Disc edema, more accurately called optic disc edema, is a medical condition in which the small area at the very back of the eyeball, where the optic nerve connects, is swollen. It can be observed by a doctor by looking through the iris of the eye using an ophthalmoscope. The most common cause of disc edema is the slowing of conduction along the optic nerve, but the most worrisome cause is intracranial pressure. Patients with disc edema sometimes report nausea, headaches, ringing in the ears, intermittent double vision, or other vision problems; they often don’t notice any symptoms at all, however.
The mechanical signs observable by a general practice doctor or ophthalmologist include visible bulging of the optic disc into the back of the eyeball, a blurring of the edges of the optical disc, and folds in the retina or choroid — a layer of connective tissue in the wall of the eye. Visible symptoms involving the venous system include small areas of necrosis or dead tissue, hemorrhages radiating from the area of the disc edema, and the presence of excess blood in the tissue. The combination of signs is used in determining the stage of development of a particular case of disc edema.
Slow conduction between the cells of the optic nerve can lead to buildup of intracellular fluids and cellular waste which then moves toward the head of the optic nerve. If swelling is seen in the optical disc of both eyes, it is referred to as bilateral disc edema and could be caused by high intracranial pressure. High intracranial pressure can be caused by hydrocephalus, tumors, or cerebral hypertension. Swelling found in only eye is called asymmetric disc edema and could be caused by blood leaking from a malformed blood vessel in the brain near that eye or the presence of an intracranial abscess in the brain on the side of the affected eye.
Procedures that can help to determine the exact cause of a case of optic disk edema include B-scan ultrasounds, computed topography (CT), and magnetic resonance imaging (MRI). The ultrasound can rule out swelling caused by the presence of hardened secretions from the optic nerve, and the CT and MRI scans can locate tumors, abscesses, or hemorrhages that might cause increased intracranial pressure. If none of these tests are conclusive, a lumbar puncture may be performed to check the pressure of fluid within the entire central nervous system as well as meningitis or spinal cord tumors.