The scanning laser ophthalmoscope--a review of its role in bioscience and medicine

In-vivo functional and structural retinal imaging using multiwavelength photoacoustic remote sensing microscopy

Many important eye diseases as well as systemic disorders manifest themselves in the retina. Retinal imaging technologies are rapidly growing and can provide ever-increasing amounts of information about the structure, function, and molecular composition of retinal tissue in-vivo. Photoacoustic remote sensing (PARS) is a novel imaging modality based on all-optical detection of photoacoustic signals, which makes it suitable for a wide range of medical applications. In this study, PARS is applied for in-vivo imaging of the retina and estimating oxygen saturation in the retinal vasculature. To our knowledge, this is the first time that a non-contact photoacoustic imaging technique is applied for in-vivo imaging of the retina. Here, optical coherence tomography is also used as a well-established retinal imaging technique to navigate the PARS imaging beams and demonstrate the capabilities of the optical imaging setup. The system is applied for in-vivo imaging of both microanatomy and the microvasculature of the retina. The developed system has the potential to advance the understanding of the ocular environment and to help in monitoring of ophthalmic diseases.

Detecting Diabetic Retinal Neuropathy Using Fundus Perimetry

Fundus perimetry is a new technique for evaluating the light sense in the retina in a point-to-point manner. Light sense is fundamentally different from visual acuity, which measures the threshold for discriminating and perceiving two points or lines, called the minimum cognoscible. The quality of measurement of retinal sensitivity has dramatically increased in the last decade, and the use of fundus perimetry is now gaining popularity. The latest model of fundus perimetry, MP-3, can be used for a wide range of measurements and has an advanced eye tracking system. High background illumination enables accurate measurement of mesopic retail sensitivity. Recent investigations have shown that neuronal damage precedes vascular abnormalities in diabetic retinopathy. The loss of retinal function has also been reported prior to morphological changes in the retina. In this review, the importance of measuring retinal sensitivity to evaluate visual function in the early stages of diabetic retinopathy was discussed. The usefulness of retinal sensitivity as an outcome measure in clinical trials for treatment modalities is also presented. The importance of fundus perimetry is promising and should be considered by both diabetes researchers and clinical ophthalmologists.

Non-invasive multimodal imaging of Diabetic Retinopathy: A survey on treatment methods and Nanotheranostics

Diabetes Retinopathy (DR) is one of the most prominent microvascular complications of diabetes. It is one of the pre-eminent causes for vision impairment followed by blindness among the working-age population worldwide. The de facto cause for DR remains challenging, despite several efforts made to unveil the mechanism underlying the pathology of DR. There is quite less availability of the low cost pre-emptive theranostic imaging tools in terms of in-depth resolution, due to the multiple factors involved in the etiology of DR. This review work comprehensively explores the various reports and research works on all perspectives of diabetic retinopathy (DR), and its mechanism. It also discusses various advanced non-destructive imaging modalities, current, and future treatment approaches. Further, the application of various nanoparticle-based drug delivery strategies used for the treatment of DR are also discussed. In a nutshell, the present review work bolsters the pursuit of the development of an advanced non-invasive optical imaging modal with a nano-theranostic approach for the future diagnosis and treatment of DR and its associated ocular complications.

Comparison between two multimodal imaging platforms: Nidek Mirante and Heidelberg Spectralis

PURPOSE

To investigate the reliability and comparability of retinal measurements obtained with spectral-domain optical coherence tomography (OCT), optical coherence tomography angiography (OCTA), confocal scanning laser ophthalmoscopy (cSLO) colour images, and fundus autofluorescence (FAF) between two multimodal imaging platforms in eyes with macular pathology and normal, healthy volunteers.

METHODS

This cross-sectional, multi-centre, instrument validation study recruited 94 consecutive subjects. All participants underwent a dilated examination and were scanned consecutively on the Heidelberg Spectralis (Heidelberg Engineering, Heidelberg, Germany) and Nidek Mirante (Nidek Co. Ltd., Gamagori, Japan) devices. Agreement between device images were evaluated from measures of the central retinal thickness (CRT), presence of segmentation and fixation imaging artefacts (IA), foveal avascular zone (FAZ) measurements; as well as sensitivity and specificity values from the detection of atrophy on fundus autofluorescence (FAF), drusen, subretinal drusenoid deposits, geographic atrophy, epiretinal membrane, fibrosis and haemorrhage on multicolour imaging, and agreement between devices and groups.

RESULTS

Compared with reference clinical examination, sensitivity values for the identification of retinal features using sole device images ranged from 100% for epiretinal membranes to 66.7% for subretinal drusenoid deposits (SSD). Mean absolute difference for CRT between OCT devices was 3.78 μm (95% confidence interval [CI]: - 21.39 to 28.95, P = 0.809). Differences in the superficial and deep capillary plexus FAZ area on OCTA between devices were not statistically significant (P = 0.881 and P = 0.595, respectively). IAs were significantly increased in the presence of macular pathology.

CONCLUSION

Comparison of retinal measurements between the OCT devices did not differ significantly. Common ultrastructural biomarkers of multiple macular pathologies were identified with high sensitivities and specificities, with good agreement between graders, indicating that they can be identified with comparable confidence in retinal imaging between the two devices.

Simultaneous photoacoustic microscopy, spectral-domain optical coherence tomography, and fluorescein microscopy multi-modality retinal imaging

The goal of this study is to further develop a multi-modality eye imaging system and evaluate its feasibility of acquiring images of different modalities simultaneously. An integrated multimodality imaging system combining spectral-domain optical coherence tomography (SD-OCT), photoacoustic microscopy (PAM), and fluorescence microscopy (FM) was developed, and its performance for eye imaging was validated on multiple clinically-relevant retinal disease models in vivo in rabbits. OCT imaging allows for visualization of the different anatomic retinal layers with high axial resolution. PAM can be used to image vasculature, angiogenesis, and hemorrhages. The leakage of neovascularization can be verified with FM and fluorescein dye. Simultaneous imaging with OCT, PAM, and FM ensures co-registration of the three modalities without being affected by motion artifacts caused by breathing, body or eye movements, and heartbeat. This simultaneous multi-modality eye imaging system could be a new tool for applications both in ophthalmology and other fields.

Ultralow energy photoacoustic microscopy for ocular imaging in vivo

SIGNIFICANCE

The development of ultralow energy photoacoustic microscopy (PAM) on the clinically relevant pigmented rabbit eye model paves a road toward translation of the emerging PAM technology in ophthalmology clinics.

AIM

Since the eye is particularly vulnerable to laser damage, we aim to develop an ultralow energy PAM system to significantly improve the laser safety of PAM by increasing the sensitivity of the system and reducing the incident laser energy for imaging.

APPROACH

A multichannel data acquisition circuit with two-stage signal amplification was specially designed, which, in combination with the application of 3 by 3 median filter in the spatial domain, significantly improved the signal-to-noise ratio of the PAM system. The safety of this system was validated by histopathology, fluorescein angiography, and fundus photography.

RESULTS

Experiments performed on pigmented rabbits demonstrated that, when using this ultralow energy PAM system, satisfactory image quality can be achieved in the eye with an incident laser fluence that is only 1% of the American National Standards Institute safety limit. Fundus photography, fluorescein angiography, and histopathology were performed after the imaging procedure, and no retinal or ocular damage was observed.

CONCLUSIONS

The proposed ultralow energy PAM system has excellent safety and holds potential to be developed into a clinical tool for ocular imaging.

Towards an Optical Biopsy during Visceral Surgical Interventions

Background

Cancer will replace cardiovascular diseases as the most frequent cause of death. Therefore, the goals of cancer treatment are prevention strategies and early detection by cancer screening and ideal stage therapy. From an oncological point of view, complete tumor resection is a significant prognostic factor. Optical coherence tomography (OCT) and confocal laser microscopy (CLM) are two techniques that have the potential to complement intraoperative frozen section analysis as in vivo and real-time optical biopsies.

Summary

In this review we present both procedures and review the progress of evaluation for intraoperative application in visceral surgery. For visceral surgery, there are promising studies evaluating OCT and CLM; however, application during routine visceral surgical interventions is still lacking.

Key Message

OCT and CLM are not competing but complementary approaches of tissue analysis to intraoperative frozen section analysis. Although intraoperative application of OCT and CLM is at an early stage, they are two promising techniques of intraoperative in vivo and real-time tissue examination. Additionally, deep learning strategies provide a significant supplement for automated tissue detection.

Novel window for cancer nanotheranostics: non-invasive ocular assessments of tumor growth and nanotherapeutic treatment efficacy in vivo

In cancer research there is a fundamental need for animal models that allow the in vivo longitudinal visualization and quantification of tumor development, nanotherapeutic delivery, the tumor microenvironment including blood vessels, macrophages, fibroblasts, immune cells, and extracellular matrix, and the tissue response to treatment. To address this need, we developed a novel mouse ocular xenograft model. Green fluorescent protein (GFP) expressing human glioblastoma cells (between 500 and 10,000) were implanted into the subretinal space of immunodeficient mice (56 eyes). The resultant xenografts were imaged in vivo non-invasively with combined fluorescence scanning laser ophthalmoscopy (SLO) and volumetric optical coherence tomography (OCT) for a period up to several months. Most xenografts exhibited a latent phase followed by a stable or rapidly increasing volume, but about 1/3 underwent spontaneous remission. After prescribed growth, a population of tumors was treated with intravenously delivered doxorubicin-containing porphyrin and cholic acid-based nanoparticles ("nanodox"). Fluorescence resonance energy transfer (FRET) emission (doxorubicin → porphyrin) was used to localize nanodox in the xenografts, and 690 nm light exposure to activate it. Such photo-nanotherapy was highly effective in reducing tumor volume. Histopathology and flow cytometry revealed CD4 + and CD8 + immune cell infiltration of xenografts. Overall, the ocular model shows potential for examining the relationships between neoplastic growth, neovascularization and other features of the immune microenvironment, and for evaluating treatment response longitudinally in vivo.

Visible light sensorless adaptive optics for retinal structure and fluorescence imaging

Optical coherence tomography (OCT) has emerged as a powerful imaging instrument and technology in biomedicine. OCT imaging is predominantly performed using wavelengths in the near infrared; however, visible light (VIS) has been recently employed in OCT systems with encouraging results for high-resolution retinal imaging. Using a broadband supercontinuum VIS source, we present a sensorless adaptive optics (SAO) multimodal imaging system driven by VIS-OCT for volumetric retinal structural imaging, followed by the acquisition of fluorescence emission. The coherence-gated, depth-resolved VIS-OCT images used for image-guided SAO aberration correction enable high-resolution structural and fluorescence imaging.

In vivo photoacoustic imaging of chorioretinal oxygen gradients

Chorioretinal imaging has a crucial role for the patients with chorioretinal vascular diseases, such as neovascular age-related macular degeneration. Imaging oxygen gradients in the eye could better diagnose and treat ocular diseases. Here, we describe the use of photoacoustic ocular imaging (PAOI) in measuring chorioretinal oxygen saturation (CR  -  sO2) gradients in New Zealand white rabbits (n  =  5) with ocular ischemia. We observed good correlation (R2  =  0.98) between pulse oximetry and PAOI as a function of different oxygen percentages in inhaled air. We then used an established ocular ischemia model in which intraocular pressure is elevated to constrict ocular blood flow, and notice a positive correlation (R2  =  0.92) between the injected volume of phosphate buffered saline (PBS) and intraocular pressure (IOP) as well as a negative correlation (R2  =  0.98) between CR  -  sO2 and injected volume of PBS. The CR  -  sO2 was measured before (baseline), during (ischemia), and after the infusion (600-μL PBS). The ischemia-reperfusion model did not affect the measurement of the sO2 using a pulse oximeter on the animal's paw, but the chorioretinal PAOI signal showed a nearly sixfold decrease in CR  -  sO2 (n  =  5, p  =  0.00001). We also observe a sixfold decrease in CR  -  sO2 after significant elevation of IOP during ischemia, with an increase close to baseline during reperfusion. These data suggest that PAOI can detect changes in chorioretinal oxygenation and may be useful for application to imaging oxygen gradients in ocular disease.

Temporal diabetes-induced biochemical changes in distinctive layers of mouse retina

To discover the mechanisms underlying the progression of diabetic retinopathy (DR), a more comprehensive understanding of the biomolecular processes in individual retinal cells subjected to hyperglycemia is required. Despite extensive studies, the changes in the biochemistry of retinal layers during the development of DR are not well known. In this study, we aimed to determine a more detailed understanding of the natural history of DR in Akita/+ (type 1 diabetes model) male mice with different duration of diabetes. Employing label-free spatially resolved Fourier transform infrared (FT-IR) chemical imaging engaged with multivariate analysis enabled us to identify temporal-dependent reproducible biomarkers of the individual retinal layers from mice with 6 weeks,12 weeks, 6 months, and 10 months of age. We report, for the first time, the nature of the biochemical alterations over time in the biochemistry of distinctive retinal layers namely photoreceptor retinal layer (PRL), inner nuclear layer (INL), and plexiform layers (OPL, IPL). Moreover, we present the molecular factors associated with the changes in the protein structure and cellular lipids of retinal layers induced by different duration of diabetes. Our paradigm provides a new conceptual framework for a better understanding of the temporal cellular changes underlying the progression of DR.

Optical Design of Adaptive Optics Confocal Scanning Laser Ophthalmoscope with Two Deformable Mirrors

We describe the optical design of a confocal scanning laser ophthalmoscope with two deformable mirrors. Spherical mirrors are used for pupil relay. Defocus aberration of the human eye is corrected by a Badal focusing structure and astigmatism aberration is corrected by a deformable mirror. The main optical system achieves a diffraction-limited performance through the entire scanning field (6 mm pupil, 3 degrees on pupil plane). The performance of the optical system, with correction of defocus and astigmatism, is also evaluated.

Fluorescent Dye Labeling of Erythrocytes and Leukocytes for Studying the Flow Dynamics in Mouse Retinal Circulation

The retinal and choroidal blood flow dynamics may provide insight into the pathophysiology and sequelae of various ocular diseases, such as glaucoma, diabetic retinopathy, age-related macular degeneration (AMD) and other ocular inflammatory conditions. It may also help to monitor the therapeutic responses in the eye. The proper labeling of the blood cells, coupled with live-cell imaging of the labeled cells, allows for the investigation of the flow dynamics in the retinal and choroidal circulation. Here, we describe the standardized protocols of 1.5% indocyanine green (ICG) and 1% sodium fluorescein labeling of mice erythrocytes and leukocytes, respectively. Scanning laser ophthalmoscopy (SLO) was applied to visualize the labeled cells in the retinal circulation of C57BL/6J mice (wild type). Both methods demonstrated distinct fluorescently labeled cells in the mouse retinal circulation. These labeling methods can have wider applications in various ocular disease models.

Photoacoustic imaging of the eye: A mini review

The eye relies on the synergistic cooperation of many different ocular components, including the cornea, crystalline lens, photoreceptors, and retinal neurons, to precisely sense visual information. Complications with a single ocular component can degrade vision and sometimes cause blindness. Immediate treatment and long-term monitoring are paramount to alleviate symptoms, restore vision, and cure ocular diseases. However, successful treatment requires understanding ocular pathological mechanisms, precisely detecting and monitoring the diseases. The investigation and diagnosis of ocular diseases require advanced medical tools. In this mini review, we discuss non-invasive photoacoustic (PA) imaging as a potential research tool and medical screening device. In the research setting, PA imaging can provide valuable information on the disease progression. In the clinical setting, PA imaging can potentially aid in disease detection and treatment monitoring.

High-resolution contrast-enhanced optical coherence tomography in mice retinae

Optical coherence tomography (OCT) is a noninvasive interferometric imaging modality providing anatomical information at depths of millimeters and a resolution of micrometers. Conventional OCT images limit our knowledge to anatomical structures alone, without any contrast enhancement. Therefore, here we have, for the first time, optimized an OCT-based contrast-enhanced imaging system for imaging single cells and blood vessels in vivo inside the living mouse retina at subnanomolar sensitivity. We used bioconjugated gold nanorods (GNRs) as exogenous OCT contrast agents. Specifically, we used anti-mouse CD45 coated GNRs to label mouse leukocytes and mPEG-coated GNRs to determine sensitivity of GNR detection in vivo inside mice retinae. We corroborated OCT observations with hyperspectral dark-field microscopy of formalin-fixed histological sections. Our results show that mouse leukocytes that otherwise do not produce OCT contrast can be labeled with GNRs leading to significant OCT intensity equivalent to a 0.5 nM GNR solution. Furthermore, GNRs injected intravenously can be detected inside retinal blood vessels at a sensitivity of ∼0.5  nM, and GNR-labeled cells injected intravenously can be detected inside retinal capillaries by enhanced OCT contrast. We envision the unprecedented resolution and sensitivity of functionalized GNRs coupled with OCT to be adopted for longitudinal studies of retinal disorders.

Clinical applications of fundus autofluorescence in retinal disease

Fundus autofluorescence (FAF) is a non-invasive retinal imaging modality used in clinical practice to provide a density map of lipofuscin, the predominant ocular fluorophore, in the retinal pigment epithelium. Multiple commercially available imaging systems, including the fundus camera, the confocal scanning laser ophthalmoscope, and the ultra-widefield imaging device, are available to the clinician. Each offers unique advantages for evaluating various retinal diseases. The clinical applications of FAF continue to expand. It is now an essential tool for evaluating age related macular degeneration, macular dystrophies, retinitis pigmentosa, white dot syndromes, retinal drug toxicities, and various other retinal disorders. FAF may detect abnormalities beyond those detected on funduscopic exam, fluorescein angiography, or optical coherence tomography, and can be used to elucidate disease pathogenesis, form genotype-phenotype correlations, diagnose and monitor disease, and evaluate novel therapies. Given its ease of use, non-invasive nature, and value in characterizing retinal disease, FAF enjoys increasing clinical relevance. This review summarizes common ocular fluorophores, imaging modalities, and FAF findings for a wide spectrum of retinal disorders.

Spontaneously occurring fundus findings observed using confocal scanning laser ophthalmoscopy in wild type Sprague Dawley rats

PURPOSE

Non-invasive in vivo imaging is an increasingly used component of pre-clinical research. However, to reliably interpret data, it may be necessary to identify and document pre-existent findings prior to initiating long-term or intensive protocols, particularly where toxicity or efficacy is under investigation. Here we report here spontaneously occurring findings from the Sprague Dawley (SD) rat eye using multi-modal confocal scanning laser ophthalmoscopy (cSLO).

METHODS

As part of ongoing studies, with the goal of excluding animals with abnormalities from further investigation, a total of 165 wild type SD rats (312 eyes) were assessed using cSLO imaging at baseline prior to initiating experiments to detect, describe, and determine the prevalence of spontaneous fundus findings.

RESULTS

Using fundus autofluorescence (FAF) as the primary screening modality, over 30% of analyzed eyes possessed some fundus finding that differed from the normal composite reference image. Unexpectedly, 100% of eyes demonstrated a diffuse hyperfluorescent region in the posterior pole that was ultimately considered normal, and formed part of the reference. Evaluated by three independent reviewers, five groups of FAF abnormalities were defined, based primarily on shape and size of the lesion. Of these, the most extensive lesions were further analyzed using infrared reflectance (IR) and red free (RF) imaging. White light and autofluorescent microscopy of excised tissue confirmed that the extensive lesions were derived from abnormalities in both the isolated retina and posterior eyecups.

CONCLUSIONS

Given the newly described hyperfluorescent glow that appears in all eyes, and the high basal rate of spontaneous lesions in the outbred SD rat, we suggest that investigators be aware of the variants of normal, and that baseline in vivo screening be considered prior to initiating intensive or expensive investigation.

Effect of scanning beam size on the lateral resolution of mouse retinal imaging with SLO

Scanning laser ophthalmoscopy (SLO) employs the eye's optics as a microscope objective for retinal imaging in vivo. The mouse retina has become an increasingly important object for investigation of ocular disease and physiology with optogenetic probes. SLO imaging of the mouse eye, in principle, can achieve submicron lateral resolution thanks to a numerical aperture (NA) of ∼0.5, about 2.5 times larger than that of the human eye. In the absence of adaptive optics, however, natural ocular aberrations limit the available optical resolution. The use of a contact lens, in principle, can correct many aberrations, permitting the use of a wider scanning beam and, thus, achieving greater resolution then would otherwise be possible. In this Letter, using an SLO equipped with a rigid contact lens, we report the effect of scanning beam size on the lateral resolution of mouse retinal imaging. Theory predicts that the maximum beam size full width at half-maximum (FWHM) that can be used without any deteriorating effects of aberrations is ∼0.6  mm. However, increasing the beam size up to the diameter of the dilated pupil is predicted to improve lateral resolution, though not to the diffraction limit. To test these predictions, the dendrites of a retinal ganglion cell expressing YFP were imaged, and transverse scans were analyzed to quantify the SLO system resolution. The results confirmed that lateral resolution increases with the beam size as predicted. With a 1.3 mm scanning beam and no high-order aberration correction, the lateral resolution is ∼1.15  μm, superior to that achievable by most human AO-SLO systems. Advantages of this approach include stabilization of the mouse eye and simplified optical design.

Optical coherence contrast imaging using gold nanorods in living mice eyes

BACKGROUND

Optical coherence tomography (OCT) is a powerful imaging modality to visualize tissue structures, with axial image pixel resolution as high as 1.6 μm in tissue. However, OCT is intrinsically limited to providing structural information as the OCT contrast is produced by optically scattering tissues.

METHODS

Gold nanorods (GNRs) were injected into the anterior chamber (AC) and cornea of mice eyes which could create a significant OCT signal and hence could be used as a contrast agent for in vivo OCT imaging.

RESULTS

A dose of 30 nM of GNRs (13 nm in diameter and 45 nm in length) were injected to the AC of mice eyes and produced an OCT contrast nearly 50-fold higher than control mice injected with saline. Furthermore, the lowest detectable concentration of GNRs in living mice AC was experimentally estimated to be as low as 120 pM.

CONCLUSIONS

The high sensitivity and low toxicity of GNRs brings great promise for OCT to uniquely become a high-resolution molecular imaging modality.

In vivo wide-field multispectral scanning laser ophthalmoscopy-optical coherence tomography mouse retinal imager: longitudinal imaging of ganglion cells, microglia, and Müller glia, and mapping of the mouse retinal and choroidal vasculature

Scanning laser ophthalmoscopy (SLO) and optical coherence tomography (OCT) provide complementary views of the retina, with the former collecting fluorescence data with good lateral but relatively low-axial resolution, and the latter collecting label-free backscattering data with comparable lateral but much higher axial resolution. To take maximal advantage of the information of both modalities in mouse retinal imaging, we have constructed a compact, four-channel, wide-field (∼50  deg) system that simultaneously acquires and automatically coregisters three channels of confocal SLO and Fourier domain OCT data. The scanner control system allows “zoomed” imaging of a region of interest identified in a wide-field image, providing efficient digital sampling and localization of cellular resolution features in longitudinal imaging of individual mice. The SLO is equipped with a “flip-in” spectrometer that enables spectral “fingerprinting” of fluorochromes. Segmentation of retina layers and en face display facilitate spatial comparison of OCT data with SLO fluorescence patterns. We demonstrate that the system can be used to image an individual retinal ganglion cell over many months, to simultaneously image microglia and Müller glia expressing different fluorochromes, to characterize the distinctive spatial distributions and clearance times of circulating fluorochromes with different molecular sizes, and to produce unequivocal images of the heretofore uncharacterized mouse choroidal vasculature.

Imaging of the peripheral retina

The technical progress of the recent years has revolutionized imaging in ophthalmology. Scanning laser ophthalmoscopy (SLO), digital angiography, optical coherence tomography (OCT), and detection of fundus autofluorescence (FAF) have fundamentally changed our understanding of numerous retinal and choroidal diseases. Besides the tremendous advances in macular diagnostics, there is more and more evidence that central pathologies are often directly linked to changes in the peripheral retina. This review provides a brief overview on current posterior segment imaging techniques with a special focus on the peripheral retina.

Spectral-domain optical coherence tomography of the rodent eye: highlighting layers of the outer retina using signal averaging and comparison with histology

Spectral-Domain Optical Coherence Tomography (SD-OCT) is a widely used method to observe retinal layers and follow pathological events in human. Recently, this technique has been adapted for animal imaging. This non-invasive technology brings a cross-sectional visualization of the retina, which permits to observe precisely each layer. There is a clear expansion of the use of this imaging modality in rodents, thus, a precise characterization of the different outer retinal layers observed by SD-OCT is now necessary to make the most of this technology. The identification of the inner strata until the outer nuclear layer has already been clearly established, while the attribution of the layers observed by SD-OCT to the structures corresponding to photoreceptors segments and retinal pigment epithelium is much more questionable. To progress in the understanding of experimental SD-OCT imaging, we developed a method for averaging SD-OCT data to generate a mean image allowing to better delineate layers in the retina of pigmented and albino strains of mice and rats. It allowed us to locate precisely the interface between photoreceptors and retinal pigment epithelium and to identify unambiguously four layers corresponding to the inner and outer parts of photoreceptors segments. We show that the thickness of the various layers can be measured as accurately in vivo on SD-OCT images, than post-mortem by a morphometric analysis of histological sections. We applied SD-OCT to different models and demonstrated that it allows analysis of focal or diffuse retinal pathological processes such as mutation-dependant damages or light-driven modification of photoreceptors. Moreover, we report a new method of combined use of SD-OCT and integration to quantify laser-induced choroidal neovascularization. In conclusion, we clearly demonstrated that SD-OCT represents a valuable tool for imaging the rodent retina that is at least as accurate as histology, non-invasive and allows longitudinal follow-up of the same animal.

Comparison of wide-field fluorescein angiography and 9-field montage angiography in uveitis

PURPOSE

To compare qualitatively and quantitatively Optos fundus camera fluorescein angiographic images of retinal vascular leakage with 9-field montage Topcon fluorescein angiography (FA) images in patients with uveitis. We hypothesized that Optos images reveal more leakage in patients with uveitis.

DESIGN

Retrospective, observational case series.

METHODS

Images of all patients with uveitis imaged with same-sitting Optos FA and 9-field montage FA during a 9-month period at a single institution (52 eyes of 31 patients) were graded for the total area of retinal vascular leakage. The main outcome measure was area of fluorescein leakage.

RESULTS

The area of apparent FA leakage was greater in Optos images than in 9-field montage images (median 22.5 mm(2) vs 4.8 mm(2), P < 0.0001). Of the 49 (45%) eyes with gradable photos, 22 had at least 25% more leakage in the Optos image than in the montage image; 2 (4.1%) had at least 25% less leakage in Optos; and 25 (51%) were similar in the 2 modalities. There were 2 eyes that had no apparent retinal vascular leakage in 9-field montage but were found to have apparent leakage in Optos images. Of the 49 eyes, 23 had posterior pole leakage, and of these, 17 (73.9%) showed more posterior pole leakage in the Optos image. A single 200-degree Optos FA image captured a mean 1.50× the area captured by montage photography.

CONCLUSIONS

More retinal vascular pathology, in both the periphery and the posterior pole, is seen with Optos FA in patients with uveitis when compared with 9-field montage. The clinical implications of Optos FA findings have yet to be determined.

Recent advances in ophthalmic molecular imaging

The aim of molecular imaging techniques is the visualization of molecular processes and functional changes in living animals and human patients before morphological changes occur at the cellular and tissue level. Ophthalmic molecular imaging is still in its infancy and has mainly been used in small animals for pre-clinical research. The goal of most of these pre-clinical studies is their translation into ophthalmic molecular imaging techniques in clinical care. We discuss various molecular imaging techniques and their applications in ophthalmology.

Spontaneous ocular and neurologic deficits in transgenic mouse models of multiple sclerosis and noninvasive investigative modalities: a review

Multiple sclerosis (MS) is an autoimmune, inflammatory, neurodegenerative, demyelinating disease of the central nervous system, predominantly involving myelinated neurons of the brain, spinal cord, and optic nerve. Optic neuritis is frequently associated with MS and often precedes other neurologic deficits associated with MS. A large number of patients experience visual defects and have abnormalities concomitant with neurologic abnormalities. Transgenic mice manifesting spontaneous neurologic and ocular disease are unique models that have revolutionized the study of MS. Spontaneous experimental autoimmune encephalomyelitis (sEAE) presents with spontaneous onset of demyelination, without the need of an injectable immunogen. This review highlights the various models of sEAE, their disease characteristics, and applicability for future research. The study of optic neuropathy and neurologic manifestations of demyelination in sEAE will expand our understanding of the pathophysiological mechanisms underlying MS. Early and precise diagnosis of MS with different noninvasive methods has opened new avenues in managing symptoms, reducing morbidity, and limiting disease burden. This review discusses the spectrum of available noninvasive techniques, such as electrophysiological and behavioral assessment, optical coherence tomography, scanning laser polarimetry, confocal scanning laser ophthalmoscopy, pupillometry, magnetic resonance imaging, positron emission tomography, gait, and cardiovascular monitoring, and their clinical relevance.

Digital ocular fundus imaging: a review

Ocular fundus imaging plays a key role in monitoring the health status of the human eye. Currently, a large number of imaging modalities allow the assessment and/or quantification of ocular changes from a healthy status. This review focuses on the main digital fundus imaging modality, color fundus photography, with a brief overview of complementary techniques, such as fluorescein angiography. While focusing on two-dimensional color fundus photography, the authors address the evolution from nondigital to digital imaging and its impact on diagnosis. They also compare several studies performed along the transitional path of this technology. Retinal image processing and analysis, automated disease detection and identification of the stage of diabetic retinopathy (DR) are addressed as well. The authors emphasize the problems of image segmentation, focusing on the major landmark structures of the ocular fundus: the vascular network, optic disk and the fovea. Several proposed approaches for the automatic detection of signs of disease onset and progression, such as microaneurysms, are surveyed. A thorough comparison is conducted among different studies with regard to the number of eyes/subjects, imaging modality, fundus camera used, field of view and image resolution to identify the large variation in characteristics from one study to another. Similarly, the main features of the proposed classifications and algorithms for the automatic detection of DR are compared, thereby addressing computer-aided diagnosis and computer-aided detection for use in screening programs.

Advances in imaging of Stargardt disease

Stargardt disease (STGD1) is an autosomal-recessively inherited condition often associated with mutations in ABCA4 and characterized by accumulation of autofluorescent lipofuscin deposits in the retinal pigment epithelium (RPE). Non-invasive imaging techniques including fundus autofluorescence (FAF), spectral domain optical coherence tomography (SD-OCT) and adaptive optics scanning laser ophthalmoscopy (AOSLO) have the potential to improve understanding of vision loss in patients with STGD. We describe a comprehensive approach to the study of patients with STGD. Measures of retinal structure and FAF were correlated with visual function including best-corrected visual acuity (BCVA), color vision, kinetic and static perimetry, fundus-guided microperimetry and full-field and multifocal electroretinography. Mutation analysis of the ABCA4 gene was carried out by sequencing the complete coding region. Preliminary data suggest that a combination of imaging modalities may provide a sensitive measure of disease progression and response to experimental therapies in patients with STGD.

In vivo imaging of the immune response in the eye

The immune system is governed by dynamic events involving in part direct intercellular interactions between an immune cell and other cells or the cell's environment. Owing to its unique optical characteristics, the eye offers remarkable opportunities for the analysis of the immune system by intravital microscopy. In this review, we present a brief overview of the current state of knowledge of leukocyte trafficking in each of three anatomically distinct and medically important regions of the eye (cornea, iris, retina) as determined by the application of intravital microscopy to animal models of disease. Additionally, we discuss the use of ocular imaging in patients and volunteers. Finally, we examine the future prospects for this field in terms of its potential for impacting our understanding of fundamental immunological phenomena.

Assessment of rat and mouse RGC apoptosis imaging in vivo with different scanning laser ophthalmoscopes

PURPOSE

We have recently described a novel way of imaging apoptosing retinal ganglion cells in vivo in the rat. This study investigated if this technique could be used in the mouse, and whether the Heidelberg Retina Angiograph II (HRAII) was appropriate.

METHODS

Retinal ganglion cell (RGC) death was induced by intravitreal injections in rat and mouse eyes using staurosporine. Fluorescent-labeled apoptosing cells were detected by imaging with both the HRAII and a prototype Zeiss confocal scanning laser ophthalmoscope (cSLO). Averaged in vivo images were analyzed and results compared with histologic analysis.

RESULTS

Fluorescent points (FPs) used as a measure of RGC apoptosis in vivo were detected in the mouse eye but only with the HRAII and not the Zeiss cSLO. The HRAII was able to detect 62% more FPs in rat than the Zeiss cSLO. Both cSLOs showed peak FP counts at the 5- to 10-microm range in rat and mouse. Maximal FP counts were detected in the superior and superior temporal regions in the rat, with no obvious pattern of distribution in the mouse. The HRAII was found to have more FP correspondence with histologically identified apoptosing RGCs.

CONCLUSIONS

To our knowledge, this is the first demonstration of visualized apoptosing RGC in vivo in a mouse. The improved image quality achieved with the HRAII compared with the Zeiss cSLO was validated by histology. This together with its enhanced maneuverability and the fact that it is already commercially available make the HRAII a potential tool for the early detection and diagnosis of glaucomatous disease in patients.

Multimodal imaging in macular diagnostics: combined OCT-SLO improves therapeutical monitoring

BACKGROUND

Digital imaging methods are a centrepiece for diagnosis and management of macular disease. A recently developed imaging device is composed of simultaneous confocal scanning laser ophthalmoscopy (SLO) and optical coherence tomography (OCT). By means of clinical samples the benefit of this technique concerning diagnostic and therapeutic follow-up will be assessed.

METHODS

The combined OCT-SLO-System (Ophthalmic Technologies Inc., Toronto, Canada) allows for confocal en-face fundus imaging and high resolution OCT scanning at the same time. OCT images are obtained from transversal line scans. One light source and the identical scanning rate yield a pixel-to-pixel correspondence of images. Three-dimensional thickness maps are derived from C-scan stacking.

RESULTS

We followed-up patients with cystoid macular edema, pigment epithelium detachment, macular hole, venous branch occlusion, and vitreoretinal tractions during their course of therapy. The new imaging method illustrates the reduction of cystoid volume, e.g. after intravitreal injections of either angiostatic drugs or steroids. C-scans are used for appreciation of lesion diameters, visualisation of pathologies involving the vitreoretinal interface, and quantification of retinal thickness change.

CONCLUSION

The combined OCT-SLO system creates both topographic and tomographic images of the retina. New therapeutic options can be followed-up closely by observing changes in lesion thickness and cyst volumes. For clinical use further studies are needed.

Macular degeneration: recent advances and therapeutic opportunities

The central retina mediates high acuity vision, and its progressive dysfunction due to macular degeneration is the leading cause of visual disability among adults in industrialized societies. Here, we summarize recent progress in understanding the pathophysiology of macular degeneration and the implications of this new knowledge for treatment and prevention. The past decade has witnessed remarkable advances in this field, including the development of new, non-invasive retinal imaging technologies, the development of animal models for macular disease, and the isolation of many of the genes responsible for both early- and late-onset macular diseases. These advances have set the stage for the development of effective mechanism-based therapies.

Quantification of optic nerve head topography in optic neuritis: a pilot study

AIMS

To investigate optic nerve head topography in patients with optic neuritis compared to controls using the Heidelberg retina tomograph-II (HRT-II) and to determine if detected changes are related to visual function and electrophysiology.

METHODS

25 patients with a previous single episode of unilateral optic neuritis and 15 controls were studied with HRT-II, visual evoked potentials, and pattern electroretinogram. Patients also had testing of visual acuity, visual field, and colour vision.

RESULTS

In affected eyes compared to fellow eyes, there was reduction of both the mean retinal nerve fibre layer (RNFL) thickness at the disc edge (p = 0.009) and the neuroretinal rim volume (p = 0.04). In affected eyes compared to control eyes, the three dimensional optic cup shape measure was increased (p = 0.01), indicative of an abnormal cup shape. There were no other significant differences in HRT-II measures. Within patient interocular difference correlation was used to investigate the functional relevance of these changes and demonstrated associations between RNFL thickness change and changes in visual acuity, visual field, and colour vision. Colour vision change was also associated with change in neuroretinal rim volume.

CONCLUSIONS

HRT detects functionally relevant changes in RNFL thickness and neuroretinal rim volume between eyes affected by optic neuritis and unaffected fellow eyes.

Characterization of optical parameters with a human forearm at the region from 1.15 to 1.52 microm using diffuse reflectance measurements

Time- and space-resolved diffuse reflectance measurements were used to identify the optical parameters, the reduced scattering and absorption coefficients, of bulk living tissue in the region from 1.15 to 1.52 microm. Although in this region the detector was limited in its temporal resolution, we applied a peak-time shift analysis successfully to determine these coefficients in a human forearm, and then determined the absorption spectrum by space-resolved diffuse reflectance measurements. The absorption spectrum of a water content of 52% determined by magnetic resonance imaging experiments is in good agreement with the absorption coefficient obtained by optical measurements. Moreover, magnetic resonance imaging measurements suggest that the deviation of the absorption coefficients from the water spectrum in the strong water absorption band is caused by the heterogeneity of water distribution in tissue: the low content of water in the skin. These findings indicate that this optical method is potentially applicable to the non-invasive measurement of water in tissue, especially in a region lower than about 1.3-1.35 microm, which may be useful in monitoring oedema and tissue swelling.

Functional and cortical adaptations to central vision loss

Age-related macular degeneration (AMD), affecting the retina, afflicts one out of ten people aged 80 years or older in the United States. AMD often results in vision loss to the central 15-20 deg of the visual field (i.e. central scotoma), and frequently afflicts both eyes. In most cases, when the central scotoma includes the fovea, patients will adopt an eccentric preferred retinal locus (PRL) for fixation. The onset of a central scotoma results in the absence of retinal inputs to corresponding regions of retinotopically mapped visual cortex. Animal studies have shown evidence for reorganization in adult mammals for such cortical areas following experimentally induced central scotomata. However, it is still unknown whether reorganization occurs in primary visual cortex (V1) of AMD patients. Nor is it known whether the adoption of a PRL corresponds to changes to the retinotopic mapping of V1. Two recent advances hold out the promise for addressing these issues and for contributing to the rehabilitation of AMD patients: improved methods for assessing visual function across the fields of AMD patients using the scanning laser ophthalmoscope, and the advent of brain-imaging methods for studying retinotopic mapping in humans. For the most part, specialists in these two areas come from different disciplines and communities, with few opportunities to interact. The purpose of this review is to summarize key findings on both the clinical and neuroscience issues related to questions about visual adaptation in AMD patients.