Noninvasive, in vivo assessment of mouse retinal structure using optical coherence tomography

Lateral and axial measurement differences between spectral-domain optical coherence tomography systems

We assessed the reproducibility of lateral and axial measurements performed with spectral-domain optical coherence tomography (SDOCT) instruments from a single manufacturer and across several manufacturers. One human retina phantom was imaged on two instruments each from four SDOCT platforms: Zeiss Cirrus, Heidelberg Spectralis, Bioptigen SDOIS, and hand-held Bioptigen Envisu. Built-in software calipers were used to perform manual measurements of a fixed lateral width (LW), central foveal thickness (CFT), and parafoveal thickness (PFT) 1 mm from foveal center. Inter- and intraplatform reproducibilities were assessed with analysis of variance and Tukey-Kramer tests. The range of measurements between platforms was 5171 to 5290 μm for mean LW (p<0.001), 162 to 196 μm for mean CFT (p<0.001), and 267 to 316 μm for mean PFT (p<0.001). All SDOCT platforms had significant differences between each other for all measurements, except LW between Bioptigen SDOIS and Envisu (p=0.27). Intraplatform differences were significantly smaller than interplatform differences for LW (p=0.020), CFT (p=0.045), and PFT (p=0.004). Conversion factors were generated for lateral and axial scaling between SDOCT platforms. Lateral and axial manual measurements have greater variance across different SDOCT platforms than between instruments from the same platform. Conversion factors for measurements from different platforms can produce normalized values for patient care and clinical studies.

Targeted ablation of CRB1 and CRB2 in retinal progenitor cells mimics Leber congenital amaurosis

Development in the central nervous system is highly dependent on the regulation of the switch from progenitor cell proliferation to differentiation, but the molecular and cellular events controlling this process remain poorly understood. Here, we report that ablation of Crb1 and Crb2 genes results in severe impairment of retinal function, abnormal lamination and thickening of the retina mimicking human Leber congenital amaurosis due to loss of CRB1 function. We show that the levels of CRB1 and CRB2 proteins are crucial for mouse retinal development, as they restrain the proliferation of retinal progenitor cells. The lack of these apical proteins results in altered cell cycle progression and increased number of mitotic cells leading to an increased number of late-born cell types such as rod photoreceptors, bipolar and Müller glia cells in postmitotic retinas. Loss of CRB1 and CRB2 in the retina results in dysregulation of target genes for the Notch1 and YAP/Hippo signaling pathways and increased levels of P120-catenin. Loss of CRB1 and CRB2 result in altered progenitor cell cycle distribution with a decrease in number of late progenitors in G1 and an increase in S and G2/M phase. These findings suggest that CRB1 and CRB2 suppress late progenitor pool expansion by regulating multiple proliferative signaling pathways.

Correlation with OCT and histology of photocoagulation lesions in patients and rabbits

PURPOSE

To examine spectral domain optical coherence tomographic (OCT) and histological images from comparable retinal photocoagulation lesions in rabbits, and to correlate these images with comparable OCT images from patients.

METHODS

508 rabbit lesions were examined by HE-stained paraffin histology. 1019 rabbit lesions versus 236 patient lesions were examined by OCT, all at the time-points 1 hr, 1 week and 4 weeks after photocoagulation. We analysed 100 μm lesions (in humans) and 133 μm lesions (in rabbits) of 200 ms exposures at powers titrated from the histological threshold up to intense damage. Lesions were matched according to morphological criteria.

RESULTS

Dome-shaped layer alterations, retinal infiltration by round, pigmented cells, outer nuclear layer interruption, and eventually full thickness retinal coagulation are detectable in histology and OCT. Horizontal damage extensions are found 1½ times larger in OCT. More intense irradiation was necessary to induce comparable layer affection in rabbit OCT as in histology. Restoration of the inner retinal layers is only shown in the OCT images. Comparable primary lesions caused more pronounced OCT changes in patients than in rabbits during healing.

CONCLUSIONS

Optical coherence tomographic images indicate different tissue changes than histologic images. After photocoagulation, they show wider horizontal damage diameters, but underestimate axial damage particularly during healing. Conclusions on retinal restoration should not be drawn from OCT findings alone. Retinal recovery after comparable initial lesions appears to be more complete in rabbit than in patient OCTs.

Cav1.4 IT mouse as model for vision impairment in human congenital stationary night blindness type 2

Mutations in the CACNA1F gene encoding the Cav1.4 Ca (2+) channel are associated with X-linked congenital stationary night blindness type 2 (CSNB2). Despite the increasing knowledge about the functional behavior of mutated channels in heterologous systems, the pathophysiological mechanisms that result in vision impairment remain to be elucidated. This work provides a thorough functional characterization of the novel IT mouse line that harbors the gain-of-function mutation I745T reported in a New Zealand CSNB2 family. (1) Electroretinographic recordings in IT mice permitted a direct comparison with human data. Our data supported the hypothesis that a hyperpolarizing shift in the voltage-dependence of channel activation-as seen in the IT gain-of-function mutant (2)-may reduce the dynamic range of photoreceptor activity. Morphologically, the retinal outer nuclear layer in adult IT mutants was reduced in size and cone outer segments appeared shorter. The organization of the outer plexiform layer was disrupted, and synaptic structures of photoreceptors had a variable, partly immature, appearance. The associated visual deficiency was substantiated in behavioral paradigms. The IT mouse line serves as a specific model for the functional phenotype of human CSNB2 patients with gain-of-function mutations and may help to further understand the dysfunction in CSNB.

Optical coherence tomography study of experimental anterior ischemic optic neuropathy and histologic confirmation

PURPOSE

The optic nerve is part of the central nervous system, and interruption of this pathway due to ischemia typically results in optic atrophy and loss of retinal ganglion cells. In this study, we assessed in vivo retinal changes following murine anterior ischemic optic neuropathy (AION) by using spectral-domain optical coherence tomography (SD-OCT) and compared these anatomic measurements to that of histology.

METHODS

We induced ischemia at the optic disc via laser-activated photochemical thrombosis, performed serial SD-OCT and manual segmentation of the retinal layers to measure the ganglion cell complex (GCC) and total retinal thickness, and correlated these measurements with that of histology.

RESULTS

There was impaired perfusion and leakage at the optic disc on fluorescein angiography immediately after AION and severe swelling and distortion of the peripapillary retina on day-1. We used SD-OCT to quantify the changes in retinal thickness following experimental AION, which revealed significant thickening of the GCC on day-1 after ischemia followed by gradual thinning that plateaued by week-3. Thickness of the peripapillary sensory retina was also increased on day-1 and thinned chronically. This pattern of acute retinal swelling and chronic thinning on SD-OCT correlated well with changes seen in histology and corresponded to loss of retinal ganglion layer cells after ischemia.

CONCLUSIONS

This was a serial SD-OCT quantification of acute and chronic changes following experimental AION, which revealed changes in the GCC similar to that of human AION, but over a time frame of weeks rather than months.

Effect of contact lens on optical coherence tomography imaging of rodent retina

PURPOSE

To evaluate the effect of powerless contact lens on improving the quality of optical coherence tomography imaging of rodent retina.

METHODS

A spectral-domain optical coherence tomography (SD-OCT) system was built for in vivo imaging of rodent retina. The calibrated depth resolution of the system was 3 µm in tissue. A commercial powerless contact lens for rat eye was tested in the experiments. For each rat eye, the retina was imaged in vivo sequentially first without wearing contact lens and then with wearing contact lens. The lateral resolution and signal-to-noise ratio of the OCT images with and without contact lens were compared to evaluate the improvement of image quality.

RESULTS

The fundus images generated from the measured 3D OCT datasets with contact lens showed sharper retinal blood vessels than those without contact lens. The contrast of the retinal blood vessels was also significantly enhanced in the OCT fundus images with contact lens. As high as 10 dB improvements in SNR was observed for OCT images with contact lens compared to the images of the same retinal area without contact lens.

CONCLUSIONS

We have demonstrated that the use of powerless contact lens on rat eye can significantly improve OCT image quality of rodent retina, which is a benefit in addition to preventing cataract formation. We believe the improvement in image quality is the result of partial compensation of the optical aberrations of the rodent eye by the contact lens.

The Ophthalmic Examination as It Pertains to General Ocular Toxicology: Basic and Advanced Techniques and Species-Associated Findings

Ocular toxicology pertains to toxicologic effects of drugs administered topically, intraocularly, or systemically. It should also include evaluation of adverse effects of ophthalmic devices such as contact lenses, intraocular lenses, and glaucoma implants. The ophthalmic examination is able to provide detailed in-life information and is used in combination with clinical observations, clinical pathology, and histopathology to assess potential toxicologic effects. The ophthalmologist must be familiar with the wide range of species used in the field of toxicology, be familiar with the anatomic variations associated with these species, be able to determine what is an inherited or a breed-related finding from a study-related effect, be competent with the required ophthalmic equipment, and be capable of examining this wide range of animals.

Gene therapy of inherited retinopathies: a long and successful road from viral vectors to patients

Inherited retinopathies (IRs) are common and untreatable blinding conditions inherited mostly as monogenic due to mutations in genes expressed in retinal photoreceptors (PRs) and in retinal pigment epithelium (RPE). Over the last two decades, the retina has emerged as one of the most favorable target tissues for gene therapy given its small size and its enclosed and immune-privileged environment. Different types of viral vectors have been developed, especially those based on the adeno-associated virus (AAV), which efficiently deliver therapeutic genes to PRs or RPE upon subretinal injections. Dozens of successful proofs of concept of the efficacy of gene therapy for recessive and dominant IRs have been generated in small and large models that have paved the way to the first clinical trials using AAV in patients with Leber congenital amaurosis, a severe form of childhood blindness. The results from these initial trials suggest that retinal gene therapy with AAV is safe in humans, that vision can be improved in patients that have suffered from severe impairment of visual function, in some cases for decades, and that readministration of AAV to the subretinal space is feasible, effective, and safe. However, none of the trials could match the levels of efficacy of gene therapy observed in a dog model of the disease, suggesting that there is room for improvement. In conclusion, these results bode well for further testing of AAV-mediated retinal gene therapy in patients with other monogenic and complex forms of blindness.

Rapamycin extends murine lifespan but has limited effects on aging

Aging is a major risk factor for a large number of disorders and functional impairments. Therapeutic targeting of the aging process may therefore represent an innovative strategy in the quest for novel and broadly effective treatments against age-related diseases. The recent report of lifespan extension in mice treated with the FDA-approved mTOR inhibitor rapamycin represented the first demonstration of pharmacological extension of maximal lifespan in mammals. Longevity effects of rapamycin may, however, be due to rapamycin's effects on specific life-limiting pathologies, such as cancers, and it remains unclear if this compound actually slows the rate of aging in mammals. Here, we present results from a comprehensive, large-scale assessment of a wide range of structural and functional aging phenotypes, which we performed to determine whether rapamycin slows the rate of aging in male C57BL/6J mice. While rapamycin did extend lifespan, it ameliorated few studied aging phenotypes. A subset of aging traits appeared to be rescued by rapamycin. Rapamycin, however, had similar effects on many of these traits in young animals, indicating that these effects were not due to a modulation of aging, but rather related to aging-independent drug effects. Therefore, our data largely dissociate rapamycin's longevity effects from effects on aging itself.

Retinal Thickness Normative Data in Wild-Type Mice Using Customized Miniature SD-OCT

OBJECTIVE

To report normative data for retinal thickness in wild-type C57BL/6 mouse utilizing a miniature SD-OCT system.

METHODS

THIRTY ADULT MICE (RANGE: 3-5 months) were anesthetized and secured into the Bioptigen Spectral Domain Ophthalmic Imaging System. Right eye SD-OCT images were standardized by centralizing the optic nerve head (ONH) prior to image acquisition. Global and quadrant total retinal thickness (TRT) values were measured from retinal nerve fiber layer to retinal pigment epithelial layer. Posterior segment analyses also included the outer retinal layer (ORL) and inner retinal layer (IRL). Further sublayer analyses of four layers from the ORL and three layers comprising the IRL were also performed.

RESULTS

The overall mean±SD global TRT in a C57BL/6 mouse model was 204.41±5.19 µm. Quadrant mean TRT values were 204.85±5.81 µm inferiorly, 204.97±6.71 µm nasally, 205.08±5.44 µm temporally, and 202.74±4.85 µm superiorly. Mean±SD thickness for ORL, and IRL were 126.37±10.01 µm, and 107.03±10.98 µm respectively. The mean±SD estimates for the four layers of the ORL were 18.23±2.73 µm, 26.04±4.21 µm, 63.8±6.23 µm, and 19.22±4.34 µm. Mean±SD values for the three IRL sublayers were 27.82±4.04 µm, 59.62±6.66 µm and 19.12±3.71 µm.

CONCLUSION

This study established normative values for the total retinal thickness and sublayer thickness for the wild-type C57BL/6 mice. Moreover, it provides a standard of retinal morphology, in a commonly used animal model, for evaluating therapeutic interventions and retinal disease pathophysiology.

Multimodal photoacoustic ophthalmoscopy in mouse

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

Longitudinal fundus and retinal studies with SD-OCT: a comparison of five mouse inbred strains

Spectral domain optical coherence tomography (SD-OCT) has recently been established as a method for in vivo imaging of fundus and retina in the mouse. It enables more effective studies of retinal diseases including investigations of etiopathologic mechanisms. In order to learn more about longitudinal fundus development and to enable recognition of disease-associated irregularities, we performed confocal scanning laser ophthalmoscopy (cSLO) and SD-OCT measurements in the inbred strains C57BL/6J, C3HeB/FeJ, FVB/NCrl, BALB/cByJ, and 129S2/SvJ when they were between 2 and 6 months of age. In general, cSLO and SD-OCT data did not reveal sex-specific or unilateral differences. C3HeB/FeJ and FVB/NCrl mice showed diffuse choroidal dysplasia. Choroidal vein-like structures appeared as dark fundus stripes in C3HeB/FeJ. In FVB/NCrl, fundus fleck accumulation was found. In contrast, only minor time-dependent changes of fundus appearance were observed in C57BL/6J, BALB/cByJ, and 129S2/SvJ. This was also found for individual fundic main blood vessel patterns in all inbred strains. Vessel numbers varied between 6 and 13 in C57BL/6J. This was comparable in most cases. We further found that retinae were significantly thicker in C57BL/6J compared to the other strains. Total retinal thickness generally did not change between 2 and 6 months of age. As a conclusion, our results indicate lifelong pathologic processes in C3HeB/FeJ and FVB/NCrl that affect choroid and orbital tissues. Inbred strains with regular retinal development did not reveal major time-dependent variations of fundus appearance, blood vessel pattern, or retinal thickness. Consequently, progressive changes of these parameters are suitable indicators for pathologic outliers.

Use of optical coherence tomography and electroretinography to evaluate retinal pathology in a mouse model of autoimmune uveitis

Experimental autoimmune uveoretinitis (EAU) in mice is a model for human autoimmune uveitis. Longitudinal follow-up is only possible by non-invasive techniques, but the information obtained by visual fundus examination can be limited. We therefore evaluated the efficacy of optical coherence tomography (OCT) and electroretinography (ERG) to monitor pathological and functional changes of the retina in vivo. OCT imaging and ERG recording as a measure of visual function were compared with visual fundoscopic imaging and histology findings in the same mouse. Our results showed that OCT imaging of the retina was well correlated with clinical and histological observations in mice during EAU. However, OCT imaging was more sensitive than fundoscopic imaging in detecting the cell infiltrates at the early phase of disease onset. Furthermore, by allowing multi-layer cross- and horizontal-sectional visualizations of retinal lesions longitudinally in a noninvasive fashion, OCT added information that could not be obtained by fundoscopic and histological examinations. Lastly, retinal thickness obtained by OCT imaging provided a key indicator reflecting disease activity, which showed a close association with visual dysfunction as measured by ERG recordings in EAU mice. Thus, our findings demonstrate that OCT is a highly sensitive and reliable technique, and a valuable method for the semi-quantitative evaluation of retinal inflammation in vivo in the mouse.

Assessment and in vivo scoring of murine experimental autoimmune uveoretinitis using optical coherence tomography

Despite advances in clinical imaging and grading our understanding of retinal immune responses and their morphological correlates in experimental autoimmune uveoretinitis (EAU), has been hindered by the requirement for post-mortem histology. To date, monitoring changes occurring during EAU disease progression and evaluating the effect of therapeutic intervention in real time has not been possible. We wanted to establish whether optical coherence tomography (OCT) could detect intraretinal changes during inflammation and to determine its utility as a tool for accurate scoring of EAU. EAU was induced in C57BL/6J mice and animals evaluated after 15, 26, 36 and 60 days. At each time-point, contemporaneous Spectralis-OCT scanning, topical endoscopic fundal imaging (TEFI), fundus fluorescein angiography (FFA) and CD45-immunolabelled histology were performed. OCT features were further characterised on retinal flat-mounts using immunohistochemistry and 3D reconstruction. Optic disc swelling and vitreous opacities detected by OCT corresponded to CD45+ cell infiltration on histology. Vasculitis identified by FFA and OCT matched perivascular myeloid and T-cell infiltrates and could be differentiated from unaffected vessels. Evolution of these changes could be followed over time in the same eye. Retinal folds were visible and found to encapsulate mixed populations of activated myeloid cells, T-cells and microglia. Using these features, an OCT-based EAU scoring system was developed, with significant correlation to validated histological (Pearson r² = 0.6392, P<0.0001, n = 31 eyes) and TEFI based scoring systems (r² = 0.6784, P<0.0001). OCT distinguishes the fundamental features of murine EAU in vivo, permits dynamic assessment of intraretinal changes and can be used to score disease severity. As a result, it allows tissue synchronisation with subsequent cellular and functional assessment and greater efficiency of animal usage. By relating OCT signals with immunohistochemistry in EAU, our findings offer the opportunity to inform the interpretation of OCT changes in human uveitis.

Adaptive optics optical coherence tomography for in vivo mouse retinal imaging

Small animal models of retinal diseases are important to vision research, and noninvasive high resolution in vivo rodent retinal imaging is becoming an increasingly important tool used in this field. We present a custom Fourier domain optical coherence tomography (FD-OCT) instrument for high resolution imaging of mouse retina. In order to overcome aberrations in the mouse eye, we incorporated a commercial adaptive optics system into the sample arm of the refractive FD-OCT system. Additionally, a commercially available refraction canceling lens was used to reduce lower order aberrations and specular back-reflection from the cornea. Performance of the adaptive optics (AO) system for correcting residual wavefront aberration in the mice eyes is presented. Results of AO FD-OCT images of mouse retina acquired in vivo with and without AO correction are shown as well.

Phenotyping of mouse models with OCT

Optical coherence tomography (OCT) is an invaluable technique to perform noninvasive retinal imaging in small animal models such as mice. It provides virtual cross sections that correlate well with histomorphometric data with the advantage that multiple iterative measurements can be acquired in time line analyses to detect dynamic changes and reduce the amount of animals needed per study.

Novel small-eye allele in paired box gene 6 (Pax6) is caused by a point mutation in intron 7 and creates a new exon

PURPOSE

Within a mutagenesis screen, we identified the new mouse mutant Aey80 with small eyes; homozygous mutants were not obtained. The aim of the study was its molecular characterization.

METHODS

We analyzed the offspring of paternally N-ethyl-N-nitrosourea (ENU)-treated C3HeB/FeJ mice for dysmorphology parameters, which can be observed with the naked eye. The Aey80 mutant (abnormality of the eye) was further characterized with laser interference biometry, Scheimpflug imaging, and optical coherence tomography. Linkage analysis of the Aey80 mutant was performed using a panel of single nucleotide polymorphisms different among C3HeB/FeJ and C57BL/6J mice. The Aey80 mutation was identified with sequence analysis of the positional candidate gene.

RESULTS

We identified a new mutant characterized by an obvious small-eye phenotype; homozygotes are not viable after birth. Embryos at embryonic day 15.5 demonstrate a clear gene-dosage effect: Heterozygotes have small eyes, whereas homozygous mutants do not have eyes. In adult mice, the lenses and the entire eyes of the heterozygous mutants were significantly smaller than those of the wild-types (p<0.01). No other ocular phenotypes were observed; the lenses were fully transparent, and no adhesion to the cornea was observed. The mutation was mapped to chromosome 2; markers between 70.8 MB and 129.5 MB showed significant linkage to the mutation resulting in paired box gene 6 (Pax6) as an excellent candidate gene. We amplified cDNAs from the embryonic eyes and observed an additional band while amplifying the region corresponding to exons 7 and 8. The additional band included an alternative exon of 141 bp, which was associated with a G->A exchange four bases downstream of the end of the alternative exon. The alternative exon in the mutants is predicted to encode 30 novel amino acids and three stop codons. This alternative exon kept the paired domain intact but led to a loss of the homeodomain and the C-terminal proline-serine-threonine (PST) domain. The mutation cosegregated in the mutant line, since all five additional small-eyed mice from this line showed the same mutation. A general polymorphism at the mutated site was excluded with sequence analysis of seven other wild-type mouse strains different from C3HeB/FeJ.

CONCLUSIONS

These findings demonstrate a novel allele of the paired box gene 6 (Pax6) that affects lens development in a semidominant manner leading to a classical small-eye phenotype. However, the site of the mutation more than 1 kb downstream of exon 7 and resulting in an alternative exon is quite unusual. It indicates the importance of sequence analysis of cDNA for mutation detection; mutations like this are unlikely to be identified by analyzing genomic sequences only. Moreover, this particular mutation demonstrates how a novel exon can be created by only a single base-pair exchange.

Endothelial SRF/MRTF ablation causes vascular disease phenotypes in murine retinae

Retinal vessel homeostasis ensures normal ocular functions. Consequently, retinal hypovascularization and neovascularization, causing a lack and an excess of vessels, respectively, are hallmarks of human retinal pathology. We provide evidence that EC-specific genetic ablation of either the transcription factor SRF or its cofactors MRTF-A and MRTF-B, but not the SRF cofactors ELK1 or ELK4, cause retinal hypovascularization in the postnatal mouse eye. Inducible, EC-specific deficiency of SRF or MRTF-A/MRTF-B during postnatal angiogenesis impaired endothelial tip cell filopodia protrusion, resulting in incomplete formation of the retinal primary vascular plexus, absence of the deep plexi, and persistence of hyaloid vessels. All of these features are typical of human hypovascularization-related vitreoretinopathies, such as familial exudative vitreoretinopathies including Norrie disease. In contrast, conditional EC deletion of Srf in adult murine vessels elicited intraretinal neovascularization that was reminiscent of the age-related human pathologies retinal angiomatous proliferation and macular telangiectasia. These results indicate that angiogenic homeostasis is ensured by differential stage-specific functions of SRF target gene products in the developing versus the mature retinal vasculature and suggest that the actin-directed MRTF-SRF signaling axis could serve as a therapeutic target in the treatment of human vascular retinal diseases.

Successful subretinal delivery and monitoring of MicroBeads in mice

Background

To monitor viability of implanted genetically engineered and microencapsulated human stem cells (MicroBeads) in the mouse eye, and to study the impact of the beads and/or xenogenic cells on retinal integrity.

Methodology/Principal Findings

MicroBeads were implanted into the subretinal space of SV126 wild type mice using an ab externo approach. Viability of microencapsulated cells was monitored by noninvasive retinal imaging (Spectralis™ HRA+OCT). Retinal integrity was also assessed with retinal imaging and upon the end of the study by light and electron microscopy. The implanted GFP-marked cells encapsulated in subretinal MicroBeads remained viable over a period of up to 4 months. Retinal integrity and viability appeared unaltered apart from the focal damage due to the surgical implantation, GFAP upregulation, and opsin mistargeting in the immediate surrounding tissue.

Conclusions/Significance

The accessibility for routine surgery and its immune privileged state make the eye an ideal target for release system implants for therapeutic substances, including neurotrophic and anti-angiogenic compounds or protein based biosimilars. Microencapsulated human stem cells (MicroBeads) promise to overcome limitations inherent with single factor release systems, as they are able to produce physiologic combinations of bioactive compounds.

Update on animal models of diabetic retinopathy: from molecular approaches to mice and higher mammals

Diabetic retinopathy (DR) is the most common microvascular complication of diabetes and one of the major causes of blindness worldwide. The pathogenesis of DR has been investigated using several animal models of diabetes. These models have been generated by pharmacological induction, feeding a galactose diet, and spontaneously by selective inbreeding or genetic modification. Among the available animal models, rodents have been studied most extensively owing to their short generation time and the inherited hyperglycemia and/or obesity that affect certain strains. In particular, mice have proven useful for studying DR and evaluating novel therapies because of their amenability to genetic manipulation. Mouse models suitable for replicating the early, non-proliferative stages of the retinopathy have been characterized, but no animal model has yet been found to demonstrate all of the vascular and neural complications that are associated with the advanced, proliferative stages of DR that occur in humans. In this review, we summarize commonly used animal models of DR, and briefly outline the in vivo imaging techniques used for characterization of DR in these models. Through highlighting the ocular pathological findings, clinical implications, advantages and disadvantages of these models, we provide essential information for planning experimental studies of DR that will lead to new strategies for its prevention and treatment.

Neuronal programmed cell death-1 ligand expression regulates retinal ganglion cell number in neonatal and adult mice

OBJECTIVES

During mouse retina maturation, the final number of retinal ganglion cells (RGCs) is determined by highly regulated programmed cell death. Previous studies demonstrated that the immunoregulatory receptor programmed cell death-1 (PD-1) promotes developmental RGC death. To identify the functional signaling partner(s) for PD-1, we identified retinal expression of PD-1 ligands and examined the effect of PD-1 ligand expression on RGC number. We also explored the hypothesis that PD-1 signaling promotes the development of functional visual circuitry.

METHODS

Characterization of retinal and brain programmed cell death-1 ligand 1 (PD-L1) expression were examined by immunofluorescence on tissue sections. The contribution of PD-ligands, PD-L1, and programmed cell death-1 ligand 2 (PD-L2) to RGC number was examined in PD-ligand knockout mice lacking 1 or both ligands. Retinal architecture was assessed by spectral-domain optical coherence tomography, and retinal function was analyzed by electroretinography in wild-type and PD-L1/L2 double-deficient mice.

RESULTS

PD-L1 expression is found throughout the neonatal retina and persists in adult RGCs, bipolar interneurons, and Müller glia. In the absence of both PD-ligands, there is a significant numerical increase in RGCs (34% at postnatal day 2 [P2] and 18% in adult), as compared to wild type, and PD-ligands have redundant function in this process. Despite the increased RGC number, adult PD-L1/L2 double-knockout mice have normal retinal architecture and outer retina function.

CONCLUSION

This study demonstrates that PD-L1 and PD-L2 together impact the final number of RGCs in adult mice and supports a novel role for active promotion of neuronal cell death through PD-1 receptor-ligand engagement.

Modified protocol for in vivo imaging of wild-type mouse retina with customized miniature spectral domain optical coherence tomography (SD-OCT) device

This protocol outlines and evaluates a modified scanning procedure for a customized spectral domain optical coherence tomography (SD-OCT) imaging apparatus within the wild-type C57Bl/6 mouse posterior segment. This modified protocol allows for the capture of a 50 degree field of view spanning 3 mm by 3 mm perimeter with the optic disc as the central point. By utilizing this scanning protocol a more reliable measurement of retinal thickness can be achieved outside the fluctuating region of the optic disc. This protocol, when applied to this high resolution device, enables non-invasive in vivo histological imaging and biometric assessment of the various layers of the rodent posterior segment within a 20 - 30 min procedural time-frame. This protocol could establish a standardized method for evaluating morphological changes, with this commercial SDOCT device, when assessing longitudinal disease pathophysiology and treatment response in mouse models for future vision science research.

Lack of the sodium-driven chloride bicarbonate exchanger NCBE impairs visual function in the mouse retina

Regulation of ion and pH homeostasis is essential for normal neuronal function. The sodium-driven chloride bicarbonate exchanger NCBE (Slc4a10), a member of the SLC4 family of bicarbonate transporters, uses the transmembrane gradient of sodium to drive cellular net uptake of bicarbonate and to extrude chloride, thereby modulating both intracellular pH (pH(i)) and chloride concentration ([Cl(-)](i)) in neurons. Here we show that NCBE is strongly expressed in the retina. As GABA(A) receptors conduct both chloride and bicarbonate, we hypothesized that NCBE may be relevant for GABAergic transmission in the retina. Importantly, we found a differential expression of NCBE in bipolar cells: whereas NCBE was expressed on ON and OFF bipolar cell axon terminals, it only localized to dendrites of OFF bipolar cells. On these compartments, NCBE colocalized with the main neuronal chloride extruder KCC2, which renders GABA hyperpolarizing. NCBE was also expressed in starburst amacrine cells, but was absent from neurons known to depolarize in response to GABA, like horizontal cells. Mice lacking NCBE showed decreased visual acuity and contrast sensitivity in behavioral experiments and smaller b-wave amplitudes and longer latencies in electroretinograms. Ganglion cells from NCBE-deficient mice also showed altered temporal response properties. In summary, our data suggest that NCBE may serve to maintain intracellular chloride and bicarbonate concentration in retinal neurons. Consequently, lack of NCBE in the retina may result in changes in pH(i) regulation and chloride-dependent inhibition, leading to altered signal transmission and impaired visual function.

Loss of CRB2 in the mouse retina mimics human retinitis pigmentosa due to mutations in the CRB1 gene

In humans, the Crumbs homolog-1 (CRB1) gene is mutated in progressive types of autosomal recessive retinitis pigmentosa and Leber congenital amaurosis. However, there is no clear genotype-phenotype correlation for CRB1 mutations, which suggests that other components of the CRB complex may influence the severity of retinal disease. Therefore, to understand the physiological role of the Crumbs complex proteins, we generated and analysed conditional knockout mice lacking CRB2 in the developing retina. Progressive disorganization was detected during late retinal development. Progressive thinning of the photoreceptor layer and sites of cellular mislocalization was detected throughout the CRB2-deficient retina by confocal scanning laser ophthalmoscopy and spectral domain optical coherence tomography. Under scotopic conditions using electroretinography, the attenuation of the a-wave was relatively stronger than that of the b-wave, suggesting progressive degeneration of photoreceptors in adult animals. Histological analysis of newborn mice showed abnormal lamination of immature rod photoreceptors and disruption of adherens junctions between photoreceptors, Müller glia and progenitor cells. The number of late-born progenitor cells, rod photoreceptors and Müller glia cells was increased, concomitant with programmed cell death of rod photoreceptors. The data suggest an essential role for CRB2 in proper lamination of the photoreceptor layer and suppression of proliferation of late-born retinal progenitor cells.

Detailed functional and structural characterization of a macular lesion in a rhesus macaque

PURPOSE

Animal models are powerful tools to broaden our understanding of disease mechanisms and to develop future treatment strategies. Here we present detailed structural and functional findings of a rhesus macaque suffering from a naturally occurring bilateral macular dystrophy (BMD), partial optic atrophy and corresponding reduction of central V1 signals in visual fMRI experiments when compared to data in a healthy macaque (CTRL) of similar age.

METHODS

Retinal imaging included infrared and autofluorescence recordings, fluorescein and indocyanine green angiography and spectral domain optical coherence tomography (OCT) on the Spectralis HRA + OCT platform. Electroretinography included multifocal and Ganzfeld-ERG recordings. Animals were killed and eyes analyzed by immunohistochemistry.

RESULTS

Angiography showed reduced macular vascularization with significantly larger foveal avascular zones (FAZ) in the affected animal (FAZBMD = 8.85 mm(2) vs. FAZCTRL = 0.32 mm(2)). OCT showed bilateral thinning of the macula within the FAZ (total retinal thickness, TRTBMD = 174 ± 9 µm) and partial optic nerve atrophy when compared to control (TRTCTRL = 303 ± 45 µm). Segmentation analysis revealed that inner retinal layers were primarily affected (inner retinal thickness, IRTBMD = 33 ± 9 µm vs. IRTCTRL = 143 ± 45 µm), while the outer retina essentially maintained its thickness (ORTBMD = 141 ± 7 µm vs. ORTCTRL = 160 ± 11 µm). Altered macular morphology corresponded to a preferential reduction of central signals in the multifocal electroretinography and to a specific attenuation of cone-derived responses in the Ganzfeld electroretinography, while rod function remained normal.

CONCLUSION

We provided detailed characterization of a primate macular disorder. This study aims to stimulate awareness and further investigation in primates with macular disorders eventually leading to the identification of a primate animal model and facilitating the preclinical development of therapeutic strategies.

Gene therapy restores vision and delays degeneration in the CNGB1(-/-) mouse model of retinitis pigmentosa

Retinitis pigmentosa (RP) is a group of genetically heterogeneous, severe retinal diseases commonly leading to legal blindness. Mutations in the CNGB1a subunit of the rod cyclic nucleotide-gated (CNG) channel have been found to cause RP in patients. Here, we demonstrate the efficacy of gene therapy as a potential treatment for RP by means of recombinant adeno-associated viral (AAV) vectors in the CNGB1 knockout (CNGB1(-/-)) mouse model. To enable efficient packaging and rod-specific expression of the relatively large CNGB1a cDNA (~4 kb), we used an AAV expression cassette with a short rod-specific promoter and short regulatory elements. After injection of therapeutic AAVs into the subretinal space of 2-week-old CNGB1(-/-) mice, we assessed the restoration of the visual system by analyzing (i) CNG channel expression and localization, (ii) retinal function and morphology and (iii) vision-guided behavior. We found that the treatment not only led to expression of full-length CNGB1a, but also restored normal levels of the previously degraded CNGA1 subunit of the rod CNG channel. Both proteins co-localized in rod outer segments and formed regular CNG channel complexes within the treated area of the CNGB1(-/-) retina, leading to significant morphological preservation and a delay of retinal degeneration. In the electroretinographic analysis, we also observed restoration of rod-driven light responses. Finally, treated CNGB1(-/-) mice performed significantly better than untreated mice in a rod-dependent vision-guided behavior test. In summary, this work provides a proof-of-concept for the treatment of rod channelopathy-associated RP by AAV-mediated gene replacement.

Long-term characterization of retinal degeneration in rd1 and rd10 mice using spectral domain optical coherence tomography

PURPOSE

We characterize the in vivo changes over time in the retinal structure of wild-type mice alongside two lines of mice deficient in the β-subunit of phosphodiesterase (rd1 and rd10 mice) using spectral domain optical coherence tomography (SD-OCT).

METHODS

SD-OCT images were obtained using the Bioptigen spectral domain ophthalmic imaging system (SDOIS). Wild-type C57BL/6J, rd1 and rd10 mice ranging in age from P14 to P206 were sedated with 1% isoflurane. Horizontal and vertical linear scans through the optic nerve, and annular scans around the optic nerve were obtained.

RESULTS

SD-OCT imaging of wild-type mice demonstrated visibility of the inner segment/outer segment (IS/OS) junction, external limiting membrane (ELM), outer nuclear layer (ONL), and outer plexiform layer (OPL). At P14, most rd10 mice exhibited normal SD-OCT profiles, but some displayed changes in the IS/OS junction. At the same time point, rd1 mice had severe outer retinal degeneration. In rd10 mice, imaging revealed loss of the IS/OS junction by P18, hyperreflective changes in the ONL at P20, hyperreflective vitreous opacities, and shallow separation of the neural retina from the RPE. Retinal separations were not observed in rd1 mice. Segmentation analysis in wild-type mice demonstrated relatively little variability between animals, while in rd10 and rd1 mice there was a steady decline in outer retinal thickness. Histologic studies demonstrated correlation of retinal features with those seen on SD-OCT scans. Segmentation analysis provides a quantitative and reproducible method for measuring in vivo retinal changes in mice.

CONCLUSIONS

SD-OCT provides a non-invasive method of following long-term retinal changes in mice in vivo. Although rd10 and rd1 mice have mutations in the same gene, they demonstrate significantly different features on SD-OCT.

Mineralocorticoid receptor is involved in rat and human ocular chorioretinopathy

Central serous chorioretinopathy (CSCR) is a vision-threatening eye disease with no validated treatment and unknown pathogeny. In CSCR, dilation and leakage of choroid vessels underneath the retina cause subretinal fluid accumulation and retinal detachment. Because glucocorticoids induce and aggravate CSCR and are known to bind to the mineralocorticoid receptor (MR), CSCR may be related to inappropriate MR activation. Our aim was to assess the effect of MR activation on rat choroidal vasculature and translate the results to CSCR patients. Intravitreous injection of the glucocorticoid corticosterone in rat eyes induced choroidal enlargement. Aldosterone, a specific MR activator, elicited the same effect, producing choroid vessel dilation -and leakage. We identified an underlying mechanism of this effect: aldosterone upregulated the endothelial vasodilatory K channel KCa2.3. Its blockade prevented aldosterone-induced thickening. To translate these findings, we treated 2 patients with chronic nonresolved CSCR with oral eplerenone, a specific MR antagonist, for 5 weeks, and observed impressive and rapid resolution of retinal detachment and choroidal vasodilation as well as improved visual acuity. The benefit was maintained 5 months after eplerenone withdrawal. Our results identify MR signaling as a pathway controlling choroidal vascular bed relaxation and provide a pathogenic link with human CSCR, which suggests that blockade of MR could be used therapeutically to reverse choroid vasculopathy.

Tomographic fundus features in pseudoxanthoma elasticum: comparison with neovascular age-related macular degeneration in Japanese patients

PURPOSE

To determine the retinal and subretinal features characteristic to pseudoxanthoma elasticum (PXE) compared with age-related macular degeneration by using spectral-domain optical coherence tomography (SD-OCT) in Japanese patients.

METHODS

We reviewed colour fundus photographs, fluorescein angiograms, and SD-OCT images of 52 eyes (27 Japanese patients) with angioid streaks (AS) due to PXE. Then we compared the incidence of tomographic features between 24 eyes (24 patient) with choroidal neovascularization (CNV) secondary to AS and 44 eyes (44 patients) with CNV secondary to age-related macular degeneration (AMD).

RESULTS

Secondary CNV was found in 44 eyes (84.6%) of 52 patients with PXE during follow-up. We found characteristic round or ovoid tubular structures with highly reflective annular lines (termed 'outer retinal tubulation' (ORT)) in 31 (70.5%) of 44 eyes with CNV, but none were found in eyes without CNV. We also found characteristic undulations of Bruch's membrane in 38 (73.1%) eyes with AS. The incidence of ORT was significantly greater in eyes with CNV secondary to AS (70.8%; P=0.005) compared with eyes with CNV secondary to AMD (34.1%). The incidence of Bruch's membrane undulation was significantly greater in eyes with CNV secondary to AS (70.8%; P<0.0001) than in eyes with CNV secondary to AMD (11.4%).

CONCLUSION

SD-OCT imaging clearly revealed a greater incidence of unique lesions, including ORT and Bruch's membrane undulation, in eyes in PXE patients with CNV secondary to AS than in eyes with CNV secondary to AMD.

Characterization of structure and function of the mouse retina using pattern electroretinography, pupil light reflex, and optical coherence tomography

OBJECTIVE

To perform in vivo analysis of retinal functional and structural parameters in healthy mouse eyes.

ANIMAL STUDIED

Adult C57BL/6 male mice (n = 37).

PROCEDURES

Retinal function was evaluated using pattern electroretinography (pERG) and the chromatic pupil light reflex (cPLR). Structural properties of the retina and nerve fiber layer (NFL) were evaluated using spectral-domain optical coherence tomography (SD-OCT).

RESULTS

The average pERG amplitudes were found to be 11.2 ± 0.7 μV (P50-N95, mean ± SEM), with an implicit time for P50-N95 interval of 90.4 ± 5.4 ms. Total retinal thickness was 229.5 ± 1.7 μm (mean ± SEM) in the area centralis region. The thickness of the retinal nerve fiber layer (mean ± SEM) using a circular peripapillary retinal scan centered on the optic nerve was 46.7 ± 0.9 μm (temporal), 46.1 ± 0.9 μm (superior), 45.8 ± 0.9 μm (nasal), and 48.4 ± 1 μm (inferior). The baseline pupil diameter was 2.1 ± 0.05 mm in darkness, and 1.1 ± 0.05 and 0.56 ± 0.03 mm after stimulation with red (630 nm, luminance 200 kcd/m(2)) or blue (480 nm, luminance 200 kcd/m(2)) light illumination, respectively.

CONCLUSIONS

Pattern electroretinography, cPLR and SD-OCT analysis are reproducible techniques, which can provide important information about retinal and optic nerve function and structure in mice.

Real-time imaging of rabbit retina with retinal degeneration by using spectral-domain optical coherence tomography

BACKGROUND

Recently, a transgenic rabbit with rhodopsin Pro 347 Leu mutation was generated as a model of retinitis pigmentosa (RP), which is characterized by a gradual loss of vision due to photoreceptor degeneration. The purpose of the current study is to noninvasively visualize and assess time-dependent changes in the retinal structures of a rabbit model of retinal degeneration by using speckle noise-reduced spectral-domain optical coherence tomography (SD-OCT).

METHODOLOGY/PRINCIPAL FINDINGS

Wild type (WT) and RP rabbits (aged 4-20 weeks) were investigated using SD-OCT. The total retinal thickness in RP rabbits decreased with age. The thickness of the outer nuclear layer (ONL) and between the external limiting membrane and Bruch's membrane (ELM-BM) were reduced in RP rabbits around the visual streak, compared to WT rabbits even at 4 weeks of age, and the differences increased with age. However, inner nuclear layer (INL) thickness in RP rabbits did not differ from that of WT during the observation period. The ganglion cell complex (GCC) thickness in RP rabbits increased near the optic nerve head but not around the visual streak in the later stages of the observation period. Hyper-reflective change was widely observed in the inner segments (IS) and outer segments (OS) of the photoreceptors in the OCT images of RP rabbits. Ultrastructural findings in RP retinas included the appearance of small rhodopsin-containing vesicles scattered in the extracellular space around the photoreceptors.

CONCLUSIONS/SIGNIFICANCE

In the current study, SD-OCT provided the pattern of photoreceptor degeneration in RP rabbits and the longitudinal changes in each retinal layer through the evaluation of identical areas over time. The time-dependent changes in the retinal structure of RP rabbits showed regional and time-stage variations. In vivo imaging of RP rabbit retinas by using SD-OCT is a powerful method for characterizing disease dynamics and for assessing the therapeutic effects of experimental interventions.

Effects of combined ketamine/xylazine anesthesia on light induced retinal degeneration in rats

Objectives

To explore the effect of ketamine-xylazine anesthesia on light-induced retinal degeneration in rats.

Methods

Rats were anesthetized with ketamine and xylazine (100 and 5 mg, respectively) for 1 h, followed by a recovery phase of 2 h before exposure to 16,000 lux of environmental illumination for 2 h. Functional assessment by electroretinography (ERG) and morphological assessment by in vivo imaging (optical coherence tomography), histology (hematoxylin/eosin staining, TUNEL assay) and immunohistochemistry (GFAP and rhodopsin staining) were performed at baseline (ERG), 36 h, 7 d and 14 d post-treatment. Non-anesthetized animals treated with light damage served as controls.

Results

Ketamine-xylazine pre-treatment preserved retinal function and protected against light-induced retinal degeneration. In vivo retinal imaging demonstrated a significant increase of outer nuclear layer (ONL) thickness in the non-anesthetized group at 36 h (p<0.01) and significant reduction one week (p<0.01) after light damage. In contrast, ketamine-xylazine pre-treated animals showed no significant alteration of total retinal or ONL thickness at either time point (p>0.05), indicating a stabilizing and/or protective effect with regard to phototoxicity. Histology confirmed light-induced photoreceptor cell death and Müller cells gliosis in non-anesthetized rats, especially in the superior hemiretina, while ketamine-xylazine treated rats showed reduced photoreceptor cell death (TUNEL staining: p<0.001 after 7 d), thicker ONL and longer IS/OS. Fourteen days after light damage, a reduction of standard flash induced a-wave amplitudes and a-wave slopes (p = 0.01) and significant alterations in parameters of the scotopic sensitivity function (e.g. Vmax of the Naka Rushton fit p = 0.03) were observed in non-treated vs. ketamine-xylazine treated animals.

Conclusions

Our results suggest that pre-treatment with ketamine-xylazine anesthesia protects retinas against light damage, reducing photoreceptor cell death. These data support the notion that anesthesia with ketamine-xylazine provides neuroprotective effects in light-induced cell damage.

Adaptive optics retinal imaging in the living mouse eye

Correction of the eye's monochromatic aberrations using adaptive optics (AO) can improve the resolution of in vivo mouse retinal images [Biss et al., Opt. Lett. 32(6), 659 (2007) and Alt et al., Proc. SPIE 7550, 755019 (2010)], but previous attempts have been limited by poor spot quality in the Shack-Hartmann wavefront sensor (SHWS). Recent advances in mouse eye wavefront sensing using an adjustable focus beacon with an annular beam profile have improved the wavefront sensor spot quality [Geng et al., Biomed. Opt. Express 2(4), 717 (2011)], and we have incorporated them into a fluorescence adaptive optics scanning laser ophthalmoscope (AOSLO). The performance of the instrument was tested on the living mouse eye, and images of multiple retinal structures, including the photoreceptor mosaic, nerve fiber bundles, fine capillaries and fluorescently labeled ganglion cells were obtained. The in vivo transverse and axial resolutions of the fluorescence channel of the AOSLO were estimated from the full width half maximum (FWHM) of the line and point spread functions (LSF and PSF), and were found to be better than 0.79 μm ± 0.03 μm (STD)(45% wider than the diffraction limit) and 10.8 μm ± 0.7 μm (STD)(two times the diffraction limit), respectively. The axial positional accuracy was estimated to be 0.36 μm. This resolution and positional accuracy has allowed us to classify many ganglion cell types, such as bistratified ganglion cells, in vivo.

In-vivo and ex-vivo characterization of laser-induced choroidal neovascularization variability in mice

BACKGROUND

Retinal argon laser coagulation is an established procedure for induction of choroidal neovascularization (CNV) in rodents. This study aimed to evaluate the in-vivo and ex-vivo morphology and variability of laser-induced CNV spots over time.

METHODS

Female C57/Bl/6 mice, 3-6 months of age, were treated with five spots of retinal argon laser coagulation per eye (150 mW, 100 ms, 50 μm). In-vivo fluorescein angiography (FA) and standard high-resolution spectral-domain optical coherence tomography (SD-OCT) were performed on day (d) 0, d1, d4, d7, d14 and d21. Ex-vivo histology, CD31 immunostaining, flatmount and confocal microscopy were also conducted. CNV size in the retinal and choroidal focus, CNV morphology, central retinal thickness (CRT) and FA CNV activity grading were assessed in-vivo at all times and compared to the ex-vivo assessments.

RESULTS

SD-OCT revealed sub-retinal and intra-retinal fluid, and permitted evaluation of longitudinal morphologic changes of the induced CNV. Laser spot area in FA and CRT in SD-OCT did not differ in longitudinal evaluation. CNV could not be consistently outlined on SD-OCT images, and CNV volume as assessed on SD-OCT did not change over time. Significant CNV activity changes were only found in FA CNV activity grading, peaking on d4 and decreasing by d7.

CONCLUSIONS

Non-invasive SD-OCT provides additional morphological information on laser-induced CNV. However, reliable evaluation of CNV requires FA. Spontaneous regression of CNV activity within 14 days after induction has to be taken into account when utilizing this model for testing the efficacies of potential future treatments.

Functional and morphological analysis of the subretinal injection of retinal pigment epithelium cells

Replacement of retinal pigment epithelium (RPE) cells by transplantation is a potential treatment for some retinal degenerations. Here, we used a combination of invasive and noninvasive methods to characterize the structural and functional consequences of subretinal injection of RPE cells. Pigmented cells from primary cultures were injected into albino mice. Recovery was monitored over 8 weeks by fundus imaging, spectral domain optical coherence tomography (sdOCT), histology, and electroretinography (ERG). sdOCT showed that retinal reattachment was nearly complete by 1 week. ERG response amplitudes were reduced after injection, with cone-mediated function then recovering better than rod function. Photoreceptor cell loss was evident by sdOCT and histology, near the site of injection, and is likely to have been the main cause of incomplete recovery. With microscopy, injected cells were identified by the presence of apical melanosomes. They either established contact with Bruch's membrane, and thus became part of the RPE monolayer, or were located on the apical surface of the host's cells, resulting in apposition of the basal surface of the injected cell with the apical surface of the host cell and the formation of a series of desmosomal junctions. RPE cell density was not increased, indicating that the incorporation of an injected cell into the RPE monolayer was concomitant with the loss of a host cell. The transplanted and remaining host cells contained large vacuoles of ingested debris as well as lipofuscin-like granules, suggesting that they had scavenged the excess injected and host cells, and were stressed by the high digestive load. Therefore, although significant functional and structural recovery was observed, the consequences of this digestive stress may be a concern for longer-term health, especially where RPE cell transplantation is used to treat diseases that include lipofuscin accumulation as part of their pathology.

Optimization of in vivo confocal autofluorescence imaging of the ocular fundus in mice and its application to models of human retinal degeneration

PURPOSE

To investigate the feasibility and to identify sources of experimental variability of quantitative and qualitative fundus autofluorescence (AF) assessment in mice.

METHODS

Blue (488 nm) and near-infrared (790 nm) fundus AF imaging was performed in various mouse strains and disease models (129S2, C57Bl/6, Abca4(-/-), C3H-Pde6b(rd1/rd1), Rho(-/-), and BALB/c mice) using a commercially available scanning laser ophthalmoscope. Gray-level analysis was used to explore factors influencing fundus AF measurements.

RESULTS

A contact lens avoided cataract development and resulted in consistent fundus AF recordings. Fundus illumination and magnification were sensitive to changes of the camera position. Standardized adjustment of the recorded confocal plane and consideration of the pupil area allowed reproducible recording of fundus AF from the retinal pigment epithelium with an intersession coefficient of repeatability of ±22%. Photopigment bleaching occurred during the first 1.5 seconds of exposure to 488 nm blue light (∼10 mW/cm(2)), resulting in an increase of fundus AF. In addition, there was a slight decrease in fundus AF during prolonged blue light exposure. Fundus AF at 488 nm was low in animals with an absence of a normal visual cycle, and high in BALB/c and Abca4(-/-) mice. Degenerative alterations in Pde6b(rd1/rd1) and Rho(-/-) were reminiscent of findings in human retinal disease.

CONCLUSIONS

Investigation of retinal phenotypes in mice is possible in vivo using standardized fundus AF imaging. Correlation with postmortem analysis is likely to lead to further understanding of human disease phenotypes and of retinal degenerations in general. Fundus AF imaging may be useful as an outcome measure in preclinical trials, such as for monitoring effects aimed at lowering lipofuscin accumulation in the retinal pigment epithelium.

PGC-1α determines light damage susceptibility of the murine retina

The peroxisome proliferator-activated receptor γ coactivator 1 (PGC-1) proteins are key regulators of cellular bioenergetics and are accordingly expressed in tissues with a high energetic demand. For example, PGC-1α and PGC-1β control organ function of brown adipose tissue, heart, brain, liver and skeletal muscle. Surprisingly, despite their prominent role in the control of mitochondrial biogenesis and oxidative metabolism, expression and function of the PGC-1 coactivators in the retina, an organ with one of the highest energy demands per tissue weight, are completely unknown. Moreover, the molecular mechanisms that coordinate energy production with repair processes in the damaged retina remain enigmatic. In the present study, we thus investigated the expression and function of the PGC-1 coactivators in the healthy and the damaged retina. We show that PGC-1α and PGC-1β are found at high levels in different structures of the mouse retina, most prominently in the photoreceptors. Furthermore, PGC-1α knockout mice suffer from a striking deterioration in retinal morphology and function upon detrimental light exposure. Gene expression studies revealed dysregulation of all major pathways involved in retinal damage and apoptosis, repair and renewal in the PGC-1α knockouts. The light-induced increase in apoptosis in vivo in the absence of PGC-1α was substantiated in vitro, where overexpression of PGC-1α evoked strong anti-apoptotic effects. Finally, we found that retinal levels of PGC-1 expression are reduced in different mouse models for retinitis pigmentosa. We demonstrate that PGC-1α is a central coordinator of energy production and, importantly, all of the major processes involved in retinal damage and subsequent repair. Together with the observed dysregulation of PGC-1α and PGC-1β in retinitis pigmentosa mouse models, these findings thus imply that PGC-1α might be an attractive target for therapeutic approaches aimed at retinal degeneration diseases.

PALS1 is essential for retinal pigment epithelium structure and neural retina stratification

The membrane-associated palmitoylated protein 5 (MPP5 or PALS1) is thought to organize intracellular PALS1-CRB-MUPP1 protein scaffolds in the retina that are involved in maintenance of photoreceptor-Müller glia cell adhesion. In humans, the Crumbs homolog 1 (CRB1) gene is mutated in progressive types of autosomal recessive retinitis pigmentosa and Leber congenital amaurosis. However, there is no clear genotype-phenotype correlation for CRB1 mutations, which suggests that other components of the CRB complex may influence the severity of retinal disease. Therefore, to understand the physiological role of the Crumbs complex proteins, especially PALS1, we generated and analyzed conditional knockdown mice for Pals1. Small irregularly shaped spots were detected throughout the PALS1 deficient retina by confocal scanning laser ophthalmoscopy and spectral domain optical coherence tomography. The electroretinography a- and b-wave was severely attenuated in the aged mutant retinas, suggesting progressive degeneration of photoreceptors. The histological analysis showed abnormal retinal pigment epithelium structure, ectopic photoreceptor nuclei in the subretinal space, an irregular outer limiting membrane, half rosettes of photoreceptors in the outer plexiform layer, and a thinner photoreceptor synaptic layer suggesting improper photoreceptor cell layering during retinal development. The PALS1 deficient retinas showed reduced levels of Crumbs complex proteins adjacent to adherens junctions, upregulation of glial fibrillary acidic protein indicative of gliosis, and persisting programmed cell death after retinal maturation. The phenotype suggests important functions of PALS1 in the retinal pigment epithelium in addition to the neural retina.

Human CRB1-associated retinal degeneration: comparison with the rd8 Crb1-mutant mouse model

PURPOSE

To investigate the human disease due to CRB1 mutations and compare results with the Crb1-mutant rd8 mouse.

METHODS

Twenty-two patients with CRB1 mutations were studied. Function was assessed with perimetry and electroretinography (ERG) and retinal structure with optical coherence tomography (OCT). Cortical structure and function were quantified with magnetic resonance imaging (MRI). Rd8 mice underwent ERG, OCT, and retinal histopathology.

RESULTS

Visual acuities ranged from 20/25 to light perception. Rod ERGs were not detectable; small cone signals were recordable. By perimetry, small central visual islands were separated by midperipheral scotomas from far temporal peripheral islands. The central islands were cone mediated, whereas the peripheral islands retained some rod function. With OCT, there were small foveal islands of thinned outer nuclear layer (ONL) surrounded by thick delaminated retina with intraretinal hyperreflective lesions. MRI showed structurally normal optic nerves and only subtle changes to occipital lobe white and gray matter. Functional MRI indicated that whole-brain responses from patients were of reduced amplitude and spatial extent compared with those of normal controls. Rd8 mice had essentially normal ERGs; OCT and histopathology showed patchy retinal disorganization with pseudorosettes more pronounced in ventral than in dorsal retina. Photoreceptor degeneration was associated with dysplastic regions.

CONCLUSIONS

CRB1 mutations lead to early-onset severe loss of vision with thickened, disorganized, nonseeing retina. Impaired peripheral vision can persist in late disease stages. Rd8 mice also have a disorganized retina, but there is sufficient photoreceptor integrity to produce largely normal retinal function. Differences between human and mouse diseases will complicate proof-of-concept studies intended to advance treatment initiatives.

Human chorioretinal layer thicknesses measured in macula-wide, high-resolution histologic sections

PURPOSE

To provide a comprehensive description of chorioretinal layer thicknesses in the normal human macula, including two-layer pairs that can produce a combined signal in some optical coherence tomography (OCT) devices (ganglion cell [GCL] and inner plexiform [IPL] layers and outer plexiform [OPL] and outer nuclear [ONL] layers).

METHODS

In 0.8-μm-thick, macula-wide sections through the foveola of 18 donors (age range, 40-92 years), 21 layers were measured at 25 locations by a trained observer and validated by a second observer. Tissue volume changes were assessed by comparing total retinal thickness in ex vivo OCT and in sections.

RESULTS

Median tissue shrinkage was 14.5% overall and 29% in the fovea. Histologic laminar boundaries resembled those in SD-OCT scans, but the shapes of the foveolar OPL and ONL differed. Histologic GCL, IPL, and OPLHenle were thickest at 0.8. to 1, 1.5, and 0.4 mm eccentricity, respectively. ONL was thickest in an inward bulge at the foveal center. At 1 mm eccentricity, GCL, INL, and OPLHenle represented 17.3% to 21.1%, 18.0% to 18.5%, and 14.2% to 16.6% of total retinal thickness, respectively. In donors ≥ 70 years of age, the RPE and choroid were 17.1% and 29.6% thinner and OPLHenle was 20.8% thicker than in donors <70 years.

CONCLUSIONS

In this study, the first graphic representation and thickness database of chorioretinal layers in normal macula were generated. Newer OCT systems can separate GCL from IPL and OPLHenle from ONL, with good agreement for the proportion of retinal thickness occupied by OPLHenle in OCT and histology. The thickening of OPLHenle in older eyes may reflect Müller cell hypertrophy associated with rod loss.

Correlation of optical coherence tomography with clinical and histopathological findings in experimental autoimmune uveoretinitis

Optical coherence tomography (OCT) is becoming the state-of-the-art method for the non-invasive imaging of a variety of ocular diseases. The aim of this study was to assess the application of OCT for the in vivo monitoring and follow-up of pathological changes during experimental autoimmune uveoretinitis (EAU) in rats. Initially we established OCT imaging in healthy brown Norway rats and correlated it with retinal histology. Subsequently, we induced EAU and imaged animals by OCT throughout the pre-peak, peak, and post-peak phases of the disease. The sensitivity of OCT imaging was determined by comparison with clinical EAU and histopathology scores obtained ex vivo at several time points throughout the disease course. Our data demonstrate that OCT imaging of the healthy rat retina closely correlates with histological observations and allows the clear visualization of all retinal layers. After induction of EAU, the first pathological changes could be detected by OCT at day (d) 8 post-immunization (p.i.) which corresponded to the time point of clinical disease onset. An increase in retinal thickness (RT) was detected from d10 p.i. onwards which peaked at d16 p.i. and decreased again to near control levels by d20 p.i. We introduce a novel semi-quantitative OCT scoring which correlates with histopathological findings and complements the clinical scores. Therefore, we conclude that OCT is an easily accessible, non-invasive tool for detection and follow-up of histopathological changes during EAU in rats. Indeed, significant differences in RT between different stages of EAU suggest that this OCT parameter is a sensitive marker for distinguishing disease phases in vivo.