[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Ophthalmology](https://durgical.com/en/ophthalmology/) › [The eye exam](https://durgical.com/en/ophthalmology/areas/exam/) › Gonioscopy: looking into the drainage angle # Gonioscopy: looking into the drainage angle - Examination A mirrored contact lens shows the drainage angle, which cannot be seen directly. It tells open from closed angles and guides glaucoma treatment. Updated Nov 13, 2026 **See it in 3D:** [Drainage angle](https://durgical.com/en/anatomy/iridocorneal-angle/) · [Iris](https://durgical.com/en/anatomy/iris/) · [Cornea](https://durgical.com/en/anatomy/cornea/) · [Ciliary body](https://durgical.com/en/anatomy/ciliary-body/) ## Key points - Total internal reflection hides the angle; a goniolens shows it. - From the iris root forwards: ciliary band, scleral spur, meshwork, Schwalbe line. - Indentation: opens = appositional; stays shut = synechiae. - Occludable angle: iridotomy. - Angle recession: lifelong glaucoma risk. ## What it is Light from the angle between the iris and the cornea is reflected back inside the eye (total internal reflection), so the angle cannot be seen directly. A goniolens placed on the cornea removes that barrier. Indirect gonioscopy at the slit lamp with a mirrored lens is routine, and indentation with a four-mirror lens shows whether a closed angle is only touching or stuck by adhesions. It is needed in every glaucoma suspect, a shallow anterior chamber, raised eye pressure, uveitis, blunt trauma and suspected new vessels. ## Normal values and scales - Shaffer grading runs from 4 (wide open) to 0 (closed); grades 2 or less are narrow. - An angle is called occludable when the posterior trabecular meshwork cannot be seen in at least half of its circumference. - The Van Herick slit-lamp estimate is a screen, not a substitute for gonioscopy. - Angle recession after blunt trauma (a widened ciliary body band) carries a lifelong glaucoma risk. - Heavy pigment suggests pigment dispersion or pseudoexfoliation; new vessels on the meshwork suggest neovascular glaucoma. ## How it is done - Explain the test and instil an anaesthetic drop; dim the room and use a short, narrow slit kept off the pupil so that it does not constrict. - Place the goniolens on the cornea (with coupling gel if the lens needs it) while the patient looks straight ahead. - Examine all four quadrants: each mirror shows the angle opposite to it, so the upper mirror shows the lower angle. - Identify the structures from the iris root forwards: ciliary body band, scleral spur, trabecular meshwork and Schwalbe line. - Indent with a four-mirror lens: an angle that opens is appositionally closed; one that stays shut has peripheral anterior synechiae. - Record the grade and width per quadrant, pigment, new vessels, synechiae, recession or foreign bodies, often as a drawing. - Clean the lens and check the cornea with fluorescein afterwards. ## How to interpret it - Open-angle glaucoma cannot be diagnosed without gonioscopy, because secondary and angle-closure causes look the same on the disc. - Too much light or pressing on the lens opens the angle artificially and gives a falsely reassuring result. - A confirmed occludable angle is usually treated with laser iridotomy to prevent an acute attack. ## Next step / Initial management - Shallow anterior chamber, narrow Van Herick or symptoms of intermittent closure (halos, headache in dim light): refer to ophthalmology for gonioscopy. - Occludable angle confirmed: ophthalmology discusses laser peripheral iridotomy. - Blunt trauma with hyphaema: gonioscopy once the eye has settled, then lifelong pressure checks if the angle is recessed. - Diabetes or vein occlusion with new iris vessels: urgent gonioscopy and retinal laser by ophthalmology. - Any glaucoma suspect or raised pressure: gonioscopy as part of the first assessment. ## Test yourself Think of the answer, then tap the question to see it. ## Why can the drainage angle not be seen without a goniolens? Light from the angle undergoes total internal reflection at the corneal surface. ## Which angle structures are seen from the iris root forwards? Ciliary body band, scleral spur, trabecular meshwork and Schwalbe line. ## During indentation gonioscopy, a closed angle does not open. What does it mean? Peripheral anterior synechiae (adhesions), rather than appositional closure. ## What late risk follows angle recession after blunt trauma? Glaucoma, which can appear years later, so pressure is checked for life. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/ophthalmology/gonioscopy-looking-into-the-drainage-angle/) ## Connections ## See it in 3D 4 The structures of Durgical's 3D anatomy where it is found. - [Drainage angle](https://durgical.com/en/anatomy/iridocorneal-angle/) - [Iris](https://durgical.com/en/anatomy/iris/) - [Cornea](https://durgical.com/en/anatomy/cornea/) - [Ciliary body](https://durgical.com/en/anatomy/ciliary-body/) ## Related 5 - [The anterior chamber and the drainage angle](https://durgical.com/en/ophthalmology/the-anterior-chamber-and-the-drainage-angle/) - [The slit lamp: what each light shows](https://durgical.com/en/ophthalmology/the-slit-lamp-what-each-light-shows/) - [Tonometry: measuring intraocular pressure](https://durgical.com/en/ophthalmology/tonometry-measuring-intraocular-pressure/) - [Glaucoma lasers and surgery: from iridotomy to tube shunts](https://durgical.com/en/ophthalmology/glaucoma-lasers-and-surgery-from-iridotomy-to-tube-shunts/) - [Acute angle closure: what to do before the ophthalmologist](https://durgical.com/en/ophthalmology/acute-angle-closure-what-to-do-before-the-ophthalmologist/) ## Related conditions 6 - [Acute angle-closure glaucoma](https://durgical.com/en/conditions/acute-angle-closure-glaucoma/) - [Open-angle glaucoma](https://durgical.com/en/conditions/open-angle-glaucoma/) - [Neovascular glaucoma](https://durgical.com/en/conditions/neovascular-glaucoma/) - [Pigment dispersion syndrome and pigmentary glaucoma](https://durgical.com/en/conditions/pigment-dispersion-syndrome-and-pigmentary-glaucoma/) - [Pseudoexfoliation syndrome and glaucoma](https://durgical.com/en/conditions/pseudoexfoliation-syndrome-and-glaucoma/) - [Ocular trauma: hyphema and open globe injury](https://durgical.com/en/conditions/ocular-trauma-hyphema-and-open-globe-injury/) ## In Pharmacology 1 - [Tetracaine](https://durgical.com/en/pharmacology/tetracaine/) [← All of ophthalmology](https://durgical.com/en/ophthalmology/) Educational content; not a clinical guideline and no substitute for assessment by a health professional. For sudden visual loss, severe eye pain, a chemical burn or an eye injury, go to an emergency department at once. Sources: [Gonioscopy](https://eyewiki.org/Gonioscopy) (EyeWiki (American Academy of Ophthalmology), 2025); [Acute Angle-Closure Glaucoma](https://www.ncbi.nlm.nih.gov/books/NBK430857/) (StatPearls Publishing (NCBI Bookshelf), 2026); [Pigment Dispersion Glaucoma](https://www.ncbi.nlm.nih.gov/books/NBK580495/) (StatPearls Publishing (NCBI Bookshelf), 2023). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/ophthalmology/gonioscopy-looking-into-the-drainage-angle/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/ophthalmology/gonioscopy-looking-into-the-drainage-angle/