Intraocular pressure does not tell you whether the angle is open. A raised pressure with a closed or occludable angle is a different disease with a different treatment, and starting a prostaglandin analogue on the number alone can leave a patient with an untreated occludable angle and a normal-looking record.
Gonioscopy is the examination, and it has a technique. Dim the room so the pupil is not constricted by ambient light, and use a short, narrow, dim slit beam kept off the pupil — a bright beam aimed through the pupil constricts it and opens an angle that is appositionally closed. Identify the scleral spur as the landmark and work round all four quadrants rather than sampling one. Where the angle looks closed, indent: indentation gonioscopy distinguishes appositional closure, which opens, from peripheral anterior synechiae, which do not, and that distinction determines whether an iridotomy will help.
This matters more here than in most of the literature. Primary angle closure disease accounts for a far larger share of glaucoma blindness in India and East Asia than in European populations, and it is the form in which sight is lost fastest. Imaging of the anterior segment supplements gonioscopy and does not replace it — the dynamic information from indentation has no imaging equivalent in routine practice.
- Perform gonioscopy before starting any pressure-lowering treatment, and record the finding by quadrant
- Dim the room and keep a narrow, dim slit beam off the pupil — a bright beam opens an appositionally closed angle
- Identify the scleral spur as the reference landmark and examine all four quadrants
- Indent where the angle appears closed, to separate appositional closure from peripheral anterior synechiae
- Treat anterior segment imaging as supplementary; it does not provide the dynamic information indentation gives
Why it matters
Treating the number without seeing the angle leaves the fastest-blinding form of glaucoma undiagnosed and the record looking normal.
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