A new technique for monitoring blood flow will help investigate eye functions and retinal disease.Poor blood supply is one of the main causes of several retinal diseases. Vascular disorders and impaired circulation are observed in major eye diseases that cause blindness, including age-related macular degeneration (AMD) 1 and glaucoma. 2 A noninvasive, 3D imaging tool for major vascular systems of the eye might be helpful for understanding and diagnosing eye diseases. Circulation abnormalities are typically diagnosed using fluorescence angiography, in which injected fluorescent dye is detected. However, this technique is invasive, may have side effects, and cannot be used for patients who are allergic to the dye. In addition, axial resolution-in the light's direction of travel-is poor. This is significant when distinguishing between vascular systems in the retina and the choroid (a layer of blood-rich tissue behind the retina), or recording details of the fine and complex 3D network of choroidal vessels.Other existing eye-imaging techniques have similar problems. Ultrasound Doppler imaging can be used to visualize the crosssectional flow distribution in the eye. However, its limited acquisition speed prevents 3D in vivo imaging while its axial resolution is also insufficient. Scanning-laser Doppler flowmetry is noninvasive and can quantify the microvascular blood flow but it cannot distinguish between the choroidal and retinal vascular systems. We have developed 3D angiography for the eyeoptical coherence angiography (OCA)-based on optical coherence tomography (OCT). OCT is widely used in clinical ophthalmology to visualize the retina's 3D microstructure. 3 OCA uses high-speed Fourier-domain OCT for 3D in vivo imaging of the human eye. To enhance the choroid's contrast, we use light sources with a central wavelength of around 1µm. 4 Scattering OCA uses differences between the optical properties of blood and the surrounding tissue to increase the contrast in the eye vasculature, 5 while Doppler OCA uses phase-resolved Doppler analysis with OCT 6 to detect blood flow. 7 Figure 1. (a) Combination of 3D volume-rendered OCT and scattering OCA in vivo images of human macula. (b) Stereo view of the macula's choroidal vessels. (c) En face projection of choroidal vessels.We developed clinical prototypes of 1µm Fourier-domain OCT, which we used to scan the eyes of healthy human volunteers in vivo. The 3D data sets obtained were processed with scattering and/or Doppler OCA.Since rich pigments are present in choroidal tissue, the backscattered-light intensity from this tissue type is larger than that from blood. Unfortunately, it also causes OCT signal decay in the choroid. This attenuation must be considered in scattering OCA when attempting to obtain a clear 3D choroidal vascular image. The retinal pigment epithelium (RPE), a monocellular layer between retina and choroid, is segmented in OCT crosssectional images. We extracted choroidal images sliced at equal distances from the RPE and applied segmentation based on image s...

Retinal, choroidal and scleral imaging by using swept-source optical coherence tomography (SS-OCT) with a 1-microm band probe light, and high-contrast and three-dimensional (3D) imaging of the choroidal vasculature are presented. This SS-OCT has a measurement speed of 28,000 A-lines/s, a depth resolution of 10.4 microm in tissue, and a sensitivity of 99.3 dB. Owing to the high penetration of the 1-microm probe light and the high sensitivity of the system, the in vivo sclera of a healthy volunteer can be observed. A software-based algorithm of scattering optical coherence angiography (S-OCA) is developed for the high-contrast and 3D imaging of the choroidal vessels. The S-OCA is used to visualize the 3D choroidal vasculature of the in vivo human macula and the optic nerve head. Comparisons of S-OCA with several other angiography techniques including Doppler OCA, Doppler OCT, fluorescein angiography, and indocyanine green angiography are also presented.

A two- and three-dimensional swept source optical coherence tomography (SS-OCT) system, which uses a ready-to-ship scanning light source, is demonstrated. The light source has a center wavelength of 1.31 mum, -3 dB wavelength range of 110 nm, scanning rate of 20 KHz, and high linearity in frequency scanning. This paper presents a simple calibration method using a fringe analysis technique for spectral rescaling. This SS-OCT system is capable of realtime display of two-dimensional OCT and can obtain three-dimensional OCT with a measurement time of 2 s. In vivo human anterior eye segments are investigated two- and three-dimensionally. The system sensitivity is experimentally determined to be 114 dB. The three-dimensional OCT volumes reveal the structures of the anterior eye segments, which are difficult to observe in two-dimensional OCT images.

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