EyeWorld is the official news magazine of the American Society of Cataract & Refractive Surgery.
Issue link: https://digital.eyeworld.org/i/387844
EW GLAUCOMA 94 October 2014 by Tony Realini, MD, MPH Using technology to detect glaucoma progression not detect early defects or changes in late-stage glaucoma." Rate of change matters The rate of change, whether by structural or functional assessment, is an important parameter when evaluating glaucoma progression. Rate of change can also help prognostication; a slow rate of change in an elderly patient is un- likely to result in visual impairment within that patient's lifetime. Conversely, rapid progression can pose a threat to visual function. "By measuring the rate of change, we can identify the fast progressors, identify risk factors for fast progression, and assess response to therapy," said Joseph Caprioli, MD, University of California, Los Angeles. "Measuring progressive NFL changes using OCT is the way to go in the future," he said. Detecting progression in advanced glaucoma "Patients with advanced glaucoma are on the cusp of or already have functional impairment," said Jody Piltz-Seymour, MD, Philadelphia, "and having greater visual field loss at baseline is a risk factor for both future progression and rapid pro- gression." "It is difficult to see progre - sion by structural assessment in Many cases of suspected progression are resolved with retesting. The Humphrey Field Analyzer (Carl Zeiss Meditec, Jena, Germany) features the Guided Progression Analysis (GPA) analytic package. This analysis averages 2 baseline tests, then compares each subse- quent test to the baseline values at each test location. The output flags locations that show change from baseline that exceeds expected inter-test variability. Based on the number and location of changed points, the test will be interpreted by the software as stable, or as indica- tive of possible or likely progression if changes are observed on 2 or 3 consecutive post-baseline tests, respectively. The GPA approach has been validated in the Early Manifest Glaucoma Trial, Dr. Johnson said. The GPA also provides a trend- based analysis derived from the rate of change of the Visual Field Index, a single metric that summarizes the entire visual field as a value between 0% (blind) and 100% (normal). The VFI is largely dependent upon the mean deviation and weighs central points more heavily than peripheral points, said Dr. Johnson. "The GPA's analysis of VFI change can provide an estimate of the rate of progression over time," said Dr. Johnson, "but because of the nature of its derivation, it will normal subjects so that thin values are flagged by the analytic software. If a change is seen, be proactive rather than reactive, Dr. Varma said. "It is advisable to not make clinical decisions based solely on the results of imaging studies," he said. Change from test to test may be artifact and not indicative of true progression. "It is important to confirm the change with retesting, and correlate the observed structural changes with functional changes seen on visual field testing. Function Interpretation of serial visual fields is an ongoing challenge for all clinicians, including glaucoma specialists. What is to be made of the patient whose field gets worse, then better, then worse, then better again? The test is subjective and highly prone to artifact. Even more so than with structural testing, change observed on serial visual fields is not necessarily indicative of true disease progression. "Practitioners tend to overcall progression," said Chris Johnson, PhD, University of Iowa, "in part be- cause of failure to confirm possible progression with retesting." Patients universally dislike the visual field test and may protest when asked to repeat the test within a short time—a week or a month— but it is crucially important to do so. W e have learned from many clinical trials that despite our best efforts to control IOP with medications, laser, or even surgery, some of our patients with glaucoma continue to progress. Detecting glaucoma progression has been a hot topic over the last several years as the technology underlying both visual fields and optic ne ve imaging has improved. We can now achieve high resolution, highly reproducible quantitative imaging of the peripap- illary nerve fiber layer (NFL) using spectral domain OCT, and validat- ed progression detection software is available for serial visual field analysis. How can we best apply this technology in clinical practice to op- timize glaucoma patients' outcomes? Structure "Structural damage usually precedes functional damage," said Rohit Varma, MD, University of Southern California. Therefore, "structural as- sessment is best suited for assessing the presence of damage and change over time in early stage glaucoma." For stable patients at low risk for progression, imaging once per year is reasonable. For patients at high risk of progression, more frequent imaging may be warrant- ed. Documenting the patient's high risk status in the medical record is important to justify medical neces- sity when imaging tests are to be conducted more often than once annually. Commercially available OCT platforms can reliably detect small changes in NFL thickness indicative of glaucoma progression. However, there are important issues to consid- er when change is detected from one scan to the next. "It is important to assess the quality of the scan," said Dr. Varma. Decentration of the optic nerve in the image field, or even small degrees of head tilt, can alter the scan results and can mimic progression, he said. Once image quality is estab- lished, the OCT output should be systematically reviewed. "Assess both the overall and the sectoral retinal NFL thickness values," Dr. Varma advised. These values will be compared to a reference database of Glaucomatous disc cupping Source: Karl Brasse, MD, EyeLand Design