It is performed during the eye examination to evaluate the eye’s internal drainage system, also called the anterior chamber angle.
The “angle” is where the cornea and iris meet. This is where the fluid inside the eye (aqueous humor) drains out of sight into the venous system.
Under normal circumstances, the angle can not be seen in the exam. A particular prism for contact lenses placed on the eye’s surface allows visualization of the rise and the drainage system.
Gonioscopy should be carried out in a dark room. If not the consensual pupil, the reaction will contract the pupil of the examined eye.
Therefore, a room with low light is relevant. You can start with a beam brightness to get an overview of the angular structures. Then the brightness and size of the slit beam must be reduced.
The word gonioscopy was used for the first time by Axios Trans. In Greek, it means “angle.” Trans described the angle of the anterior chamber using a direct ophthalmoscope and simultaneous digital pressure at the edge of the cornea.
Years later, Maximilian Salzmann would be the first to use a contact lens and indirect gonioscopy to examine the angle. Both are considered to be the “fathers of gonioscopy.”
The pressure inside the eye is maintained by the constant production and drainage of the liquid. If the drainage system is not working correctly, the pressure inside the eye, also known as intraocular pressure, may increase.
High intraocular pressure can cause damage to the optic nerve, the “wire” that sends images from the eye to the brain. This type of damage is called glaucoma, the second cause of blindness worldwide.
By observing the “angle,” doctors can determine if it is open or closed, as well as if there are abnormal blood vessels, adhesions (synechiae), or damage from previous eye trauma.
A closed-angle is an anomaly that can predispose the patient to a sudden or rapid increase in intraocular pressure.
This increased pressure can cause severe and acute glaucoma that can be treated and even prevented with laser treatment ( iridotomy ) if the predisposing angle anomaly is recognized by 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.
Relevance of Gonioscopy
Many pathologies change the angle configuration, such as tumors that have nothing to do with glaucoma.
As a foreign body that may be hidden behind the periphery of the cornea and the patient only remembers “some pain” and does not present a blurred vision or red eye. Glaucoma is not the only condition that is diagnosed through a gonioscopy.
Gonioscopy is performed with the head placed on the slit lamp (the special microscope used to observe the eyes).
After numbing the eye with drops, a unique contact lens is placed directly over the eye, and a beam of light is used to illuminate the angle. While the eyelids can feel the presence of the lens, there is usually no pain associated with this examination. The examination of both eyes usually takes a few minutes.
Types of gonioscopy
Gonioscopy is required to visualize the camera angle because, under normal conditions, the light of the angular structures undergoes a total internal reflection at the tear-air interface.
To overcome this, a lens must be placed against the eye. Depending on the lens used, the angle can be examined directly or indirectly.
It allows you to see the camera angle directly. Examples of direct goniolenses include Koeppe, Barkan, Wurst, Richardson, and Swan-Jacob.
The ophthalmologist has a vertical view of the angular structures during direct gonioscopy. This is done simply with the patient in the supine position in the operating room under anesthesia for a MIGS examination or procedure.
It is frequently used in the clinical setting. Examples of indirect gonioscopy lenses include Posner, Sussman, Zeiss, and Goldmann lenses.