Question:
Four months ago I complained to my optometrist that my peripheral
vision was blurred. I asked if it could be glaucoma. My pressures were
17 and 18. I asked about normal tension glaucoma. She explained that
they look at three things to diaganose glaucoma: the pressures, the
optic nerve, and the visual field. I did a visual field test three
times but it was so inconsistent (even with my good eye) she said she
could not explain it. She did a dilated eye exam and told me my optic
nerves looked healthy but "large." She went through my records for the
past several years and noted there had been no change in the optic
nerve. I have high myopia so she explained that "large nerves"--I guess
she meant large cups--were typical with myopes. She said to show my
visual field tests to my retina specialist, which I did. He said the
test was so inconsistent it was meaningless and not to worry about
it--something about that kind of test not being sensitive enough for
high myopes.
Now my blurry peripheral vision has advanced considerably and I am
expecting, as my doctor now says is likely, a diagnosis of very
advanced glaucoma. My retina specialist, who also didn't notice any
optic nerve damage but finally had me do another visual field test,
says that sometimes optic nerve damage is subtle and easily missed.
Does that sound likely? If so, how do normal tension glaucoma patients
ever get diagnosed before it's almost too late? I have so much vision
loss now I think it's almost too late for that eye.
Answer:
In some ways glaucoma can be one of the most difficult things to test for...
there is no single "glaucoma test" that gives you a straight yes or no
diagnosis. Glaucoma is diagnosed by doing a number of tests (including
pressures, visual fields, and optic nerve evaluation, and others too), then
looking at the patient's age, family history, and forming an overall
opinion. Sometimes the information gathered makes it easy to say "yes you've
got it", but often the information is not conclusive and it's a bit of a
judgement call.
Optic nerve apperance varies between individuals, and some people are born
with a healthy optic nerve that has the appearance of a glaucomatous one.
Therefore a suspicious looking nerve is an indicator of possible glaucoma,
but certainly not definitive proof. Even the same test repeated over time
can give different results - eg. pressures can vary from day to day, and
within the day; and visual field tests can fluctuate from one test to the
next - only a consistent defect repeated over time is conclusive. Often
concentration or tiredness can create an inconsistent visual field result,
so a suspcious visual field is usually just repeated at some future date for
verification.
Normal-tension glaucoma is even harder to diagnose, as one of the main
indicators of glaucoma (raised intra-ocular pressure) is not present. And
the decision to diagnose glaucoma, and therefore put someone on daily
eyedrops for the rest of their life, is not taken likely. So the diagnosis
is not made on the basis of just one or two suspicious findings, but a more
complete pattern or some more definititive test results.
Having said all of this, if your glaucoma is advanced enough that you can
notice blurry peripheral vision yourself, then this should have been very,
very obvious on the visual field test. Usually computerised field tests pick
up defects years earlier than they are actually noticed by the person.
