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Guided Progression Analysis highly specific, study finds
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A study recently published in Ophthalmology found that, on average, the guided progression analysis showed high specificity in determining glaucoma progression.
Researchers also found that some patients are more likely to demonstrate false positives of progression than others, as detailed in their report.
Artes and colleagues conducted an observational cohort study in which they evaluated 30 patients with open angle-glaucoma from the glaucoma clinics at the Queen Elizabeth Health Sciences Centre in Halifax, Nova Scotia. Over the course of 3 months, each participant had 1 eye tested 12 times with program 24-2 SITA-Standard of the Humphrey Field Analyzer (Carl Zeiss Meditec), according to the study. Researchers then determined possible progression and likely progression with the guided progression analysis (GPA) (Carl Zeiss Meditec).
"The GPA compares each test result, point by point, with values from two earlier baseline tests," the researchers noted. "Points are highlighted on a probability plot if changes exceed the typical measurement variability derived from a group of patients with stable glaucoma. If such changes occur at three or more points and in two consecutive follow-up tests, the GPA raises an alert of “possible progression;” if they occur in three consecutive tests, an alert of “likely progression” is raised. Criteria similar to “likely progression” were used in the Early Manifest Glaucoma Trial, and the GPA has subsequently been widely adopted in clinical practice and research."
Results showed that specificity of the GPA likely progression alert was high with a false-positive alert rate of 2.6%; specificity of the GPA possible progression alert was lower with a false-positive alert rate of 18.5%.
The researchers noted that visual field variability as well as reliability indices were associated with the false-positive alerts.
"We have shown that the GPA criterion of ‘likely progression’ has high specificity on average, but that some patients are more prone to false-positive alerts than others," the authors concluded. "Rather than discouraging clinicians from using the GPA, we hope that this report helps to avoid false-positive decisions on progression in patients with uncharacteristically large variability and frequent response errors."
Disclosures: The authors have no relevant financial disclosures.
Perspective
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Carl H. Jacobsen, OD, FAAO
Visual field testing is a vitally important tool in glaucoma management. Unfortunately, obtaining quality field data and accurately noting glaucoma-related field loss is a true clinical challenge. To assist in the determination of visual field loss, Humphrey-Zeiss has developed the glaucoma progression analysis (GPA) feature.
Artes and colleagues in their cleverly designed study shed some light on the GPA’s specificity for change. They found that the GPA designation of “likely progression” is highly specific for change, while “possible progression” is less likely to be indicative of actual field loss. Interestingly, they noted a few individuals that did not follow this trend and were prone to false-positive alerts by the GPA. Having two high-quality baseline tests is one key to limiting GPA errors.
Despite the limitations of this study (duly noted in the discussion section), I feel clinicians can benefit from these results. As in other areas of glaucoma inquiry, there is considerable individual variability, but the GPA can be a helpful tool for many patients. The key is determining what tests and analyses work best for your particular patient.
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