Adam Boretsky

In vivo imaging of photoreceptor disruption associated with age-related macular degeneration: A pilot study

Age‐related macular degeneration is one of the leading causes of vision loss in the developed world. As the disease progresses, the central part of the retina, called the macula, is compromised leading to a disruption of both structure and visual function. In this study, we investigate the disruption of macular photoreceptor cells in vivo as a function of disease stage in patients with the dry form of age‐related macular degeneration AMD.

Dermal scatter reduction in human skin: a method using controlled application of glycerol.

Previous studies in a hairless Guinea pig model showed that transdermal application of glycerol effected a temporary reduction in dermal scatter of light. This study focuses on the application of this protocol on human patients.

Retinal optical coherence tomography image enhancement via shrinkage denoising using double-density dual-tree complex wavelet transform

Abstract. Image enhancement of retinal structures, in optical coherence tomography (OCT) scans through denoising, has the potential to aid in the diagnosis of several eye diseases. In this paper, a locally adaptive denoising algorithm using double-density dual-tree complex wavelet transform, a combination of the double-density wavelet transform and the dual-tree complex wavelet transform, is applied to reduce speckle noise in OCT images of the retina. The algorithm overcomes the limitations of commonly used multiple frame averaging technique, namely the limited number of frames that can be recorded due to eye movements, by providing a comparable image quality in significantly less acquisition time equal to an order of magnitude less time compared to the averaging method. In addition, improvements of image quality metrics and 5 dB increase in the signal-to-noise ratio are attained.

High-resolution multimodal imaging of multiple evanescent white dot syndrome

The integrity of macular morphology was examined in a patient with multiple evanescent white dot syndrome (MEWDS) diagnosed through clinical and investigational adaptive optics (AO) retinal imaging techniques. Imaging was performed during the acute and recovery phases to examine changes in retinal morphology, revealing characteristic small multifocal white dots in the perifoveal region and a granular appearance in the fovea. Fluorescein angiography revealed early and intermediate hyperfluorescence, and regions of decreased fundus autofluorescence were observed. Photoreceptor disruption was apparent during the acute phase and recurrence. Conventional multimodal imaging combined with AO imaging offers more insight into the pathology of MEWDS by providing complementary views of the retina throughout the acute phase, recovery, and recurrence.

Nicotine exposure exacerbates development of cataracts in a type 1 diabetic rat model.

Diabetes and smoking are known risk factors for cataract development. In this study, we evaluated the effect of nicotine on the progression of cataracts in a type 1 diabetic rat model. Diabetes was induced in Sprague-Dawley rats by a single injection of 65 mg/kg streptozotocin. Daily nicotine injections were administered subcutaneously. Forty-five rats were divided into groups of diabetics with and without nicotine treatment and controls with and without nicotine treatment. Progression of lens opacity was monitored using a slit lamp biomicroscope and scores were assigned. To assess whether systemic inflammation played a role in mediating cataractogenesis, we studied serum levels of eotaxin, IL-6, and IL-4. The levels of the measured cytokines increased significantly in nicotine-treated and untreated diabetic animals versus controls and demonstrated a positive trend in the nicotine-treated diabetic rats. Our data suggest the presence of a synergistic relationship between nicotine and diabetes that accelerated cataract formation via inflammatory mediators.

Quantitative evaluation of retinal response to laser photocoagulation using dual-wavelength fundus autofluorescence imaging in a small animal model.

PURPOSE To demonstrate the usefulness of dual-wavelength fundus autofluorescence (FAF) imaging for noninvasive, quantitative monitoring of dynamic changes associated with healing of retinal photocoagulation lesions in a small animal model. METHODS Brown Norway rats, exhibiting substantial age-dependent lipofuscin autofluorescence, were used to characterize the kinetics of FAF recovery after retinal photocoagulation. An argon laser with a beam diameter of 100 μm, exposure duration of 0.1 seconds, and a range of laser powers (8-22 mW) were used to create subthreshold, threshold, and suprathreshold lesions. A modified retinal angiograph was used to obtain dual-wavelength FAF images at 488 and 514 nm to quantify and monitor changes in retinal fluorescence up to 6 months. RESULTS Compared to white light funduscopy, the FAF images exhibited heightened definition and clarity of lesion boundaries immediately after laser exposure. No significant reduction in FAF was measured at or below laser powers of 8 mW. Furthermore, a linear, dose-dependent decrease in FAF (R(2) = 0.9605) was observed immediately after laser exposures of 13 to 22 mW. Complete recovery of baseline FAF was observed for 13.5 and 16 mW exposures at 3 weeks and 4 months, respectively. However, retinal damage was still evident at 6 months after suprathreshold exposure induced using 22 mW laser power. CONCLUSIONS The accumulation of lipofuscin in the aged Brown Norway rat makes it a suitable small animal model for the characterization of laser-induced injury in the retina based on FAF. Dual-wavelength FAF measurements provide a sensitive, quantitative, noninvasive means of monitoring recovery of laser-induced retinal injury.

Nicotine Accelerates Diabetes-Induced Retinal Changes

Abstract Purpose: To investigate the effects of nicotine on retinal alterations in early-stage diabetes in an established rodent model. Materials and Methods: Sprague–Dawley rats were examined using a combination of confocal scanning laser ophthalmoscopy and spectral domain optical coherence tomography to determine changes in retinal structure in response to nicotine exposure, diabetes and the combined effects of nicotine and diabetes. Diabetes was induced by a single injection of 65 mg/kg streptozotocin and nicotine injections were administered subcutaneously daily. Retinal thickness in the superior, inferior, nasal and temporal quadrants were determined based on the spectral domain optical coherence tomography (SD-OCT) volume scans (20° × 20°) centered on the optic disc. Segmentation of discrete retinal layers was performed on a subset of SD-OCT cross-sections to further examine changes in each treatment group. Survival of neurons within the ganglion cell layer (GCL) was assessed by confocal morphometric imaging. Results: The control group did not experience any significant change throughout the study. The nicotine treatment group experienced an average decrease in total retinal thickness (TRT) of 9.4 µm with the majority of the loss localized within the outer nuclear layer (ONL) as determined by segmentation analysis (p < 0.05). The diabetic group exhibited a trend toward decreased TRT while segmentation analysis of the diabetic retinopathy (DR) group revealed significant thinning within the ONL (p < 0.05). The combination of nicotine and diabetes revealed a significant increase of 8.9 µm in the TRT (p < 0.05) accompanied by a decrease in the number of GCL neurons. Conclusions: We demonstrated significant temporal changes in retinal morphology in response to nicotine exposure, diabetes and with the combined effects of nicotine and diabetes. These findings may have implications in determining treatment strategies for diabetic patients using products containing nicotine, such as cigarettes, smokeless tobacco, electronic cigarettes or smoking cessation products.

Laser injury and in vivo multimodal imaging using a mouse model

Balb/c wild type mice were used to perform in vivo experiments of laser-induced thermal damage to the retina. A Heidelberg Spectralis HRA confocal scanning laser ophthalmoscope with a spectral domain optical coherence tomographer was used to obtain fundus and cross-sectional images of laser induced injury in the retina. Sub-threshold, threshold, and supra-threshold lesions were observed using optical coherence tomography (OCT), infrared reflectance, red-free reflectance, fluorescence angiography, and autofluorescence imaging modalities at different time points post-exposure. Lesions observed using all imaging modalities, except autofluorescence, were not visible immediately after exposure but did resolve within an hour and grew in size over a 24 hour period. There was a decrease in fundus autofluorescence at exposure sites immediately following exposure that developed into hyper-fluorescence 24-48 hours later. OCT images revealed threshold damage that was localized to the RPE but extended into the neural retina over a 24 hour period. Volumetric representations of the mouse retina were created to visualize the extent of damage within the retina over a 24 hour period. Multimodal imaging provides complementary information regarding damage mechanisms that may be used to quantify the extent of the damage as well as the effectiveness of treatments without need for histology.

Automated retinal layer segmentation and characterization

Spectral Domain Optical Coherence Tomography (SD-OCT) is a valuable diagnostic tool in both clinical and research settings. The depth-resolved intensity profiles generated by light backscattered from discrete layers of the retina provide a non-invasive method of investigating progressive diseases and injury within the eye. This study demonstrates the application of steerable convolution filters capable of automatically separating gradient orientations to identify edges and delineate tissue boundaries. The edge maps were recombined to measure thickness of individual retinal layers. This technique was successfully applied to longitudinally monitor changes in retinal morphology in a mouse model of laser-induced choroidal neovascularization (CNV) and human data from age-related macular degeneration patients. The steerable filters allow for direct segmentation of noisy images, while novel recombination of weaker segmentations allow for denoising post-segmentation. The segmentation before denoising strategy allows the rapid detection of thin retinal layers even under suboptimal imaging conditions.

NF-kB Activation as a Biomarker of Light Injury Using a Transgenic Mouse Model

The spatial and temporal activation of NF-kB (p65) was monitored in the retina of a transgenic mouse model (cis-NFkB-EGFP) in vivo after receiving varying grades of laser induced thermal injury in one eye. Baseline images of the retinas from 26 mice were collected prior to injury and up to five months post-exposure using a Heidelberg Spectralis HRA confocal scanning laser ophthalmoscope (cSLO) with a spectral domain optical coherence tomographer (SDOCT). Injured and control eyes were enucleated at discrete time points following laser exposure for cryosectioning to determine localization of NF-kB dependent enhanced green fluorescent protein (EGFP) reporter gene expression within the retina using fluorescence microscopy. In addition, EGFP basal expression in brain and retinal tissue from the cis-NFkB-EGFP was characterized using two-photon imaging. Regions of the retina exposed to threshold and supra-threshold laser damage evaluated using fluorescence cSLO showed increased EGFP fluorescence localized to the exposed region for a duration that was dependent upon the degree of injury. Fluorescence microscopy of threshold damage revealed EGFP localized to the outer nuclear region and retinal pigment epithelial layer. Basal expression of EGFP imaged using two-photon microscopy was heterogeneously distributed throughout brain tissue and confined to the inner retina. Results show cis-NF-kB-EGFP reporter mouse can be used for in vivo studies of light induced injury to the retina and possibly brain injury.