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Akihito Uji, Masanori Hangai, Sotaro Ooto, Nagahisa Yoshimura, Hiroshi Imamura; Hemodynamic Analysis Of Parafoveal Capillaries Using AOSLO. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4475.
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© ARVO (1962-2015); The Authors (2016-present)
Recently, adaptive optics scanning laser ophthalmoscope (AOSLO) is reportedly useful in the imaging of parafoveal capillary leukocytes and measurement of leukocyte velocity. In this study, we quantified the blood-flow velocity pulse in parafoveal capillaries and calculated hemodynamic parameters by using our prototype AOSLO system developed by Canon Inc.
We developed a novel AOSLO system with a high wavefront correction efficiency using dual liquid crystal phase modulator (LCOS-SLM). The wavelength of the imaging light was 840 nm and the frame rate was 60 Hz. The exposure level of the imaging light was set lower than the maximum permissible exposure suggested by the American National Standards Institute. The imaging area was 350 × 700 µm at the retina and was sampled at 200 × 400 pixels. Images of the parafoveal zone were taken for 2 s in a row in 1 healthy subject with no ocular or systemic disease. Images of the capillaries were constructed as projections of the sequential division images and diameters of the capillaries were measured. Blood-flow velocities were measured using spatiotemporal images of target capillary obtained by reslicing the sequential division images. We calculated the pulsatility index (PI) and resistive index (RI) in order to quantify the amplitude of pulsation and assessed correlation with the diameters of the capillaries. All digital image processing procedures, including image warping, for correcting image distortion were performed by public-domain software ImageJ.
We successfully constructed high contrast images of capillaries. Additionally, with our modified image processing technique, images of capillaries could be obtained using only 10 sequential frames. Velocity measurements were taken from 40 different capillaries ranging 4.7-12.2 µm in diameter. From each capillary, velocities of 8-40 particles were measured and 846 measurements were obtained. Velocities of all capillaries ranged from 0.36 to 4.2 mm/s and the mean value was 1.16 mm/s (SD = ± 0.50 mm/s). The mean PI and RI were 1.16 (± 0.41) and 0.63 (± 0.12), respectively. The RI had a relatively low correlation with the diameter (r = 0.37; P < 0.05).
We could obtain high contrast images of capillaries and hemodynamic parameters noninvasively using AOSLO images recorded for only 2 s.
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