Gonioscopy is an eye test that checks for signs of glaucoma. It uses a special lens and slit lamp to evaluate your eye’s drainage angle (anterior chamber angle). If the drainage angle is blocked or closed, you may have glaucoma. Gonioscopy is one of many tests you may need if you are at risk for glaucoma.


What is gonioscopy?

This test checks whether your eye’s drainage system (anterior chamber angle) is working properly. Gonioscopy is one of many tests that eye care specialists (ophthalmologists) use to detect glaucoma. Gonioscopy helps determine which type of glaucoma you have and guides treatment decisions.


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What is the drainage angle?

This structure is near the front of your eye. It's between the colored part of your eye (iris) and the protective outer layer (cornea). The drainage angle enables fluid inside your eye (aqueous humor) to drain.

Why is gonioscopy necessary?

If the drainage angle is blocked, your eye cannot clear fluid. This causes fluid and pressure to build up within the eye. Over time, this can lead to glaucoma, optic nerve damage and blindness. The drainage angle is challenging to access, which is why gonioscopy is necessary.

This test is especially helpful in detecting:

  • Closed-angle glaucoma: Fluid isn’t draining correctly because the angle is closed.
  • Open-angle glaucoma: The anterior chamber angle is open, but fluid isn’t draining as it should.
  • Pigmentary glaucoma: This rare condition occurs when pigment from your iris flakes off and clogs the drainage angle.
  • Pseudoexfoliation syndrome: Tiny dandruff-like flakes of protein fibers build up in organs, including your eye’s drainage angle.
  • Eye cancer: Tumors and certain types of eye cancer can occur on the eyelid and other eye structures.


Who needs gonioscopy?

This test may be right for you if you have glaucoma risk factors. These include:

How does gonioscopy work?

The test uses a lens with special prisms and a slit lamp (type of microscope) to determine whether the drainage angle is open or closed. It also checks for:

  • Abnormal blood vessels.
  • Extra pigment in the iris or drainage angle.
  • Scarring or damage to the drainage angle.
  • Signs of eye infection, such as uveitis.


Are there other methods for checking the drainage angle?

It’s possible to use imaging studies such as ultrasound and optical coherence tomography. But these methods are more costly than gonioscopy. They also don't provide the same level of detail.

Gonioscopy is not used as often as it could be. It requires special techniques that take time to learn. If you need this test, it’s best to receive it from an experienced ophthalmologist.

Test Details

How do I prepare for gonioscopy?

There is not much you need to do to prepare. If you wear contact lenses, you will need to remove them. You will not be able to put them back in until an hour after the exam. You may wish to bring glasses with you if you cannot see without corrective lenses.

What does gonioscopy feel like?

The test is painless. You receive medications that numb your eye to help you stay comfortable. You may feel pressure on your upper eyelid as the ophthalmologist places the gonioscopy lens on your eye.

What are the different types of gonioscopy lenses?

Your ophthalmologist may use a lens that has three or four mirrors in it:

  • Three-mirror gonioscopy lens: This lens is easier for ophthalmologists to use. It requires a special solution to eliminate air bubbles between the lens and the surface of your cornea. The solution can make it difficult to view certain features of the drainage angle. It’s also necessary to fully rotate the lens, which puts pressure on the outside of the eye.
  • Four-mirror gonioscopy lens: This lens requires more skill to use. But you will not need a solution on your eye. It provides enhanced views of the drainage angle. Only slight adjustments are necessary to view the entire area.

What happens during gonioscopy?

Here’s what happens:

  1. The ophthalmologist uses medicated drops to numb your eye.
  2. They adjust the chair you’re sitting in so that your face is close to a special microscope (slit lamp).
  3. You place your chin on the chinrest and lean forward so that your forehead touches the support bar.
  4. The ophthalmologist places a three- or four-mirror gonioscopy lens on your eye.
  5. They use the slit lamp to shine a narrow light beam on your eye.
  6. The light reflects off the mirrors, making it possible to assess the drainage angle.

Results and Follow-Up

What do the results of gonioscopy mean?

Your ophthalmologist will let you know the results immediately.

  • Normal means that the drainage angle is healthy and aqueous humor is draining as it should.
  • Abnormal means the drainage angle is narrow or blocked, which may indicate glaucoma. You may need additional glaucoma tests to confirm.

What other tests might I need?

Your care may also include:

A note from Cleveland Clinic

Gonioscopy is an eye test that ophthalmologists use to check for signs of glaucoma. This test provides detailed information that can help confirm a glaucoma diagnosis. It also enables you to receive the appropriate therapies for your needs. Gonioscopy is quick and painless. For best results, it’s essential to receive care from an experienced ophthalmologist.

Medically Reviewed

Last reviewed on 02/16/2022.

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