The retina of the left eye of a healthy human volunteer was imaged after informed consent was obtained. Two-dimensional images were obtained in the fovea centralis region, from the nerve head two- and three dimensional data sets were obtained. In recording sessions for 2D imaging typically 20 to 40 horizontal cross sectional images were recorded in 1 – 2 seconds, in a 3D imaging session, 60 2D images were obtained in 3 sec., while the y-scanner was slowly scanning the horizontal sectioning plane in the vertical direction. To stabilize the subject’s head and minimize motion artifacts to obtain smooth 3D data sets, a bite-bar was used.
shows images of intensity (a), (single pass) retardation (b), and (cumulative) fast axis orientation (c) recorded across the fovea centralis. In the intensity image () the individual retinal layers known from ultrahigh resolution OCT [38
] can be observed. The retardation image () shows low retardation, indicated by dark blue color, in most of the retinal layers (the small retardation offset is caused by the corneal birefringence). The very last strongly reflecting layer (last bright layer in ), however, shows retardation values changing randomly in transverse direction, yielding an average green color in the retardation image. This result is similar to our recent findings of a polarization scrambling (or depolarizing) layer by time domain PS-OCT [12
]. First clinical trials on patients with certain retinal pathologies indicated that this layer is probably the RPE [16
]. This possibility to localize the RPE via its polarization properties might be of great interest for diagnosis of RPE pathologies.
Fig. 3 B-scan images of human fovea in vivo. (a) Intensity (log scale); (b) retardation; (c) fast axis orientation. Image size: 3 mm (horizontal) × 0.75 mm (vertical). Values on color bars: degrees (to avoid erroneous birefringence data, areas below (more ...)
shows an image of the fast axis orientation. The anterior retinal layers show rather constant green color. Since these layers are not birefringent (the nerve fiber layer is very thin in the imaged area), the observed axis corresponds to that of the cornea (slight variations of the observed color between individual measurement sessions can be caused by decentration of the measurement beam with respect to the corneal apex because the optical axis is not constant across the cornea [21
]). In the posterior layers, a color change to light blue can be observed, probably caused by the birefringent Henle’s fiber layer that is located within the weakly backscattering area marked by H. Near the center of the fovea, where no Henle fibers are, this color change from green to light blue is not observed. The polarization scrambling effect of the last layer (probably RPE) is also observed in by the random color distribution across this layer.
shows 2D images of intensity (a), retardation (b), and axis orientation (c), recorded across the center of the optic nerve head. In the intensity image (), well-known features can be observed: the layers of the retina, the excavation of the optic disk, cross sections through vessels, and structures of the lamina cribrosa. In , polarization changing features that have not yet been reported, can be observed: A small, strongly birefringent structure temporal to the nerve head (marked by arrows), probably the rim of the scleral canal; retardation and axis orientation changes in parts of the lamina cribrosa, indicating that this structure consists of birefringent tissue with varying orientation.
B-scan images of human optic nerve head in vivo. (a) Intensity (log scale); (b) retardation; (c) fast axis orientation. Image size: 3 mm (horizontal) × 1.75 mm (vertical). Values on color bars: degrees. Arrow: temporal rim of scleral canal.
shows images of intensity (a), retardation (b), and axis orientation (c), recorded superior to the nerve head. In the retardation image () the increase of retardation with depth caused by the birefringence of the retinal nerve fiber layer (RNFL) can be observed. This retardation increase is strongest at the thickest nerve fiber bundles. In the axis orientation image () the horizontally varying axis orientation of the nerve fibers which emerge approximately radially from the nerve head can be observed. The most superficial green color on the left hand side of the image corresponds to the corneal axis orientation (the cornea’s birefringence is not compensated for), only in deeper areas the birefringence of the RNFL dominates, and the cumulative fast axis orientation approaches the true orientation of the RNFL fast axis (perpendicular to the orientation of the nerve fibers).
B-scans superior to human optic nerve head in vivo. (a) Intensity (log scale); (b) retardation; (c) fast axis orientation. Image size: 3 mm (horizontal) × 1 mm (vertical). Values on color bars: degrees.
shows a fly-through movie of B-scans across the nerve head obtained from a 3D data set. The movie shows intensity (top), retardation (middle), and fast axis orientation (bottom). The movie starts with cross sections inferior to the nerve head, moving up through the nerve head, and ends with cross sections superior to the nerve head. In the intensity movie, the evolution of retinal layers, the excavation of the optic disk, and vessels can be observed in detail. Furthermore, details of the lamina cribrosa structure are visible. In the retardation movie, the birefringence of the RNFL (increasing retardation with depth) inferior and superior to the nerve head is clearly visible, as well as the temporal rim of the scleral canal. The axis orientation movie shows clearly that the horizontal axis orientation gradient inferior to the nerve head is oppositely oriented as compared to locations superior to the nerve head, as expected from nerve fibers emerging approximately radially from the nerve head.
Fig. 6 (2.5 MB) Frame no. 31 of fly-through movie of 3D dataset of human nerve head in vivo. Top: intensity; middle: retardation; bottom: axis orientation (color scales similar to Figs. -). Image size: ~ 3mm (x) × 3mm (y) (more ...)
From the 3D data set shown in the movie of , 3D volume rendered data sets were derived [39
]. shows a movie of such an animated volume rendered 3D data set. The movie combines information on the backscattered intensity (corresponding to the opacity) and on the retardation (corresponding to the color coding). For better visualization, areas below a certain intensity threshold are displayed totally transparent. At the beginning of the movie the nerve head is viewed from inferior towards superior. The depolarizing layer can be seen (due to the data reduction necessary to generate a movie of sufficiently small file size, the contrast of this layer is somewhat weak), as well as the increasing retardation with depth caused by the birefringence of the RNFL. In the views from the bottom, the strongly birefringent temporal rim of the scleral canal is clearly visible. Retardation is also observed in parts of the lamina cribrosa.
Fig. 7 (1.2 MB) Frame no. 4 of animation of a 3 dimensional volume rendered data set from a human nerve head in vivo. The opacity corresponds to the backscattered intensity, the retardation corresponds to the color coding (color coding similar to Figs. (more ...)
shows a movie of an animated 3D volume rendered data set providing information on axis orientation (color coding) while backscattered intensity corresponds again to opacity. The animation pattern is approximately similar to that in . The varying axis orientation caused by the RNFL can best be seen in the perspective from the bottom, which also provides good views of the variable axis of the lamina.
Fig. 8 (2.2 MB) Frame no. 3 of animation of a 3 dimensional volume rendered data set from a human nerve head in vivo. The opacity corresponds to the backscattered intensity, the fast axis orientation corresponds to the color coding (color coding similar to Figs. (more ...)