Optic Disc Edema and Papilledema
SIGNS AND SYMPTOMS
Patients with optic disc edema may present asymptomatically, but this can vary depending upon the etiology of the nerve swelling. In cases of optic neuropathy due to inflammation, infiltration, ischemia or demyelinization, visual acuity is often significantly diminished. Papilledema, a specific form of disc edema resulting from elevated intracranial pressure, generally exhibits a minimal acuity deficit, but may demonstrate transient visual obscurations associated with postural changes. Patients with papilledema also may report headache, intermittent diplopia, vomiting and/or nausea, and pulsatile tinnitus. Visual field defects vary widely as well.
In general, you may observe an enlarged physiologic blind spot in any form of disc edema which displaces the peripapillary photoreceptors. Arcuate scotomas are also common when the inferior and superior poles of the disc are compromised. Altitudinal defects may be seen in ischemic and demyelinating neuropathies; central and cecocentral scotomas are common in primary optic nerve inflammations and infections. If disc swelling is unilateral and vision is poor, expect to find a relative afferent pupillary defect in the involved eye.
True bilateral papilledema will not present with an afferent pupillary defect. The earliest signs of disc edema include striations within the nerve fiber layer in conjunction with blurring of the superior and inferior margins of the neural rim tissue. The disc itself will, in time, protrude from the retinal surface. In cases of inflammation or papilledema, it may display hyperemia and capillary dilation. In ischemic optic neuropathy, the disc is swollen and elevated, but characteristically pale. In more severe presentations of optic disc edema, the retinal venules become engorged and tortuous, hemorrhages and/or cotton wool spots form in the peripapillary area, and you'll see circumferential retinal microfolds (Paton's lines) in the region surrounding the disc. Chronic disc edema may ultimately result in atrophy of the nerve head, with associated pallor and gliosis of the rim tissue.
Optic disc edema results primarily because of axoplasmic stasis, or slowed cellular conduction along the nerve. When this occurs, intracellular fluids and metabolic by-products accumulate and are eventually regurgitated at the level of the optic nerve head. Mechanical compression, infiltration, infection, inflammatory disease, demyelinating disease, or compromised vascular perfusion to the nerve may all lead to disc edema. Papilledema is not a primary neural inflammation but rather a direct sequela of elevated intracranial pressure. In this disorder, cerebral edema is effectively transmitted along the common meningeal sheaths of the brain and optic nerve producing an engorged, swollen disc. The condition is bilateral in almost all cases. True papilledema is a critical sign of intracranial hypertension, a potentially life-threatening situation.
Management of optic disc edema begins with a correct diagnosis. Most importantly, it is crucial to distinguish between papilledema and the many other forms of optic disc edema, including "masqueraders" such as buried optic disc drusen. Consider the acuity, visual fields, ophthalmoscopy findings and especially the laterality of presentation carefully in the initial work-up. Order or perform a B-scan ultrasound, which is invaluable in differentiating swelling of the nerve head from infiltration by hyaline bodies (drusen).
If the signs indicate an optic neuropathy such as papillitis or anterior ischemic optic neuropathy, management is aimed at treating the underlying disorder. Often, this involves systemic steroids, particularly when the etiology is inflammatory. You must obtain a CT or MRI scan of the brain within 24 hours of any tentative diagnosis of papilledema (i.e., when you suspect that increased intracranial pressure is the cause of the disc edema). These tests may help to identify an intracranial mass lesion, such as tumor, hemorrhage or abscess; in addition, the appearance of the cerebral ventricles may indicate hydrocephalus or pseudotumor cerebri. In the absence of positive radiographic studies, lumbar puncture may yield information regarding meningitis, encephalitis, or spinal cord tumors. Neurological consultation and co-management is obligatory in all cases of intracranial hypertension.
The treatment of papilledema and its underlying causes may be medical or surgical, depending upon the disorder. Neuro-ophthalmologists have attempted surgical therapy of the optic nerve using optic nerve sheath decompression to alleviate fluid retention within the surrounding meninges by creating a small fenestration site within the intraorbital portion of the nerve. While this procedure has yielded some positive results, it is extremely complex work and may fail in up to one-third of all cases.
There are two critical points to remember: (1) Not all swollen optic discs constitute optic disc edema and (2) Not all cases of optic disc edema constitute papilledema. Many benign clinical entities can simulate an edematous nerve head, even to the most experienced practitioners. Malinserted discs, congenitally full discs (seen often in hypermetropes), or especially buried drusen may sometimes be mistaken for optic disc edema, even though all are non-pathological conditions.
By the same token, many primary inflammations of the optic nerve which are treatable and in some cases self-limiting are often misdiagnosed as papilledema, a condition which constitutes a medical emergency to the general practitioner. Take care to distinguish these disorders and initiate or refer for proper management in all cases.