What is gonioscopy?

It’s common to have not heard of gonioscopy, even if you already have a glaucoma diagnosis. However, it’s likely that you’ve already experienced it during your visit to the eye hospital.

During the test, an ophthalmologist uses a lens which is placed in contact with your eye to assess the health of the angle where fluid drains from your eye. The lens can do this because it incorporates mirrors and a prism which bends light, giving the ophthalmologist a clear view. Gonioscopy is completely painless and an essential part of checking for glaucoma.

What happens during gonioscopy?

Gonioscopy is used to view the angle at the place where the coloured part of your eye (your iris) joins the cornea (the clear layer at the front of your eye). The reason why it’s important to assess this angle, and how wide it is, is because this is where fluid drains out of your eye, and the balance of fluid pressure inside the eye is crucial in diagnosing, managing and treating glaucoma.

During your visit to the hospital, your ophthalmologist will ask you to place your chin on the rest of a slit lamp, a microscope designed to examine the front of your eye.

You’ll then be given some anaesthetic eye drops before the gonioscopy lens is placed on your eye’s front surface. The light from the slit lamp, shining through the gonioscopy lens, will allow the eye doctor to assess the drainage angle.

Determining the type of glaucoma

Following this, the ophthalmologist will assess the type of angle where the iris meets the cornea which will help to determine which, if any, type of glaucoma you have. If your iris is pushing up against the cornea, the angle between them can become narrowed, blocked, or closed altogether in certain types of glaucoma – you can read more about the different types of glaucoma in our guide.

The majority of diagnoses will be primary open-angle glaucoma (the most common form) where the angle at which the iris joins the cornea is open. However, a smaller group have primary angle-closure glaucoma where an increase in pressure is caused by a narrow drainage angle. This can happen gradually or suddenly: sudden angle closure can be very painful, but this type of glaucoma only affects a very small number of people. Treatments will vary depending on the type, so it’s important to assess which type of glaucoma you’re affected by.

Other factors in glaucoma

Gonioscopy is also used to identify other factors that can affect the pressure inside your eye. Secondary glaucoma is so-called because the rise in pressure is secondary to other factors or illnesses. For example, someone with poorly controlled diabetes may have a growth of abnormal blood vessels which can leak or block the drainage angle. Other inflammatory conditions can lead to debris in the fluid in the front section of the eye which can partially block the drainage angle, leading to a rise in pressure.

Examination using gonioscopy allows the ophthalmologist to view any blockages in the drainage angle due to causes like these. It is important to understand if any other factors are involved in causing glaucoma as these will need to be treated in order to reduce the pressure inside your eye and prevent sight loss.

For more information on glaucoma diagnosis, glaucoma causes or glaucoma treatment, you can learn more in our dedicated glaucoma resource. Remember to discuss any of your questions with your ophthalmologist or your optometrist who can provide advice based on your particular circumstances.