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Photic Trigeminal Neuralgia or Photic Headshaking

Neuralgia = pain at the nerve endings, usually induced by a disturbed "food" supply of a nerve


What is called Photic Headshaking in our horses is called Photic Sneeze Reflex in human. The ongoing research in horses is based on the ongoing research in human.

The website "Photic Sneezing" authored by Mr. Martin Haegenheim, reports of 4 existing theories:

Several theories have been advanced to explain the phenomenon, but the generally accepted explanation is the " crossed wires " theory.

The sudden exposure to bright light sends a signal through the optic nerve fibers. These fibers run close to and into the same hub as the trigeminal nerve. The second division of the trigeminal nerve supplies sensory fibers to the nasal mucosa. The assumption is that nerve impulses in the optic nerve cause a sympathetic discharge in the trigeminal nerve fibers. which produces the sneezing.

A second theory involves the simultaneous activation of neighboring parasympathetic branches. In this case, the stimulus to the retina also causes tears to be formed, leading to congestion in the nose and a " trickling sensation ". A third scenario posits a more generalized parasympathetic system hypersensitivity, and could be linked to the subject's emotional state. The fourth theory links intraorbital trigeminal nerve stimulation and increased ocular sensitivity to light ; this would account for photic sneezing in cases of nephropathic cystinosis.

These theories are discussed at length in Everett (1964) and Whitman and Packer (1993) in the bibliography.

Re-published with friendly permission by above author.

At the website Wikepedia we can read follwing article:

Photic sneeze reflex, also whimsically called ACHOO, a backronym for Autosomal dominant Compelling Helio-Ophthalmic Outburst) is a medical condition by which people exposed to bright light involuntarily sneeze. It has been suggested that the photic sneeze reflex occurs only after someone has been adapted to the dark for at least five minutes, although this is not certain, and is not uniform amongst people with the photic sneeze reflex. The condition occurs in one-sixth to one-quarter of humans, with more common occurrence in Caucasians than other human races. The trait is passed along genetically, with a 50 percent chance of inheritance. It is more often seen in children than in adults.

The probable cause is a congenital malfunction in nerve signals in the trigeminal nerve nucleus. The fifth cranial nerve, called the trigeminal nerve, is apparently responsible for sneezes. Research suggests that some people have an association between this nerve and the nerve that transmits visual impulses to the brain. Over-stimulation of the optic nerve triggers the trigeminal nerve, and this causes the photic sneeze reflex. Another theory suggests that tears leaking into the nose through the nasolacrimal duct are a cause of the photic sneeze reflex. The speed of the reflex seems to favour the first theory, as it happens much too quickly for tears to be generated and drain into the nose.

The photic sneeze reflex is considered a risk factor to combat pilots: people suffering from photic sneeze reflex may not fly combat aircraft.

Headshaking appeared to be light-stimulated in approximately 60% of the horses examined (Madigen 1998 Nov;(27):28-9.) http://www.ncbi.nlm.nih.gov/pubmed/10485000

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Semes LP, Amos JF, Waterbor JW. "The Photic Sneeze Response: Descriptive Report of a Clinic Population." Journal of American Optometry Association June 1995, 66(6): p372-377

Deshmukh, N. "Sneezing photic response to bright light. Is it a cause of accidents?" The Guthrie Journal, 1995, 64(3): 104-105

Breitenbach, R.A, "The Photic Sneeze Reflex as a Risk Factor to Combat Pilots." Military Medicine, 158, December 1993: 806-809, Abstract: [3] 
External links
MadSci article on the photic sneeze reflex (link
Scientific American notes on the photic sneeze reflex (link
Annotated biography on medical journals on the photic sneeze reflex (link
The Straight Dope on photic sneeze reflex (link)

The contents of this article is licensed from Wikepedia under the GNU Free Documentation License. 



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