title: The effect of rebreathing and hyperventilation on retinal and choroidal vessels measured by spectral domain optical coherence tomography.
abstract: OBJECTIVE
  The purpose of this study was to examine the vasoreactivity in retina and choroid of the healthy eyes in response to experimentally altered partial arterial pressure of carbon dioxide (PaCO(2)) using a non-invasive technique, spectral domain optical coherence tomography (SD-OCT).
  
  
  METHODS
  The study included non-smoking participants between 18 and 35 years of age, having visual acuity of 20/20 and with no systemic and ocular diseases. At baseline, the participants breathed room air (normocapnia). Hypocapnia was created with the help of hyperventilation; for this, the participants were instructed to draw deep and quick breaths, resulting one breathing cycle per 2 s. To create hypercapnia subjects rebreathed from a 5 l bag at least 3 min. Choroidal thickness and retinal artery diameter were measured at baseline, and hyperventilation and rebreathing conditions by SD-OCT.
  
  
  RESULTS
  Twenty eyes of 20 healthy subjects were included in this study. Their mean age was 24.90 ± 5.32 years. Hyperventilation caused a significant reduction in choroidal thickness, compared with baseline, at all points; whereas rebreathing caused no significant change at all points. The mean diameters of the arteries were 151.80 ± 7.88 μm, with a significant decline to 148.90 ± 7.25 μm at hyperventilation condition and a significant increase to 153.50 ± 7.88 μm at rebreathing condition (p = 0.018, p = 0.043, respectively).
  
  
  CONCLUSIONS
  This study demonstrated that, SD-OCT was a useful tool in measuring the ocular vascular response under hypercapnia and hypocapnia conditions. These findings may be helpful for further understanding the physiological nature of ocular blood flow and this preliminary study provides a basis for future studies.
authors.affiliation: a Department of Ophthalmology , Konya Training and Research Hospital , Konya , Turkey .
authors.forename: Muammer
authors.initials: M
authors.lastname: Ozcimen
authors.affiliation: a Department of Ophthalmology , Konya Training and Research Hospital , Konya , Turkey .
authors.forename: Yasar
authors.initials: Y
authors.lastname: Sakarya
authors.affiliation: a Department of Ophthalmology , Konya Training and Research Hospital , Konya , Turkey .
authors.forename: Sertan
authors.initials: S
authors.lastname: Goktas
authors.affiliation: a Department of Ophthalmology , Konya Training and Research Hospital , Konya , Turkey .
authors.forename: Rabia
authors.initials: R
authors.lastname: Sakarya
authors.affiliation: a Department of Ophthalmology , Konya Training and Research Hospital , Konya , Turkey .
authors.forename: Ismail
authors.initials: I
authors.lastname: Alpfidan
authors.affiliation: b Konya Eye Clinic , Konya , Turkey , and.
authors.forename: Halil I
authors.initials: HI
authors.lastname: Yener
authors.affiliation: c Department of Public Health , Necmettin Erbakan University, Faculty of Medicine , Konya , Turkey.
authors.forename: Lutfi S
authors.initials: LS
authors.lastname: Demir
mesh_terms: D000293:Adolescent; D000328:Adult; D002245:Carbon Dioxide / Q000097:blood*; D002829:Choroid / Q000033:anatomy & histology / Q000098:blood supply*; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000097:blood / Q000503:physiopathology; D006985:Hyperventilation / Q000097:blood / Q000503:physiopathology*; D016857:Hypocapnia / Q000097:blood / Q000503:physiopathology; D008297:Male; D010313:Partial Pressure; D011446:Prospective Studies; D012119:Respiration; D012171:Retinal Vessels / Q000033:anatomy & histology*; D041623:Tomography, Optical Coherence; D014661:Vasoconstriction / Q000502:physiology; D014664:Vasodilation / Q000502:physiology; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide
keywords: Carbon dioxide; choroidal blood flow; ocular blood flow; retinal artery