Functional optical coherence tomography with a commercial device - a pilot study

Purpose: To evaluate reproducibility and reliability of measurements of visually evoked retinal intrinsic optical signals (IOS) in humans by a commercially available spectral-domain OCT. Methods: We measured visually evoked IOS in 16 healthy volunteers with a Spectralis OCT, extended by a custom made optical stimulator. After 20 minutes of dark adaptation, a 3 mm2 area of the temporal perimacula was stimulated with a white flash of 0.1 seconds duration and 5.9 log scot. tld. luminance. A single-line OCT scan was recorded on-line before (baseline), during and after stimulation. From this OCT time-series we extracted IOS by calculating changes in reflectivity from baseline after application of the light stimulus. Custom software was used to compare reflectivity changes in the stimulated area to the non-stimulated area. To improve the signal-to-noise ratio, we averaged the results of three single IOS recordings of each eye. Results: IOS of the stimulated area could repeatedly be recorded with reproducible results. Axial motion of the OCT scans during the measurements caused substantial noise which could significantly be reduced by averaging. Conclusions: We were able to reproducibly record visually evoked IOS with the Spectralis OCT coupled to an optical stimulator. Due to the high noise level, averaging of multiple measurements is necessary to clearly identify and analyze retinal signals. IOS imaging may be improved by three-dimensional eye tracking, since axial motion artifacts seem to be of significant influence.