When we are checking someone for glaucoma in the clinic, one quiet but crucial step is gonioscopy. Patients often see me place a small lens on the eye and ask, “Doctor, what exactly are you looking at?”
That little lens lets us see the drainage angle of the eye directly. Without this gonioscopy test, we are partially guessing about the type and risk of glaucoma.
What Is Gonioscopy?
Gonioscopy is a specialized procedure which we perform with a contact lens that has mirrors (a gonioscope) and a slit lamp to look at the drainage angle in the eye.
At that point which is where the clear front structure of the eye (cornea) meets the colored part (iris) we find the anterior chamber angle which has what we call key gonioscopy structures including the trabecular meshwork, the scleral spur, and the ciliary body band which play a role in how the eye’s fluid (aqueous humor) exits the eye.
If this outflow is reduced, blocked or out of the ordinary eye pressure goes up which in turn may cause damage to the optic nerve and lead to glaucoma.
Why Gonioscopy Matters for Glaucoma
From the perspective of glaucoma we do not have a choice with gonioscopy; it is a basic component of a full exam
It also does:
- Determine the type of angle you have open, narrow, or closed (angle closure risk).
- We differentiate between open angle glaucoma, angle closure glaucoma, and secondary glaucomas (pigmentary, pseudoexfoliation, neovascular, traumatic, etc..
- Note the presence of synechiae (permanent adhesions), new blood vessels, pigment deposits, or angle damage.
Without the use of gonioscopy we may mislabel a patient as ‘open angle’ when in fact the angle is narrow and at risk of sudden closure which in turn changes the glaucoma treatment plan.
What Does the Doctor See in Gonioscopy?
During gonioscopy, we are looking at a ring of fine gonioscopy structures all the way around the iris root. These gonioscopy structures typically include:
- The corneal wedge and Schwalbe’s line (front edge of the drainage area).
- The trabecular meshwork (the main drainage “filter” for eye fluid).
- The scleral spur (a white line of support tissue).
- The ciliary body band (part of the focusing muscle).
By seeing how much of these are visible, we grade how open or narrow the angle is and whether any abnormal tissue is present. That information is vital before certain glaucoma surgery procedures, especially newer MIGS (micro‑invasive glaucoma surgeries) that work directly in this region.
How the Gonioscopy Test Is Done
Most patients are surprised by how simple the gonioscopy test feels. In the clinic, it usually goes like this:
- Numbing drops are placed in the eye so you do not feel the lens.
- You sit at the slit‑lamp microscope with your chin and forehead supported.
- A small gel is placed on the front of the lens to protect the cornea and give a clear view.
- The doctor gently places the gonioscope on the eye and looks at the angle in 4–8 directions.
- The test usually takes around 5–10 minutes for both eyes.
You may feel some pressure from the lens but not pain. Once we finish, we remove the lens, wipe the gel, and you can blink normally. Vision may be a little smeary for a short while from the gel or drops.
Types of Gonioscopy
In practice, we use a few different types of gonioscopy, mainly based on the lens and technique.
Direct gonioscopy
- Uses lenses like the Koeppe lens.
- The patient is usually lying down, and the doctor uses an operating microscope.
- Common in the operating theatre or special examination settings rather than routine OPD.
Indirect gonioscopy
- Uses lenses like Goldmann or four‑mirror Zeiss lenses.
- Done at the slit lamp with the patient sitting.
- This is the standard method in most glaucoma clinics.
Static vs dynamic (indentation) gonioscopy
- Static gonioscopy: We notice the angle as is.
- Dynamic (indentation) gonioscopy: In dynamic (indentation) gonioscopy which uses a special four mirror lens the doctor gently applies pressure to determine if the angle opens (appositional closure) or stays closed (true synechial closure).
This info helps us determine which eye treatments if any to proceed with and also if angle damage is reversible or permanent.
Benefits from Gonioscopy in Routine Eye Health Care.
Gonioscopy is known for its use in glaucoma diagnosis, but also it plays a role in general eye health check ups.
It can:
- Detect signs of narrow angles early which may lead to an angle closure attack.
- Note out of the ordinary blood vessels in the angle (neovascularization) that may be related to diabetes or vein occlusions.
- Report on pigment dispersion, angle recession from trauma, or congenital angle defects.
- Use for making decisions related to glaucoma treatment and timing of glaucoma surgery and MIGS.
In the case of people at high risk of glaucoma family history, high eye pressure, abnormal looking nerves, certain ethnic groups gonioscopy is a very important part of a full examination, not an optional extra.
At What Age Does Glaucoma Start?
Glaucoma can appear at different ages:
- Primary open‑angle glaucoma becomes more common after about 40 years of age.
- Angle‑closure risk also increases with age as the lens grows and the angle becomes more crowded.
- Rarely, there are juvenile or childhood glaucomas, but these are separate conditions with different patterns.
Because early glaucoma is usually silent, regular eye examinations with pressure check, optic nerve evaluation, and gonioscopy are important once you enter the higher‑risk decades, especially if you have a family history.
Is Gonioscopy Included in a Routine Eye Exam?
In a basic spectacle‑power check, gonioscopy is often not done. But in a comprehensive medical eye exam, especially when glaucoma is suspected or risk factors are present, gonioscopy is considered part of the standard evaluation.
Guidelines and glaucoma experts recommend performing gonioscopy in all patients with glaucoma or who are glaucoma suspects, and at least once in anyone with raised pressure or suspicious nerves.
At a centre like Vasan Eye Care, gonioscopy is routinely integrated into glaucoma work‑ups, follow‑up visits, and pre‑surgical planning.
Gonioscopy and Glaucoma Surgery Planning
Before any angle‑based procedure, such as certain laser treatments or MIGS, we need a clear map of the angle.
Gonioscopy helps us:
- Decide whether angle‑closure prophylaxis (like peripheral iridotomy) is needed before cataract or other eye surgery.
- Assess if angle gonioscopy structures are suitable for stents or other angle‑based devices.
- Identify synechiae or damage that might make angle surgery less effective and push us towards other glaucoma treatment options.
In that sense, gonioscopy is like a detailed road map before we do any “road work” inside the drainage system of the eye.
Eye Care at Vasan Eye Care
At Vasan Eye Care, gonioscopy is part of a structured glaucoma evaluation. When we check patients with raised intraocular pressure, suspicious optic nerves, or a strong family history, the gonioscopy test helps us decide:
- Whether the angle is truly open or narrow.
- Which type of glaucoma (or risk pattern) is present.
- Which eye treatments medication, laser, or glaucoma surgery are safest and most effective.
Our aim is always the same: detect risk early, personalise treatment, and protect vision for the long term.
Frequently Asked Questions
We do direct gonioscopy which is performed with Koeppe type lenses with the patient in a supine position and also do indirect gonioscopy which we do with Goldmann or four mirror lenses at the slit lamp. Also we look at static gonoscopy which is just a look at what is there and dynamic/indentation gonoscopy which involves gently pressing with a four mirror lens to see if the angle opens or stays closed.
In a gonioscopy test we put a special lens on the eye to see the drainage angle between the cornea and the iris in detail. It is done to determine if the angle is open, narrow, or blocked which in turn helps in the diagnosis and management of glaucoma.
Most primary open angle glaucoma is diagnosed at 40 and the risk goes up with age. But glaucoma can present at a younger age in people with strong risk factors and in rare childhood forms, which also means that age is not a determining factor.
In a complete health eye exam especially for glaucoma suspects or patients with high eye pressure gonioscopy is a key element of the assessment. May not be included in very basic “power only” exams, but in a glaucoma centered visit it should be a routine part.
Reference Links
- PubMed – Gonioscopy: mandatory for diagnosis and management of glaucoma
https://pubmed.ncbi.nlm.nih.gov/10218313/ - Glaucoma Today – Gonioscopy: Essential to Patient Care
https://glaucomatoday.com/articles/2008-sept-oct/GT0908_07-php - New England College of Optometry – What is Gonioscopy?
https://www.neco.edu/gonioscopy/