Article Date: 8/1/2006

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.

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.

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