title: The effect of high- to low-altitude adaptation on the multifocal electroretinogram.
abstract: OBJECTIVE
  To examine variations in retinal electrophysiology assessed by multifocal electroretinogram (mfERG) during acclimatization of native highlanders to normobaric normoxia at sea level.
  
  
  METHODS
  Eight healthy residents of the greater La Paz area in Bolivia (3600 m above sea level) were examined over 72 days after arriving in Copenhagen, Denmark (sea level). A control group of eight healthy lowlanders was used for comparison.
  
  
  RESULTS
  During the period of observation, hemoglobin decreased from 16.7 to 15.0 g/dL (P = 0.0031), erythrocytes decreased from 5.3 to 4.6 trillion cells/L (P = 0.0006), and hematocrit decreased from 49.4% to 42.2% (P = 0.0008). At baseline, day 2 after arrival, the amplitudes (N1, P1, and N2) of the mfERG were 43.1% to 59.9% higher in the highlanders than in the lowlanders (P < 0.017). During acclimatization, the mfERG amplitudes increased 16.9% to 20.4% (P < 0.028) to a level of 73.2% to 87.0% higher in the highlanders than in the lowlanders (P < 0.0008). The increase in numerical amplitudes was proportional to the decrease in erythrocyte concentration (P = 0.023, 0.053, and 0.12 for N1, P1, and N2, respectively).
  
  
  CONCLUSIONS
  On arrival at sea level, the highlanders had markedly supernormal multifocal electroretinographic amplitudes that continued to increase during the 72-day period of observation where the highlanders' hematocrit normalized. The results suggest that acclimatization after a change in altitude and hence in ambient oxygen tension involves intrinsic retinal mechanisms and that acclimatization was not complete by the end of the study.
authors.affiliation: Department of Ophthalmology, Glostrup Hospital, University of Copenhagen, Copenhagen, Denmark. peter.k@dadlnet.dk
authors.forename: Peter Kristian
authors.initials: PK
authors.lastname: Kofoed
authors.forename: Birgit
authors.initials: B
authors.lastname: Sander
authors.forename: Gustavo
authors.initials: G
authors.lastname: Zubieta-Calleja
authors.forename: Line
authors.initials: L
authors.lastname: Kessel
authors.forename: Kristian
authors.initials: K
authors.lastname: Klemp
authors.forename: Michael
authors.initials: M
authors.lastname: Larsen
mesh_terms: D000064:Acclimatization / Q000502:physiology*; D000328:Adult; D000531:Altitude; D001786:Blood Glucose / Q000032:analysis; D004596:Electroretinography; D004906:Erythrocyte Count; D005260:Female; D006400:Hematocrit; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D010100:Oxygen / Q000097:blood; D010101:Oxygen Consumption / Q000502:physiology; D012160:Retina / Q000502:physiology*
chemical_list: D001786:Blood Glucose; D006454:Hemoglobins; D010100:Oxygen