Fourier-domain 3D OCT shows substantially more retinal details than time-domain OCT

Fourier-domain three-dimensional (3D) optical coherence tomography (OCT) covers 100% of the mapped area anddetected 19% more pathologies such as cystoid macular edema (CME) and subretinal fluid compared with time-domain(TD) OCT, that if left undetected might have changed management in patients with retinal pathologies, saidAlexander Walsh, MD, from the Keck School of Medicine, Doheny Eye Institute, University of Southern California,Los Angeles.

"Both of these instruments provide dense, rich data, but 3D OCT would be more helpful because it measures 100%of the mapped area compared with less than 5% of retinal coverage provided by TD OCT," Dr. Walsh said.

He and his colleagues conducted a prospective study of 50 consecutive patients. They noted a big difference inthe ability to detect clinical features between the two OCT instruments, in that 3D OCT had 97% sensitivitycompared with 83% for TD OCT.

In light of this, the investigators then did a study in which they compared the findings of the two instrumentsin 45 patients (62 eyes) who had been treated with ranibizumab (Lucentis, Genentech) or bevacizumab (Avastin,Genentech). The images obtained were graded for the presence of CME, subretinal fluid, or pigment epithelialdetachment (PED). Seventy percent of the patients received ranibizumab and most had CME.

"Of the 62 eyes, 33 had CME, 40 had subretinal fluid, and 53 had a PED," Dr. Walsh said. "TD OCT missed fivecases of CME, seven cases of subretinal fluid, and two cases of PED. The 3D OCT detected 100% of thepathologies. In general, it appears the TD OCT has about 85% sensitivity for these retinal pathologies."

He concluded that 3D OCT found at least one factor not detected by TD OCT in 19% of cases. If all we relied onwere these three findings, CME, subretinal fluid, and PED, the difference would have changed our management in10% of cases.

"However, the findings show that 3D OCT is relevant to the clinical management of these patients," hesaid.

The investigators also found that the fast macular thickness scans were more prone to errors than radial linescans.

"I encourage anyone who is using OCT [Stratus OCT, Carl Zeiss Meditec] always to do high-resolution radial linescans," he said.