Diagnostic Tests

Questions & Answers Reprinted from Our Newsletters

My mother and many of her sisters had glaucoma. So far no one in our generation (eight of us over age 64) has glaucoma. I had HRT testing four years ago. It was negative. How often should I be tested?

Glaucoma is hereditary and can run in families. Because your mother had glaucoma, her children are at higher risk. It is important for you to be screened yearly even if everything is okay.

HRT is a topographic map of the optic nerve. After a baseline test, repeated tests look for loss of optic nerve tissue. It takes at least three tests to detect a change. The more the test is done, and the shorter the space between tests, the quicker damage to the optic nerve is detected. The test should be repeated yearly but twice yearly would pick up damage quicker.

Are there any easy to use inexpensive tonometers for home use?

Not yet.

How many visual field tests should a person with advanced glaucoma have in a year?

It is recommended that patients with moderate glaucoma or worse have at least two visual fields per year. As the tests are difficult to perform and time-consuming with little extra benefit, there is no need to have them more frequently.

Is Diurnal Tension Curve useful in treating primary open angle glaucoma and where can I be tested?

Diurnal tension curves are very helpful in managing patients with glaucoma. They give a true indication of eye pressure fluctuation over the course of the day.

The difficulty is measuring eye pressure in the evening as most eye clinics are not open then. I suggest getting pressure checks at 8 am, 12 noon and 4 pm and make an appointment for an 8 pm pressure check with an optometrist who is open in the evening. Governments don’t reimburse for this test, so you will have to pay.

I have normal pressure glaucoma and would like to be screened regularly to determine the effectiveness of my treatment plan and to assess the progression of my glaucoma. I am willing to pay for the screening tests but my ophthalmologist does not want to test me more than once a year.

There is no value in screening tests more than once a year as normal tension glaucoma is a slowly progressive disease.

My eye surgeon suggested I get the HRT test which I would have to pay for as it’s not covered by OHIP. I had the OCT test, why do I need a second test? Is there a standard charge for HRT?

OCT (Optical Coherence Tomography) detects damage of only the nerve fibre layer. HRT (Heidelberg Retina Tomography) looks at changes in the topography of the optic nerve - like looking at the erosion of a mountain. OCT and HRT complement each other. Cost for HRT varies between $100 to $150 depending on the physician.

Does the HRT test have merit?

Yes. It is useful as it may detect glaucoma worsening sooner and allow the doctor to intervene with treatment to prevent further deterioration.

Is the OCT test (which is covered by OHIP) as effective as the HRT test (costing $75) for determining damage to the optic nerve? I want to take the appropriate test, but I also want value for my money if I do elect to take repeated HRT exams.

HRT (Heidelberg Retina Tomography) and OCT (Optical Coherence Tomography) are different tests looking at different information.

OCT and HRT complement each other and can be helpful in determining if glaucoma is worsening.

HRT examines the topography of the optic nerve. Over time there may be erosion (damage to the optic nerve) which may be detected earlier with HRT than with a clinical exam. HRT has been around for many years and once an image is taken, it is always useful.

OCT is newer technology. For glaucoma OCT assesses the nerve fibre layer around the optic nerve and ganglion cell density in the macula. OCT may detect glaucoma earlier than any other test. It can also detect if glaucoma is worsening over time.

The current machines we use for OCT are about four years old. Unfortunately, images taken now may not be useful in a few years as technology advances and new machines are released.

What is HRT?

A fast scanning laser ophthalmoscope called a Heidelberg Retinal Tomograph (HRT) produces a 3-D image of the optic nerve so specialists can diagnose damage early on. HRT can also detect early progression of glaucoma caused by nerve damage.

My doctor has recommended an HRT test, what is this?

HRT (Heidelberg Retinal Tomography) is a diagnostic test that scans the optic nerve to generate a 3-D image. This image provides information about the size, shape and contour of your optic nerve, and may help in predicting if you have early glaucoma. The test may be repeated every six months or yearly and images are then compared to earlier images to see if the glaucoma is worsening. This information helps your doctor determine if you need treatment for glaucoma or an increase in therapy for better eye pressure control.

My doctor has asked me to stay in his office all day and evening to check my eye pressure. Why?

Your doctor is obtaining a diurnal intraocular tension curve which looks at your eye pressure over the course of the day. Eye pressure is dynamic and fluctuates throughout the day. Patients with glaucoma may have their eye pressures vary by up to ten units (mm Hg) in one day. One eye pressure reading may not accurately reflect your eye pressure control and may miss elevations at other times of the day. This full day pressure allows your doctor to alter your treatment for better eye pressure control.

I had cataracts removed from both eyes 30 years ago and several years later had an implant in one eye. In the other eye, I use a soft contact lens. I have had 3 Heidelberg tests over the last 3 years without good results. The technician has tried taking the Heidelberg – both with my contact lens in and with it out. Why is it difficult to get an image in this eye?

The test is probably difficult because you don ’t have a lens in the eye. Most diagnostic machines have a certain focal range and when you are aphakic (no lens in the eye), you fall out of the machine’s focal range. As well, your contact lens may blur the image.

Some attachment lenses for the HRT can extend the focal range and also correct for astigmatism. Another option is to try to get the image with your regular glasses on instead of a contact lens .

Because you are aphakic and have worn a contact lens for many years, issues with your cornea may block the image quality.

During my annual vision test, my eye doctor discovered that I have two different sized optic nerves and the pressures are high as well. I don’t think I did well on a subsequent field test. Any advice?

Diagnosing glaucoma can be difficult. Your doctor needs to consider a number of factors before making a diagnosis and starting treatment. He or she will take into account your eye pressure and its range over the day, what your optic nerves look like, how different the two of them are, and the visual field test result.

Don’t worry if you didn’t do well on the visual field test, as there is a learning curve and it may take three to four tests to get better at it.

Your doctor will also consider your past medical history, as major surgeries, blood loss, and previous medications such as oral steroids, may influence your IOP or the look of the optic nerves.

If you do have glaucoma, remember there is no cure. The majority of cases are managed with eye drops, laser treatment and surgery. Treatment is individually determined.