The photic sneeze reflex (also known as Autosomal Dominant Compelling Helio-Ophthalmic Outburst (ACHOO) syndrome) is an inherited and congenital autosomal dominant reflex condition that causes sneezing in response to numerous stimuli, such as looking at bright lights or periocular (surrounding the eyeball) injection. The condition affects 18–35% of the world's population, but its exact mechanism of action is not well understood.
Symptoms and signs
The photic sneeze reflex manifests itself in the form of uncontrollable sneezing in response to a stimulus which would not produce a sneeze in people without the trait. The sneezes generally occur in bursts of 1 to 10 sneezes, followed by a refractory period that can be as long as 24 hours.
Photic sneezing
A photic sneeze results from exposure to a bright light and is the most common manifestation of the photic sneeze reflex. This reflex seems to be caused by a change in light intensity rather than by a specific wavelength of light.
A survey conducted by the School of Optometry at the University of Alabama at Birmingham found that 67% of respondents who identified as photic sneezers were female and 94% were Caucasian. The study also found that photic sneezing was significantly more common in people with a deviated nasal septum.
Further studies have revealed this mechanism to be inherited.
Response to periocular injection
Even less well understood than photic sneezing is sneezing in response to periocular injection, a trait that appears to be inherited in an autosomal dominant fashion. During surgeries in and around the eye, such as corneal transplant surgery, the patient often requires injection of a local anesthetic into the eye. In patients who show the photic sneeze reflex, an injection into the eye, such as that undergone in a retrobulbar or peribulbar block, can often elicit a sneeze from the patient. During these procedures, the patient may be sedated prior to the periocular injection. The patient begins to sneeze just as the needle is inserted into the eye, often resulting in the anesthesiologist having to remove the needle before injecting the local anesthetic.
Sneezing after eating
A condition called gustatory rhinitis can cause some individuals to sneeze after eating, particularly after the consumption of spicy foods. Stomach fullness is another example of a stimulus that can cause uncontrollable sneezing. Those who exhibit this symptom or disorder, called snatiation, undergo uncontrollable fits of 3–15 sneezes immediately after eating large meals that completely fill the stomach, regardless of the type of food eaten. Snatiation is not believed to be an allergic reaction of any kind.
Risks
Sneezing generally does not present any particular risks to the individual, and is usually more an annoyance than a risk of injury. The fits of sneezing brought about by the photic sneeze reflex can, however, have dangerous implications during certain scenarios and activities, such as operating a vehicle, or while undergoing operations (dental, optical) and having bright lights directed towards the patient's face.
Vehicle operation
A fit of sneezing while operating a vehicle can cause the operator to lose control of that vehicle, resulting in injury to the person, and damage to the vehicle and/or surroundings. In particular, photic sneezing poses a considerable risk to pilots, due to the frequent presence of bright sunlight and the precise reactions needed to successfully control the aircraft. For the pilot of a fighter aircraft, if an uncontrollable fit of sneezing were to occur during aerial combat, the pilot could be incapacitated when their situational awareness needs to be greatest. A plane landing on an aircraft carrier or shoreline also requires precise movements and quick reflexes. The reflection of the sun from surrounding water has a high probability of producing at least one photic sneeze for pilots who have the reflex. Any amount of sneezing while attempting to land could cause the pilot to lose control, potentially resulting in disaster.
Medical procedures
Uncontrollable fits of sneezing are common in patients under propofol sedation who undergo periocular or retrobulbar injection.