Purpose
To analyze birefringence, retardation, and thickness of the retinal nerve fiber layer (RNFL) along traces of retinal nerve fiber bundles in the human eye in vivo.
Methods
A polarization sensitive (PS) OCT system with an integrated retinal tracker was used to record 3D data sets in healthy human eyes in vivo. En face maps of RNFL thickness, retardation, axis orientation, and birefringence were generated from the PS-OCT data sets. Based on the axis orientation and thickness maps, traces of nerve fiber bundles were extracted. A new type of graphic data representation was developed: a 2D false color map that plots birefringence, retardation, and thickness along the nerve fiber bundle (y-direction) as a function of azimuthal angle (x-direction) around the optic nerve head (ONH). Based on these plots, a quantitative analysis of the variations of parameters along the nerve fiber bundle is made.
Results
We analyzed the variations of retardation, thickness, and birefringence along superior and inferior nerve fiber bundles in 4 healthy eyes. If measured from the ONH outward, retardation and thickness showed a pronounced decrease along fiber traces near the ONH of > 8°/mm and > 50 µm/mm, respectively, while birefringence was rather constant, with a change of < 0.05°/µm/mm.
Conclusions
In healthy eyes, RNFL birefringence is rather constant along the nerve fiber bundle length. Deviations from this pattern might be indicative of diseases like glaucoma.