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Gonioscopy is a quick and painless test that an eye doctor uses to look at the drainage angle of your eye. This is the area at the front of the eye where the clear fluid, called aqueous humor, drains out. Checking this angle is very important for diagnosing and managing glaucoma.
read more about gonioscopy ...The main reason for a gonioscopy exam is to check for glaucoma. The test helps your doctor figure out what type of glaucoma you have. It shows if the drainage angle is open or closed. An open angle means the fluid can reach the drain but might be clogged. A closed angle means the drain is blocked by the iris, which can cause a sudden and painful rise in eye pressure.
First, your doctor will put numbing drops in your eye so you do not feel anything. Then, you will rest your head on a machine called a slit lamp. The doctor will gently place a small, special contact lens with mirrors on your eye. By shining a light and looking through the mirrors, the doctor gets a clear view of your eye's drainage angle.
This exam tells your doctor if your drainage angle is wide open, narrow, or fully closed. It can also show if there is scar tissue, abnormal blood vessels, or other problems in the area that could be blocking fluid from draining properly. The results help your doctor decide on the best treatment for you, such as eye drops, laser therapy, or surgery.
During the exam, your doctor isn't just looking for "open" or "closed." They use a grading system (such as the Shaffer or Spaeth system) to score the angle. Grade 4 is a wide-open angle, indicating a healthy drainage system. Grade 0 is a completely closed angle, indicating an emergency where the iris is touching the cornea. Grades 1 and 2 indicate "narrow angles," which are high-risk zones that may require preventative laser treatment.
Sometimes, the doctor may gently push against your eye with the gonioscopy lens. This technique, called dynamic or indentation gonioscopy, helps differentiate between an angle that is permanently closed by scar tissue and one that is just "appositionally" closed (touching but not stuck). If the pressure opens the angle, it tells the doctor that a laser procedure (iridotomy) will likely be successful in treating the glaucoma risk.
No, it is not painful. Your eye is completely numbed with eye drops before the lens touches your eye. You might feel a slight pressure from the lens, but you should not feel any pain.
The test itself is very fast. It usually takes only a minute or two for the doctor to examine the angle in each eye.
The most common side effects are temporary blurriness from the numbing drops and the gel used with the lens. These effects wear off quickly. It is a very safe procedure.
Your eye doctor will perform a gonioscopy if they suspect you have glaucoma or if you are at high risk for it. It is a standard part of a full glaucoma workup. If your doctor recommends the test, feel free to ask any questions you have about what they are looking for or what you can expect.
1. Gonioscopy: What Is It And Why Is It Needed? Glaucoma Research Foundation. https://glaucoma.org/articles/gonioscopy-what-is-it-and-why-is-it-needed. Accessed March 26, 2026.
2. Gonioscopy: What It Is, Procedure Details & Results. Cleveland Clinic. https://my.clevelandclinic.org/health/diagnostics/22421-gonioscopy. July 23, 2024.
3. Glaucoma Tests. MedlinePlus. https://medlineplus.gov/lab-tests/glaucoma-tests/. October 24, 2023.
4. Techniques of Slit-Lamp Gonioscopy. American Academy of Ophthalmology. https://www.aao.org/education/disease-review/techniques-of-slit-lamp-gonioscopy. November 8, 2017.
5. Gonioscopic Grading Systems. American Academy of Ophthalmology. https://www.aao.org/education/disease-review/gonioscopic-grading-systems. November 8, 2017.
6. Gonioscopy. EyeWiki. https://eyewiki.org/Gonioscopy. October 31, 2025.