SEARCHING FOR THE "Holy Grail"
SEARCHING FOR THE "Holy Grail"
The first part in this series describes how the evolution in glaucoma progression technology is impacting optometrists.
BY THE OPTOMETRIC MANAGEMENT STAFF
The single, gold-standard test to detect glaucoma progression is elusive — "the ‘Holy Grail’ for optometrists, ophthalmologists and vision scientists alike," says Mitchell Dul, M.S., O.D., New York.
"Obviously, the earlier we can make the diagnosis and intervene, the better the long-term prognosis," says Deepak Gupta, O.D., Stamford, Ct. "The same basic principle applies for early detection of glaucoma progression." Dr. Gupta notes that while the options for managing glaucoma are superior "to what we had 20 years ago, many patients will still demonstrate a worsening of their condition."
To manage progression, clinicians depend on several diagnostic tests. "We commonly consider some combination of field progression and structural nerve changes to be our most reliable barometer," says Elliot Kirstein, O.D., Cincinnati, Ohio. "As glaucoma progresses, we may see field changes in advance of notable structural changes, or we may see the opposite."
Change in IOP
As a basic step in an examination for a patient with glaucoma or a glaucoma suspect, the clinician ensures that intraocular pressure is controlled at the target level or below. James Fanelli, O.D., Wilmington, N.C., emphasizes the importance of looking at all glaucoma measurements, including IOP, in depth.
"The term ‘controlled IOP’ is not simply a matter of having a flow chart in your patients' records and looking at IOP trends over time," says Dr. Fanelli. "In busy clinical practice, these flow sheets are immensely helpful, but we need to keep in mind that they give us only a snapshot of what IOP is at any given time, usually four to five times per year with the typical glaucoma patient. At face value, the glaucoma flow sheet that we use in clinic tells us overall ranges of IOP on our quarterly glaucoma checks."
Dr. Fanelli notes that IOP fluctuations and diurnal curves play a role in progression. "Therefore, it is important to measure IOP over various times of the day to determine if those nicely compacted IOP measurements that we get for a patient at each 9 a.m. visit still hold true later in the day."
Dr. Fanelli says that when IOP is generally within 2 mm Hg to 3mm Hg of the target at various times of the day, "it is fair to assume that IOP is ‘stable.’"
Comparing visual fields tests over time provides "insight into the progressive damage to a patient's visual field, but it has limitations," says Dr. Gupta. For example, if the field demonstrated signs of functional change, it was difficult and subjective to determine if the change was a result of test variability or true disease progression. For this reason, Dr. Gupta recommends multiple visual field tests before changes can be labeled as "true progression."
|"As glaucoma progresses, we may see field changes in advance of notable structural changes, or we may see the opposite."|
— Elliot Kirstein, O.D.
An obstacle to identifying progression with visual field tests is in differentiating "true progression vs. patient variability among tests" says Dr. Gupta. "In fact, readings are rarely the same from test to test, even in patients with no ocular disease. Patients with glaucoma demonstrate even a greater test/re-test variability." Progression analysis software (Glaucoma Progression Analysis, developed for the Humphrey Field Analyzer II [Carl Zeiss Meditec] uses mathematical formulas to calculate variability. This software can help identify progression in the presence of visual fields defect caused by cataracts or other ocular disease.
Many optometrists employ retinal cameras to look at the optic nerves of patients who have glaucoma. With fundus photography, "the careful comparison of serial photographs often demonstrates change, but only after enough structural damage has been done for the clinician to notice the changes," says Dr. Gupta.
Janet M. Mint, O.D., Jacksonville, Fl., says that the introduction of scanning laser technology provided a new way of thinking when evaluating glaucoma progression. "With this new information, eye care practitioners can focus on structural analysis to determine glaucoma progression," says Dr. Mint. "We are able to look at the optic nerve, nerve fiber layer and macula in a way that we never could before."
Dr. Dul cautions that progression analysis is "still maturing" in imaging devices (i.e., the Heidelberg Retinal Tomograph [HRT, Heidelberg Engineering], scanning laser polarimetry [GDx, Carl Zeiss Meditec] optical coherence tomography [OCT] and more recent technologies, including the retinal thickness analyzer [RTA 5, Marco] and spectral domain OCT). Each of these technologies now offers some form of progression analysis (which will be explored in the September issue of OM).
At a recent glaucoma symposium at the National Institute of Health, Wiley Chambers II, M.D., acting director of the Division of Anti-Infective and Ophthalmic Products of FDA's Center for Drug Evaluation and Research, reminded attendess that the FDA does not yet consider structural change a valid endpoint in glaucoma. "Structural measurements are more likely than visual function outcomes to be used in the future as primary endpoints," said Dr. Chambers. (The FDA-recognized endpoints for glaucoma are visual acuities, color vision, contrast sensitivity and visual fields.)
While there are no longitudinal, multicenter double-blind studies on imaging devices and glaucoma progression, "there are several cross-sectional studies suggesting that structural change is important," says Dr. Dul. "Clinically, it is intuitive to assume that structural change should warrant consideration of a change in treatment."
Shades of gray
As far as technology has come, effective glaucoma management must "stem from excellent individualization of care," says Dr. Kirstein. "While it should seem obvious that large changes in fields, imaging, new disc hemorrhage or pressures should send clear signals to step up the therapeutic pace, our decisions are seldom so black and white," says Dr. Kirstein. "Variables such as age, systemic health and stage of disease tend to make these clinical determinations very gray."
The key is excellent clinical data, says Dr. Kirstein, which means "reliable IOP measurement, repeatable fields and imaging progression analyses, supported by careful individualized clinical evaluation."" OM
In our September issue, Optometric Management will present a guide to how manufacturers are incorporating glaucoma progression technology into their diagnostic instruments.
Optometric Management, Issue: August 2008