Angular width (10°, 20°, 30°, 40°) — similar to Shaffer.
- Iris insertion level: A = anterior to SL (rare, aniridia); B = behind SL; C = at SS; D = deep (on CBB); E = extremely deep (beyond CBB).
- Iris profile (Spaeth 1971 original notation): r = regular flat; s = steep convex (pupil block / plateau iris); q = queer (concave / reverse pupil block — pigmentary glaucoma). Modern SGGS uses f = flat, b = bowing anteriorly (1–4+), p = plateau, c = concave — both conventions are in use.
- Example notation: 40° D r = wide open angle, iris inserts on CBB, flat iris profile.
The 'q' (concave / reverse) iris profile — or 'c' in modern SGGS — is the classic gonioscopic finding in Pigmentary Glaucoma. Posterior bowing of the iris causes lens–iris contact and mechanical rubbing of the posterior pigmented epithelium against lens zonules.
Principle: Gentle central corneal pressure forces aqueous into the angle, opening appositional closure. If PAS are present, the angle remains closed despite indentation.
- Instrument: Zeiss / Posner / Sussman 4-mirror lens ONLY.
- Technique: Light central pressure → aqueous pushed into angle periphery.
- Appositional closure: opens on indentation (reversible).
- Synechial closure (PAS): does NOT open on indentation (irreversible).
- Critical for deciding between laser PI (appositional) vs goniosynechiolysis (synechial).
- Also helps differentiate plateau iris from pupil block: plateau iris remains closed despite PI; persistent narrow angle on indentation confirms plateau iris configuration.
Viva trap: Can the Goldmann 3-mirror lens be used for indentation gonioscopy? NO — its large footplate cannot indent the central cornea effectively. Always use the small-diameter Zeiss-type lens.
| Condition | Key Gonioscopic Finding |
|---|---|
| POAG | Open angle; increased TM pigmentation; no pathognomonic finding |
| PACG | Narrow / closed angle; PAS (superiorly > inferiorly); appositional or synechial |
| Pseudoexfoliation (PXF) | Sampaolesi's line (pigment anterior to SL); patchy TM hyperpigmentation; PXF material on TM |
| Pigmentary Glaucoma (PDS) | Dense, uniform, homogeneous TM pigmentation (especially inferiorly); Sampaolesi's line; concave iris profile |
| Neovascular Glaucoma (NVG) | Fine NV vessels on angle (early); fibrovascular membrane → zip-like PAS; angle closes from below upward |
| Angle Recession Glaucoma | Widened CBB (torn ciliary body); irregular angle; abnormal band between SS and iris insertion; look for hyphaema |
| Traumatic cyclodialysis | Direct communication between AC and suprachoroidal space; dark cleft posterior to SS; hypotony |
| Juvenile Open-Angle Glaucoma | Open angle; prominent insertion of uveal meshwork — 'wine-glass' or bushy appearance |
| ICE syndrome | Beaten-metal appearance of corneal endothelium; broad PAS; ectropion uvea; endothelialization of angle |
| Aniridia | Rudimentary iris stub; adherent to TM; progressive angle closure; glaucoma in ~50% |
| Axenfeld-Rieger | Prominent SL (posterior embryotoxon); iris strands bridging to SL; angle dysgenesis |
| Peters anomaly | Central corneal opacity; absent Descemet; iris-corneal adhesions; iridocorneal strands |
- Goniotomy: incision of Barkan membrane under direct gonioscopic view (Koeppe lens) — for congenital glaucoma.
- Trabeculotomy: external approach; gonioscopy confirms correct TM plane entry.
- Goniosynechiolysis: sweeping PAS under gonioscopic view with viscoelastic.
- Ab-interno trabeculectomy (Trabectome, KDB goniotomy): gonioscopy-guided TM removal; angle view via Swan-Jacob or similar surgical gonioprism.
- iStent / Hydrus MIGS: Schlemm's canal cannulation under gonioscopic guidance using operative gonioprism (Swan-Jacob lens).
- Laser Trabeculoplasty (ALT / SLT): Goldmann 1-mirror or Ritch trabeculoplasty lens used to deliver laser to posterior TM under slit-lamp.
- Laser peripheral iridotomy (LPI): gonioscopy post-LPI to confirm angle opening.
Operative gonioprisms: Swan-Jacob, Hill, Volk G-6 — provide a clear, magnified, undistorted intraoperative angle view through the operating microscope. Essential for MIGS procedures.
- Use dim room illumination — bright light causes pupil miosis → angle artificially deepened.
- Use narrow, short slit beam — broad beam causes pupil constriction.
- Corneal topography artefact: pressure on cornea → Descemet folds → distorted view; use minimal pressure.
- Always document: angle width (Shaffer grade), pigmentation (0–4+ scale), PAS (clock hours and extent), NV vessels, recession, pathological deposits.
- 4-quadrant examination mandatory: superior angle consistently narrowest (due to thicker peripheral iris superiorly).
- Record TM pigmentation using Scheie pigmentation grading: 0 = no pigment; 1+ = faint; 2+ = moderate anterior; 3+ = dense posterior; 4+ = all TM obscured.
| Parameter | Gonioscopy | UBM | AS-OCT |
|---|---|---|---|
| Gold standard | Yes — for angle | For post-iris structures | Anterior angle screening |
| Dynamic assessment | Yes (indentation) | Yes (with probe) | No (non-contact) |
| Corneal contact | Yes | Yes (immersion) | No |
| View behind iris | No | Yes (ciliary body, lens zonules) | No |
| Quantitative data | Limited (grading) | Limited | Excellent (AOD, TISA, ARA) |
| In media opacity | Limited | Good | Poor |
| Clinical use | Diagnosis, treatment guidance | Plateau iris, cysts, UBM-guided MIGS | Mass screening, follow-up |
AS-OCT angle parameters: AOD 500/750 (angle opening distance at 500/750 µm from SS), TISA 500/750 (trabecular-iris space area), ARA (angle recess area), TIA (trabecular iris angle). Superior angle is consistently the narrowest quadrant — assess all four quadrants on gonioscopy.
Trap 1 — FALSE
“The critical angle for TIR at the corneal surface is approximately 42°.”
The critical angle at the air–cornea interface is approximately 46° — not 42° or 48°. Light striking the cornea at > 46° undergoes total internal reflection and cannot reach the observer without a gonioscopy lens to eliminate the air–cornea interface.
Trap 2 — FALSE
“Scheie Grade IV and Shaffer Grade 4 both describe the widest (most open) angle.”
The two systems go in OPPOSITE directions. Scheie Grade IV = most closed (only Schwalbe's line visible); Shaffer Grade 4 = most open (35–45°). Mis-direction between these two systems is a classic exam trap.
Trap 3 — FALSE
“Indentation gonioscopy can be performed with either the Goldmann 3-mirror or the Zeiss / Posner / Sussman 4-mirror lens.”
Indentation gonioscopy can ONLY be performed with the Zeiss / Posner / Sussman 4-mirror lens (9 mm contact, small footplate). The Goldmann 3-mirror has a large contact lens and cannot effectively indent the central cornea to distinguish appositional from synechial closure.
Trap 4 — FALSE
“TM pigmentation in pigment dispersion syndrome (PDS) is patchy and irregular, while pseudoexfoliation (PXF) gives uniform dense pigmentation.”
It is the other way around. PDS produces homogeneous, uniform, dense TM pigmentation that is heaviest inferiorly (convection-current driven). PXF produces patchy, irregular pigmentation and is classically associated with Sampaolesi's line — pigment deposited at and anterior to Schwalbe's line.
Trap 5 — FALSE
“In neovascular glaucoma the angle closes from superior to inferior.”
NVG angle closes from below upward (inferior → superior) — zip-like PAS formation as the fibrovascular membrane contracts across the angle.
Trap 6 — FALSE
“In angle recession the entire ciliary body detaches from the scleral spur.”
Angle recession is a longitudinal tear between the circular and longitudinal fibres of the ciliary muscle, widening the ciliary body band on gonioscopy. Detachment of the longitudinal fibres from the scleral spur (with communication between the anterior chamber and the suprachoroidal space) is cyclodialysis — a different entity causing hypotony.
Trap 7 — FALSE
“The Spaeth 'q' iris profile corresponds to plateau iris configuration.”
Spaeth 'q' (queer / concave) iris profile corresponds to pigmentary glaucoma (reverse pupillary block, concave iris). The 's' profile (steep convex anteriorly) corresponds to plateau iris or classical pupillary block. In the modern SGGS these are denoted 'c' (concave) and 'b' (bowing anteriorly) respectively.
Trap 8 — FALSE
“MIGS procedures such as iStent and Hydrus use the standard clinical Zeiss 4-mirror lens for intraoperative angle visualisation.”
For MIGS procedures (iStent, Hydrus, KDB goniotomy, Trabectome), the surgeon uses a dedicated operative gonioprism — typically a Swan-Jacob, Hill, or Volk G-6 lens — which is designed for use under the operating microscope. The standard clinical Zeiss 4-mirror is a slit-lamp lens and is not used intraoperatively.
Trap 9 — FALSE
“Pigmentation is the most reliable gonioscopic landmark for identifying the scleral spur.”
The scleral spur is the single most reliable gonioscopic landmark because it appears as a bright white band regardless of pigmentation. Pigmentation of the trabecular meshwork is highly variable and an unreliable guide.
Trap 10 — FALSE
“Posterior embryotoxon always indicates Axenfeld anomaly or Axenfeld-Rieger syndrome.”
Posterior embryotoxon (a prominent / anteriorly-displaced Schwalbe's line) is a normal variant in roughly 8–15% of the general population. It is pathological only when accompanied by iris strands bridging to the prominent Schwalbe's line (Axenfeld anomaly) or additional systemic features (Axenfeld-Rieger syndrome).
Q: Why is the superior angle consistently narrower than the inferior angle on gonioscopy?
A: The peripheral iris is thicker superiorly because of greater bulk of iris stroma under the upper lid, and the superior portion of the ciliary body sits slightly more anteriorly. In addition, gravity causes the lens-iris diaphragm to sag slightly inferiorly in the upright patient. The net effect is that the iridocorneal angle is narrowest superiorly — making the superior quadrant the highest-risk location for appositional closure and the first quadrant to form PAS in primary angle-closure disease.
Q: How do you differentiate angle recession from cyclodialysis on gonioscopy?
A: Angle recession shows a widened, irregular ciliary body band (CBB) — the iris root appears displaced posteriorly relative to the scleral spur, with a deepened angle recess between the spur and the iris insertion. There is no direct communication with the suprachoroidal space and IOP tends to be normal or elevated. Cyclodialysis shows an overt dark cleft between the scleral spur and the ciliary body — a direct open communication between the anterior chamber and the suprachoroidal space — and is classically associated with hypotony. Angle recession is a tear between the circular and longitudinal ciliary muscle fibres; cyclodialysis is disinsertion of the longitudinal fibres from the scleral spur.
Q: A patient with PACG undergoes LPI but still shows a narrow angle on gonioscopy. What is the most likely diagnosis and how will you confirm it?
A: The most likely diagnosis is plateau iris configuration. After a patent laser peripheral iridotomy abolishes any pupillary-block component, the peripheral iris remains anteriorly displaced because the ciliary processes are rotated forward, pushing the peripheral iris forward against the trabecular meshwork. Confirmation: indentation gonioscopy shows persistent peripheral iris–TM contact despite aqueous being pushed into the angle periphery (the classic 'double hump sign'). Ultrasound biomicroscopy (UBM) is diagnostic — it shows anterior ciliary body rotation with anteriorly positioned ciliary processes supporting the peripheral iris. Management is argon laser peripheral iridoplasty and long-term pilocarpine or LASERplasty if iridoplasty fails.
Q: Describe the mechanism of Sampaolesi's line formation in PXF.
A: In pseudoexfoliation (PXF) syndrome, abnormal fibrillogranular exfoliation material is produced at multiple intraocular sites and, along with dispersed iris-pigment-epithelium melanin (liberated during iridolenticular rubbing), is carried by aqueous convection currents into the anterior chamber. Gravity and the inferior flow of aqueous deposit this pigment on the trabecular meshwork — heavier inferiorly — and, crucially, anterior to Schwalbe's line where it accumulates as a brown pigmented band on the peripheral cornea. This deposit anterior to Schwalbe's line is Sampaolesi's line. It is not pathognomonic of PXF — it is also seen in pigment dispersion syndrome — but is one of the earliest gonioscopic findings in PXF and is often the most inferior quadrant's earliest sign.
Q: What is the difference between appositional and synechial closure? How does indentation gonioscopy help?
A: Appositional closure is a reversible apposition of the peripheral iris against the trabecular meshwork with no scarring — typically caused by pupillary block, plateau iris configuration, or ciliochoroidal effusion. Synechial closure (peripheral anterior synechiae, PAS) is an irreversible fibrotic adhesion between the peripheral iris and the trabecular meshwork / cornea. Indentation gonioscopy differentiates the two: gentle central pressure with a Zeiss / Posner / Sussman 4-mirror lens forces aqueous into the periphery. Appositional closure opens and angle structures become visible; synechial closure does not open and the PAS remain visible. This distinction is critical for management — appositional closure responds to laser peripheral iridotomy, whereas synechial closure requires goniosynechiolysis, filtration surgery, or medical IOP lowering.
A 32-year-old myope presents with IOP of 32 mmHg and dense, homogeneous inferior TM pigmentation with a concave iris profile on gonioscopy. Explain the complete pathophysiological mechanism linking his myopia to his glaucoma. How does the 'reverse pupillary block' mechanism differ from classical pupillary block, and what gonioscopic manoeuvre could confirm it? What is the role of the pigment paradox in this condition, and how does pharmacological miosis paradoxically worsen the situation?
Diagnosis
This patient has Pigment Dispersion Syndrome (PDS) / Pigmentary Glaucoma. The mechanism in myopes involves a larger lens diameter relative to anterior segment size, causing the peripheral iris to bow posteriorly (concave configuration, Spaeth 'q' profile; 'c' in modern SGGS). This brings the posterior pigmented iris epithelium into contact with the anterior lens zonules during accommodation / pupillary movement — causing mechanical abrasion and release of pigment granules. Pigment is deposited on the TM (dense, uniform, inferior > superior due to convection currents), Schwalbe's line (Sampaolesi's line), corneal endothelium (Krukenberg spindle), lens (Zentmayer ring / Scheie stripe), and anterior vitreous.
Reverse pupillary block vs classical pupillary block
In classical pupillary block: iridolenticular apposition raises the posterior-chamber pressure above the anterior-chamber pressure, causing anterior bowing of the iris and narrowing of the angle. In reverse pupillary block (PDS): anterior-chamber pressure is transiently higher than posterior-chamber pressure — each blink and each pupillary movement burps a small volume of aqueous from posterior to anterior chamber. A flap-valve effect at the iris margin prevents back-flow, so the peripheral iris is sucked backward, producing the concave iris configuration and iris–zonule contact.
Gonioscopic confirmation
Direct gonioscopy reveals a Spaeth 'q' (or modern 'c') iris profile — peripheral iris concavity with posterior iris surface contacting the anterior zonules. The finding is often dynamic and exaggerated in light / by accommodation and is abolished after laser peripheral iridotomy. Ultrasound biomicroscopy (UBM) is confirmatory — it directly visualises posterior iris bowing and iris–zonule apposition in the posterior chamber.
Pigment paradox and pilocarpine
The 'pigment paradox' in pigmentary glaucoma refers to the clinical observation that IOP does not correlate linearly with the total pigment burden or the degree of iris transillumination — instead, IOP spikes follow acute pigment-release events (exercise, pupillary dilatation) and the IOP tends to decline in older patients as pigment-liberation events subside. Pharmacological miosis with pilocarpine actually REDUCES pigment release because the constricted pupil flattens the peripheral iris and pulls it forward away from the zonules, abolishing iridozonular contact. However, pilocarpine is generally avoided in this cohort — most are young, highly-myopic patients in whom pilocarpine causes accommodative spasm, worsening of myopia, headache, and a recognised increased risk of rhegmatogenous retinal detachment. Laser peripheral iridotomy equalises the trans-iris pressure gradient and reverses the concave iris configuration on UBM; however, long-term evidence that LPI alters visual-field progression or the natural history of the disease is limited, so it is a mechanism-specific but not proven disease-modifying intervention.
References
- Kanski JJ, Bowling B. Clinical Ophthalmology: A Systematic Approach. 8th ed. Elsevier Saunders; 2016.
- Yanoff M, Duker JS. Ophthalmology. 5th ed. Elsevier; 2019.
- Allingham RR, Damji KF, Freedman S, Moroi SE, Rhee DJ, Shields MB. Shields' Textbook of Glaucoma. 6th ed. Lippincott Williams & Wilkins; 2011.
- Spaeth GL. The normal development of the human anterior chamber angle: a new system of descriptive grading. Trans Ophthalmol Soc UK. 1971;91:709-739.
- Shaffer RN. A new classification of the glaucomas. In: Newell FW, ed. Glaucoma: Transactions of the First Conference. 1956.
- Scheie HG. Width and pigmentation of the angle of the anterior chamber. AMA Arch Ophthalmol. 1957;58(4):510-512.
- Kumar A. Principles and Practice of Ophthalmology. 3rd ed. Jaypee Brothers; 2014.
- American Academy of Ophthalmology. Basic and Clinical Science Course: Glaucoma. Section 10. 2022-23.
- Liebmann JM, Ritch R. Gonioscopy. In: Ritch R, Shields MB, Krupin T, eds. The Glaucomas. Mosby; 1996.
- Nolan WP, Aung T, et al. Anterior segment imaging: gonioscopy versus AS-OCT. Surv Ophthalmol. 2007;52(2):143-148.
- Tello C, Liebmann JM, Ritch R. An improved coupling medium for laser goniotomy. Ophthalmic Surg. 1993.
- Allingham RR, Damji KF, Freedman S, et al. Shields' Study Guide and Review for Glaucoma. Lippincott; 2011.