[The use of computerized axial x-ray-tomography (EMI-scan) in ophthalmology (author's transl)]

There now exist protocols for specific scanning which make it possible to obtain tranverse sections of a few millimetres in thickness of the orbits and their contents, with minimum sweep and with a very low dose of radiation for the lens. Normal scanner anatomical findings in the orbit may thus be defined for the eyeball (outer coats, vitreous, lens) as well as retrobulbar structures (optic nerve, oculomotor muscles in particular). Intraocular tumours (e.g. retinoblastoma) are visible on enlarged scan films. The value of scannings lies above all in the determination of the site, size and shape of orbital lesions and, where applicable, their relations with neighbouring extra- and intra-cerebral structures. In addition, certain conditions such as exophthalmos during hyperthyroidism have characteristic scan findings. It nevertheless remains difficult to attempt to predict a histological diagnosis on the basis of scan findings, the risk of a false positive being particularly significant. Particular emphasis must be placed upon the contribution of techniques of treatment of the films obtained (enlargement, contrast media, histograms, lateral views) as well as the complementary use of other methods of radiological investigation (in particular arteriography and phlebography) which scanning cannot replace but which it should usually precede since it is atraumatic and non-invase.