Glaucoma

What is gonioscopy and why is it done?

Gonioscopy is an examination of the drainage angle, where fluid leaves the eye. After a numbing drop, a small mirrored lens is placed gently against the surface of the eye at the slit lamp so the angle can be seen. It takes a minute or two per eye and decides whether glaucoma is the open angle or angle closure type.

Why the angle matters so much

Open angle and angle closure glaucoma look similar on a pressure reading but need different treatment. Angle closure may be treated with a laser opening in the iris or with cataract surgery to deepen the angle, while open angle glaucoma is usually managed with pressure lowering drops, laser to the drainage tissue or drainage surgery. Without gonioscopy the wrong path can be chosen.

What it feels like

The anaesthetic drop stings for a second and then the eye feels numb. You may feel light pressure and see bright reflections. It is not painful. Vision may be slightly blurred for a few minutes from the gel used with the lens.

What is found

An open angle, where the drainage structures are clearly visible
A narrow or occludable angle, which carries a risk of an acute attack and may need preventive laser
A closed angle, where iris tissue blocks the drainage structures
Additional findings such as scarring, pigment, new blood vessels or damage after injury, which point to secondary glaucoma

Frequently asked questions

How often is gonioscopy repeated?: It is done at diagnosis and then repeated periodically, because angles narrow gradually with age and as the natural lens thickens.
Can it be replaced by a scan?: Imaging of the front of the eye can support the assessment, but a careful gonioscopy examination remains the practical reference for grading the angle.

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