February 14, 2011
Lesions at the junction of the optic nerve and optic chiasm may produce a characteristic visual field defect. Ipsilateral optic nerve involvement results in a central scotoma. The fibers from the inferonasal retina of the contralateral eye may loop anteriorly for a short distance in the ipsilateral optic nerve (known as Wilbrand's knee). Involvement of Wilbrand's knee produces a supero-temporal scotoma in the contralateral eye.
The combination of ipsilateral central scotoma and contralateral supero-temporal scotoma is known as a junctional scotoma. The cause should be assumed to be a compressive lesion at the junction of the optic nerve and chiasm until proven otherwise. Caveat: some have questioned whether the phenomenon of Wilbrand's knee is an artifact of anatomical preparation or eye enculeation, however.
Suresh Subramaniam, MD, MSc, Chief Neurology Resident University of Calgary
Disclosure: Dr. Subramaniam has nothing to disclose.
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