title: An experimental study of the neurophysical mechanisms of photophobia induced by subarachnoid hemorrhage.
abstract: BACKGROUND
  Photophobia is defined as a painful psychosomatic discomfort triggered by intense light flow through the pupils to the brain, but the exact mechanism through which photophobia is induced by subarachnoid hemorrhage (SAH) is not well understood. In this study, we aimed to investigate whether there was any relationship between the mydriasis induced by the degeneration of the ciliary ganglion (CG) and photophobia in instances of SAH.
  
  
  METHODS
  Five of a total of 25 rabbits were used as the intact control group; five were used in the sham-operated control group; and the remaining 15 were used as the SAH group, which was created by injecting autologous blood into their cisterna magna. All animals were examined daily for 20days to evaluate their level of photophobia, after which their brains, CGs and superior cervical ganglia (SCGs) were extracted bilaterally. The densities of normal and degenerated neurons in these ganglia were examined by stereological methods.
  
  
  RESULTS
  In SAH animals with a high photophobia score, the mean pupil diameter and density of degenerated neurons density in the CG were greater than in cases with a low photophobia score (p<0.05). Further analysis revealed that the increase in the density of degenerated neurons in the CG following SAH resulted in the paralysis of the parasympathetic pathway of the pupillary muscles and mydriasis, which facilitates the excessive transfer of light to the brain and photophobia.
  
  
  CONCLUSIONS
  Our findings indicate that SAH results in a high density of degenerated neurons in the CG, which induces mydriasis and is an important factor in the onset of photophobia. This phenomenon is likely due to more light energy being transferred through mydriatic pupils to the brain, resulting in vasospasm of the supplying arteries.
authors.affiliation: Department of Psychiatry, Bakirkoy Mazhar Osman Education Hospital, Istanbul, Turkey.
authors.forename: Nazan
authors.initials: N
authors.lastname: Aydin
authors.affiliation: Department of Neurology, Sakarya Universty School of Medicine, Sakarya, Turkey. Electronic address: dilcankotan@yahoo.com.
authors.forename: Dilcan
authors.initials: D
authors.lastname: Kotan
authors.affiliation: Department of Ophthalmology, Ataturk Universty School of Medicine, Erzurum, Turkey.
authors.forename: Sadullah
authors.initials: S
authors.lastname: Keles
authors.affiliation: Opthalmology Clinic of Tokat-Erbaa Satate Hospital, Tokat, Turkey.
authors.forename: Osman
authors.initials: O
authors.lastname: Ondas
authors.affiliation: Department of Neurosurgery, Ataturk Universty School of Medicine, Erzurum, Turkey.
authors.forename: Mehmet Dumlu
authors.initials: MD
authors.lastname: Aydin
authors.affiliation: Department of Ophthalmology, Ataturk Universty School of Medicine, Erzurum, Turkey.
authors.forename: Orhan
authors.initials: O
authors.lastname: Baykal
authors.affiliation: Department of Pathology, Ataturk Universty School of Medicine, Erzurum, Turkey.
authors.forename: Betul
authors.initials: B
authors.lastname: Gundogdu
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D005726:Ganglia, Parasympathetic / Q000473:pathology*; D015878:Mydriasis / Q000209:etiology / Q000473:pathology*; D009802:Oculomotor Nerve / Q000473:pathology; D020795:Photophobia / Q000209:etiology / Q000473:pathology* / Q000503:physiopathology*; D011817:Rabbits; D013345:Subarachnoid Hemorrhage / Q000150:complications*
keywords: Ciliary ganglion; Photophobia; Rabbit; Subarachnoid hemorrhage; Vasospasm