Hypoplastic optic nerves studied with B-scan ultrasonography and axial tomography of the optic canals

Radiologic studies of the optic foramina in cases of optic nerve hypoplasia have been inconsistent, some authors reporting normal foramina, others finding small foramina. The technique of axial tomography of the optic canals has been found more useful in this regard than plain foramen views, and has demonstrated small canals in cases of optic nerve hypoplasia. A case of bilateral hypoplasia is presented in which the discs were one half normal size, the optic nerves measured 2 mm in diameter on B-scan ultrasonography, and the optic canals were about 4 mm in diameter radiographically on the axial tomograms. These measurements are compared with normals of 4 to 4.5 mm for scans of the optic nerve, and a reported average optic canal width of 5.5 mm. A second case of less severe hypoplasia also presented a small ultrasonic nerve pattern of 3.5 mm. With the techniques of ultrasonography and axial tomography, the course of hypoplasic nerves can be followed from the level of the retina to the optic chiasm posteriorly. It is suggested that the optic canal dimensions correspond closely to the size of the optic nerve in cases of hypoplasia. When the nerve is only slightly hypoplastic the radiographic change in foramen or canal dimensions may not be detectable. Reasonably accurate measurements of the nerve may be more easily obtained with ultrasound.