A Clinical Case from the Archives : 24/05/2006

This little Siamese has esotropia – its cross-eyed if you want it in normal language! When you look at its retina with an ophthalmoscope its always moving around. Why cross-eyed and why the nystagmus?

The answer lies in the weird projections of the retina ganglion cell axons in these sub-albinotic animals. The key paper is Hubert and Weisel back in 1971 (Aberrant visual projections in the Siamese cat. J Physiol. 1971 218:33-62). If you think that you would never be able to access this, it is online at http://www.pubmedcentral.gov/articlerender.fcgi?tool=pubmed&pubmedid=5130620! (Exclamation mark mine not part of the web address!) Even the structured abstract takes me half an hour to read and understand, so here I’ve drawn a simplified diagram of what I think is happening. The most lateral portions of retina, rather than sending axons which stay ipsilateral, send fibres which aberrantly decussate (drawn in red). Basically by being cross-eyed, the cat is avoiding using the lateral portions of its retinas to look forward at all. The nystagmus is caused by the poor retina not knowing quite where to look!

 

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