title: The impact of flash intensity on retinal vessel oxygen saturation measurements using dual wavelength oximetry.
abstract: OBJECTIVE
  To establish the optimal flash settings for retinal vessel oxygen saturation parameters using dual-wavelength imaging in a multiethnic group.
  
  
  METHODS
  Twelve healthy young subjects (mean age 32 years [SD 7]; three Mediterranean, two South Asian, and seven Caucasian individuals) underwent retinal vessel oxygen saturation measurements using dual-wavelength oximetry, noncontact tonometry, and manual sphygmomanometry. In order to evaluate the impact of flash intensity, we obtained three images (fundus camera angle 30°, ONH centered) per flash setting. Flash settings of the fundus camera were increased in steps of 2 (initial setting of 6 and the final of 22), which reflect logarithmic increasing intensities from 13.5 to 214 Watt seconds (Ws).
  
  
  RESULTS
  Flash settings below 27 Ws were too low to obtain saturation measurements, whereas flash settings of more than 214 Ws resulted in overexposed images. Retinal arteriolar and venular oxygen saturation was comparable at flash settings of 27 to 76 Ws (arterioles' range: 85%-92%; venules' range: 45%-53%). Higher flash settings lead to increased saturation measurements in both retinal arterioles (up to 110%) and venules (up to 92%), with a more pronounced increase in venules.
  
  
  CONCLUSIONS
  Flash intensity has a significant impact on retinal vessel oxygen saturation measurements using dual-wavelength retinal oximetry. High flash intensities lead to supranormal oxygen saturation measurements with a magnified effect in retinal venules compared with arteries. In addition to even retinal illumination, the correct flash setting is of paramount importance for clinical acquisition of images in retinal oximetry. We recommend flash settings between 27 to 76 Ws.
authors.affiliation: Aston University, School of Life and Health Sciences, Birmingham, United Kingdom. R.Heitmar1@aston.ac.uk
authors.forename: Rebekka
authors.initials: R
authors.lastname: Heitmar
authors.forename: Robert Peter
authors.initials: RP
authors.lastname: Cubbidge
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D005127:Eye Color; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007429:Intraocular Pressure / Q000502:physiology; D008027:Light; D008297:Male; D010092:Oximetry / Q000379:methods; D010100:Oxygen / Q000097:blood*; D010108:Oxyhemoglobins / Q000378:metabolism; D010775:Photic Stimulation; D012161:Retinal Artery / Q000502:physiology / Q000528:radiation effects*; D012169:Retinal Vein / Q000502:physiology / Q000528:radiation effects*; D019722:Sphygmomanometers; D014065:Tonometry, Ocular
chemical_list: D006454:Hemoglobins; D010108:Oxyhemoglobins; C100003:deoxyhemoglobin; D010100:Oxygen