Abstract
Purpose: :
To evaluate Digital Interference Holography (DIH), for imaging of human optic nerve head, cornea, macula and retina with resolution comparable to the existing techniques.
Methods: :
Two formaldehyde preserved human eyes from the Lions Eye Institute for Transplant & Research were investigated for this purpose. Samples of the peripheral retina, macula, cornea, and the optic nerve head were removed to be imaged. The DIH technique can reconstruct tomographic images of an object volume with narrow axial resolution of 10 µm. In DIH many holograms (50-300) are acquired by a CCD camera using a range of wavelengths and each hologram is numerically reconstructed. Superposition of the holograms yields tomographic images. The DIH image is an accurate copy of the 3D tissue structure. The laser wavelength scanning range reliably controls the axial or depth resolution. Also, by scanning a wide range of wavelengths, a synthesized short coherence length is created and the coherence function of the laser becomes delta-function like at an arbitrary location. The physical process of reflection, or scattering, can be detected as an interference signal from that location. The light source was a solid state pumped dye laser with a tunable wavelength range between 565 nm to 595 nm. The holograms are captured by a monochrome CCD camera (Sony XC-ST50, with 780 x 640 pixels and a pixel size of ~ 9 µm). An image acquisition board (NI IMAQ PCI-1407) digitizes the image with 8 bit resolution. All software was developed in house with the NI LabView.
Results: :
Holograms of all tissues samples were successfully obtained with a signal-to-noise ratio of 50 dB. Different layers are distinguishable in the cross-sectional images of the human optic head, cornea, macula and retina. Topographic mapping within the ocular tissue reveals the principal features of the tissue anatomy, clearly delineating borders of blood vessels segments (208 µm). The volume of each sample was built and different orientations were given for specific Euler angles τ , ϕ , ψ.
Conclusions: :
We have successfully imaged human ocular tissue using DIH. These results indicate that DIH technique has the potential to become an important tool to researchers and clinicians.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • retina • topography