Degenerative conditions such as keratoconus and Fuch’s dystrophy can alter over time the cellular structure of the human corneal epithelium and endothelium respectively. A high-speed UHR-OCT system, capable of generating volumetric images of the cellular structure of the human cornea was built. The UHR-OCT system has a compact fiber-optic design that utilizes a commercial femtolaser with the central wavelength of 790 nm and 3dB spectral bandwidth of 150 nm to achieve ~ 1.4 µm axial resolution in corneal tissue. The optical design of the OCT imaging probe ensured ~2 µm OCT lateral resolution in corneal tissue. At the detection end of the UHR-OCT system, a high-resolution spectrometer (Cobra, Wasatch Photonics) is interfaced with a novel line scan camera. The camera has a tall pixel design, 2048 pixel array and a maximum readout rate of 250 kHz. The system’s SNR was 96 dB at 100 µm away from the zero delay line, with a 10 dB roll-off over 1.5 mm scanning range for ~800 µm power of the imaging beam incident on the corneal surface. Volumetric images of healthy and pathological corneas were acquired in-vivo from healthy volunteers and subjects with keratoconus and Fuch’s dystrophy and the images were compared with typical histological images. This study was approved by the University of Waterloo Research Ethics Committee.
Limbal stem cell dysfunction (LSCD) causes morphological and physiological changes in the limbus that result in decreased vision, photophobia, tearing, chronic inflammation and hyperemia, recurrent episodes of pain, and blindness in severe cases. Currently, clinical in-vivo imaging of the palisaded of Vogt (POV) and the cellular structure of the limbal crypts in the human corneo-scleral limbus is accomplished by in-vivo confocal microscopy (IVCM). However, IVCM requires physical contact with the limbal tissue that can cause pain and inflammation. In this study, we used a novel high speed, ultra-high resolution optical coherence tomography (UHR-OCT) system to generate volumetric, cellular resolution image of the healthy and pathological human corneo-scleral limbus. The UHR-OCT system has a compact fiber-optic design. A femtosecond laser with 790 nm central wavelength and ~150 nm spectral bandwidth (at 3dB) was used to achieve ~1.4 µm axial resolution in biological tissue. The UHR-OCT system also utilizes a high resolution spectrometer (Cobra, Wasatch Photonics) connected to a novel line scan camera with a tall pixel design, 2048 pixel array and a maximum readout rate of 250 kHz. The system’s SNR was 96 dB at 100 µm away from the zero delay line, with ~10 dB roll-off over 1.5 mm scanning range for ~800 µm power of the imaging beam. Volumetric images of the POV and the cellular structure of the limbal crypts were acquired in-vivo and without contact with the limbal tissue from healthy and LSCD and subjects. This study was approved by the University of Waterloo Research Ethics Committee.
Keratoconus causes progressive morphological changes in the corneal epithelium (EPI), Bowman’s membrane (BM) and anterior stroma. However, it is still not well understood if KC originates in the corneal epithelium and propagates to the anterior stroma through disruptions of the BM, or vice versa. In this study we used a sub-micrometer axial resolution OCT system to image in-vivo the cellular structure of the EPI layer and the fibrous structure of the BM and the anterior stroma in mild to advanced keratoconics, as well as healthy subjects. The imaging study was approved by the University of Waterloo Human Research Ethics Committee. The OCT system operates in the 800 nm spectral region at 34 kHz image acquisition rate and provides 0.95 um axial and < 2 um lateral resolution in corneal tissue, which is sufficient to visualize the cellular structure of the corneal epithelium and the fibrous structure of the BM. In some subjects, localized thinning and thickening of the EPI layer was observed, while there was no visible damage to the BM or anterior stroma. In other subjects, localized breakage of the stromal collagen fibrils was observed with no significant morphological changes of the corneal EPI.
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