title: Suppression of melatonin secretion in some blind patients by exposure to bright light.
abstract: BACKGROUND
  Complete blindness generally results in the loss of synchronization of circadian rhythms to the 24-hour day and in recurrent insomnia. However, some blind patients maintain circadian entrainment. We undertook this study to determine whether some blind patients' eyes convey sufficient photic information to entrain the hypothalamic circadian pacemaker and suppress melatonin secretion, despite an apparently complete loss of visual function.
  
  
  METHODS
  We evaluated the input of light to the circadian pacemaker by testing the ability of bright light to decrease plasma melatonin concentrations in 11 blind patients with no conscious perception of light and in 6 normal subjects. We also evaluated circadian entrainment over time in the blind patients.
  
  
  RESULTS
  Plasma melatonin concentrations decreased during exposure to bright light in three sightless patients by an average (+/- SD) of 69 +/- 21 percent and in the normal subjects by an average of 66 +/- 15 percent. When two of these blind patients were tested with their eyes covered during exposure to light, plasma melatonin did not decrease. The three blind patients reported no difficulty sleeping and maintained apparent circadian entrainment to the 24-hour day. Plasma melatonin concentrations did not decrease during exposure to bright light in seven of the remaining blind patients; in the eighth, plasma melatonin was undetectable. These eight patients reported a history of insomnia, and in four the circadian temperature rhythm was not entrained to the 24-hour day.
  
  
  CONCLUSIONS
  The visual subsystem that mediates light-induced suppression of melatonin secretion remains functionally intact in some sightless patients. The absence of photic input to the circadian system thus constitutes a distinct form of blindness, associated with periodic insomnia, that afflicts most but not all patients with no conscious perception of light.
authors.affiliation: Department of Medicine, Harvard Medical School, Boston, MA 02115.
authors.forename: C A
authors.initials: CA
authors.lastname: Czeisler
authors.forename: T L
authors.initials: TL
authors.lastname: Shanahan
authors.forename: E B
authors.initials: EB
authors.lastname: Klerman
authors.forename: H
authors.initials: H
authors.lastname: Martens
authors.forename: D J
authors.initials: DJ
authors.lastname: Brotman
authors.forename: J S
authors.initials: JS
authors.lastname: Emens
authors.forename: T
authors.initials: T
authors.lastname: Klein
authors.forename: J F
authors.initials: JF
authors.lastname: Rizzo
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001766:Blindness / Q000209:etiology / Q000503:physiopathology*; D002940:Circadian Rhythm; D005260:Female; D006801:Humans; D008027:Light; D008297:Male; D008550:Melatonin / Q000097:blood / Q000378:metabolism*; D008875:Middle Aged; D010775:Photic Stimulation; D007319:Sleep Initiation and Maintenance Disorders / Q000503:physiopathology; D014796:Visual Perception
chemical_list: D008550:Melatonin