الفهرس 
IMAGING DEVICESOnly 14 pages are availabe for public view
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Abstract
Glaucoma is a chronic neurodegenerative disease characterized by loss of retinal ganglion cells, resulting in distinctive changes in the optic nerve head and retinal nerve fiber layer. However, diagnosis may be challenging even for an experienced clinician due to wide variability among normal and glaucomatous eyes. Standard automated perimetry is routinely used to establish the diagnosis of glaucoma. However, there is evidence that substantial retinal ganglion cell damage may occur in glaucoma before visual field defects are seen. The introduction of newer imaging devices such as confocal scanning laser ophthalmoscopy, scanning laser polarimetry and optical coherence tomography for measuring structural changes in the optic nerve head and retinal nerve fiber la.yer seems promising for early detection of glaucoma. New functional tests may also help in the diagnosis.
SLP takes advantage of the birefringence property of the RNFL that modifies the polarization of the light (retardation) when illuminated. The commercially available SLP instruments are the GDx VCC (variable cornea compensation) and the latest GDx ECC (enhanced corneal compensation). This important issue was later addressed by providing the GDx with a variable corneal compensator. The GDx has been shown to discriminate well between glaucomatous and healthy eyes. However, a major challenge in the ability of the instrument to describe the RNFL thickness pattern relies in the occurrence of atypical retardation patterns (ARPs), likely the result of poor signal-to-noise ratio (SNR) as a consequence of light scattering in the eye.
CSLO is an imaging tool designed to provide the examiner with a quantitative three-dimensional composite image of the ONH and posterior segment. The commercially available instrument, the Heidelberg Retina Tomograph (HRT; Heidelberg Engineering, Heidelberg, Germany), works by emitting a 670-nm diode laser beam. The HRT may detect structural glaucomatous changes before visual field loss manifests itself.
Optical coherence tomography uses low-coherence interferometry to acquire high-resolution cross-sectional imaging of ocular struc¬tures, providing an optical biopsy. It is similar to ultrasound B-mode imaging but uses light instead of sound. Low-coherence near-infrared light is transmitted from a diode light source to the retina via a fiber optic delivery system. Backscatter from the retina is captured and used to construct a cross-sectional tomo¬graphic image of the retina. OCT has good reproducibility and has been shown to identify RNFL defects in areas corresponding to visual field defects. Although OCT was originally designed to evaluate retinal appearance, recent devel¬opment of software permits ONH analysis by quantification of the thickness of the papillary RNFL. It is also useful for macu¬lar volume assessment. RNFL thickness parameters have been reported to provide better discrimination between normal and glaucomatous eyes compared with total macular thickness.
Assessment of the anterior segment in glaucoma using ultrasound biomicroscopy and optical coherence tomography.UBM systems use frequencies ranging from approximately 35 to 80 MHz, as compared with typical 10-MHz systems used for general-purpose ophthalmic imaging. OCT systems use low-coherence, near-infrared light to provide detailed images of anterior segment structures at resolutions exceeding that of UBM. Both technologies allow visualization of the iridocorneal angle and, thus, can contribute to the diagnosis and management of glaucoma.