158 INTRODUCTION Alteration in blood supply to the retina occurs in most retinal pathologies, such as glaucoma 1,2 or diabetic retinopathy. 3–5 An understanding of the hemodynamic mechanisms generated during retinal damage is essential for the development of new therapeutic avenues. Laser Doppler fowmetry (LDF) is used to assess ocular blood fow in the clinical setting. 6 LDF is attractive because it is noninvasive, it enables continuous assessment of the blood fow changes, and can be used at near infrared wavelength so that it does not infuence retinal activity. It is based on the Doppler effect, which describes the frequency shift that a photon undergoes when scattered from a moving particle (such as a red blood cell) whereas light scattered by stationary cells remains un-shifted. 7,8 When a laser beam illuminates a number of red blood cells moving through a network of capillaries at various velocities and in different directions, the light scattered by the red blood cells consists of a summation of waves with various frequency shifts. The difference between frequency of the emitted light and the spectrum of backscattered light is directly proportional to the mean velocity of the blood and the amplitude is proportional to the number of cells; the product of both gives a measure of the tissue perfusion. 9 When directly apposed to the tissue, the temporal resolution of the probe is in the tenth of second range and the spatial resolution is in the range of 0.1–1 mm. 6,10–12 LDF was previously used in Current Eye Research, 38(1), 158–167, 2013 © 2013 Informa Healthcare USA, Inc. ISSN: 0271-3683 print/1460-2202 online DOI: 10.3109/02713683.2012.723296 Received 25 February 2011; revised 20 July 2012; accepted 15 August 2012 Correspondence: Elvire Vaucher, Ph.D., Associate Professor, School of Optometry, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, Canada, H3C 3J7. Tel: +1 514 343 7537. Fax: +1 514 343 2382. E-mail: elvire.vaucher@umontreal.ca ORIGINAL ARTICLE Assessment of Retinal and Choroidal Blood Flow Changes Using Laser Doppler Flowmetry in Rats Simon Hétu 1,2 , Mylène Pouliot 1,2 , Ghassan Cordahi 3 , Réjean Couture 2 , and Elvire Vaucher 1 1 School of Optometry, Université de Montréal, Montréal, Québec, Canada, 2 Department of Physiology, Université de Montréal, Montréal, Québec, Canada, and 3 Department of Ophthalmology, Maisonneuve-Rosemont Hospital, Université de Montréal, Montréal, Québec, Canada ABSTRACT Purpose: A new noninvasive laser Doppler fowmetry (LDF) probe (one emitting fber surrounded by a ring of eight collecting fbers, 1-mm interaxis distance) was tested for its sensitivity to assess the retinal/choroidal blood fow variations in response to hypercapnia, hyperoxia, diverse vasoactive agents and following retinal arteries photocoagulation in the rat. Materials and Methods: After pupil dilation, a LDF probe was placed in contact to the cornea of anesthetized rats in the optic axis. Hypercapnia and hyperoxia were induced by inhalation of CO 2 (8% in medical air) and O 2 (100%) while pharmacological agents were injected intravitreously. The relative contribution of the choroidal circulation to the LDF signal was estimated after retinal artery occlusion by photocoagulation. Results: Blood fow was signifcantly increased by hypercapnia (18%), adenosine (14%) and sodium nitroprus- side (16%) as compared to baseline values while it was decreased by hyperoxia (-8%) and endothelin-1 (-11%). Photocoagulation of retinal arteries signifcantly decreased blood fow level (-45%). Conclusions: Although choroidal circulation most likely contributes to the LDF signal in this setting, the results demonstrate that LDF represents a suitable in vivo noninvasive technique to monitor online relative reactivity of retinal perfusion to metabolic or pharmacological challenge. This technique could be used for repeatedly assessing blood fow reactivity in rodent models of ocular diseases. KEYWORDS: Blood fow, Microcirculation, Choroid, Retina, Rodents Curr Eye Res Downloaded from informahealthcare.com by University of Montreal on 02/11/13 For personal use only.