Optic Disc Imaging
Chat Highlights
March 17, 2010
Steven Beck, Editor
On Wednesday, March 17, 2010, Dr.
Michael Pro, a glaucoma specialist at Wills, and the glaucoma
chat group discussed " Optic Disc Imaging".
Moderator:
Welcome back Dr Pro. Our topic this evening is Imaging of the
Optic Disc. First, can you tell us what is the optic disc? Is
that the same thing as the optic nerve?
Dr. Pro:
Yes, it is the same thing, except to say that the optic disc refers
to the segment of the nerve visible when you look in the eye.
The nerve itself courses back through the skull to eventually
connect with the back part of the brain, where the raw image information
is converted into sight that you can perceive.
P:
So you really don't see the entire nerve, you see the disc?
Dr. Pro:
Yes, you see the very end of the nerve, sort of the like slicing
a TV cable and looking at only the round end of that cable.
P:
Dr Pro, what can you tell us about new information on imaging
that was presented at the recent AGS meeting?
Dr. Pro:
Well, the big news was trying to correlate imaging studies into
expected visual field defects. This is interesting, because we
generally look at these things a bit in isolation. We have always
tried to correlate the visual field abnormality with the appearance
of the nerve. But we have not been able to accurately predict
what a visual field defect would look like after examination of
the nerve. In fact, in many cases we are surprised by how different
the field can look in two different individuals who have very
similar appearing nerves. Ultimately this type of research may
lead to an era where it is less important to subject the patient
to frequent visual fields and where the status of an individual's
glaucoma is assessed by serial optic disc imaging.
P:
What is the difference between optic disc photography and optic
disc topography?
Dr. Pro:
Topography generally refers to scanning laser ophthalmoscopy.
This technology is used in the Heidelberg Retinal Tomograph (HRT).
The concept here is to take a recording of the elevation points
of the optic nerve as it enters the eye. Where the elevation of
the nerve is less than a normal database population, this suggests
possible glaucoma. Also the nerve can be scanned periodically
and compared to a baseline scan. If there is progressive change,
that may indicate the glaucoma is getting worse. With a photo,
the examiner looks at a baseline image, and a follow-up, and tries
to find areas where there has been a change.
P:
Are these tests used for diagnosing glaucoma or for tracking progress?
Dr. Pro: Both.
The strength of a photo is that it is an old technology that is
readily understood by any ophthalmologist. Newer imaging devices
can come and go, but a disc photo from 1990 looks just like a
disc photo from 2010. An HRT has software to help detect glaucoma
and track progression. With a photo, the doctor has to be educated
to detect glaucoma and track progression. Funny thing is, with
an experienced examiner, the detection of glaucoma and of progression
is about equal with disc photos and current imaging technologies.
That will probably change as the imaging devices evolve and the
detection/progression software matures.
[At this point there was a power outage and the doctor was disconnected.
The Optic Nerve Imagining chat continued
on May 19]
On April 7, Dr. Pro discussed "Glaucoma Drainage Implant Complications"
in the Chat room. Click here for highlights
of that meeting.
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