Sneezing at the sudden exposure to bright light is known as autosomal dominant compelling helio-ophthalmic outburst (ACHOO) syndrome, or photic sneezing, and affects up to 35% of the population (Eur Arch Otorhinolaryngol. 2017;274:1721–1725). The disorder is characterized as paroxysms of sneezing provoked as a reflex, ranging anywhere from two to 40 sneezes.
Up until recently, the cause of this phenomenon had not been thoroughly investigated. A 1993 study found that the physiologic response was not a reaction to specific wavelengths of light, but instead to changes in brightness (Mil Med. 1993;158:806–809). This is why very often, people sneeze when they look up at the sun.
A study conducted in 2016 found that 67% of participants diagnosed with ACHOO syndrome had prominent corneal nerves, to some degree (Arch Soc Esp Oftalmol. 2016;91:305–309). This could possibly be associated with the disorder; however, the study only examined 12 members of one family.
Authors of a 2010 study proposed that the rapid sneezing is a cause of sensitivity to stimuli in the visual cortex (PLoS One. 2010;5:e9208). They concluded that the reflex does not just occur at the brainstem, but also in specific cortical areas. Extreme sensitivity of parts innervated by the fifth cranial nerves may cause eye irritation that triggers the protective reflexes of the nose to act accordingly. Considering the research currently available, prominent corneal nerves in a patient is more like than not associated with ACHOO syndrome. Further studies are still needed to fully comprehend the physiology.