Overview of gonioscopy
Gonioscopy is performed during the eye exam to evaluate the internal drainage system of the eye, also referred to as the anterior chamber angle. The “angle” is where the cornea and the iris meet. This is the location where fluid inside the eye drains out of the eye and into the venous system.
Under normal circumstances, the angle is not visible on the test. The prism of a contact lens placed on the surface of the eye allows visualization of the angle and the drainage system.
What is gonioscopy used for?
Our eyes constantly make aqueous humour. As new aqueous flows into your eye, about the same amount should leave the eye through the drainage angle. This process keeps pressure in your eye (called intraocular pressure or IOP) stable. If the drainage angle is not working properly, fluid builds up. Pressure in the eye rises, damaging the optic nerve. This is often how glaucoma develops.
Your ophthalmologist will perform a gonioscopy if certain conditions are found during an eye examination. Most commonly, cerebral endoscopy is performed to check for signs of glaucoma. The examination can show whether the drainage angle is too narrow for fluid to drain properly, or if it is blocked by a portion of the iris.
In other cases, a goon endoscopy may be performed when signs of uveitis, eye trauma, tumours, or other conditions appear.
Why is it needed?
The pressure inside the eye is maintained through continuous production and drainage of fluids. If the drainage system is not working properly, the pressure inside the eye, also known as intraocular pressure, may increase. High intraocular pressure can damage the optic nerve, the “cable” that sends images from the eye to the brain. This type of damage is called glaucoma, and it is the second leading cause of blindness worldwide.
By looking at the “angle,” doctors can determine whether it is open or closed as well as whether there are abnormal blood vessels, synechiae, or damage from previous trauma to the eye. The closed-angle is an abnormal condition that can predispose the patient to a sudden or rapid increase in eye pressure. This increase in pressure can cause a very severe form of glaucoma that can be treated and even prevented with laser treatment (iridotomy) if the predisposing angle anomaly is recognized with a goon endoscopy.
Also, acupuncture allows the ophthalmologist to note the more accurate characteristics of the eye’s drainage system, to guide a diagnosis and plan treatment.
When should you have a gonioscopy?
Early signs of vision changes and eye disease may begin around age 40. This is when all adults should get a baseline eye disease screening with an ophthalmologist.
To detect signs of glaucoma, your ophthalmologist will perform a gonioscopy to check the appearance and function of the drainage angle. Some people are suspected of having glaucoma. They may or may not have an eye pressure that is higher than normal, but the eye doctor may notice other signs that could develop into glaucoma. In this case, the ophthalmologist will want to perform gonioscopy and other glaucoma exams regularly to check for changes over time.
How is it done?
Gonioscopy is performed with the head placed in a slit lamp (the special microscope used to look at the eyes). After the eye is numbed with drops, a special contact lens is placed directly on the eye and a beam of light is used to illuminate the angle. While the eyelids may feel the presence of the lens, there is no pain associated with this examination. The examination of both eyes usually takes a few minutes.