الفهرس 
aim of the WorkOnly 14 pages are availabe for public view
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Abstract
Assessment of anterior segment structures is an integral part of ophthalmic examination. In clinical practice imaging of the anterior segment has traditionally been carried out with slit lamp biomicroscopy. Objective quantitative assessment of anterior segment structures is limited and direct iridocorneal angle visualisation can only be carried out with the use of diagnostic contact lenses. New anterior segment imaging instruments promise to overcome these limitations. New modalities such as rotating Scheimpflug imaging and AS-OCT have recently become available; they supplement the more established imaging devices of Orbscan scanning slit topography and UBM. All devices promise quantitative information and qualitative imaging of the cornea, anterior chamber, iris, iridocorneal angle and lens. Direct angle visualisation is possible with the AS-OCT and UBM; they provide images of the scleral spur, ciliary body, ciliary sulcus and even canal of Schlemm in some eyes. UBM is an imaging technology that uses high frequency ultrasound and thus allows detailed observation of the anterior portion of the globe in microscopic resolution. UBM has a 50 MHz transducer. This allows resolution of structures up to 60 micrometers with a depth of penetration of approximately 4 mm. It is necessary to have knowledge of the normal appearance of ocular anatomical structures as imaged by UBM before pathological conditions can be analyzed. UBM is a contact exploration technique with an immersion system which requires patients to be in recumbent position. The technique can be slightly uncomfortable for some patients and not very well tolerated in some cases. In addition, the position of the echography sound and the patient eye can vary in the course of the test and this involves a potential increase in the variability of the measurements. In fact, the reliability of the test largely depends on the collaboration of the patient and the experience of the operator. UBM is useful to define a series of measurement parameters that can be used for comparison between normal and pathological eyes. The scleral spur in particular is a very useful landmark presenting a constant reference point for measurement in the angle region. UBM is powerful tool for obtaining precise images and mesurement of anterior chamber depth, trabecular-iris angle, angle opening distances, and iris thickness. Therefore, it is especially suitable for diagnosis of various forms of angle closure glaucoma as pupillary block, plateau iris syndrome, cystic angle closure (iridociliary cysts), and anterior synechiae. AS-OCT is a non-invasive optical imaging technique; it uses the property of optical reflectivity to give a cross-sectional imaging of biological tissue with a high resolution and micrometer scale. AS-OCT can detect quantitatively subtle changes to the eye caused during the early stages of ocular disease, such as glaucoma, and by procedures like cataract surgery. It can measure residual stromal thickness in LASIK patients who are candidates for re-treatment. This capability has made OCT an attractive imaging and measurement technique to aid photorefractive surgery for the correction of myopia, hyperopia and astigmatism. It is used to investigate and monitor post-operative side-effects. AS-OCT system provides clear, highly detailed, in-depth cross-sectional images of the anterior segment -including the angle- without the need for ocular anesthesia or messy, time-consuming water hath. It is so easy to use and efficient to operate. This dramatically expands the potential for diagnostic confidence and therapeutic