Signs and Symptoms
Funduscopic evaluation of patients with PTC demonstrates bilaterally swollen, edematous optic nerves consistent with true papilledema. Ophthalmoscopy may reveal striations within the nerve fiber layer, blurring of the superior and inferior margins of the neural rim, disc hyperemia, and capillary dilatation. More severe presentations involve engorged and tortuous retinal venules, peripapillary hemorrhages and/or cotton wool spots, and circumferential retinal microfolds (Patons lines). Chronic papilledema mayresult in atrophy of the nerve head, with associated pallor and gliosis. Most cases of true papilledema will not present with a relative afferent pupillary defect, although visual field deficits may be present. The most common visual field defect associated with PTC is an enlarged blind spot, followed by a nasal deficit, typically affecting the inferior quadrants. Other field losses seen in PTC include arcuate defects, nasal step, generalized constriction, and least commonly, cecocentral scotoma.
While the mechanism of PTC is not fully understood, most experts agree that the disorder results from poor absorption of cerebrospinal fluid by the meninges surrounding the brain and spinal cord. The subsequent increase in extracerebral fluid volume leads to elevated intracranial pressure. However, because the process is slow and insidious, there is ample time for the ventricular system to compensate and this explains why there is no dilation of the cerebral ventricles in PTC. Increased intracranial pressure induces stress on the peripheral aspects of the brain, including the cranial nerves. Stagnation of axoplasmic flow in the optic nerve (CN II) results in papilledema and transient visual obscurations; when the abducens nerve (CN VI) is involved, the result is intermittent nerve palsy and diplopia.
Many conditions and factors have been proposed as causative agents of PTC, including excessive dosages of some exogenously administered medications (e.g., vitamin A, tetracycline, minocycline, naladixic acid, corticosteroids), endocrinologic abnormalities, anemias, blood dyscrasias, and chronic respiratory insufficiency. However the majority of cases remain idiopathic in nature.
Therapy for patients with PTC varies, but in most instances initiate systemic medications as a first line treatment. Typically, the drug of choice for the initial management of PTC is oral acetazolamide (Diamox), although other diuretics including chlorthalidone (Hygroton) and furosemide (Lasix) may also be used effectively. Corticosteroid therapy is considered controversial in the management of PTC. While a short-term course of oral or intravenous dexamethasone may be helpful in initially lowering intracranial pressure, it is not considered to be an effective long-term therapy because of the potential for systemic and ocular complications.
For patients in whom conventional medical therapy fails to alleviate the symptoms and prevent pathologic decline, surgical intervention is the only definitive treatment. Cerebrospinal fluid shunting procedures are commonly employed in recalcitrant cases of PTC, but are successful in only 70 to 80 percent of cases. Optic nerve sheath decompression has also been advocated as a method to alleviate chronic disc edema, although this technique fails to directly address the issue of elevated intracranial pressure. It also demonstrates a particularly high failure rate.
Optometric management of patients diagnosed with PTC includes careful and frequent evaluation, including threshold visual fields, acuity measurement, contrast sensitivity, and indirect ophthalmoscopy. Photodocu-mentation of the nerve heads should also be performed.
Other reports in this section
Eyelids & Eyelashes | Conjunctiva & Sclera | Cornea
Uvea | Vitreous & Retina | Optic Nerve & Brain | Oculosystemic Disease
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