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Optic chiasm
Published in Fiona Rowe, Visual Fields via the Visual Pathway, 2016
Crossed and uncrossed retinal nerve fibres begin to separate at the termination of the optic nerve at the anterior angle of the optic chiasm (Erskine and Herrera 2007; Petros et al. 2008). Wilbrand (1926) claimed that the crossed fibres, from nasal retina, lie medial to the pial septum. The inferior-crossed fibres, primarily peripheral, remain inferior and after decussating, they loop anteriorly into the terminal portion of the opposite optic nerve (Wilbrand’s knee) before turning posteriorly to continue through the optic chiasm and into the optic tract. Doubt has been cast as to the presence of Wilbrand’s knee following anatomical studies (Horton 1997; Lee et al. 2006). Superior crossing fibres pass posteriorly and enter the superomedial ipsilateral optic tract before looping forward to decussate and enter the contralateral optic tract. Uncrossed temporal retinal fibres maintain their relative position at the lateral aspects of the optic chiasm. Nasal macular fibres cross primarily in the central and posterior portions of the optic chiasm.
Dr Gordon Plant’s Festschrift Tidings
Published in Neuro-Ophthalmology, 2022
Sui H. Wong, Susan Mollan, Simon J Hickman, Stephen Madill, Luke Bennetto, Sarah Cooper
Professor Jonathan Horton tackled the issue of whether Wilbrand’s knee exists. Wilbrand had described a contingent of fibres emanating from axons from the inferonasal retina that deviated into the contralateral optic nerve before proceeding into the optic tract that appeared to elegantly explain the phenomenon of junctional scotoma. In the 1990s, Professor Horton, aided by a troop of macaques, diligently went in search of the knee but found none. When he presented his findings to Professor Hoyt, he too revealed his own search some 30 years previously had also concluded that there was no knee. Professor Horton attributed the knee to an artefact of enucleation in Wilbrand’s original experiments and artistic licence in textbooks. He proposed that junctional scotomas can be fully explained by common pathology, which asymmetrically injures optic nerves and chiasm, such as a compressive pituitary tumour. At the group discussion, Dr Plant clarified that Wilbrand’s knee does exist – just not in the way that Wilbrand had described – it is purely an anatomical phenomenon of enucleation that is clinically irrelevant. Professor Horton drew the lesson from Wilbrand that one should not mould the facts to fit even a very clever idea.
Multicentric Glioblastoma Multiforme Mimicking Optic Neuritis
Published in Neuro-Ophthalmology, 2018
Francesco Pellegrini, Andrew G. Lee, Cristina Cercato
Wilbrand and Saenger2,3 studied the anatomy of the optic chiasm after enucleation and noted that inferonasal crossing fibres curved anteriorly into the contralateral optic nerve for 1–2 mm, before bending back into the chiasm and then into the optic tract. This anatomical finding was known as the “Wilbrand knee” and was invoked to explain the contralateral superotemporal visual field defect when the optic nerve is damaged at the chiasmal junction. About 90 years later, Horton4 argued that the Wilbrand knee may be an enucleation artefact. In his detail anatomical studies on primates and human cadavers, he argued that the Wilbrand knee might be the result of loss of myelin and atrophy of the remaining portion of the optic nerve proximal to transaction. He noted that the Wilbrand knee was absent up to a few months after enucleation or transaction of the nerve, but developed after long-term enucleation, and concluded that the Wilbrand knee does not exist in the normal primate optic chiasm and may occur as an artefact from the shrinkage of the optic chiasm and atrophy of fibres from the enucleated eye. In contrast, Shin et al.5 were able to demonstrate the Wilbrand knee. These authors made thin (25 µm) sections of the chiasm that were illuminated and digitally imaged from different angles. They used the anisotropic light-reflecting properties of myelinated axons in the human chiasm, and each of the images was reproduced in a pseudo-colour map in red, green, or blue. Whereas superior chiasm sections showed no curving of crossing fibres, in the inferior chiasm sections there was a sheet of crossing fibres originating from the anterior chiasm and bending towards the contralateral optic nerve before arching back towards the optic tract, consistent with the original descriptions of Wilbrand and Saenger. Regardless of the anatomical existence of the Willbrand knee, however, the clinical localising value to the junction in a patient with an ipsilateral optic neuropathy and a contralateral superotemporal visual field defect remains unchanged.