What is gonioscopy?

Gonioscopy is a diagnostic technique used to study the space between the iris and the cornea. It is a useful technique because there are important structures involved in the regulation of the pressure of the eye.


What is the purpose of gonioscopy?

The exam is particularly useful for detecting and differentiating the various types of glaucoma and thus it provides a guideline towards therapy. Moreover, the exam is performed to check how fluid drains from the eye and whether the drainage angle (the area where fluid drains out of the eye) is open or closed as well as to detect any birth defects that may cause glaucoma.

Standard of preparation

Prior to the beginning of the examination anaesthetic eye drops are instilled in the eye of the patient. A special lens comes to contact with the eye, which is protected by a viscose substance (a transparent gel-based hydroxypropyl methylcellulose). After the examination, the protective gel is removed by washing the eyes with eye drops. The examination may temporarily cause a reduction in vision (for about 30 minutes). Therefore, it is best to arrive at the hospital accompanied by a friend or a family member.

Which patients can undergo the exam?

Everyone can undergo the examination. Patients that usually wear contact lenses should remove the contact lenses before the exam and avoid putting them back on for 1 hour after the exam or until the anaesthesia wears off. Pregnant women can undergo the exam only if it is clearly necessary as well as undergo eye surgery only if indicated by a doctor.

Is the exam painful and/or dangerous?

Gonioscopy is performed easily, safely, and quickly when the patient relies on the doctor and follows the given instructions and recommendations. Moreover, the exam is not a painful procedure. On the other hand, patients who express resistance may cause unnecessary inconvenience to the manoeuvres that the doctor is forced to do in order to successfully perform the examination.


The exam carries a very small risk of an eye infection or an allergic reaction to the eye drops that are used to numb the eye. In addition, if the patient’s pupils were dilated, their vision may appear blurry for several hours after the exam. It is recommended that the patient does not rub the eyes for around 20 minutes after the test or until the anaesthetic wears off.

How is the exam performed?

Initially, anaesthetic eye drops are used to numb the eye so that the patient does not feel the lens that touches the eye during the examination. Then, the patient may be asked to lie down or sit. The ophthalmologist then looks inside the patient’s eye through a microscope. If the patient is sitting, they will be required to place their chin on a chin rest and the forehead against a support bar and look ahead. The next step involves the affixation of a particular lens, which contains reflecting surfaces on the inside, while a beam of bright light is pointed at the inside of the eye for about 20-30 seconds. The light helps the ophthalmologist look at the width of the drainage angle. The average duration of the exam is less than 5 minutes.