Gonioscopy is a special procedure that an eye doctor will perform to view parts of the front of the eye. The procedure is performed in an exam room and will frequently be performed along with a comprehensive eye exam. The most common use for gonioscopy is monitoring types of glaucoma.
The Corneoscleral Angle
In the front of the eye, the cornea which is the clear center part of the eye, merges with the sclera — the white part of the eye. This occurs at a structure called the corneoscleral angle.
The cornea is steeper than the sclera and causes the meeting to form an angle instead of being flat against one another.
The corneoscleral angle is also the location of the drainage system for the fluid in the front of the eye.
If the corneoscleral angle is more narrow, it can impede the drainage flow of fluid out of the eye.
Viewing the Corneoscleral Angle
In normal, direct viewing the corneoscleral angle cannot be seen.
When light is shone into the eye on the corneoscleral angle, it is entirely reflected back into the eye rather than exiting the eye.
To overcome this problem, a special lens is placed in contact with the eye that directs light into a mirror that can be used to view the corneoscleral angle.
Process of Gonioscopy
Prior to performing the procedure, a numbing eye drop is used to numb the front of the eye.
Once the eye is numb, a gonioscopy lens is placed in the eye with or without a liquid gel to provide lubrication.
The gonioscopy lens will have a mirror built in that can be used by the eye doctor to observe and evaluate the corneoscleral angle.
With the lens on the eye, the doctor will direct the mirror at different portions of the corneoscleral angle to identify any potential issues or problems.
After viewing the entire angle, the doctor will remove the gonioscopy lens and finish the procedure.
Why Gonioscopy is Performed
Any time that there is elevated eye pressure, gonioscopy can be performed to rule out a blockage of the drainage system in the eyes.
To properly diagnose glaucoma as open angle versus narrow angle glaucoma, gonioscopy is performed.
Gonioscopy may also be performed any time there is a risk of new blood vessel growth in the corneoscleral angle such as after a vein occlusion in the retina or with proliferative diabetic retinopathy.
Another reason to perform gonioscopy is prior to considering a selective laser trabeculoplasty (SLT) as a treatment for glaucoma. This procedure relies on gonioscopy to view the corneoscleral angle and uses a laser to open the drainage system.
Contraindications to Gonioscopy
There are a few cases where performing gonioscopy is not recommended.
One of the main times that gonioscopy is not recommended is if there is a large amount of blood in the front of the eye — known as a hyphema.
Similarly, if there is any open wound to the cornea or the eyeball, gonioscopy should not be performed.