Excerpts
From: The International Glaucoma Review, Volume 8-1,
2006
(Fifth in a Series)
Glaucoma Worldwide
- A recent review of the data on prevalence of glaucoma for
the coming 4 to 14 years indicates that the vast majority of
angle-closure glaucoma (ACG) patients will be seen in Asia
(87%), and half of the predicted blindness is due to ACG.
M & T Commentary
We need to be very attentive to our Asian patients since they
tend to be genetically predisposed to narrow angles. It may
well be that all Asian patients should undergo gonioscopy
(unless they are highly myopic with wide open Van Herrick
angles).
The number of people with glaucoma worldwide in 2010 and
2020: Quigley HA; Broman AT
British Journal of Ophthalmology 2006; 90: 262-267
Results: Women will comprise 55% of OAG (open-angle glaucoma),
70% of ACG, and 59% of all glaucoma in 2010. Asians will represent
47% of those with glaucoma and 67% of those with ACG.
Conclusion: Glaucoma is the second leading cause of blindness,
disproportionately affecting women and Asians.
IOP and Glaucomatous Damage
- Erik Greve, MD, PhD states, “we are not so much interested
in the absolute level of IOP (unless it is high) as in the
relative raised IOP. It is the raised IOP (relative to the
original) that is considered a risk factor for the development
of glaucomatous damage.” He explains, ”An original IOP of 12mmHg
may rise by as much as 50% to 18mmHg and still be considered
normal.” Thus, “a good percentage of so-called normal pressure
glaucomas are ‘simply’ raised pressure glaucomas.” Greve concludes,
”we will have to rely on the detection of the earliest damage,
or even better, the earliest change of damage,” to identify
disease.
M & T Commentary
A very excellent point. This also emphasizes the value of getting
prior patient records as these may provide an indication
of IOP behavior over the past few years.
CCT and Optic Disc Morphology
- The Australian Twins Eye Studies recent report states that
based on their findings, “CCT is highly inheritable.” This
same group reports that optic disc morphology is highly inheritable
as well.
Correlating Structure and Function
- Reported at the Glaucoma Society of India Meeting, “Measures
of function and structure are synergistic in everyday clinical
practice and should be used in combination whenever diagnostic
uncertainty exists.”
Glaucoma Screening
- In The Nottingham Family Glaucoma Screening Study (Sung et
al.), “High frequencies of OAG/suspect OAG in siblings were
confirmed.” This study found that, “About half of siblings
initially diagnosed with OAG had visited optometrists in the
previous year, indicating low sensitivity for OAG detection
at those visits.”
M & T Commentary
We are unaware of the details of this study, but it indicates
optometric care is equally as poor as ophthalmologic care,
where roughly 50% of patients with glaucoma were missed or
misdiagnosed, regardless of whether seen by an optometrist
or ophthalmologist. For goodness sake, we all need to wake
up and be attentive!
- The AIGS (Associated International Glaucoma Society) reports
concludes, “mass screening is not well justified, but screening
of high-risk groups improves yield and lowers costs per positive
test.”
Basic Glaucoma Research Notes
- The underlying defect in the trabecular meshwork that causes
the relatively elevated IOP in open-angle glaucoma is unknown.
- The pathophysiology that leads to obstructed aqueous humor
outflow in the trabecular meshwork in glaucoma is not fully
understood. Mechanical stress is emerging as an important regulator
of homeostasis in many tissues including the trabecular meshwork
(TM), which is distended and stretched during IOP elevation.
Visual Field Progression
- One of the most challenging aspects of detection of visual
field progression is the determination of optimal frequency
of testing. Jansonius proposed a theoretical framework to compare
two different strategies for detection of progressive visual
field loss in glaucoma. In the first strategy, visual field
testing is performed at fixed intervals of six months. In the
second strategy, the frequency of testing is set to one test
per year as long as the fields are apparently unchanged, but
as soon as progression is suspected, subsequent visual field
tests are performed shortly thereafter to confirm or discard
progression. Considering a need of two additional visual fields
to confirm progression, he concluded that the first strategy
results in a maximum delay of 18 months until progression can
be confirmed, where the second strategy results in a maximum
delay of only 12 months.
The results of Jansonius are interesting and in line with what
is generally done in clinical practice, that is, in the presence
of suspicious progression, clinicians tend to request confirmatory
visual fields in a short time interval, However, the calculations
of time delay until confirmation of progression, as presented
in the paper, are a simplification of the reality. They assume
that a clinician is able to unambiguously detect a visual field
that shows suspicious progression and that confirmation of
deterioration can always be performed with two additional tests.
Clinical experience and results from clinical trials show us
that this might not always be the casex In fact, a combination
of an optimal frequency of testing and optimal strategy for
detection of visual field progression in glaucoma has yet to
be determined.
M & T Commentary
We simply do visual fields on an annual basis unless one or
more clinical parameters prompt us to shorten the time between
evaluations; in this specific case, visual field testing.
Each patient’s care must individualized.
Measuring Ocular Perfusion
- Despite much research, x a number of issues regarding the
reproducibility and validity of Heidelberg retinal flowmetry
(HRF) measurements remainx Further research regarding ocular
blood flow technologies utilized, and cautious interpretation,
will continue to shed light on the accuracy and limitations
of perfusion measurements.
M & T Commentary
For now, assessing presumed “ocular blood flow” is still in
research. There is no uniform recommendation to include such
measures (because they are not yet ready for use in clinical
care) into the office care of patients. When there is tried
and proven technology, we have no doubt it will (one day)
be a component of the comprehensive glaucoma evaluation.
That day is not yet here.
Cataract Extraction for ACG (Angle-closure Glaucoma)
- Eyes with a thin artificial lens do not develop ACG. All papers
point in the direction of a benefit of cataract extraction
for both acute and chronic ACG, at least for the majority of
patients. It is suggested that even in the presence of early
cataract, there is a good reason for cataract extraction as
a primary procedure, particularly in APACG (acute partial angle-closure
glaucoma) where angle closure is recent and the effect on IOP
large. The effect of cataract extraction in ACG is thought
to depend on the elimination of pupillary block and most importantly
on the remaining function of the trabecular meshwork. Cataract
extraction in ACG may not always be easy. In experienced hands
this should not influence the final result. Furthermore the
increased surgical difficulty is off-set by the increased safety
of the subsequent trabeculectomy if needed.
M & T Commentary
We completely agree! Once iridocorneal angle patency is truly
threatened remove the crystalline lens if at all reasonable.
We can think of no cataract surgeon who would quarrel with
this definitive approach.
Latanoprost and MMP
- Intraocular pressure reduction following topical treatment
with latanoprost has been linked with increased ciliary muscle
expression of four types of human matrix metalloproteinases
(MMPs), and two types of tissue inhibitors of matrix metalloproteinases
(TIMPs). x Variable inductions for many MMP types may contribute
to the variable IOP reductions observed among different patients
receiving latanoprost.
M & T Commentary
This point/counterpoint of various extracellular proteinases
certainly squares with the known mechanisms of prostaglandin
influence, and may indeed offer an explanation as to why
some patients exhibit unique responses to prostaglandins.
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