Variable lateral size imaging of the human retina in vivo by combined confocal/en face optical coherence tomography with closed loop OPD-locked low coherence interferometry based active axial eye motion tracking

We reported recently an active tracking device based on white light coherence ranging using a spectrally interrogated Michelson interferometer, which was used to monitor and correct for the axial displacement of the eye and head of the imaged subject in a confocal scanning ophthalmoscope/ en face OCT system (SLO/OCT) by tracking the axial position of the eye fundus. Both the tracking and imaging interferometers share the eye interface optics and the patient eye and also an optical path difference (OPD) changing device in the reference (fast voice coil mounted retroreflector), that keeps them locked at constant OPD values. As a consequence, the sensitivity of the tracking interferometer is not affected by the spectrometer sensitivity roll-off with increased OPD and mirror term ambiguity tracking errors close to OPD = 0 are eliminated. Moreover, the axial tracking range is only limited by the voice coil stage travel range and the tracking system has an update time better than 5 ms. We investigate the potential of the new configuration for acquiring volumetric data free of axial eye motion artifacts for two different lateral field sizes. Sets of SLO and en face OCT images at progressively deeper locations in the retina are simultaneously acquired for two lateral sizes, 15°x15° and 3.5°x3.5°. The large lateral field size provides a means of navigating the retina, while the high magnification small lateral size imaging reveals interesting microscopic details of the retinal morphology.