In Vivo Imaging of Secondary Neurodegeneration Associated With Phosphatidylserine Externalization Along Axotomized Axons

Purpose

Axonal degeneration in acute and chronic disorders is well-characterized, comprising retrograde (proximal) and Wallerian (distal) degeneration, but the mechanism of propagation remains less understood.

Methods

Laser injury with a diode-pumped solid-state 532 nm laser was used to axotomize retinal ganglion cell axons. We used confocal in vivo imaging to demonstrate that phosphatidylserine externalization is a biomarker of early axonal degeneration after selective intraretinal axotomy.

Results

Quantitative dynamic analysis revealed that the rate of axonal degeneration was fastest within 40 minutes, then decreased exponentially afterwards. Axonal degeneration was constrained within the same axotomized axonal bundles. Remarkably, axon degeneration arising from the site of injury induced a secondary degeneration of distal normal axons.

Conclusions

Axonal degeneration in vivo is a progressive process associated with phosphatidylserine externalization, which can propagate not only along the axon but to adjacent uninjured axons. This finding has implications for acute and chronic neurodegenerative disorders associated with axonal injury.

Non-invasive in vivo imaging of brain and retinal microglia in neurodegenerative diseases

Microglia play crucial roles in immune responses and contribute to fundamental biological processes within the central nervous system (CNS). In neurodegenerative diseases, microglia undergo functional changes and can have both protective and pathogenic roles. Microglia in the retina, as an extension of the CNS, have also been shown to be affected in many neurological diseases. While our understanding of how microglia contribute to pathological conditions is incomplete, non-invasive in vivo imaging of brain and retinal microglia in living subjects could provide valuable insights into their role in the neurodegenerative diseases and open new avenues for diagnostic biomarkers. This mini-review provides an overview of the current brain and retinal imaging tools for studying microglia in vivo. We focus on microglia targets, the advantages and limitations of in vivo microglia imaging approaches, and applications for evaluating the pathogenesis of neurological conditions, such as Alzheimer's disease and multiple sclerosis.

Multicolor Imaging for Detection of Retinal Nerve Fiber Layer Defect in Myopic Eyes With Glaucoma

PURPOSE

To investigate the diagnostic performance of multicolor imaging for detection of retinal nerve fiber layer (RNFL) defects in myopic eyes with glaucoma.

DESIGN

Comparative diagnostic analysis.

METHODS

A total of 150 myopic eyes of 138 patients (< -1.00 diopter or axial length >24 mm) underwent multicolor imaging by Spectralis (Heidelberg Engineering GmbH) optical coherence tomography (OCT). Two independent observers graded the RNFL visibility score and determined the location of the RNFL defect on each image. Readings were taken from the superior and inferior areas. The diagnostic performances of multicolor, green-reflectance, and blue-reflectance images for detection of the RNFL defect were compared with those of conventional fundus and red-free RNFL photographs.

RESULTS

The interobserver agreement on the RNFL visibility score was substantial for fundus and RNFL photographs and multicolor and green-reflectance images and was perfect for blue-reflectance images. The interobserver agreement on the location of the RNFL defect was better when using multicolor imaging than when using conventional photography. The green-reflectance image (2.89 ± 0.31) showed the highest RNFL visibility score, followed by blue-reflectance (2.88 ± 0.32) and multicolor (2.57 ± 0.63) images. The sensitivity of multicolor imaging (94.9%, 93.2%, and 91.5% for green-reflectance, blue-reflectance, and multicolor images, respectively) was significantly higher than that of fundus photography (83.1%) for detection of superotemporal RNFL defects (all P < .05). It was significantly higher for inferotemporal defects than those of fundus and RNFL photographs (all P < .05).

CONCLUSIONS

Multicolor imaging can visualize the glaucomatous RNFL defects in myopic eyes that are indistinguishable on conventional photography.

Semi-Automated Live Tracking of Microglial Activation in CX3CR1GFP Mice During Experimental Autoimmune Encephalomyelitis by Confocal Scanning Laser Ophthalmoscopy

Confocal scanning laser ophthalmoscopy (cSLO) is a non-invasive technique for real-time imaging of the retina. We developed a step-by-step protocol for the semi-automatic evaluation of myeloid cells in cSLO images from CX3CR1GFP mice, expressing green fluorescent protein (GFP) under control of the endogenous CX3C chemokine receptor 1 locus. We identified cSLO parameters allowing us to distinguish animals with experimental autoimmune encephalomyelitis (EAE) from sham-treated/naïve animals. Especially cell count (CC) and the total microglial area (SuA) turned out to be reliable parameters. Comparing the cSLO results with clinical parameters, we found significant correlations between the clinical EAE score and the SuA and of the inner retinal layer thickness, measured by optical coherence tomography, with the CC as well as the SuA. As a final step, we performed immunohistochemistry to confirm that the GFP-expressing cells visualized by the cSLO are Iba1 positive and validated the step-by-step protocol against manual counting. We present a semi-automatic step-by-step protocol with a balance between fast data evaluation and adequate accuracy, which is optimized by the option to manually adapt the contrast threshold. This protocol may be useful for numerous research questions on the role of microglial polarization in models of inflammatory and degenerating CNS diseases involving the retina.

The presence and progression of choroidal neurofibromas in a predominantly pediatric population with neurofibromatosis type-1

Background: Obtaining a definitive neurofibromatosis type-1 (NF1) diagnosis may take years. The natural history of choroidal neurofibromas in NF1 is unknown. This study evaluates a predominantly pediatric patient cohort for ocular features in NF1, including presence and progression of choroidal abnormalities, to determine their natural history, relationship to other NF1 features, and additive value in NF1 diagnosis.Methods: Retrospective analysis of 106 patients referred for Ophthalmic monitoring or diagnosis of NF1 between January 2012 and December 2018. Clinical records and Near-Infrared Reflectance (NIR) Optical Coherence Tomography imaging were analyzed for prevalence and progression of choroidal neurofibromas on NIR, and relation to other NF1 diagnostic criteria.Results: 54.7% of patients referred had a confirmed NF1 diagnosis, and 45.4% were NF1 suspects. First ophthalmic review resulted in an additional 6.6% patients meeting the diagnostic criteria, and 14.2% later developed sufficient features (total n = 80). Choroidal neurofibromas were present in 75.7% of patients that had NIR imaging and met diagnostic criteria, and detected in the absence of, or prior to Lisch nodules in 13.5%. Progression in the size and number of choroidal neurofibromas occurred in 26 eyes (32.5%) of 14 patients (35.0%), all under 16 years old. Patients without choroidal neurofibromas at first examination never developed them over the study period.Conclusion: Choroidal neurofibromas, detected by NIR imaging, are common in NF1, present early with frequent progression, and represent an additional tool to aid NF1 diagnosis in young children.

Quantifiable In Vivo Imaging Biomarkers of Retinal Regeneration by Photoreceptor Cell Transplantation

Purpose

Short-term improvements in retinal anatomy are known to occur in preclinical models of photoreceptor transplantation. However, correlative changes over the long term are poorly understood. We aimed to develop a quantifiable imaging biomarker grading scheme, using noninvasive multimodal confocal scanning laser ophthalmoscopy (cSLO) imaging, to enable serial evaluation of photoreceptor transplantation over the long term.

Methods

Photoreceptor cell suspensions or sheets from rhodopsin-green fluorescent protein mice were transplanted subretinally, into either NOD.CB17-Prkdc^scid/J or C3H/HeJ-Pde6b^rd1 mice. Multimodal cSLO imaging was performed serially for up to three months after transplantation. Imaging biomarkers were scored, and a grade was defined for each eye by integrating the scores. Image grades were correlated with immunohistochemistry (IHC) data.

Results

Multimodal imaging enabled the extraction of quantitative imaging biomarkers including graft size, GFP intensity, graft length, on-target graft placement, intra-graft lamination, hemorrhage, retinal atrophy, and periretinal proliferation. Migration of transplanted material was observed. Changes in biomarker scores and grades were detected in 14/16 and 7/16 eyes, respectively. A high correlation was found between image grades and IHC parameters.

Conclusions

Serial evaluation of multiple imaging biomarkers, when integrated into a per-eye grading scheme, enabled comprehensive tracking of longitudinal changes in photoreceptor cell grafts over time. The application of systematic multimodal in vivo imaging could be useful in increasing the efficiency of preclinical retinal cell transplantation studies in rodents and other animal models.

Translational Relevance

By allowing longitudinal evaluation of the same animal over time, and providing quantifiable biomarkers, non-invasive multimodal imaging improves the efficiency of retinal transplantation studies in animal models. Such assays will facilitate the development of cell therapy for retinal diseases.

Rhodopsin: A Potential Biomarker for Neurodegenerative Diseases

Retinal alterations have recently been associated with numerous neurodegenerative diseases. Rhodopsin is a G-protein coupled receptor found in the rod cells of the retina. As a biomarker associated with retinal thinning and degeneration, it bears potential in the early detection and monitoring of several neurodegenerative diseases. In this review article, we summarize the findings of correlations between rhodopsin and several neurodegenerative disorders as well as the potential of a novel technique, cSLO, in the quantification of rhodopsin.

Widefield imaging of retinal and choroidal tumors

Background

Wide-field imaging plays an increasingly important role in ocular oncology clinics. The purpose of this review is to describe the commonly used wide-field imaging devices and review conditions seen in ocular oncology clinic that underwent wide-field imaging as part of the multimodal evaluation.

Summary of review

Wide-field or wide-angle imaging is defined as greater than 50° field of view. Modern devices can reach far beyond this reporting fields of view up to 267°, when utilizing montage features, with increasingly impressive resolution. Wide-field imaging modalities include fundus photography, fluorescein angiography (FA), fundus autofluorescence (FAF), indocyanine angiography (ICG), spectral domain optical coherence tomography (SD-OCT), and recently wide-field OCT Angiography (OCTA). These imaging modalities are increasingly prevalent in practice. The wide-field systems include laser, optical, and lens based systems that are contact or non-contact lens systems each with its own benefits and drawbacks. The purpose of this review is to discuss commonly used wide-field imaging modalities for retinal and choroidal tumors and demonstrate the use of various widefield imaging modalities in select ocular oncology cases.

Conclusions

Clinical examination remains the gold standard for the evaluation of choroidal and retinal tumors. Wide-field imaging plays an important role in ocular oncology for initial documentation, surgical planning, determining the relationship of the tumor to adjacent ocular structures, following tumor size after treatment, and monitoring for recurrence.

Response of vascular pigment epithelium detachment due to age-related macular degeneration to monthly treatment with ranibizumab: the prospective, multicentre RECOVER study

PURPOSE

To assess the effects of monthly intravitreal ranibizumab injections in patients with vascularized pigment epithelium detachment (vPED) secondary to age-related macular degeneration (AMD).

METHODS

A total of 40 patients were prospectively observed and treated monthly with 0.5 mg ranibizumab injections (ClinicalTrials.gov Ident. NCT00976222). Inclusion criterion was a treatment-naïve vPED lesion with a minimum height of ≥200 μm. Best-corrected visual acuity (BCVA) and spectral-domain optical coherence tomography (SD-OCT) were evaluated at all visits. Fluorescein angiography and indocyanine green angiography were performed at baseline and quarterly. Lesions were differentiated between serous vascular PED (svPED, group A, 29 patients) and fibrovascular PED (fPED, group B, 11 patients). Primary outcome was the effectivity of continuous monthly treatment during a 12-month period as measured in change in BCVA. Secondary outcomes were change in PED height and PED greatest linear diameter (GLD). Further secondary outcomes were the presence of subretinal fluid and prognostic markers of an impending retinal pigment epithelium (RPE) tear: PED lesion height and diameter, ratio of choroidal neovascularization (CNV) size to PED size, hyperreflective lines in near-infrared images, microrips and subretinal cleft.

RESULTS

Mean BCVA was 56.9 ± 11.5 letters (A: 55.4 ± 10.8; B: 59.1 ± 13.4) at baseline and 55.1 ± 15.9 (A: 53.7 ± 17.0; B: 58.9 ± 12.7) at 12-month follow-up. Excluding the RPE tear patients, the svPED group showed an increase in BCVA from 56.1 ± 10.3 at baseline to 62.4 ± 10.2 at 12-month follow-up (p = 0.048). Best-corrected visual acuity in patient who developed a RPE tear was 55.8 ± 12.5 at baseline and 37.1 ± 14.9 at 12-month follow-up. The mean change in PED height was -242.1 μm ± 285.5 (A: -427.3 μm ± 299.7; B: -51.6 μm ± 99.5). The mean decrease in PED GLD was -471.8 μm ± 727.6 (A: -738.9 μm ± 788.2; B: -10.4 μm ± 185.6). In group A, 10 patients developed a RPE tear (25%) after a mean of 3.6 injections. No tear was documented in group B. Lesion height, ratio of CNV size to PED size and presence of hyperreflective lines differed significantly between patients with and without RPE tear development.

CONCLUSION

Serous vascular PED lesions showed an improvement regarding BCVA and morphologic characteristics unless an RPE tear occurred. In fPED lesions, a functional and morphological stabilization was observed. Monthly ranibizumab injections are an effective treatment regarding the resorption of subretinal fluid in vPED due to AMD. Patients should be screened for the presence of morphologic risk factors for RPE tear development before and during treatment.

What rates of glaucoma progression are clinically significant?

Clinically important rates of glaucoma progression (worsening) are ones that put a patient at risk of future functional impairment or reduction of vision-related quality of life. Rates of progression can be evaluated through measuring structural or functional changes of the optic nerve. Most treated eyes do not progress at rates that will lead to future visual impairment, but there are a significant proportion (3-17%) of eyes, that are at risk of impairment even under clinical care. While very fast rates of progression (e.g. MD progression of -1.5 dB/year) are generally problematic, much slower rates also may be deleterious for young patients, particularly those diagnosed with late disease. As a result, it is important to consider life expectancy, disease severity and vision-related quality of life based treatment targets to estimate future prognosis when evaluating whether a rate of glaucoma progression can be clinically relevant.