Abstract
Purpose: :
To evaluate full–field optical coherence tomography (FF–OCT) for retinal ganglion cell (RGC) imaging.
Methods: :
Unfixed and unstained porcine eye cups were imaged using a FF–OCT system that is based on a Linnik–type interferometer. A halogen lamp coupled to a Kohler illumination system was chosen as the broadband light source. Effective bandwidth was set to 80nm centered at 800nm by optical filers. The axial resolution was determined by the coherence length of the source to be ∼2.6 µm in tissue sample. The sample was illuminated with the probe beam and a horizontal cross–sectional image at a fixed depth was measured using a silicon CCD array. A field of view of 850 µm x 850 µm was covered by the 500 x 500 array elements. Using the phase–shift detection method an en–face image could be acquired in 1.5 sec. A series of en–face images were acquired at a 2–µm step, and they were used for the reconstruction of tomography images along different cutting planes.
Results: :
RGCs were clearly visualized as low reflective round shapes with varying sizes in en face (x–y) images. Individual RGCs were resolved and their number was countable. Retinal nerve fiber bundles were also clearly visualized as high reflective fibrous images. Reconstruction of x–z and y–z images clearly revealed cellular level sectional images in the inner retina in which low reflective RGC images were located beneath the high reflective images of nerve fibers. En face images also visualized the detailed image of the whole lamina cribrosa in which lamina pores were clearly observed from the superficial to the bottom and x–z and y–z reconstruction displayed the lamellar constructs. The volume rendering of the tomography data set allowed the acquisition of 3D images for RGCs and lamina cribrosa.
Conclusions: :
Three dimensional imaging of RGCs, nerve fiver bundles and lamina cribrosa was feasible ex vivo by full–field OCT. This technology potentially enables non–invasive human retinal ganglion cell imaging.
Keywords: ganglion cells • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • lamina cribrosa