Occludable Angle - Stages and Classification

The term "occludable angle" refers to an angle at risk of iridotrabecular contact (ITC) blocking aqueous outflow. The classification has evolved from symptom-based to a disease-stage model based on gonioscopic findings, IOP, and optic nerve status.

A. AIGS Disease-Stage Classification (Kanski's, 10th ed.)

This is the consensus scheme recommended by the Association of International Glaucoma Societies and is the most clinically relevant staging system:

Stage 1: Primary Angle-Closure Suspect (PACS)

Shallow axial anterior chamber depth (eclipse sign positive - crescentic shadow on nasal iris)
Gonioscopy: ITC in 3 or more quadrants but no PAS and no raised IOP
Lower threshold: 2 quadrants of ITC + pigment smudging (signs of intermittent closure)
Normal IOP, optic disc, and visual field
AS-OCT confirms an occludable angle
Risk of progression to overt angle-closure disease is low

Stage 2: Primary Angle Closure (PAC)

Gonioscopy: ITC in 3 or more quadrants PLUS raised IOP and/or PAS (assessed by indentation gonioscopy)
Normal optic disc and visual field (no glaucomatous damage yet)
Subcategory: non-ischaemic vs. ischaemic PAC (the latter shows iris changes or glaukomflecken from prior severe IOP elevation)

Stage 3: Primary Angle-Closure Glaucoma (PACG)

ITC in 3 or more quadrants
Glaucomatous optic neuropathy present (structural and/or functional damage)
Note: Optic nerve damage from acute angle closure may not show typical cupping

B. Shaffer Gonioscopic Grading System

The most widely used grading system for angle width:

Grading of angle width by visible structures - Kanski's

Fig. 11.31 - Kanski's Clinical Ophthalmology, 10th ed.

Grade	Angle	Structures visible	Clinical significance
4	35-45°	Ciliary body visible without lens tilt	Widest; seen in myopia/pseudophakia - closure not possible
3	25-35°	Scleral spur visible	Open angle - closure not possible
2	20°	Trabecular meshwork only (no scleral spur)	Closure possible - gonioscopy mandatory
1	10°	Schwalbe line ± top of trabeculum	Very narrow - closure probable
Slit	-	No iridocorneal contact but no structures seen	Dangerously narrow
0	0°	Iridocorneal contact present	Closed (appositional vs. synechial distinguished by indentation)

Grades 0-1 (and slit) are occludable. Grade 2 is potentially occludable.

C. Van Herick Slit-Lamp Grading (Screening Tool)

Compares peripheral anterior chamber depth to corneal thickness:

Grade	AC depth : Corneal thickness	Clinical interpretation
4	≥ 1 (equal or greater)	Wide open
3	1/4 - 1/2	Incapable of closure
2	= 1/4	Angle closure possible - formal gonioscopy needed
1	< 1/4	Gonioscopy will usually show a dangerously narrow angle

Important caveat: Van Herick overestimates angle width in plateau iris configuration. It is a screening tool only - not a substitute for gonioscopy.

D. Wills Eye Manual - Spaeth System Guidelines for Occludability

The Spaeth system encodes iris insertion (A/B/C/D/E), angular approach, and peripheral iris curvature. General guidelines for occludability:

Definite occludable angles include:

Any angle narrower than 10 degrees
Any "p" (posterior bowing) iris configuration

Potentially occludable angles include:

Any angle narrower than 20 degrees
Any "B" (behind Schwalbe line) iris insertion

Examples:

C15b 2+ ptm = Open but narrow, occludable angle
A40f = Closed angle
(B)D30p 0 ptm = Open, atypical narrow angle, occludable with dilation

Key Points

The primary staging framework is PACS → PAC → PACG based on presence of ITC, PAS, IOP elevation, and optic nerve damage
Shaffer grades 0 and 1 are definitively occludable; grade 2 is potentially occludable
Van Herick grade ≤ 2 warrants formal gonioscopy
Indentation gonioscopy distinguishes appositional (reversible) from synechial (permanent) closure - a management-critical distinction

Sources: Kanski's Clinical Ophthalmology: A Systematic Approach, 10th ed. (pp. 389-390); The Wills Eye Manual, pp. 1132-1134

This is a shared conversation. Sign in to Orris to start your own chat.