For this experiment, an FD-OCT system was constructed based on a Mach–Zehnder interferometer, which employed a high-speed wavelength-swept laser (Axsun Technologies, Billerica, Massachusetts) with a center wavelength of and repetition rate of 50 kHz. A fiber coupler and a circulator were used to guide 90% of the laser output to the sample stage. The average power incident on the sample was kept as low as 10 mW, well below the American National Standards Institute maximum permissible exposure of 15.4 mW [for intrabeam viewing through a 7-mm pupil and exposure times of up to 8 h (Ref. 17)]. The OCT interference signal was detected by a balanced photodetector (PDB460C, Thorlabs, Newton, New Jersey) and 4096 samples were collected, more than enough to see the cornea, via an A-line with a 14-bit high-speed digitizer (PX14400, Signatec Inc., Lockport, Illinois). The spectrum interpolation for resampling to -space was performed on all A-line data prior to the fast Fourier transform (FFT) process. The scan range was set as wide as with an interval of for both A- and B-scans such that one 3-D image was composed of equally spaced A-lines. Considering the sweep rate of the 50-kHz laser, the 2-D imaging frame rate was 71.43 fps, and one 3-D volume image was acquired within 9.8 s, which is faster than the normal human TBUT. The objective lens (LSM03, Thorlabs, Newton, New Jersey) had a focal length of 36 mm, which gave a spot size of at the focal plane when the input beam was Gaussian with a 4-mm diameter. Thus, the lateral resolution was just enough to allow for visualization of -thick nerve bundles. The axial resolution of the system was measured to be in air.