Diagnosing Glaucoma | Detection & Symptoms

Importance of early glaucoma diagnosis

If untreated, glaucoma damages the optic nerve that carries information from the eye to the brain, which first causes peripheral vision loss, and eventually blindness. Since glaucoma usually has few or no initial symptoms, seeing your eye doctor on a regular basis is the best way to find out if you have glaucoma, which is generally indicated by high eye pressure (high intraocular pressure, or IOP). Finding out early that you have high eye pressure, getting proper treatment, and following your eye doctor’s recommendations and treatment instructions are the best ways to prevent loss of eyesight caused by the most common type of glaucoma, open-angle glaucoma.

Are cataracts and glaucoma related?

Many individuals, typically over the age of 60, are diagnosed with cataracts – the clouding of the lens in the eye. Trauma to the eye or certain medications may lead to glaucoma or cataracts. It is important to be well informed of the possible side effects of medications. Although some patients have both cataracts and glaucoma, having glaucoma does not necessarily mean that you will get cataracts and having cataracts does not necessarily mean that you will get glaucoma.

Glaucoma screening and tests

Glaucoma is diagnosed by an examination of the eye that emphasizes eye pressure measurement, examining the optic nerve visually, and assessment of optic nerve function. A glaucoma eye exam provides important information to your eye doctor about the health of your eyes. It is often part of a routine eye exam and is painless.

During a glaucoma eye exam, you will have a combination of tests:

  • Visual field test (Perimetry)
    • While you’re looking into a machine with a special monitor screen, your eye doctor will ask you to find and identify images that appear on the screen. You will click a button when you notice a blinking light in your peripheral vision. This allows your eye doctor to determine what you can see in your direct and peripheral vision and if there is any glaucoma damage, such as vision loss or any blind spots in your field of vision.
  • Optic nerve scan (Ophthalmoscopy)
    • Your eye doctor will give you eye drops that dilate your eyes to make your pupils larger so that the optic nerve may be magnified and examined with an ophthalmoscope. You will be asked to look into a diagnostic machine that allows your doctor to view your optic nerve. Some eye doctors use a machine that takes pictures of your optic nerve and other structures of your eye. This exam allows your eye doctor to see if your optic nerve is healthy or damaged.
  • Eye pressure measuring (Tonometry)
    • A tonometry test is done using an instrument to apply slight pressure upon the eyeball with a puff of air to measure your eye pressure. Alternatively, some tonometers gently touch the surface of the eye to measure the pressure. Your eye doctor will give you eye numbing drops for this.
  • Cornea thickness measuring (Pachymetry)
    • Recently, researchers also discovered a new risk factor for glaucoma — cornea thickness. Having a thin cornea gives a falsely low IOP reading, and thus may mask elevated IOP. The thickness of the cornea is measured in the center of the eye with a pachymeter instrument. The test uses ultrasound and is painless and quick.
  • Gonioscopy or ultrasound biomicroscopy
    • One of these tests may be performed to examine whether the aqueous humor (fluid) can drain freely from the eye. In these procedures, advanced equipment enable your eye doctor to see the drainage angle of the structure inside the eye that controls the outflow of fluid, which affects your eye pressure.

Preparing for your eye exam

Ask your eye doctor or his or her office staff if there are any special preparations you should make for the appointment. Usually, it is recommended to have someone drive you to and from your eye exam appointment, as you may have blurry eyesight or sensitivity to light for several hours after the eye exam, due to the pupil dilation for the optic nerve scan.

What you can do before your exam

  • List any symptoms you’ve been having, and length of time you’ve been experiencing each.
  • List any history you may have with eye problems, such as vision changes, other eye problems you’ve been diagnosed with, and any eye discomfort.
  • Write down your medical information, including other conditions like diabetes or vascular issues you have and all medications and supplements you're taking.
  • Write questions to ask your doctor, so you remember them to help you make the most of your appointment time.