Qs & As about Diagnostic Tests Reprinted from Our Newsletters

My optometrist has scheduled a field of vision scan and an optical coherence tomography (OCT) as I am near-sighted and have high pressure (20 & 22) in both my eyes. These tests are not covered by OHIP. Are they important?

Risk factors for glaucoma include age, race, family history, eye pressure, and myopia. Information from both a comprehensive eye exam and various tests may be necessary to diagnose glaucoma.

The usual tests include visual field testing and OCT, a non-invasive imaging test that uses light waves to take cross-section pictures of your retina.

I have been diagnosed with open angle glaucoma with normal eye pressure of 16, how soon will I experience peripheral vision loss?

Glaucoma progression may take years to occur and varies among individuals. Frequent eye exams with optic nerve imaging and visual field testing are the best way to detect glaucoma progression. Recent studies recommend doing 6 visual fields in the first 2 years of diagnosis.

Is any reliable DNA testing available as glaucoma runs in my family?

Glaucoma risk increases when family members are affected. However routine genetic testing for glaucoma is only indicated in research settings. Less than 5% of primary open-angle glaucoma cases currently have an associated genetic defect. The genes tested so far – myocilan, OPTN and TKB1 – have a low positive rate.

Genetic testing is helpful for juvenile open-angle glaucoma (JOAG) (onset of glaucoma younger than age 30). Different myocilan gene variants are associated with JOAG and they can be present in up to 63% of cases. The other situation where genetic testing is used is in primary congenital glaucoma (age less than one year).

If you are over 40 with no family history of JOAG, then genetic testing is not advised.

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.

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.

I have glaucoma and use drops every day. My levels are consistent most of the time. My doctor wants me to undergo the Heidelberg ocular imaging test every 6 months. How often do I need the test?

Most glaucoma tests are recommended once to twice a year. Tests will vary in image quality and alignment from visit to visit. The more tests that are done the less variable the results will be and the more accurately any change in the appearance of the optic nerve will be detected. Sometimes it can take 10 tests before any meaningful change is detected and reliable.

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.

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.

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.

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.

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.

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.

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.