Name: quantitative fundus autofluorescence for the evaluation of retinal diseases
Uploaded: 2016-03-11T14:00:00
Description: Watch this Scientific Journal Video about Quantitative Fundus Autofluorescence for the Evaluation of Retinal Diseases at JoVE.com

We would like to thank our collaborators, Francois Delori, Tomas Burke, and Tobias Duncker.
Research Support: NIH/NEI R01 EY015520 (RTS, JPG), and unrestricted funds from Research to Prevent Blindness (RTB).

Ethics Statement: All patients enrolled in these studies were done so in accordance with approved institutional review board oversight at New York University School of Medicine.
1. Patient Selection and Initial Preparation for Imaging
Note: The following materials are required: 0.5% tropicamide ophthalmic solution, 2.5% phenylephrine ophthalmic solution, cSLO equipped with spectral domain optical coherence tomography (SD-OCT), and internal fluorescence reference.
...

<ol>
	<li>Strauss, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+retinal+pigment+epithelium+in+visual+function.">The retinal pigment epithelium in visual function.</a> Physiological reviews. 85, 845-881 (2005).</li><li>Ach, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+autofluorescence+and+cell+density+maps+of+the+human+retinal+pigment+epithelium.">Quantitative autofluorescence and cell density maps of the human retinal pigment epithelium.</a> Investigative ophthalmology &amp; visual science. 55, 4832-4841 (2014).</li><li>Ach, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lipofuscin+redistribution+and+loss+accompanied+by+cytoskeletal+stress+in+retinal+pigment+epithelium+of+eyes+with+age-related+macular+degeneration.">Lipofuscin redistribution and loss accompanied by cytoskeletal stress in retinal pigment epithelium of eyes with age-related macular degeneration.</a> Investigative ophthalmology &amp; visual science. 56, 3242-3252 (2015).</li><li>Schmitz-Valckenberg, S., Jorzik, J., Unnebrink, K., Holz, F. 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G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inhibition+of+lysosomal+degradative+functions+in+RPE+cells+by+a+retinoid+component+of+lipofuscin.">Inhibition of lysosomal degradative functions in RPE cells by a retinoid component of lipofuscin.</a> Investigative ophthalmology &amp; visual science. 40, 737-743 (1999).</li><li>Sparrow, J. R., Nakanishi, K., Parish, C. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+lipofuscin+fluorophore+A2E+mediates+blue+light-induced+damage+to+retinal+pigmented+epithelial+cells.">The lipofuscin fluorophore A2E mediates blue light-induced damage to retinal pigmented epithelial cells.</a> Investigative ophthalmology &amp; visual science. 41, 1981-1989 (2000).</li><li>Smith, R. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Lipofuscin+and+autofluorescence+metrics+in+progressive+STGD.">Lipofuscin and autofluorescence metrics in progressive STGD.</a> Investigative ophthalmology &amp; visual science. 50, 3907-3914 (2009).</li><li>Delori, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+measurements+of+autofluorescence+with+the+scanning+laser+ophthalmoscope.">Quantitative measurements of autofluorescence with the scanning laser ophthalmoscope.</a> Investigative ophthalmology &amp; visual science. 52, 9379-9390 (2011).</li><li>Burke, T. 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Abnormal RPE lipofuscin distribution, whether increased or decreased, is a sensitive marker of retinal disease and is generally associated with loss of sensory retina function. Here, we describe application of qAF for the evaluation of RPE lipofuscin. Incorporation of an internal fluorescent reference to correct for variable laser power and detector sensitivity9 alongside our standardized imaging technique allows for reliable quantitation of AF levels. It is our goal that this method will aid in the diagnosis ...

The retinal pigment epithelium (RPE) supports the function of the sensory retina through numerous processes 1. Age-related macular degeneration (AMD) is the most important cause of untreatable blindness in industrialized countries and is characterized by changes in the RPE, including loss of pigment, loss of function and atrophy. In AMD and in normal aging, the RPE accumulates fluorescent, lysosome-derived organelles containing phagocytosed photoreceptor fragments, referred to as lipofuscin granules. The accumulation of RPE lipofuscin has been thought to indicate oxidative dysfunction 1, but recent studies have shown that the RPE morphology remains normal in aged eyes with high lipofuscin levels 2. However, abnormal patterns of lipofuscin distribution, in particular loss of lipofuscin, are documented markers for AMD and AMD progression, both histologically and clinically 3,4
Defective processing of RPE lipofuscin has also been shown to occur in certain inherited retinal degenerations. Patients suffering from Stargardt disease (STGD) accumulate lipofuscin in the RPE at a young age, eventually developing vision loss similar to that seen in AMD 5. These findings suggested that lipofuscin accumulation may itself be toxic and drive RPE dysfunction 6,7. However, a detailed imaging study of subjects with STGD over time did not confirm that focal lipofuscin accumulation led to subsequent RPE loss 8. Hence, although lipofuscin abnormalities are markers for retinal degenerations, a role for direct toxicity of lipofuscin remains unproven.
The RPE is the most posterior cell layer of the retina, but generates the majority of fluorescent signal from the ocular fundus. Generation and detection of autofluorescence (AF) derived from the RPE can be performed using confocal scanning laser ophthalmoscopy (cSLO), which allows for visualization of the spatial distribution of fundus AF. Certain retinal degenerations demonstrate distinctive patterns of fundus AF, and AF imaging aids in the diagnosis and monitoring of these conditions. Although standard AF imaging is clinically important, quantitative AF (qAF) has become an important means of assessing RPE health. We and others have developed a standardized approach that can reliably determine qAF levels at specific retinal locations 9. qAF has potential applications in the diagnosis and monitoring of retinal conditions, and may also have utility in prognosis and risk stratification. In addition, the diagnostic capabilities of qAF have also been described for certain retinal disorders 10-12. Here, we provide step-wise details for performing our technique accompanied by a visual demonstration of its application in the evaluation of healthy and diseased eyes.

<table border="0" cellpadding="0" cellspacing="0" width="671">
	<tbody>
		<tr height="19">
			<td height="19" style="height:19px;width:243px;">Spectralis HRA + OCT</td>
			<td style="width:143px;">Heidelberg Engineering</td>
			<td style="width:119px;">n/a</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;">0.5% tropicamide ophthalmic solution</td>
			<td style="width:143px;">n/a</td>
			<td style="width:119px;">n/a</td>
			<td>Any brand can be used</td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;">2.5% phenylephrine ophthalmic solution</td>
			<td style="width:143px;">n/a</td>
			<td style="width:119px;">n/a</td>
			<td>Any brand can be used</td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;width:243px;">Internal fluorescent reference</td>
			<td style="width:143px;">Heidelberg Engineering</td>
			<td style="width:119px;">n/a</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">IGOR Pro software</td>
			<td style="width:143px;">WaveMetrics</td>
			<td style="width:119px;">n/a</td>
			<td></td>
		</tr>
	</tbody>
</table>

quantitative fundus autofluorescence for the evaluation of retinal diseases

The retinal pigment epithelium (RPE) is juxtaposed to the overlying sensory retina, and supports the function of the visual system. Among the tasks performed by the RPE are phagocytosis and processing of outer photoreceptor segments through lysosome-derived organelles. These degradation products, stored and referred to as lipofuscin granules, are composed partially of bisretinoids, which have broad fluorescence absorption and emission spectra that can be detected clinically as fundus autofluorescence with confocal scanning laser ophthalmoscopy (cSLO). Lipofuscin accumulation is associated with increasing age, but is also found in various patterns in both acquired and inherited degenerative diseases of the retina. Thus, studying its pattern of accumulation and correlating such patterns with changes in the overlying sensory retina are essential to understanding the pathophysiology and progression of retinal disease. Here, we describe a technique employed by our lab and others that uses cSLO in order to quantify the level of RPE lipofuscin in both healthy and diseased eyes.

This technique was used to study qAF in both healthy 13 and disease states 10-12. In healthy eyes (Figure 1), AF emitted from the RPE is distributed relatively uniformly throughout the fundus (Figure 1A). Reduced intensity is seen in the central macular region due to blocking of light by macular pigment, and at the sides and corners of the image due to the optics of the eye and camera. Vessels appear dark and should be in clear focus...

Watch this Scientific Journal Video about Quantitative Fundus Autofluorescence for the Evaluation of Retinal Diseases at JoVE.com

Quantitative Fundus Autofluorescence for the Evaluation of Retinal Diseases

The retinal pigment epithelium (RPE) supports the sensory retina through recycling visual cycle byproducts, which accumulate as lipofuscin. These products are autofluorescent and can be qualitatively imaged in vivo. Here, we describe a method to quantitatively image RPE lipofuscin using confocal scanning laser ophthalmoscopy.

The retinal pigment epithelium (RPE) is juxtaposed to the overlying sensory retina, and supports the function of the visual system. Among the tasks ...

The overall goal of quantitative autofluorescence, or qAF, is to evaluate the overall level of lipofuscin in the support cells of the retina, the retinal pigment epithelium, or RPE, in both healthy and diseased eyes. This technique can help answer key questions in retinal cell biology, such as how the health of the retinal pigment epithelium interacts with the development of age related macular degeneration, or AMD. The main advantage of this technique is that it allows for the determination of absolute levels of lipofuscin autofluorescence in the fundus, and therefore quantitative and reproducive follow up between patients, between patient imaging sessions, and in large study populations.Prior to imaging, appropriately set up confocal scanning laser opthamoscopy, or CSLO, for data acquisition according to the manufacturer's instructions. To mount an internal fluorescent reference, which is purchased from the manufacturer, twist the lens to remove it, unscrew the machine's metal ring, and replace it with the new metal ring containing the reference. It is essential for pupils to be dilated to at least 6mm for uninterrupted passage of light.With 0.5%tropicamide, and 2.5%phenylephrine, dilate the patient's pupils at least 6mm, which is essential for uninterrupted passage of light to see and to measure the fundus. Properly position the patient on the CSLO with chin resting on the chinrest, forehead placed against the forehead rest, and lateral canthi properly aligned with the indicators. To acquire baseline images, first image the fundus with near-infrared reflectance, or IR light, in order to centralize the camera over the macula and obtain rough focus.With the patient properly positioned, switch the hardware setting on the control panel to IR imaging mode, manually position the camera until the fundus is in full focus, and take an image. Adjust the setting on the control panel to IROCT, which uses spectral domain optical coherence tomography, or SDOCT, in conjunction with IR imaging, to evaluate the macula for underlying disease. Use the guides present in the imaging window to correctly orient the OCT to the IR image of the fundus.To achieve optimal SDOCT quality, position the camera such that the OCT image is in the top third of its imaging window. Acquire at least one horizontal line scan through the fovea, and spanning the entire imaging field. To set up qAF imaging, use high speed image acquisition, which decreases risk of signal loss due to patient movement, and blockage of light by iris or eyelids.Use Mean of 9 frames, which rapidly and sequentially captures nine image frames that are then averaged to reduce noise and artifact. Choose a 30 x 30 degree field, which refers to the degrees of retinal area captured during image acquisition. After warning the patient about the blue light, turn on the AF mode and align the camera axis so that the screen is maximally filled with fundus AF, with minimal darkening of sides and corners of image.If patients have difficulty tolerating the bright blue light, move the camera further away from the eye to start imaging, and slowly bring the camera toward the patient until the fundus is in full view. Either manually or with the opthamoscope joystick, adjust the camera alignment by moving the CSLO to reposition the camera such that the AF signal is at its highest level throughout the field, rather than achieving the sharpest image. During image acquisition, colored pixels visible in either the internal reference or the fundus indicate over saturation, and thus loss of signal.Fully expose the retina to AF light for at least 20 seconds to minimize the absorption of light by rhodopsin in the sensory retina during imaging. Use this period to optimize camera alignment, focus, and sensitivity. Have the subjects blink before each image acquistion, as a fresh tear film improves signal quality.Avoid eyelids in the plane of acquistion and take the image. It's important to generate at least two high quality images per imaging session to have for data analysis. Perform post-image processing by using the CSLO software to compute the mean of the nine frame stack, to increase the signal to noise ratio.Carry out image analysis according to the text protocol. As shown here, in healthy eyes, AF emitted from the RPE is distributed relatively uniformly throughout the fundus. Reduced intensity is seen in the central macular region due to the blocking of light by macular pigment, and at the sides and corners due to the optics of the eye and camera.Vessels should be dark and in clear focus. This figure represents a corresponding heat map presentation of the qAF levels from this figure. Cooler colors correspond to areas of lower AF intensity, while warmer colors correspond to areas of higher AF intensity.Maximum intensity is generally seen in the second concentric eight segment ring, and the mean intensities in this area are used for most data analysis. Shown here is a representative analysis of the eye with AMD, demonstrating geopgraphic atrophy, an advanced form of AMD. This form of AMD results in localized areas of RPE loss, evidenced by markedly reduced or absent AF, and causes progressive central vision loss.While attempting this procedure it's important to remember to select candidate patients carefully and obtain high quality images reproduceably to maximize data quality. Use of this procedure can allow for the longitudinal follow up of retinal health to determine the progress of retinal degenerations. After its development, this technique paved the way for researchers in the field of opthamology to follow and analyze retinal degenerations.After watching this video, you should have a good understanding of how to use quantitative autofluorescence to evaluate your patients with retinal degenerations. Thanks for watching, and good luck with your experiments.

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Automated Radiochemical Synthesis of [18F]3F4AP: A Novel PET Tracer for Imaging Demyelinating Diseases

3-[18F]fluoro-4-aminopyridine, [18F]3F4AP, is a radiofluorinated analog of the FDA-approved drug for multiple sclerosis 4-aminopyridine (4AP). This compound is currently under investigation as a PET tracer for demyelination. We recently described a novel chemical reaction to produce metafluorinated pyridines consisting of direct fluorination of a pyridine N-oxide and the utilization of this reaction for the radiochemical synthesis of [18F]3F4AP. In this article, we demonstrate how to produce this tracer using an automated synthesizer and an in-house made flow hydrogenation reactor. We also show the standard quality control procedures performed before releasing the radiotracer for preclinical animal imaging studies. This semi-automated procedure may serve as the basis for future production of [18F]3F4AP for clinical studies.

Automated Radiochemical Synthesis of [18F]3F4AP: A Novel PET Tracer for Imaging Demyelinating Diseases

We demonstrate the semi-automated radiochemical synthesis of [18F]3F4AP and quality control procedures.

3-[18F]fluoro-4-aminopyridine, [18F]3F4AP, is a radiofluorinated analog of the FDA-approved drug for multiple sclerosis 4-aminopyridine (4AP). This ...

Invasive Hemodynamic Assessment for the Right Ventricular System and Hypoxia-Induced Pulmonary Arterial Hypertension in Mice

Pulmonary arterial hypertension (PAH) is a chronic and severe cardiopulmonary disorder. Mice are a popular animal model used to mimic this disease. However, the evaluation of right ventricular pressure (RVP) and pulmonary artery pressure (PAP) remains technically challenging in mice. RVP and PAP are more difficult to measure than left ventricular pressure because of the anatomical differences between the left and right heart systems. In this paper, we describe a stable right heart hemodynamic measurement method and its validation using healthy and PAH mice. This method is based on open-chest surgery and mechanical ventilation support. It is a complicated procedure compared to closed chest procedures. While a well-trained surgeon is required for this surgery, the advantage of this procedure is that it can generate both RVP and PAP parameters at the same time, so it is a preferable procedure for the evaluation of PAH models.

Here, we present a protocol to perform an invasive hemodynamic assessment of the right ventricle and pulmonary artery in mice using an open-chest surgery approach.

Pulmonary arterial hypertension (PAH) is a chronic and severe cardiopulmonary disorder. Mice are a popular animal model used to mimic this disease. ...

Oxygen-Induced Retinopathy Model for Ischemic Retinal Diseases in Rodents

One of the commonly used models for ischemic retinopathies is the oxygen-induced retinopathy (OIR) model. Here we describe detailed protocols for the OIR model induction and its readouts in both mice and rats. Retinal neovascularization is induced in OIR by exposing rodent pups either to hyperoxia (mice) or alternating levels of hyperoxia and hypoxia (rats). The primary readouts of these models are the size of neovascular (NV) and avascular (AVA) areas in the retina. This preclinical in vivo model can be used to evaluate the efficacy of potential anti-angiogenic drugs or to address the role of specific genes in the retinal angiogenesis by using genetically manipulated animals. The model has some strain and vendor specific variation in the OIR induction which should be taken into consideration when designing the experiments.

Oxygen-induced retinopathy (OIR) can be used to model ischemic retinal diseases such as retinopathy of prematurity and proliferative diabetic retinopathy and to serve as a model for proof-of-concept studies in evaluating antiangiogenic drugs for neovascular diseases. OIR induces robust and reproducible neovascularization in the retina that can be quantified.

One of the commonly used models for ischemic retinopathies is the oxygen-induced retinopathy (OIR) model. Here we describe detailed protocols for the OIR ...

Retinal Pigment Epithelium Transplantation in a Non-human Primate Model for Degenerative Retinal Diseases

Retinal pigment epithelial (RPE) transplantation holds great promise for the treatment of inherited and acquired retinal degenerative diseases. These conditions include retinitis pigmentosa (RP) and advanced forms of age-related macular degeneration (AMD), such as geographic atrophy (GA). Together, these disorders represent a significant proportion of currently untreatable blindness globally. These unmet medical needs have generated heightened academic interest in developing methods of RPE replacement. Among the animal models commonly utilized for preclinical testing of therapeutics, the non-human primate (NHP) is the only animal model that has a macula. As it shares this anatomical similarity with the human eye, the NHP eye is an important and appropriate preclinical animal model for the development of advanced therapy medicinal products (ATMPs) such as RPE cell therapy.
This manuscript describes a method for the submacular transplantation of an RPE monolayer, cultured on a polyethylene terephthalate (PET) cell carrier, underneath the macula onto a surgically created RPE wound in immunosuppressed NHPs. The fovea-the central avascular portion of the macula-is the site of the greatest mechanical weakness during the transplantation. Foveal trauma will occur if the initial subretinal fluid injection generates an excessive force on the retina. Hence, slow injection under perfluorocarbon liquid (PFCL) vitreous tamponade is recommended with a dual-bore subretinal injection cannula at low intraocular pressure (IOP) settings to create a retinal bleb. 
Pretreatment with an intravitreal plasminogen injection to release parafoveal RPE-photoreceptor adhesions is also advised. These combined strategies can reduce the likelihood of foveal tears when compared to conventional techniques. The NHP is a key animal model in the preclinical phase of RPE cell therapy development. This protocol addresses the technical challenges associated with the delivery of RPE cellular therapy in the NHP eye.

The non-human primate (NHP) is an ideal model for studying human retinal cellular therapeutics due to the anatomical and genetic similarities. This manuscript describes a method for submacular transplantation of retinal pigment epithelial cells in the NHP eye and strategies to prevent intraoperative complications associated with macular manipulation.

Retinal pigment epithelial (RPE) transplantation holds great promise for the treatment of inherited and acquired retinal degenerative diseases. These ...

Retinal Pathophysiological Evaluation in a Rat Model

A posterior segment eye disease like diabetic retinopathy alters the physiology of the retina. Diabetic retinopathy is characterized by a retinal detachment, breakdown of the blood-retinal barrier (BRB), and retinal angiogenesis. An in vivo rat model is a valuable experimental tool to examine the changes in the structure and function of the retina. We propose three different experimental techniques in the rat model to identify morphological changes of retinal cells, retinal vasculature, and compromised BRB. Retinal histology is used to study the morphology of various retinal cells. Also, quantitative measurement is performed by retinal cell count and thickness measurement of different retinal layers. A BRB breakdown assay is used to determine the leakage of extraocular proteins from the plasma to vitreous tissue due to the breakdown of BRB. Fluorescence angiography is used to study angiogenesis and leakage of blood vessels by visualizing retinal vasculature using FITC-dextran dye.

Diabetic retinopathy is one of the leading causes of blindness. Histology, blood-retinal barrier breakdown assay, and fluorescence angiography are valuable techniques to understand the pathophysiology of the retina, which could further enhance the efficient drug screening against diabetic retinopathy.

A posterior segment eye disease like diabetic retinopathy alters the physiology of the retina. Diabetic retinopathy is characterized by a retinal ...

Repetitive Blood Sampling from the Subclavian Vein of Conscious Rat

Rats are widely used in pharmacokinetics (PK) and toxicokinetic (TK) studies that need to collect a certain amount of blood at specific time points to detect drug exposure. The rat blood sampling method determines the quality of the plasma and further affects the precision of the test results. The subclavian vein blood collection method described in this protocol collects blood samples repeatedly in the conscious state of animals to meet the needs of PK and TK tests. The skills of restraint handling and appropriate procedure of needle incision ensure the success rate of blood collection. It is easy to operate while ensuring the quality of plasma and at the same time catering to animal welfare. However, this method requires skilled operation, and an improper one may cause animal weakness, pain, lameness, and even mortality. The current method has been used in the testing facility for a 4-week oral toxicity study in Sprague Dawley (SD) rats with TK. The maximum amount of blood collected within 24 h did not exceed 20% of the animal's total blood. The animals' body weight was more than 200 g for males and females. The data showed that the animals' bodyweight increased steadily every week, and the clinical observation was normal after repetitive sample collection.

The present protocol describes a simple and efficient method for collecting blood from the subclavian vein in rats. It enables rapid, timely, and easily identifiable sampling without anesthesia and obtains high-quality blood through repetitive sample collection.

Rats are widely used in pharmacokinetics (PK) and toxicokinetic (TK) studies that need to collect a certain amount of blood at specific time points to ...

Retinal Explant of the Adult Mouse Retina as an Ex Vivo Model for Studying Retinal Neurovascular Diseases

One of the challenges in retina research is studying the cross-talk between different retinal cells such as retinal neurons, glial cells, and vascular cells. Isolating, culturing, and sustaining retinal neurons in vitro have technical and biological limitations. Culturing retinal explants may overcome these limitations and offer a unique ex vivo model to study the cross-talk between various retinal cells with well-controlled biochemical parameters and independent of the vascular system. Moreover, retinal explants are an effective screening tool for studying novel pharmacological interventions in various retinal vascular and neurodegenerative diseases such as diabetic retinopathy. Here, we describe a detailed protocol for retinal explants' isolation and culture for an extended period. The manuscript also presents some of the technical problems during this procedure that may affect the desired outcomes and reproducibility of the retinal explant culture. The immunostaining of the retinal vessels, glial cells, and neurons demonstrated intact retinal capillaries and neuroglial cells after 2 weeks from the beginning of the retinal explant culture. This establishes retinal explants as a reliable tool for studying changes in the retinal vasculature and neuroglial cells under conditions that mimic retinal diseases such as diabetic retinopathy.

Retinal Explant of the Adult Mouse Retina as an Ex Vivo Model for Studying Retinal Neurovascular Diseases

This protocol presents and describes steps for the isolation, dissection, culturing, and staining of retinal explants obtained from an adult mouse. This method is beneficial as an ex vivo model for studying different retinal neurovascular diseases such as diabetic retinopathy.

One of the challenges in retina research is studying the cross-talk between different retinal cells such as retinal neurons, glial cells, and vascular ...

Exploring Quantitative Autofluorescence in Age-Related Macular Degeneration

A Workflow to Quantitatively Determine Age-Related Macular Degeneration Lesion-Specific Variations in Fundus Autofluorescence

Fundus autofluorescence (FAF) imaging allows the noninvasive mapping of intrinsic fluorophores of the ocular fundus, particularly the retinal pigment epithelium (RPE), now quantifiable with the advent of confocal scanning laser ophthalmoscopy-based quantitative autofluorescence (QAF). QAF has been shown to be generally decreased at the posterior pole in age-related macular degeneration (AMD). The relationship between QAF and various AMD lesions (drusen, subretinal drusenoid deposits) is still unclear.
This paper describes a workflow to determine lesion-specific QAF in AMD. A multimodal in vivo imaging approach is used, including but not limited to spectral domain optical coherence tomography (SD-OCT) macular volume scanning and QAF. Using customized FIJI plug-ins, the corresponding QAF image is aligned with the near-infrared image from the SD-OCT scan (characteristic landmarks; i.e., vessel bifurcations). The foveola and the edge of the optic nerve head are marked in the OCT images (and transferred to the registered QAF image) for accurate positioning of the analysis grids.
AMD-specific lesions can then be marked on individual OCT BScans or the QAF image itself. Normative QAF maps are created to account for the varying mean and standard deviation of QAF values throughout the fundus (QAF images from a representative AMD group were averaged to build normative standard retinal QAF AMD maps). The plug-ins record the X and Y coordinates, z-score (a numerical measurement that describes the QAF value in relation to the mean of AF maps in terms of standard deviation from the mean), mean intensity value, standard deviation, and number of pixels marked. The tools also determine z-scores from the border zone of marked lesions.&#160;This workflow and the analysis tools will improve the understanding of the pathophysiology and clinical AF image interpretation in AMD.

Author Spotlight: Understanding Age-Related Macular Degeneration Pathophysiology with QAF Workflow 

This research describes a workflow to determine and compare autofluorescence levels from individual regions of interest (e.g., drusen and subretinal drusenoid deposits in age-related macular degeneration [AMD]) while accounting for varying autofluorescence levels throughout the fundus.

Fundus autofluorescence (FAF) imaging allows the noninvasive mapping of intrinsic fluorophores of the ocular fundus, particularly the retinal pigment ...

Quantitative Autofluorescence (QAF) Image Acquisition

To begin, get the participant seated comfortably in front of the quantitative autofluorescence, or qAF device to ensure accurate image acquisition. Have the participant's chin and forehead pressed against the chin and headrest. Adjust the height of the chin rest until the lateral eyelid angle is at the same height as the red marking.Then rotate the wheel on the recording device until the small vessels are in focus to ensure the image is focused in the near infrared modus. Zoom in on the eye by moving the camera forward until the image corners are evenly illuminated. As a rule of thumb, adjust the focus to the spherical equivalent.Reduce the focus before qAF imaging by one or two diopters as blue QAF uses a shorter wavelength, and switch to the modus of the qAF device from the near infrared to the qAF mode. Readjust and upscale the illumination and fine-tune the focus of the image until the small vessels closest to the fovea are in focus and the image is brightly illuminated without red dots. To bleach the photoreceptor pigment in the field of view of the camera, wait for at least 30 seconds in the qAF mode before image acquisition.To capture images, press Image Acquisition on the touchpad of the imaging device. Capture more than one qAF image in case of blinking or sudden eye movements during acquisition.

Quantitative Autofluorescence (QAF) Image Processing for Analysis

To access the open source plugins for Quantitative Autofluorescence or QAF analyses, in the software Fiji. Click on Manage Update sites to add the displayed creative computation update site to the pre-existing update sites. To install the Spectralis pipeline plugin, download the plugins and restart Fiji.The different Spectralis plugins will be located under the plugins dropdown menu in Spectralis or Spectralis batch. The Spectralis QAF XML export files stored in red, green, blue, or RGB format are limited to a measured AF value scale of zero to 255 and include standard and black calibration regions. To produce a QAF image, open the plugins dropdown menu.Click Spectralis, select QAF XML reader, and discard the opening screen. A new window showing the prompt, choose a directory containing a spectral XML QAF export will appear. Select the directory and click select.In the window QAF parameters enter the reference calibration factor or RCF included in the image information, and the patient's age when the image was taken. After clicking okay, when a pop-up labeled map to eight bit appears, enter the minimum QAF or QAF min value, and maximum QAF or QAF max value for a color-coded QAF image. To add one image at a time under plugins, select Spectralis followed by add to standard retina_OCT, and dismiss the opening screen.When a window displays, choose a directory containing a Spectralis OCT XML export. Select the folder and click select to open the BScan. After the OCT volume loads and the prompt, choose a directory containing registered en Face images appears.Select the appropriate folder and click select. At this stage, three windows will pop up. One labeled en Face stack, displaying the stacked images from the selected folder.The second labeled BScan stack, displaying the OCTB scan, and the middle or third one labeled choose modality. Select a modality from the en Face stack. As a new window with the prompt, choose a directory containing the standard retina pops up, select or create the directory containing standard retina.Examine the new standard retina, scroll and move the cursor to view the mean, and standard deviation for that specific location. Click on the button Accept, to either add the latest photo to the standard retina, or discard it. To add multiple images at a time using Batch_QAF_ standard retina first, prepare a manifest.txt file in the same folder as the case IDs. The relative path from the location of the dot txt file to the OCT and the enFace stack must be listed, and separated by a tab space without any additional white space before and after the names. To scroll through the BScan stack, drag the bar at the bottom to the left or right, or select the BScan frame, and use the left and right arrow keys on the keyboard.An overview of the current BScan stack area, is provided by the red line on the enFace stack window, and on the top left of the BScan window where the BScan number is displayed. To mark a region, select mark in the draw line segment in BScan window, and start by right clicking and dragging the mouse cursor to the end of the lesion. Press the plus key to zoom in, and the minus key to zoom out.Finally, click okay to mark the region of interest. The QAF image of an eye of an 84 year old patient with intermediate age related macular degeneration, showed a singular marked soft drusen. A closeup of the area showed a brown center representing the marked drusen, and colored bands representing the surrounding ISO holes.The output file contained the case ID, the laterality of the file, and the chosen imaging modality. Each row referred to an ISO hole, whose distances from the outer edge of the lesion were specified in the lower, and upper columns of the spreadsheet. The QAF measurements contained the minimum median, and maximum values of a pixel in an ISO hole, the number of pixels, the mean pixel value, and the standard deviation of the mean.The QAF image of an eye of an 80 year old patient with early age-related macular degeneration, showed subretinal, drusenoid deposits. Around each marked lesion, the ISO holes were depicted with color coding.