title: The effect of dehydration and fasting on ocular blood flow.
abstract: OBJECTIVE
  To investigate the effects of dehydration and fasting on retrobulbar-vessel blood velocity in healthy subjects.
  
  
  METHODS
  Twenty-eight eyes of 28 normal subjects without ocular disease were enrolled in this study. Each subject had a baseline color-Doppler imaging ultrasound of the central retinal artery, temporal short posterior ciliary arteries, and ophthalmic artery after 14 hours of religious fasting and dehydration. The first measurements were performed in the fasting conditions. The mean blood flow velocities and resistive index were measured in each artery. One month after the fasting period, color-Doppler imaging measurements were performed in nonfasting conditions. Blood pressure, heart rate, and intraocular pressure were measured before color-Doppler imaging measurements in both the fasting and nonfasting conditions.
  
  
  RESULTS
  Although systolic/diastolic blood pressure, heart rate, and intraocular pressure (111.78 +/- 8.18/76.42 +/- 5.75 mm Hg, 71.00 +/- 2.88 beats/min, and 12.71 +/- 2.25 mm Hg) were higher in nonfasting conditions (112.32 +/- 7.97/78.98 +/- 5.50 mm Hg, 70.71 +/- 2.77 beats/min, and 13.14 +/- 2.62 mm Hg, respectively), differences were not statistically significant. A statistically significant increase in peak systolic velocity in the ophthalmic artery, central retinal artery, and temporal short posterior ciliary artery was noted at the second measurements. A peak systolic velocity value of 48.90 +/- 14.66 cm/sec in the ophthalmic artery increased to 58.28 +/- 14.65 cm/sec in the nonfasting conditions ( < 0.05). A peak systolic velocity value of 16.88 +/- 4.30 cm/sec and an end diastolic velocity of 6.69 +/- 2.15 cm/sec in the central retinal artery increased to 24.24 +/- 6.45 cm/sec and 9.32 +/- 3.08 cm/sec, respectively, was recorded in the nonfasting and nondehydration condition ( < 0.05). Peak systolic velocity measurement of 23.42 +/- 6.19 cm/sec in temporal short posterior ciliary artery increased to 26.68 +/- 7.52 cm/sec at the second measurement ( < 0.05). The only significant change observed in the resistive index measurements was an increase in the ophthalmic artery resistive index in the nonfasting conditions ( < 0.05).
  
  
  CONCLUSIONS
  Color-Doppler measurement may vary significantly in conditions of fasting and dehydration conditions compared with hydrated conditions. Therefore, the fasting and dehydration conditions should be considered when interpreting color-Doppler imaging results and comparing different groups of diseased or healthy subjects.
mesh_terms: D000328:Adult; D001783:Blood Flow Velocity; D019842:Ciliary Arteries / Q000000981:diagnostic imaging / Q000502:physiology; D003681:Dehydration / Q000503:physiopathology*; D005123:Eye / Q000098:blood supply*; D005215:Fasting; D005260:Female; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D009880:Ophthalmic Artery / Q000000981:diagnostic imaging / Q000502:physiology; D012161:Retinal Artery / Q000000981:diagnostic imaging / Q000502:physiology; D018615:Ultrasonography, Doppler, Color