Biomedical Engineering Reference
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Fig. 7.4 Images of cornea ( a ) SHG showing the collagen fibrils structure and ( b ) confocal
reflectance image showing the fibroblast cells
and the fibroblasts. Combination of confocal microscopy and a second harmonic
generation microscopy reveals the detailed morphology of the cellular changes and
the organization of the collagen matrix. Such a microscope may allow 3-D images to
be rapidly constructed from noninvasive scans of the patient's cornea. Some images
of collagen and cellular structure of cornea in its natural state with the backscattered
second harmonic imaging method are shown in Fig. 7.4 . Second harmonic signal
gives a strong imaging contrast from collagen fibers lying deep in the stroma. The
longer wavelength helps in deep tissue imaging, and backscattered nonlinear signal
can potentially be used for in vivo imaging of cornea.
In another application of the multiphoton imaging, the microscope was used
to image a vital part of the optic nerve head called lamina cribrosa. The lamina
cribrosa provides metabolic and mechanical support for the retinal ganglion cell
axons passing through the optic nerve and also serves as an interface between the
pressurized interior of the eye and retrobulbar tissue, preventing the outflow of
intraocular contents and maintaining an adequate intraocular pressure. Neuronal
signals from the retinal photoreceptor layer of the eye are conveyed via retinal
ganglion cell axons, through the optic nerve head and optic nerve, eventually
reaching the visual cortices of the brain. The lamina cribrosa is a multilayered
cribriform structure of laminar beams composed of collagen, glial cells, and
capillaries. Damage to the lamina under raised intraocular pressure has been shown
to be both a risk factor for and a cause of glaucoma, and there is strong evidence
which suggests that lowering of the intra-ocular pressure reduces the incidence and
the progression of glaucoma. Understanding the structure and function of lamina
is crucial for finding the causes of blindness due to glaucoma and other ocular
diseases. An image of porcine lamina cribrosa is shown Fig. 7.5 , from a freshly
acquired porcine eye.
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