Gonioscopy

Gonioscopy is a specialized eye examination used to evaluate the "drainage angle" of the eye—the critical area where the cornea meets the iris. This is the "plumbing system" where fluid (aqueous humor) drains out of the eye. If this angle is blocked, narrowed, or damaged, eye pressure can rise, leading to permanent vision loss from glaucoma.

Because of the way light reflects off the surface of the eye (total internal reflection), a doctor cannot see this angle directly. A specialized contact lens called a goniolens, which contains mirrors, is used to "see around the corner" and visualize the drainage structures.

1. Why is it Performed? (Indications)

• Glaucoma Classification: To determine if a patient has Open-Angle or Angle-Closure glaucoma. This is the single most important reason for the test, as the treatments for these two conditions are completely different.
• High Eye Pressure: If a routine "puff test" or tonometry shows high intraocular pressure (IOP).
• Eye Trauma: To check for internal tearing or bleeding (hyphema) after an injury.
• Laser Planning: To see if a patient needs a laser procedure (like a Peripheral Iridotomy) to open a narrow drainage system.

2. Common Symptoms: When to Meet a Doctor

Glaucoma is often the "silent thief of sight" and has no early symptoms. However, gonioscopy is urgently needed if you experience:

• Sudden, severe eye pain.
• Seeing "halos" or rainbows around lights.
• Red eyes accompanied by nausea or vomiting.
• Sudden "tunnel vision" or blurred sight.

3. List of Associated Conditions

• Primary Open-Angle Glaucoma (POAG): The drainage angle looks "open" and normal, but the microscopic filters are clogged.
• Angle-Closure Glaucoma: The iris is physically bunched up against the drainage port, blocking fluid flow.
• Pigmentary Glaucoma: Tiny bits of pigment from the iris flake off and clog the drain.
• Neovascular Glaucoma: Abnormal blood vessels (often from diabetes) grow across the angle and "zip" it shut.

4. What to Expect (The Procedure)

1. Numbing: The doctor applies anesthetic drops so you won't feel the lens touching your eye.
2. The Setup: You rest your chin and forehead on a slit-lamp microscope.
3. The Lens: The doctor gently places the goniolens on your eye. You may feel a slight "tightness" or a cool sensation from the thick lubricating gel used with the lens.
4. The Exam: The doctor shines a beam of light and rotates the lens to inspect all 360 degrees of the drainage angle.
5. Duration: The entire process usually takes 2 to 5 minutes.

5. Pre and Post-Care Requirements

Pre-Care:

• Contact Lenses: You must remove your regular contact lenses before the exam.
• No Dilation (Usually): Gonioscopy is typically done before your eyes are dilated, as dilating drops can physically change the shape of the angle and mask a "narrow angle" problem.

Post-Care:

• Do Not Rub Your Eyes: Because your eye is numb, you could accidentally scratch your cornea without feeling it. Avoid rubbing your eyes for at least 30 to 60 minutes until the anesthesia wears off.
• Rinse the Gel: The thick gel used during the test may leave your vision feeling "goopy" or blurry for a few minutes. You can use artificial tears to rinse it out.

6. Hospitalization and Timeline

• Setting: This is a routine outpatient diagnostic test performed in the ophthalmologist's office.
• Hospital Stay: None. You can go home immediately after the exam.

7. Benefits of Gonioscopy

• Prevents Emergencies: It can identify a "narrow angle" before it turns into a painful, sight-threatening acute glaucoma attack.
• Directs Treatment: It tells the doctor if you need simple eye drops, a laser procedure, or surgery.
• Diagnostic Precision: Unlike imaging tests (like OCT), gonioscopy allows the doctor to see the color and texture of the drainage tissue, which can reveal secondary causes of high pressure like inflammation or pigment loss.