Photic sneeze reflex

Photic sneeze reflex 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.

The probable cause is a congenital malfuction 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. Overstimulation of the optic nerve triggers the trigeminal nerve, and this causes the photic sneezing reflex. Another theory suggests a passage connecting the tear ducts[?] to the nose called the nasolacrimal duct[?]. It enables tears to drain out of the eye. Tears leaking into the nose through the nasolocrimal duct are a possible cause of photic sneeze reflex.

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

References

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 [On-line], Available http://www.ncbi.nlm.nih.gov/htbin-post/Entrez/query?db=m_d

Deshmukh, N. "Sneezing response to bright light. Is it a cause of accidents?" The Guthrie Journal, 1995, 64(3): 104-105 [On-line], Available http://www.cathouse.org/medical/photic_sneeze

Breitenbach, R.A, "The Photic Sneeze Reflex as a Risk Factor to Combat Pilots." Military Medicine, 158, December 1993: 806-809 [On-line], Available http://www.cathouse.org/medical/photic_sneeze

External links

• MadSci article on the photic sneeze reflex (http://www.madsci.org/posts/archives/aug97/865380242.Me.r)

• Scientific American notes on the photic sneeze reflex (http://www.sciam.com/askexpert_question.cfm?articleID=0004BA86-E838-1DD3-A838809EC588F2D7)

• Annotated biography on medical journals on the photic sneeze reflex (http://loin.free.fr/john/medical_articles)