feature
Taking
Glaucoma Diagnosis and Management to the Next Level
New
diagnostic instruments and drug therapies are giving clinicians the tools they need
to manage glaucoma better than ever before. Still, challenges remain. Read on for
the latest news.
By Murray Fingeret, O.D
The
art of diagnosing and managing open-angle glaucoma continues to evolve before our
eyes at breathtaking speed.
Over the past decade, new, well-tolerated drug
therapies, technologies and instrumentation in the area of diagnostic testing have
been developed, providing clinicians unqualified help in the detection and management
of the disease.
Just around the corner are new tools
that will give doctors the ability to gauge IOP more accurately and that are less
affected by corneal thickness measurements. We have new structural tests to measure
optic nerve and retinal nerve fiber layer (RNFL) damage at the earliest stages and
new functional tests for more accurate assessments of visual field loss. And new
developments are yet to come.
Here's a snapshot of where we've been
and where we're headed in the future.
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Top: The Moorfields Analysis printout from the HRT II reveals several suspicious
sectors in both eyes. Bottom: The GDx VCC printout shows the retinal nerve fiber
layer (RNFL) reduced in thickness.
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Pachymetry comes of age
Not long ago, the landmark Ocular Hypertension
Treatment Study (OHTS) alerted us to the fact that corneal thickness plays a significant
role when interpreting IOP measurements accurately.1 We learned that
measured IOP is lower in thin corneas and higher in thick corneas than true IOP.2
Findings from the OHTS study also support
routine use of pachymetry in glaucoma patients, and this test is now considered
an integral part of glaucoma evaluation.
Looking ahead, several companies have,
or plan to develop, new tools to measure IOP that may produce readings less affected
by corneal thickness. What needs to be determined, however, is the role pachymetry
will play when these new forms of tonometry are used.
Since thin corneas appear to be a risk
factor for glaucoma, even when IOP is corrected, this information still may be important
regardless of the method of tonometry.3
What we do know is that IOP is not
part of the definition of glaucoma. IOP simply conveys risk, both for developing
glaucoma when ocular hypertension is present and for progression when glaucomatous
optic neuropathy is diagnosed.
Strides in optic nerve, RNFL evaluation
Twenty years ago, a quest began to develop methods
that would measure the optic nerve and surrounding retinal tissue automatically
and objectively — similar to how an automated perimeter evaluates functional
vision.
The goal was to reduce the subjectivity
in evaluating the optic nerve and the RNFL. We wanted to use methods that would
give us measurements for areas (quantification) where qualitative answers (how large,
how deep) were previously given.
We've gotten close to succeeding.
Optic nerve and RNFL imaging instrumentation
have been commercially available for more than 10 years. In the last 5 years, it's
become increasingly important in our evaluation of patients at risk for glaucoma
and those already diagnosed (Figures 1A, 1B).
Visual field still important
We've
also seen a strong drive to develop new tools for detecting visual field loss at
its earliest stages.
Standard threshold visual field
testing, using a white-on-white target, is an excellent test, but it may not detect
damage at the point when optic nerve and RNFL loss occurs.
We've learned and have now accepted
that a patient can have glaucomatous optic nerve damage and still have a full visual
field (preperimetric or early glaucoma).3
This type of patient has sparked the
development of blue-yellow or Short-Wavelength Automated Perimetry (SWAP), and Frequency
Doubling Technology (FDT) peri-
metry4,5 to detect early visual field
loss.
Both SWAP and FDT
have, in turn, spurred newer versions, which were recently released, such as SITA SWAP and FDT Matrix.
Unlike imaging instrumentation, these tests haven't been widely accepted by clinicians
as early diagnostic tools, although they're still evolving and offer important
information for certain patients.
For instance, these tests may reveal
early field loss in certain individuals.
The issue of compliance
Many patients under therapy for ocular hypertension
or glaucoma often don't take their medications as directed.
Recent studies have illustrated the
magnitude of this problem and stressed the importance for clinicians to recognize
that lack of compliance commonly occurs. 6,7,8,9
Luckily, prostaglandin analogues, the
most commonly prescribed agents for glaucoma, offer significant advantages and help
in improving compliance.
Still,
as good as these agents are in reducing IOP, approximately 40% of patients require
additional medications to lower it even further. 10,11
Recent studies have shown that
topical carbonic anhydrase inhibitors have additional IOP-lowering effects when
added to prostaglandins.12
Undoubtedly, our understanding of glaucoma
diagnosis and management has and will continue to evolve over time as new therapies
and diagnostic tools become available. In this supplement, we hope to share some
of the latest trends with you.
Murray Fingeret, O.D., is Chief of Optometry
at the Brooklyn/St. Albans Campus of the Department of Veterans Affairs, New York
Harbor Health System. He is a Clinical Professor at the State University of New
York College of Optometry in New York City. In addition to publishing articles and
co-authoring several textbooks, Dr. Fingeret is President of the Optometric Glaucoma
Society.
References
11.
Gordon MO, Beiser JA, Brandt JD, Heuer DK, et al. The Ocular Hypertension Treatment
Study. Baseline Factors That Predict the Onset of Primary Open Angle Glaucoma. Arch
Ophthalmol. 2002;120:714-720.
12.
Tonnu PA, Ho T, Newson T, Sheikh A EL, et al. The influence of central corneal thickness
and age on intraocular pressure measured by pneumotonometry, non-contact tonometry,
the Tono-Pen XL, and Goldmann applanation tonometry. Br J Ophthalmol. 2005;89:851-854.
13.
Mederios FA, Sample PA, Zangwill LM, Bowd C, et al. Corneal thickness as a risk
factor for visual field loss in patients with preperimetric glaucomatous optic neuropathy.
Am J Ophthalmol. 2003;136:805-813.
14.
Bagga H, Feuer WJ, Greenfield DS. Detection of psychophysical and structural injury
in eyes with glaucomatous optic neuropathy and normal standard automated perimetry.
Arch Ophthalmol. 2006;124:169-176.
15.
Spry PG, Johnson CA, Mansberger SL, Cioffi GA. Psychophysical investigation of ganglion
cell loss in early glaucoma. J Glaucoma. 2005;14:11-19.
16.
Kass MA, Meltzer DW, Gordon M, Cooper D, et al. Compliance with topical pilocarpine
treatment. Am J Ophthalmol. 1986;101:515-523.
17.
Kass MA, Gordon M, Meltzer DW. Can ophthalmologists correctly identify patients
defaulting from pilocarpine therapy? Am J Ophthalmol. 1986;101:524-530.
18.
Kass MA, Gordon M, Morley RE Jr, Meltzer DW, et al. Compliance with topical timolol
treatment. Am J Ophthalmol. 1987;103:188-193.
19.
Tsai JC, McClure CA, Ramos SE, et al. Compliance barriers in glaucoma: a systematic
classification. J Glaucoma. 2003;12:393-398.
10. Kass MS, Heuer DK. The Ocular
Hypertension Treatment Study. Arch Ophthalmol. 2002;120:701-713.
11. Wolters Kluwer Health, Concomitancy
Analysis, May 2006.
12. Feldman RM, Prager TC. Additivity
of Brinzolamide vs. Brimonidine 0.15% to Travoprost 0.004%. Presented at The
Association for Research in Vision and Ophthalmology; April 30-May 4, 2006;
Fort Lauderdale, FL.
Optometric Management, Issue: August 2006