Gonioscopy: How We Measure the Eye’s Drainage Angles and Assess Glaucoma Risk

Gonioscopy is a quick, specialized eye examination used to evaluate the eye’s internal drainage system, known as the anterior chamber angle. This angle is located where the cornea—the clear front surface of the eye—meets the iris, the colored part of the eye.

Fluid continuously circulates through the front of the eye and normally drains through tissue located within this angle. When the drainage angle becomes narrow, blocked, damaged, or abnormal, pressure may build inside the eye and increase the risk of glaucoma.

Eye doctor performs gonioscopy on seated patient in bright clinic; charts and diagram label open, narrow, and closed angles.

Why Is Gonioscopy Performed?

Gonioscopy helps your eye doctor determine whether the drainage angle is:

• Open and functioning normally

• Narrow and at risk of closing

• Partially or completely closed

• Damaged by a previous eye injury

• Affected by abnormal pigment, inflammation, scar tissue, or new blood vessels

The examination is especially important when evaluating glaucoma, elevated eye pressure, a history of eye trauma, or an unusually shallow anterior chamber. Gonioscopy remains the standard clinical examination for distinguishing open-angle from angle-closure disease.

What Should You Expect?

Before the examination, your eye doctor places a numbing drop in the eye. A small mirrored contact lens, called a gonioscopy lens, is then gently placed on the eye while you sit at the slit-lamp microscope.

The lens allows the doctor to see the drainage angle, which cannot be viewed directly during a routine eye examination because of the way light travels through the cornea. The test usually takes only a few minutes and should not be painful, although you may notice mild pressure from the lens.

Identify the angle structures

When performing gonioscopy, you identify the angle structures from posterior (deepest) to anterior (most superficial). Remember the mnemonic:

"I See The Ciliary Body" (or I See TM CB)

1. Iris Root

   • Most anterior structure.

   • Last structure encountered before the angle closes.

   • Broad or steep insertion may suggest plateau iris or congenital abnormalities.

2. Scleral Spur (SS)

   • Bright white line.

   • Important landmark separating the trabecular meshwork from the ciliary body.

   • Often the easiest landmark to identify in normal eyes.

3. Trabecular Meshwork (TM)

   • Divided into:

     • Anterior (non-pigmented) TM – little aqueous outflow.

     • Posterior (pigmented) TM – primary site of aqueous drainage.

   • Increased pigmentation may be seen in pigment dispersion syndrome or pseudoexfoliation.

4. Schwalbe's Line (SL)

   • Thin glistening line marking the termination of Descemet's membrane.

   • Most anterior angle landmark.

   • Can be highlighted using the corneal wedge technique.

5. Ciliary Body Band (CBB)

   • Brown or gray band posterior to the scleral spur.

   • Width varies with iris insertion:

     • Wide in myopes.

     • Narrow or absent in hyperopes.

   • Very wide CBB may indicate angle recession after trauma.

Shaffer Grading System

This grades the angular width, estimating the risk of angle closure.

Shaffer GradeAngle WidthVisible StructuresRisk of Closure
4	35–45°	Ciliary body band visible	Impossible
3	25–35°	Scleral spur easily visible; often CBB	Very unlikely
2	~20°	Trabecular meshwork visible	Possible
1	~10°	Schwalbe's line only	High risk
0	0°	No angle structures visible	Closed angle

Spaeth Classification (More Comprehensive)

For documentation, many glaucoma specialists also use the Spaeth classification, which includes:

• Level of iris insertion (A–E)

• Angular width (10–40°)

• Iris configuration (r = regular, s = steep, q = queer/concave, etc.)

• Pigmentation (0–4+)

Example:

• D40r 2+

  • Iris inserts at the deep scleral spur.

  • 40° angle.

  • Regular iris contour.

  • Moderate pigmentation.

Clinical Pearls

• Normal open angle: Pigmented TM, scleral spur, and usually a ciliary body band are visible (Shaffer 3–4).

• Occludable angle: Posterior TM is not visible in ≥180° of the angle.

• Angle recession: Abnormally wide ciliary body band.

• Pigment dispersion syndrome: Dense, homogeneous pigmentation of the TM.

• Pseudoexfoliation syndrome: Patchy TM pigmentation, often greatest inferiorly.

• Neovascular glaucoma: Fine blood vessels crossing the scleral spur onto the TM.

• Peripheral anterior synechiae (PAS): Permanent iris adhesions to the angle structures, unlike temporary appositional closure.

A systematic gonioscopy exam should evaluate all four quadrants, document the deepest visible structure, assign a Shaffer grade, note pigmentation, identify any PAS, angle recession, neovascularization, or other abnormalities, and determine whether indentation gonioscopy is needed to distinguish appositional from synechial angle closure.

Why Gonioscopy Matters

Many changes within the drainage angle do not cause early symptoms. Gonioscopy can identify patients at risk for angle closure and help determine the correct type of glaucoma treatment.

Sudden angle closure may cause severe eye pain, redness, blurry vision, headache, nausea, or vomiting. These symptoms require immediate medical attention because vision loss can occur quickly without treatment.

At OPT-ISM Eye Care, gonioscopy may be included as part of a comprehensive glaucoma evaluation when clinically indicated. Examining the drainage angle gives us important information that cannot be obtained from eye-pressure measurements alone.