Excerpts
From: The International Glaucoma
Review, Volume 10-2, 2008
(and it's supplement)
Establishing Glaucoma Guidelines for Clinical Glaucoma Care
It seems that we cannot scan a journal or open our mail without
finding information about a new clinical practice guideline
being promulgated by a professional organization or a manufacturer
who assembles a group of experts to opine on a particular
topic.
All guidelines should describe explicitly the methods used
to search, grade, and synthesize the evidence. The strength
of the recommendations should be graded on the quality of the
identified evidence. Such systematic validation is a formidable
task as it is tedious, time consuming and costly. This may
be, in large part, why there are so few worthy guidelines.
Glaucoma guidelines provide the promise of providing valid
and practical information to busy clinicians. However, much
of glaucoma clinical care is still based on weak or no evidence.
Therefore, it also should be clear that there is a compelling
need for more and higher quality clinical investigation to
enhance our evidence-based knowledge base of glaucoma management.
Diurnal Aqueous Flow
It is well known that the rate of aqueous humor flow during
the nocturnal/sleep period is about half the rate during
the diurnal/wake period. This implies a 2:1 ratio for the
daytime versus the nighttime rate of aqueous humor flow.
Most importantly, change in the outflow facility was found
to be insignificant, which failed to explain why the nighttime
IOP did not drop along with the nighttime drop in aqueous humor
formation.
For a drug acting on aqueous humor formation, a significant
nighttime efficacy is not expected since aqueous formation
is already very low. Recent studies also indicated that, for
a drug acting on aqueous flow, such as a prostaglandin analog,
the nighttime efficacy can be less than its daytime efficacy.
This intricacy occurs possibly because the outflow resistance
is not a major player in setting up the nighttime IOP as shown
in this article. None of the currently available IOP-lowering
drugs have a significant effect on episcleral venous pressure.
IOP Fluctuation and Progression
Based on data from the Diagnostic Innovations in Glaucoma Study
(DIGS), which confirmed the findings of the Early Manifest
Glaucoma Trial:
“Long-term IOP fluctuation or variation was not found to be
an independent risk factor for progression.”
“At the present time, there is no Oxford Level I evidence that
short-term or long-term IOP fluctuation or variation is an
independent risk factor for glaucoma progression.”
Event- Versus Trend-based Criterion for Progression
“We must also realize that only if fields are obtained with
reasonable time intervals will progression be detectable
within a reasonable time – demonstration of progression will
require a minimum of four to five tests.”
M & T:
This is an excellent opportunity to stress to the reader that
“progression” seen at one or two (or even three) follow-up
visual fields is perhaps “apparent” (or “pseudo”) progression.
Always remember that visual fields, like any other single piece
of the glaucoma diagnostic puzzle, is indeed, only one parameter
of the multifaceted glaucoma evaluation, and must be considered
in light of ALL the diagnostic entities.
Caffeine is NOT a Risk Factor for Glaucoma
In a rigorous cohort study with nearly thirty years of follow-up,
the authors found no increased risk of glaucoma with increasing
amounts of caffeine (even though) the large sample size of
the study increases the risk of finding a statistically significant
result that is not clinically significant. When our patients
ask us about caffeine intake and glaucoma, we should tell
them that caffeine was not found to be associated with glaucoma.
Anticoagulants in Glaucoma Surgery
In this study, there was no consensus on how to manage anticoagulation
in patients undergoing glaucoma surgery. The balance between
risking a bleeding issue, such as a suprachoroidal hemorrhage,
hyphema, or subconjunctival blood in the filtration zone
is weighed against the concern about a thromboembolic event,
such as a cerebrovascular accident or pulmonary embolism.
The majority of the surgeons who were surveyed (2/3) did
not discontinue any anticoagulation prior to the operation
(but) there needs to be a case-by-case determination about
cessation of anticoagulation.
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