Excerpts
From: The International Glaucoma
Review, Volume 10-3, 2008
Imaging Technology in Glaucoma
Today we have several instruments that provide objective and
quantitative measurements that are highly reproducible and
show very good agreement with clinical estimates of optic
disc and visual function. Yet, many clinicians continue to
wonder how to use these in their clinical practices and clinical
trials. Now, more than ever, it seems to be an appropriate
time to assess the use of imaging in clinical practice.
Optic nerve head photography, particularly stereoscopic, provides
a permanent record, but generally is not used because it is
impractical and cameras generally are not available. Moreover,
the differences among clinicians in their interpretation of
photographs, either for diagnosis or progression, are remarkably
large.
Given the substantial advances in glaucoma imaging, it is important
to remind clinicians that current glaucoma diagnosis cannot
be solely instrument-based. Rather, the imaging information
should be considered as being complementary to other clinical
measures. Nevertheless, given the variability of drawings and
subjective photographic interpretation, imaging may elevate
the assessment of the optic nerve by the general clinician,
perhaps to the level of a fellowship-trained glaucoma specialist.
Moreover, imaging enables the clinician to objectively evaluate
the papillary RNFL (retina nerve fiber layer) that changes
early in the course of the disease, which cannot be readily
measured by clinical examination. Finally, imaging enables
a practical comparison of a patient with a population of age-matched
normals, facilitating the ability to identify abnormal structural
features. Clinicians should not make clinical decisions based
solely on the results of one single test or technology.
M & T:
This is wonderfully stated, and should be earnestly taken to
heart by all clinicians!
Appropriate Use of Technology in Glaucoma
Diagnosis
Clinicians should be cautious when using a single parameter,
or a single technology, to facilitate glaucoma diagnosis.
The range of normal optic disc topography and RNFL thickness
values is large, and study results often vary across populations.
Glaucoma Management
Clinical assessment of the optic nerve is a cornerstone of
managing patient with glaucoma, as well as those at risk for
glaucoma. Glaucomatous optic discs can predict visual function
loss. Careful clinical examination of the optic nerve structure
is essential for accurate diagnosis of glaucoma.
Corneal Hysteresis
Corneal hysteresis is at present a manifestation of some aspect
of the material properties of the cornea, but what those properties
are remains unclear.
Swimming Goggles and IOP
A study found that IOP increased by a mean of 4.5mmHg while
wearing swimming goggles, and this increase was sustained
for the duration of goggle wear. The study provides useful
practical information for at-risk glaucoma patients who wish
to go swimming (and wear goggles).
Stratus OCT and RNFL Measurement in Myopes
Vernon et al. sound a note of caution in interpreting Stratus
OCT results in highly myopic eyes. The retinal nerve fiber
layer (RNFL) measures significantly thinner in high myopes
than in eyes with less than six diopters of myopia, most
prominently in the nasal clock hours.
Glaucoma Screening
- Primary angle-closure glaucoma (PACG) accounts for approximately
25% of all glaucomatous optic neuropathy worldwide, but 50%
of bilateral glaucoma blindness.
- Some Asian populations
have a high prevalence of advanced angle-closure glaucoma.
- There is evidence that limbal anterior chamber depth (LCD)
may be an appropriate screening test for angle closure.
- Using a LCD of 25% corneal thickness as a cut-off, all
those cases falling below this level would require gonioscopy.
Approximately 4% of occludable angles may be missed by this
method.
M & T:
Being that the glass is half full, this gives a 96% level
of sensitivity without the extra time and effort of gonioscopy.
- Screening of high-risk subgroups could be more cost-effective
than screening the entire population.
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