While OCT does not directly represent a patient’s visual function, the use of its measurements often predicts clinically relevant outcomes, such as loss of vision. A study conducted at Duke University has determined that rapid OCT RNFL thinning during the initial follow-up period of an eye with glaucoma was associated with a large magnitude of visual field loss during the total follow-up period.

The study assessed 1,150 eyes of 839 glaucoma patients. Rates of RNFL loss were obtained from global RNFL thickness values of the first five OCT scans. Rates of visual field loss were assessed using SAP mean deviation during the entire follow-up period. Eyes were categorized as fast, moderate or slow progressors based on rates of RNFL loss, with cutoffs of ≤-2µm/year, -2µm/year to -1µm/year and ≥-1µm/year, respectively.

The rate of RNFL change was -0.76µm/y during initial follow-up, which occurred over 3.7 years. The study classified 66% of eyes as slow, 29% as moderate and 5% as fast progressors, with rates of RNFL thinning of -0.36µm/year, -1.34µm/year, and -2.87µm/year respectively.

The researchers found that eyes with fast OCT progression detected early in the course of follow-up had approximately four times faster rates of SAP loss during the extended follow-up period compared with eyes that had slow OCT progression (-0.71dB/year vs. -0.16dB/year). In terms of total magnitude of SAP loss, eyes with rapid initial OCT progression ended up losing an average of 5.51dB over the extended follow-up period, over twice the amount in eyes that were deemed to have slow OCT progression initially.

“A clinician who observes rapid RNFL thinning is justified in believing that this thinning will likely be accompanied by concurrent or future rapid visual field loss,” the researchers noted. “Patients classified as fast progressors by OCT may be at higher risk for developing subsequent functional disability.”

They suggest intensifying treatment based on rapid structural loss in order to mitigate future functional loss.