Assessing visual field progression in glaucoma may be more of an art than a science—and there is no one test to give reliable information that is needed about a patient, said Chris A. Johnson, PhD, DSc, FAAO, FARVO, professor, Department of Ophthalmology, and director, Visual Field Reading Center, University of Iowa, Iowa City.
One barrier when looking at progression of visual field loss in glaucoma is there can be various types of impairment, be they systemic or ocular. This can include cataracts, corneal problems, retina disease, or optic neuropathies or systemic issues such as diabetes, inflammatory, infiltrative, or compression lesions.
Other challenges include subjective analyses and reliability of results, as well as considerable variability from one test to another, Dr. Johnson said.
Another challenge is that assessing progression is usually different when comparing multi-center trials with routine management.
Click here to enlarge Image 1. The first slide presents two initial baseline visual fields and a representation of the Mean Deviation (MD) values over time in the lower left plot.
Click here to enlarge image 2. The second slide presents visual fields obtained for six follow up exams. It uses a combination of event analysis (change from baseline) and trend analysis (confirmation of change from baseline for additional tests). A change from baseline that is confirmed on the next test is classified as possible progression, and if it is confirmed on 2 successive tests (three in a row, counting the initial occurrence) it is classified as likely progression. Images courtesy of Chris A. Johnson, PhD, DSc, FAAO, FARVO.
Sometimes, circumstances specific to a patient can make assessment of visual field progression difficult. Dr. Johnson referred to a visual field from a patient who would seem to get worse every 6 months and then get better, but then get worse again before getting better.
“Has this person progressed or not? That’s the critical issue,” he said.
Track progression
A variety of systems are used to track visual field progression, including classification systems (including several scoring systems), event analysis (such as Glaucoma Change Progression and Glaucoma Progression Analysis), and trend analysis (such as Progressor and Linear Regression).
Each approach has pros and cons.
“Event analysis is designed to detect progression but not necessarily the rate,” Dr. Johnson said.
“Trend analysis gives the rate of progression, which is important,” he said. “Event analysis looks at change from baseline, while trend analysis examines all the data. In general, event analysis, given the right decision criteria, can detect progression earlier than trend analysis. But rate of progression is a critical factor for patient management.”
Research done by Dr. Johnson and colleagues has found that the follow-up time to determine visual field progression varies two- to three-fold depending on the kind of trend or event analysis used and the decision criteria.
“The critical thing is that they only agree with each other 50% to 60% of the time,” Dr. Johnson said. “This illustrates that no single test or method of analyzing can give you the final result.”