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Quantitatively determining physiological parameters at a microscopic level in the retina furthers the understanding of the molecular pathways of blinding diseases, such as diabetic retinopathy and glaucoma. An essential parameter, which has yet to be quantified noninvasively, is the retinal oxygen metabolic rate (rMRO2). Quantifying rMRO2 is challenging because two parameters, the blood flow rate and hemoglobin oxygen saturation (sO2), must be measured together. We combined photoacoustic ophthalmoscopy (PAOM) with spectral domain-optical coherence tomography (SD-OCT) to tackle this challenge, in which PAOM measured the sO2 and SD-OCT mapped the blood flow rate. We tested the integrated system on normal wild-type rats, in which the measured rMRO2 was 297.86 ± 70.23 nl/minute. This quantitative method may shed new light on both fundamental research and clinical care in ophthalmology in the future.

Photoacoustic ophthalmoscopy (PAOM) is a high-resolution in vivo imaging modality that is capable of providing specific optical absorption information for the retina. A high-frequency ultrasonic transducer is one of the key components in PAOM, which is in contact with the eyelid through coupling gel during imaging. The ultrasonic transducer plays a crucial role in determining the image quality affected by parameters such as spatial resolution, signal-to-noise ratio, and field of view. In this paper, we present the results of a systematic study on a high-frequency ultrasonic transducer design for PAOM. The design includes piezoelectric material selection, frequency selection, and the fabrication process. Transducers of various designs were successfully applied for capturing images of biological samples in vivo. The performances of these designs are compared and evaluated.

Purpose: To demonstrate the feasibility of fundus camera guided photoacoustic ophthalmoscopy (PAOM) system and its multimodal imaging capabilities., Methods: We integrated PAOM and a fundus camera consisting of a white-light illuminator and a high-sensitivity, high-speed CCD. The fundus camera captures both retinal anatomy and PAOM illumination at the same time to provide a real-time feedback when we position the PAOM illuminating light. We applied the integrated system to image rat eyes in vivo and used full-spectrum, visible (VIS), and near infrared (NIR) illuminations in fundus photography., Results: Both albino and pigmented rat eyes were imaged in vivo. During alignment, different trajectories of PAOM laser scanning were successfully visualized by the fundus camera, which reduced the PAOM alignment time from several minutes to 30 s. In albino eyes, in addition to retinal vessels, main choroidal vessels were observed using VIS-illumination, which is similar to PAOM images. In pigmented eyes, the radial striations of retinal nerve fiber layer were visualized by fundus photography using full-spectrum illumination; meanwhile, PAOM imaged both retinal vessels and the retinal pigmented epithelium melanin distribution., Conclusions: The results demonstrated that PAOM can be well-integrated with fundus camera without affecting its functionality. The fundus camera guidance is faster and easier comparing with our previous work. The integrated system also set the stage for the next-step verification between oximetry methods based on PAOM and fundus photography.

Photoacoustic ophthalmoscopy (PAOM) is a novel imaging technology that measures optical absorption in the retina. The capability of PAOM can be further enhanced if it could image mouse eyes, because mouse models are widely used for various retinal diseases. The challenges in achieving high-quality imaging of mouse retina, however, come from the much smaller eyeball size. Here, we report an optimized imaging system, which integrates PAOM, spectral-domain optical coherence tomography (SD-OCT), and autofluorescence-scanning laser ophthalmoscopy (AF-SLO), for mouse eyes. Its multimodal capability was demonstrated by imaging transgenic Nrl-GFP mice that express green fluorescent protein (GFP) in photoreceptors. SD-OCT provided guidance of optical alignment for PAOM and AF-SLO, and complementary contrast with high depth-resolution retinal cross sections. PAOM visualized the retinal vasculature and retinal pigment epithelium melanin, and AF-SLO measured GFP-expressing in retinal photoreceptors. The in vivo imaging results were verified by histology and confocal microscopy., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Both the clinical diagnosis and fundamental investigation of major ocular diseases greatly benefit from various non-invasive ophthalmic imaging technologies. Existing retinal imaging modalities, such as fundus photography, confocal scanning laser ophthalmoscopy (cSLO), and optical coherence tomography (OCT), have significant contributions in monitoring disease onsets and progressions, and developing new therapeutic strategies. However, they predominantly rely on the back-reflected photons from the retina. As a consequence, the optical absorption properties of the retina, which are usually strongly associated with retinal pathophysiology status, are inaccessible by the traditional imaging technologies. Photoacoustic ophthalmoscopy (PAOM) is an emerging retinal imaging modality that permits the detection of the optical absorption contrasts in the eye with a high sensitivity. In PAOM nanosecond laser pulses are delivered through the pupil and scanned across the posterior eye to induce photoacoustic (PA) signals, which are detected by an unfocused ultrasonic transducer attached to the eyelid. Because of the strong optical absorption of hemoglobin and melanin, PAOM is capable of non-invasively imaging the retinal and choroidal vasculatures, and the retinal pigment epithelium (RPE) melanin at high contrasts. More importantly, based on the well-developed spectroscopic photoacoustic imaging, PAOM has the potential to map the hemoglobin oxygen saturation in retinal vessels, which can be critical in studying the physiology and pathology of several blinding diseases such as diabetic retinopathy and neovascular age-related macular degeneration. Moreover, being the only existing optical-absorption-based ophthalmic imaging modality, PAOM can be integrated with well-established clinical ophthalmic imaging techniques to achieve more comprehensive anatomic and functional evaluations of the eye based on multiple optical contrasts. In this work, we integrate PAOM and spectral-domain OCT (SD-OCT) for simultaneously in vivo retinal imaging of rat, where both optical absorption and scattering properties of the retina are revealed. The system configuration, system alignment and imaging acquisition are presented.

Photoacoustic ophthalmoscopy (PAOM) is a newly developed retinal imaging technology that holds promise for both fundamental investigation and clinical diagnosis of several blinding diseases. Hence, integrating PAOM with other existing ophthalmic imaging modalities is important to identify and verify the strengths of PAOM compared with the established technologies and to provide the foundation for more comprehensive multimodal imaging. To this end, we developed a retinal imaging platform integrating PAOM with scanning laser ophthalmoscopy (SLO), spectral-domain optical coherence tomography (SD-OCT), and fluorescein angiography (FA). In the system, all the imaging modalities shared the same optical scanning and delivery mechanisms, which enabled registered retinal imaging from all the modalities. High-resolution PAOM, SD-OCT, SLO, and FA images were acquired in both albino and pigmented rat eyes. The reported in vivo results demonstrate the capability of the integrated system to provide comprehensive anatomic imaging based on multiple optical contrasts.

Photoacoustic ophthalmoscopy (PAOM) is a new retinal imaging technology that offers the unique capability to measure optical absorption in the retina. Because PAOM is compatible with optical coherence tomography, scanning laser ophthalmoscopy, and autofluorescence imaging, registered multimodal images can be acquired from a single device at comparable resolution for comprehensive anatomic and functional retinal characterizations. Therefore, PAOM is anticipated to have applications in both research and clinical diagnosis of many blinding diseases. The authors explain the basic principles of the photoacoustic effect and imaging. Then, different types of photoacoustic microscopy are introduced and compared. Finally, the current status of photoacoustic imaging in animal eyes is presented and the prospects of future development of PAOM are suggested., (Copyright 2011, SLACK Incorporated.)

We imaged the microvascular network in both the retina and the choroid in an albino rat eye using photoacoustic ophthalmoscopy guided by optical coherence tomography. Relying on optical absorption and ultrasonic detection, photoacoustic ophthalmoscopy can image both retinal and choroidal vessel networks with high contrast. [ABSTRACT FROM PUBLISHER]