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J.A. Martin, A. Roorda; Direct and Non–Invasive Parafoveal Microvascular Density and Foveal Avascular Zone Measurement . Invest. Ophthalmol. Vis. Sci. 2006;47(13):3505.
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© ARVO (1962-2015); The Authors (2016-present)
The foveal avascular zone (FAZ) has been reported to increase with the normal aging process and in diseases effecting retina microvasculature including diabetes. The increase in the FAZ is most likely due to the presence of non–perfused capillaries adjacent to the FAZ. Fluorescein angiography has been the only method used to objectively measure the FAZ and the density of the adjacent parafoveal microvasculature. However, this method relies on the use of fluorescein, an invasive contrast agent. With the development of an Adaptive Optics Scanning Laser Ophthalmoscope (AOSLO) microvasculature bordering the FAZ and leukocytes traveling through these microvasculature can now be resolved without the use of contrast agents. In this paper we demonstrate a new method to directly and non–invasively measure the FAZ and the adjacent parafoveal microvascular density using an AOSLO.
Eight normal healthy subjects ranging from 20 to 38 years of age with clear ocular media were imaged using an AOSLO. All subjects were dilated with tropicamide 1% and phenylephrine hydrochloride 2.5%. An imaging wavelength of 532 nm and a frame rate of 30 Hz were used when recording videos. The AOSLO field of view was 2.35° X 2.5° Single frames were selected and registered from videos recorded with the AOSLO. A foveal montage was then created by aligning these single frames. Measurements of foveal diameter were taken at 45° increments directly from the foveal montage. FAZ area was found by fitting a polygon to the FAZ perimeter and then calculating the area of the polygon. Parafoveal microvascular density was measured for 1 subject in 1°x1° sample sizes from 0° to 2.5° away from the fovea center. Microvascular density was calculated as the total linear distance of all vessels per 1° x 1° sample.
The mean FAZ diameter for all subjects was 0.5274 mm. The range of FAZ diameters was from 0.2624 mm to 0.8342 mm. The mean FAZ area was 0.260 mm2 and ranged from 0.077 mm2 to 0.538 mm2. The mean microvascular density for 1 subject at 1° and 2° eccentricities respectively was 13.8636(1/mm) and 29.1193(1/mm).
It is possible to measure the FAZ and adjacent parafoveal microvascular density non–invasively and directly using the AOSLO. Parafoveal microvascular functionality may also be assessed based on leukocyte movement through the microvasculature. These new methods could allow for the direct and repeated monitoring of changes due to disease and age in microvasculature adjacent to the FAZ.
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