The corneal sub-basal nerve plexus (SNP) is a network of thin, unmyelinated nerve fibers located between the basal epithelium and the Bowman’s membrane. Both corneal and systemic diseases such as keratoconus and diabetic can alter the nerve fiber density, thickness and tortuosity. Recent developments of cellular resolution OCT technology allowed for in-vivo visualization and mapping of the corneal SNP. We have developed a fully automated algorithm for segmentation of corneal nerves. The performance of the algorithm was tested on a series of enface UHR-OCT images acquired in-vivo from healthy human subjects. The proposed algorithm traces most of the sub-basal corneal nerves correctly. The achieved processing time and tracing quality are the major advantages of the proposed method. Results show the potential application of proposed method for nerve analysis and morphometric quantification of human sub-basal corneal nerves which is an important tool in corneal related diseases.
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.
Keratoconus (KC) is a progressive degenerative corneal disease that can lead to a strong
deformation of the cornea and loss of clarity, causing distorted or blurred vision. Surgical treatment for
severe cases requires precise evaluation of the corneal curvature, thickness, layer structure, and clarity.
Current clinical instruments for assessing the corneal shape cannot resolve the internal structure, and
high-resolution microscopy techniques are limited to a small field of view. We have implemented a
swept-source OCT (SS-OCT) system that enables high-speed imaging (100 kA-scans/s) of the entire
cornea and provides ~5.1μm axial resolution in corneal tissue. With an imaging range of 5.6 mm
(in air), we can cover the full length from the cornea’s apex to the anterior surface of the lens. We have
acquired volumetric corneal images from human subjects with different stages of KC and from
subjects who underwent surgery or cross-linking therapy. We developed an automatic algorithm for
segmenting the outer and inner surfaces of the cornea in the images which will enable precise
measurement of the corneal curvature and thickness. This makes SS-OCT an ideal instrument for
comprehensive examination of keratoconic corneas.
The upper eyelid is a biological tissue with complex structure, essential for the maintenance of an optically clear ocular surface due to its physical (blinking) effect. The Meibomian glands (MGs) are structures that lie beneath the surface of the inner eyelid and are partially responsible for the production of the superficial oily layer of the tear film. The MGs are only superficially visible under magnification when the eyelid is everted. We present for the first time in vivo 3-D images of healthy and inflamed human MGs. Tomograms were acquired from the tarsal plate of everted human eyelids with a 1060-nm ultrahigh-resolution optical coherence tomography (UHOCT) system, with ∼3μm×10μm (axial×lateral) resolution in biological tissue at the rate of 91,911 A-scans/s. Comparison with histology shows that the UHOCT images reveal a spatial distribution of structures that appear to correspond with the MGs’ acini and ducts (in healthy subjects), and accumulation of heterogeneous, highly scattering biological material and clear fluids in the visibly blocked glands. Noninvasive, volumetric high-resolution morphological imaging of the human tarsal area could have a significant impact in the clinical diagnosis of inflammatory and noninflammatory lid pathologies.
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