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Describe gonioscopy with the grading of the angle.

Ophthalmology · 3rd Professional

Gonioscopy is the examination of the anterior chamber angle.
It is necessary because the angle cannot be seen directly: light from it undergoes total internal reflection at the corneal surface.
A goniolens overcomes this by replacing the cornea-air interface.
Direct gonioscopy — the KOEPPE lens gives an erect, direct view; it needs the patient supine and a hand-held microscope, and is used chiefly in examination under anaesthesia in children

Structure, anterior to posterior	Appearance
Schwalbe’S line	The termination of Descemet membrane; a fine glistening ridge. It is identified by the corneal wedge — the point where the two limbs of a narrow slit beam meet — which is the reliable way to orientate oneself in a narrow angle
Trabecular meshwork	A ground-glass band; the anterior portion is non-pigmented and non-functional, and the posterior portion is pigmented and is where filtration occurs. It is the posterior pigmented meshwork whose visibility defines an open angle
Scleral spur	A prominent white line, the most reliable landmark in the angle; it is the anterior lip of the scleral sulcus and the insertion of the longitudinal ciliary muscle
Ciliary body band	A grey-brown band; its width is abnormally increased in angle recession.
Iris root and processes	Fine iris processes crossing to the scleral spur are normal; broad sheets adherent to the cornea are peripheral anterior synechiae

Shaffer grade	Angle width and interpretation
Grade 4	35 to 45 degrees; wide open; ciliary body band easily seen. Closure impossible
Grade 3	20 to 35 degrees; open; scleral spur visible. Closure impossible
Grade 2	20 degrees; narrow; only the trabecular meshwork visible. Closure possible
Grade 1	10 degrees; extremely narrow; only Schwalbe line and perhaps the top of the meshwork. Closure probable
Grade 0 (slit)	Closed; no angle structures visible; iridocorneal contact may be present

Perform gonioscopy on every glaucoma patient and suspect; it decides the classification and therefore the entire treatment
Use indentation to separate appositional from synechial closure; only the first will be relieved by an iridotomy
Keep the beam off the pupil and the room dim; light constricts the pupil and opens the angle, giving a falsely reassuring view
Do not press with a Goldmann lens; inadvertent indentation opens a narrow angle and conceals the diagnosis
Find the scleral spur first; it is the most reliable landmark, and the corneal wedge locates Schwalbe line in a difficult angle

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