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.

The value of scanning lies above all in the determination of the site, size and shape of orbital lesions and, where applicable, their relations with neighbouring extra or intra cerebral structures. But certain conditions such as exophthalmos during hyperthyroïdosis have characteristic scan findings. Even intra-ocular tumors are visible on elarged scanfilms. It nevertheless remains difficult to attempt to predict a histological diagnosis on the only basis of scan findings. 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 phlebography and ultrasonography.

A standardized method for the CT exploration of the orbital region has been searched for. This method makes it possible to visualize the entire orbital region with a minimum of 4 tomographic scans, each section 6 mm thick. The reference line chosen for this exploration is parallel to the optic nerve and joins the projection of the inferior border of the orbit on the lateral view with the upper border of the ear to the scalp. After each tomographic scan the patient is moved so that the new scanning line is still parallel to the reference line but distant by 9 mm from the previous one.

The practical value of density measurements with computed tomography of orbital lesions is demonstrated.