65
EW GLAUCOMA
August 2017
Contact information
Chen: Theresa_chen@meei.harvard.edu
Kook: mskook@amc.seoul.kr
Tanna: atanna@northwestern.edu
help distinguish between myopic
and glaucomatous changes."
Unfortunately, myopia can
cause artifacts that make even the
OCT unreliable.
"Myopic eyes magnify the scan
circle around the optic disc so we
are actually measuring the RNFL
thickness farther away from the
ONH than usual," Dr. Tanna said.
The RNFL is thinner more distally to
the optic nerve and when compared
to values for the more proximal lo-
cations in reference databases, may
appear to be thinner than normal,
he explained.
"For each diopter of myopia, the
average RNFL thickness is reduced
by an average of 1.3 microns," he
said. "Also, the superotemporal
and inferotemporal RNFL bundles
are often shifted temporally, more
closely together, in myopic eyes," he
said. This has the effect of creating
a mismatch between the expected
RNFL thicknesses in the reference
database and the actual thicknesses
that arise due to altered distribution
of the RNFL around the optic nerve.
A careful look at the RNFL thickness
map provided in each OCT printout
can often help identify these RNFL
thickness profile shifts in myopic
eyes.
To make matters worse, other
artifacts in myopic eyes may not
be consistent over time, such as
segmentation algorithm errors due
to peripapillary atrophy. Therefore,
baseline scans may not provide
an adequate benchmark to detect
change in these eyes over time, as
the artifacts can change as well, he
said.
Practical applications
Imaging of the RNFL with OCT is
tremendously helpful in most eyes
with glaucoma. Some scans will be
invalid due to the presence of arti-
facts. Knowing what these artifacts
are and where to look to identify
them can help clinicians avoid
making clinical decisions based on
incorrect information. EW
Reference
1. Liu Y, et al. Patient characteristics asso-
ciated with artifacts in Spectralis optical
coherence tomography imaging of the retinal
nerve fiber layer in glaucoma. Am J Ophthal-
mol. 2015;159:565–576.
Editors' note: Dr. Tanna has financial
interests with Carl Zeiss Meditec. Drs.
Chen and Kook have no financial
interests related to their comments.
Pinch no
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