Excerpts
From: The International Glaucoma
Review, Volume 10-4, 2008
Disc Hemorrhages and Treatment in the Early Manifest Glaucoma
Trail (EMGT)
The disease progression in glaucoma eyes with disc hemorrhage
is much more than that in eyes without disc hemorrhage. This
result is supported by many previous reports. It is clear that
we must treat glaucoma eyes with disc hemorrhage much more
carefully than those without disc hemorrhage.
The authors conclude that there is no relationship between
IOP lowering therapy and disc hemorrhages. While this may be
true, the mean IOP decrease from baseline at all study visits
in the EMGT was 22%. It is possible that a larger reduction
in IOP is required to diminish the frequency of disc hemorrhages.
The relationship between treatment and disc hemorrhages may
be answered definitively when we unlock the mystery of their
pathogenesis.
It is well known that the occurrence of a disc hemorrhage portends
the progression of glaucoma. The clinician is naturally going
to advance therapy, which may very well slow the progression
of glaucoma, but does not decrease the likelihood of optic
disc hemorrhages from occurring in the future. In some way,
disc hemorrhages, then, are a sign of progression of glaucoma,
but not directly related to the level of IOP, and they are
not a causal pathway of IOP resulting in glaucoma, but are
an associated sign of, perhaps, some other causative factor
as yet unidentified.
Measuring Structural and Functional Changes in the Glaucomatous
Patient
The apparent dissociation of structure and function tests does
not necessarily imply that structure and function are actually
changing at different rates. Reasons for dissociation include
high test-retest variability, learning effect, functional loss
occurring unrelated to structural damage (ganglion cell dysfunction,
media opacity) and damage is not necessarily synonymous with
retinal ganglion cell loss.
Measurement noise in part explains poor agreement between
current tests in detecting structural and functional progression.
Measurement noise is certainly unrelated: a patient with highly
variable images will not necessarily give highly variable field
results and vice versa. Further work is needed to understand
and improve measurement noise. Until noise is reduced, studies
will continue to find that structural and functional test do
not correlate when progression is evaluated.
Asymmetric POAG and Asymmetric IOP
In a study of 48 patients (96 eyes) with asymmetric POAG and
asymmetric IOP there was no evidence that ocular pulse amplitude
(OPA) – an indirect indicator for the choroidal perfusion
which reflects the ocular blood flow corresponding to the
heart pulse as a function of time – is reduced in the more
affected eye.
Findings from the Guangzhou Twin Eye Study
The Guangzhou Twin Eye Study showed that the heritability is
approximately 70-90% for axial anterior chamber depth and
drainage angle width, 60% for iris thickness and 80% for
optic disc parameters. The variations of biometric traits
that related to drainage angle dimension and glaucoma are
largely attributable to genetic effects.
Dietary Antioxidants
Many compounds with powerful antioxidant activity exist in
nature. Some of these are regarded as food and others are
plant extracts which form the basis of many traditional medical
systems, such as Chinese traditional medicine and Ayurvedic
medicine. The polyphenolic flavonoids, such as the catechins
in tea and resveratrol in red wine, have received much attention,
while coffee, dark chocolate, and soy sauce have more recently
been suggested as beneficial. The most important plant extract
currently known is that of Gingko biloba, which has both
vasoprotective and neuroprotective properties. It increases
ocular, cerebral and peripheral blood flow, improves symptoms
of Raynaud’s and intermittent claudication, reduces ischemia-reperfusion
injury, inhibits apoptosis, and stabilizes mitochondrial
function. Proof of clinical efficacy of these compounds in
glaucoma is lacking for the most part, but [are] also very
difficult to achieve. For the foreseeable future, evidence
will remain inferential and extrapolative, but there is certainly
little to lose and potentially much to gain in advocating
them.
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