Definition & Overview

Gonioscopy is a type of eye examination performed to check the internal structures of the eyes. It goal is to thoroughly evaluate eye health and properly diagnose eye diseases such as glaucoma, which is the second leading cause of blindness. In this test, the internal anterior chamber of the eye between the iris and the cornea is evaluated using an apparatus that is similar to a microscope. The eye structures seen in gonioscopy cannot be visualised with a penlight or even slit lamp bio-microscope.

The pressure inside the eye is well maintained through a balanced, constant production, and drainage of eye fluid. When this balance is disturbed (an eye condition called glaucoma), the pressure inside the eyes (intraocular pressure) can increase, which can then damage the optic nerve. If not treated, the condition can lead to blindness.

Gonioscopy test is done to:

  • Check for glaucoma
  • To determine whether the drainage angle of the eye is closed or open (to evaluate the type of glaucoma)
  • Treat and control glaucoma in conjunction with laser treatment to decrease eye pressure
  • Check for congenital defects that may eventually lead to glaucoma

Who Should Undergo & Expected Results

Gonioscopy is an important test performed by an ophthalmologist on those who show symptoms of glaucoma. It is often suggested for patients who have elevated eye pressure, narrow anterior chamber, ocular hypertension, eye trauma, pseudoexfoliation syndrome, central retinal vein occlusion, diabetic retinopathy, and pigmentary dispersion syndrome, among others.

After diagnosis, laser iridotomy treatment is pursued to effectively prevent the progress of glaucoma.

Often in conjunction with other eye tests, gonioscopy is suggested in patients with the following symptoms:

  • Unusual inability to adjust vision in dark rooms
  • Unusual sensitivity to light or glare
  • Recurrent pain around the eyes
  • Change in iris colour
  • Excess tearing or abnormally dry eyes
  • Red-rimmed, swollen or encrusted eyelids
  • Seeing “ghost-like” images
  • Double vision
  • Lines or edges appearing wavy or distorted


A thorough eye exam like gonioscopy may be immediately required in emergency situations when:

  • There is sudden loss of vision in one eye
  • There is sudden blurred or hazy vision
  • The patient sees halos or rainbows around light
  • The patient experiences flashes of light or black spots in vision

How is the Procedure Performed?

Gonioscopy is performed using a special contact lens prism that is placed on the surface of the eye. The patient will initially be instructed to remove their eyeglasses or contact lenses before lying down or sitting in a chair. The eye is then numbed with eye drops to minimise discomfort when the lens touches the eye.

The chin will be placed on a chin rest and the forehead will be positioned against a support bar. A special contact lens is placed gently on the front of the eye. The head is then positioned in the slit lamp (microscope), after which a beam of light is shone onto the eye to illuminate the angle.

Under normal condition, the anterior chamber angle, where the cornea and iris meet, cannot be seen on the exam. The drainage angle will appear normal, open, and not blocked. When glaucoma is present, however, the drainage angle will appear narrow, blocked or closed. This is what the eye specialist will measure during the test.

If the drainage angle of the eye is partially or completely blocked, there is a risk that it might close in the future, a condition called close-angle glaucoma. Drainage angle blockage is caused by a variety of reasons such as the presence of scar tissue, eye injury or infection, abnormal blood vessels, and hyperpigmentation of the iris.

Furthermore, a gonioscopic examination can help eye doctors note other subtle characteristics of the drainage system of the eye to guide diagnosis and to help them plan appropriate treatment.

Possible Risks and Complications

There is usually no pain felt in a gonioscopy exam, and the test only lasts a few minutes. While the test itself does not usually cause discomfort, the initial application of the anaesthetic eyedrops may cause a slight burning sensation.

When the pupils become dilated due to the exam, the patient may experience blurred vision in the next several hours after the test. It is important for the eyes not to be rubbed for the next 30 minutes after the test is done, or until the eye drop medicine wears off. Contact lenses must not be worn during this time as well.

Among minor risks associated with this test include allergic reaction to the anaesthetic eyedrops and/or eye infection.

Gonioscopy is usually suggested along with other tests to confirm and evaluate gravity of eye problems. Other tests may include tonometry (to measure eye pressure), slit lamp examination, perimetry (to determine range of vision), and ophthalmoscopy (to check the optic nerves).

References:

  • Faschinger, C; Hommer, A. Gonioscopy. Springer. Heidelberg. 2012 BCSC Glaucoma page 38-42 www.gonioscopy.org Arch Ophthalmology 2003; 121:
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