Optical coherence tomography methods comparable for AMD assessments

By Lucy Piper, Senior medwireNews Reporter

There is good accordance between spectral-domain (SD) and time-domain (TD) optical coherence tomography (OCT) image assessments of eyes treated for neovascular age-related macular degeneration (AMD), show study findings.

During the first year of the Comparison of AMD Treatment Trials (CATT), treatment for AMD was administered primarily based on TD OCT assessments. But by the second year of the study, SD OCT platforms, which offered faster scanning, improved image registration and higher axial resolution, were available and used alongside TD OCT.

To determine agreement between these two modes of OCT, the researchers compared 1213 pairs of SD OCT and TD OCT scans from a subset of 384 eyes.

Both OCT modalities were accurate for grading all fluid types on 93% to 99% of scans. Agreement between the two types of OCT on the presence of any fluid was moderate to good, at 82%, with just 5% more SD OCT scans demonstrating fluid than TD OCT scans.

For subretinal fluid, agreement was 87% and for subretinal pigment epithelium (sub-RPE) fluid it was 80%, while agreement was lower for intraretinal fluid, at 74%.

Intraretinal fluid was detected with 6% greater frequency with TD OCT than SD OCT, whereas subretinal and sub-RPE fluid were detected at 7% and 11% greater frequencies, respectively, with SD OCT than with TD OCT.

The researchers point out that the greater detection of intraretinal fluid on TD OCT may be a false–positive finding, because its lower axial resolution can cause dark areas to be misinterpreted as cystoid oedema.

There was also comparable agreement between the two modes of OCT for manual thickness measurements, with small mean differences that were statistically significant but clinically similar, the team reports in Ophthalmology.

Retinal thickness was 5 µm greater on TD OCT than SD OCT, whereas subretinal fluid thickness was 1.5 µm greater on SD OCT than TD OCT. Subretinal tissue complex thickness was 5 µm greater and total central foveal thickness 2 µm greater on SD OCT, compared with TD OCT.

“This report provides a basis for interpretation of the TD OCT-based fluid assessments in CATT and provides data that will be useful to compare the results of CATT with future SD OCT-based trials for neovascular AMD”, say researchers Cynthia Toth (Duke Eye Center, Durham, North Carolina, USA) and colleagues.

They add that their findings “may also allow clinicians and patients to incorporate the results of the CATT reports confidently into their decision making for the treatment of neovascular AMD.”

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