Photoacoustic Ophthalmoscopy: Principle, Application, and Future Directions

Abstract

Photoacoustic ophthalmoscopy (PAOM) is a novel, hybrid, non-ionizing, and non-invasive imaging technology that has been used to assess the retina. PAOM can provide both anatomic and functional retinal characterizations with high resolution, high sensitivity, high contrast, and a high depth of penetration. Thus, ocular diseases can be precisely detected and visualized at earlier stages, resulting in an improved understanding of pathophysiology, improved management, and the improved monitoring of retinal treatment to prevent vision loss. To better visualize ocular components such as retinal vessels, choroidal vessels, choroidal neovascularization, retinal neovascularization, and the retinal pigment epithelium, an advanced multimodal ocular imaging platform has been developed by a combination of PAOM with other optical imaging techniques such as optical coherence tomography (OCT), scanning laser ophthalmoscopy (SLO), and fluorescence microscopy. The multimodal images can be acquired from a single imaging system and co-registered on the same image plane, enabling an improved evaluation of disease. In this review, the potential application of photoacoustic ophthalmoscopy in both research and clinical diagnosis are discussed as a medical screening technique for the visualization of various ocular diseases. The basic principle and requirements of photoacoustic ocular imaging are introduced. Then, various photoacoustic microscopy imaging systems of the retina in animals are presented. Finally, the future development of PAOM and multimodal imaging is discussed.

Ex vivo assessment of the optical characteristics of human brain and tumour tissue

“…Similar to previous studies, the absorption spectra of all samples were dominated by the absorption bands of haemoglobin below 600 nm and water above 900 nm, with characteristic low absorption values within the 600 to 900 nm wavelength range [7] [9]. However, our results demonstrated a further striking peak in µa at 1450 nm, not previously reported, but again consistent with the absorption spectra of water [15]. The reduced scattering coefficient spectra of all tissues generally decreased with increasing wavelength, while the values of reduced scattering were very different across all tissue types.…”

Photoacoustic Imaging of the Eye

“…Photoacoustic imaging systems can be divided into several categories which include: optical-resolution photoacoustic microscopy (OR-PAM), acoustic-resolution photoacoustic microscopy (AR-PAM), photoacoustic computed tomography (PACT), photoacoustic tomography (PAT) [5,6]. Ocular PAI systems are primarily OR-PAM and AR-PAM systems due to the importance of high resolution imaging in the eye [7][8][9]. AR-PAM is used to image deep-tissues, where an illumination laser is diffusively delivered to the tissue and a focused acoustic detector is used to detect the induced PA signals.…”

“…Figure 1b illustrates the physical setup [11]. Compared with mechanical-scanning, optical-scanning can provide higher scanning speed, and it is suitable for chorioretinal microvasculature imaging, and compatibility with OCT and SLO [9,12].…”

Overview of Ultrasound Detection Technologies for Photoacoustic Imaging

“…Due to the widely used intermediate penetration depth achieved by IR light, higher sensitivity of IR devices, and the fast growing advancement of IR optical components, most of photoacoustic systems are implemented in this regime. Infrared photoacoustic technology has been successfully used in both preclinical (to study small animal brain [19][20][21][22], eye [23][24][25][26], and skin [27][28][29]) and clinical (to detect breast cancer [30][31][32], cervical cancer [33,34], skin melanoma [35,36], and brain tumor [37,38]) applications.…”