What do you need to know about gonioscopy?
Gonioscopy is an examination of the front of the eye (anterior chamber), between the cornea and the iris. It is a painless, non-invasive examination to see if the area where fluid drains from the eye (called the drainage angle) is open or closed. This is the location where fluid inside the eye (aqueous humor) drains from the eye and into the venous system. Under normal circumstances, the angle cannot be seen on examination. A special contact lens prism placed on the surface of the eye allows visualization of the angle and drainage system.
Gonioscopy is often done during a regular eye exam, depending on your age and whether you have an increased risk of glaucoma. Or, if your doctor thinks you need to be examined for glaucoma. Glaucoma is an eye disease, with an insidious onset and relatively asymptomatic until advanced stages, that can cause blindness through damage to the optic nerve.
The pressure inside the eye is maintained by the constant production and drainage of fluid. If the drainage system is not working properly, the pressure inside the eye, also known as intraocular pressure, can increase. High intraocular pressure can cause damage to the optic nerve, which sends images from the eye to the brain. Glaucoma is the second leading cause of blindness worldwide.
With the help of gonioscopy and other investigations, we can determine whether the angle is open or closed, as well as whether there are abnormal blood vessels, adhesions (synechiae) or injuries caused by previous eye injuries.
A closed angle is an abnormality that can predispose the patient to a sudden or rapid increase of intraocular pressure. This increase in pressure can cause a very serious, acute form of glaucoma that can be treated and even prevented with laser treatment (iridotomy) if the predisposing angle abnormality is recognized using gonioscopy.
In addition, gonioscopy allows the ophthalmologist to observe more subtle features of the eye’s drainage system to guide its diagnosis and treatment plan.
What does Gonioscopy involve?
First, your eyes will be anesthetized with special drops to make sure you don’t feel any discomfort during the examination. Then your ophthalmologist will examine your eyes with a gonioscope – a small device designed with inner mirrors and a lens at one end that rests on the cornea like a contact lens. When the lens is placed above the cornea, the inner mirrors allow the doctor to see the anterior angle of the eye.
Once the objective is placed on the eye, a beam of light is directed into the eye using a slit-lamp microscope. You may feel pressure on your eyelids or eyelashes during a gonioscopy, but the test should otherwise be painless.
Gonioscopy is performed with the head positioned in the slit lamp (the special microscope used to examine the eyes). Examination of both eyes usually takes a few minutes.
Recommendations before the procedure:
- If you wear contact lenses, it is recommended that you do not use them a few hours before the procedure;
- After the investigation you may have blurred vision (for a few minutes or hours) and for this reason it is recommended not to drive immediately afterwards.
What can be diagnosed by Gonioscopy?
Vision changes that begin to appear around age of 40 put adults at greater risk of developing various eye disorders, including glaucoma. Gonioscopy may be recommended for adults at this age and above, especially for those at higher risk of developing glaucoma.
For example, glaucoma can be inherited, so if you are a “suspect” for glaucoma because of your family’s medical history, your ophthalmologist may recommend a routine gonioscopy to monitor for any indication of developing the disorder. In addition, if certain related abnormalities are detected during a basic eye examination, a gonioscopy is also recommended.