Researchers now believe many patients with severe glaucoma may still have useful remaining retinal nerve fiber layer (RNFL), which suggests structural—rather than functional—criteria would be more appropriate as guidelines for OCT imaging, a study in the Journal of Glaucoma reports.

For glaucomatous eyes with advanced structural damage, RNFL loss eventually becomes so significant that thinning is no longer detectable using OCT, the researchers explained. As such, insurers are considering limiting coverage for OCT imaging in “severe stage glaucoma” as defined by the Centers for Medicare and Medicaid Services (CMS). However, CMS defines severe glaucoma based primarily on visual field criteria, and many of these patients may have preserved RNFL in other sectors, the researchers countered.

In their study, the investigators reviewed the medical records of patients with CMS-defined severe glaucoma and looked at the average RNFL thickness and visual field deviation results. Additionally, they used previous estimates of average, superior and inferior RNFL floor measures and test-retest variability for OCT to set three RNFL threshold values.

The investigation included 129 eyes with an average RNFL thickness of 60.9.

A majority (66%) of eyes met severe glaucoma criteria with defects in both hemifields, and only 34% met the paracentral defect criteria. The researchers found the proportion of eyes that had significant remaining average, superior or inferior RNFL was 21% to 54%, 29% to 51% and 16% to 37%, respectively.

Of note: at least one vertical quadrant had significant remaining RNFL in 35% to 66% of eyes, depending on the threshold used, the researchers noted in their paper.

Specifically, in eyes with CMS-defined severe glaucoma, a clinically useful residual RNFL was present in at least one vertical quadrant in more than 35% of eyes using the most conservative estimate, threshold 3, and 66% of eyes had RNFL values greater than the estimated floor, the researchers said. Additionally, more than half of the eyes had significant residual RNFL in at least one quadrant if they had either (but not both) a defect in the paracentral region or in both hemifields, they added.

“This study is the first to our knowledge to address the potential clinical utility of OCT RNFL in a real world group of patients with severe glaucoma; the results of this study could help steer guidelines and reimbursement for testing at a national level,” the researchers wrote.