Diagnostic Testing of Glaucoma

Your eye doctor has a variety of diagnostic tools which aid in determining whether or not you have glaucoma -- even before you have any symptoms. Let us explore these tools and what they do.

The Tonometer

The tonometer measures the intraocular pressure in your eye. A numbing eye drop is instilled in your eye, before you are seated at a slit-lamp, resting your chin and forehead on a support that keeps your head steady. The lamp, which lets your doctor see a magnified view of your eye, is moved forward until the tonometer (a plastic prism) barely touches the cornea to measure your IOP. The test is quick, simple and painless.

Visual Field Test

Visual field is an important measure of the extent of damage to your optic nerve. In glaucoma, it is the peripheral (side) vision that is most commonly affected first. Testing your visual field lets your doctor know if peripheral vision is being lost. There are several methods of examination available to your doctor.

In computerized visual field testing, you will be asked to place your chin on a stand which appears before a concave computerized screen. Whenever you see a flash of light appear, you press your buzzer. At the end of this test, your doctor will receive a printout of your field of vision. New software has been developed to help your doctor analyse these tests as well as monitor progression of visual field loss over successive tests.

Ophthalmoscopy

Using an instrument called an ophthalmoscope, your eye doctor can look directly through the pupil at the optic nerve. Its colour and appearance can indicate whether or not damage from glaucoma is present and how extensive it is. This technique remains very important in diagnosing and monitoring glaucoma.

Imaging Technology

A number of new and highly sophisticated image analysis systems such as: ocular coherence tomography or OCT are now available to evaluate the optic nerve and retinal nerve fibre layer, the areas of the eye damaged by glaucoma. These instruments can help your doctor by giving a quantitative measure of the anatomical structures in the eye.

Photographs of the optic nerve can also be useful to follow the progression of damage over time. Large databases have been established to compare an individual's anatomic structures to those of other patients in the same age group. This software and technology are developing rapidly and show great promise. However, they have not yet evolved to replace ophthalmoscopy, where the doctor looks directly at the optic nerve.

Gonioscopy

Your doctor will perform gonioscopy to closely examine the trabecular meshwork and the angle where fluid drains out of the eye. After numbing the eye with anaesthetic drops, the doctor places a special type of hand-held contact lens, with mirrors inside, on the eye. The mirrors enable the doctor to view the interior of the eye from different directions. In this procedure, the doctor can determine whether the angle is open, narrow, or closed. Individuals with narrow angles have an increased risk for a sudden closure of the angle, which can cause an acute glaucoma attack. Gonioscopy can also determine if anything, such as abnormal blood vessels or excessive pigment, might be blocking the drainage of the aqueous humour out of the eye.