Morphological changes of retinal pigment epithelium and choroid in rd-mice

Choroidal vascularity index and choroidal thickness: potential biomarkers in retinitis pigmentosa

Retinitis pigmentosa (RP) is the commonest inherited retinal dystrophy. It is characterized by progressive photoreceptor degeneration and cell death and ongoing neuronal and vascular impairment. In recent years, pathophysiological alterations of the choroid have begun to be appreciated in RP. Thus, representing a potential diagnostic and therapeutic biomarker. In particular, choroidal thickness and the choroidal vascularity index can be used to understand the pathogenesis of disease and evaluate new therapeutic possibilities. Photoreceptor changes seen in eyes with RP are directly correlated to a decrease of choroidal flow, leading to a strong association between relative choroidal ischemia and visual impairment. In this review we analyse the literature on choroidal thickness and choroidal vascularity index in patients with RP and assess whether these markers may reflect progression of disease from an anatomical and functional point of view.

Longitudinal Microstructure Changes of the Retina and Choroid in Retinitis Pigmentosa

PURPOSE

To investigate longitudinal changes in the retinal and choroidal microstructure of the macula in patients with retinitis pigmentosa (RP).

DESIGN

Retrospective, observational cohort study.

METHODS

A total of 69 patients with RP and 69 age- and sex-matched controls who underwent optical coherence tomography (OCT) over a 4-year follow-up period were included. The severity of RP was classified into 3 stages according to the integrity of the inner segment ellipsoid zone. The retinal and choroidal layers were segmented manually from OCT images. The areas of retinal pigment epithelium (RPE) atrophy and choroidal vascular index (CVI) were also analyzed. Longitudinal changes in the OCT parameters were compared among the groups.

RESULTS

Significant decreases (median [interquartile range]) in the thickness of the ganglion cell inner plexiform layer (GCIPL; -1.04 [-2.41 to -0.17]), outer nuclear layer (ONL; -1.44 [-1.86 to -0.28]), and inner segment ellipsoid (ISE; -0.74 [-1.33 to -0.49]) at the moderate stage and retinal nerve fiber layer (RNFL; -1.49 [-2.08 to -0.66]) and GCIPL (0.58 [-1.79 to 0.06]) at the advanced stage were observed. Choroidal thickness decreased significantly from -7.62 to -9.40 μm per year at all stages. RPE atrophy and CVI reduction were observed at the advanced stage. There was no change in the control group.

CONCLUSIONS

ONL and GCIPL thicknesses decreased at the moderate and advanced stages of RP; RNFL thickness decreased only at the advanced stage; and choroidal thickness decreased continuously. In addition, RPE atrophy and CVI reduction were prominent at the advanced stage. These results indicate that there is a temporal variation in the damage of each retinal layer and the choroid in RP patients.

The choroid-sclera interface: An ultrastructural study

Emmetropization is an active and visually guided process that involves the retina, choroid and sclera, and results in compensatory changes in eye growth. This guided growth is the result of visual cues and possibly mechanical interactions being translated into growth signals via molecular events from the retina into the choroid and sclera, through the choroidal scleral transition zone. If mechanical interactions were a part of the choroid-sclera signaling transduction cascade, specific morphological arrangements should be detectable in this region at the ultrastructural level. The goal of this study was to investigate the ultrastructural features of the choroidal scleral transition zone by comparing avian, non-human primate and human eyes, with the goal to confirm whether specific mechanical structures are present. Choroidal and scleral tissue from chicken, marmoset, and human eyes were imaged using transmission electron microscopy to document the choroid-sclera transition zone. In chicken eyes, fibroblast lamellae bordered the scleral matrix and formed thin end elongated processes that were undercut by scleral collagen fibrils. These processes back-looped into the scleral matrix, and displayed small club-like membrane protrusions. Differences in these arrangements in mature vs young chickens were not detected. The club-like membrane protrusions identified in chickens were rare in marmoset eyes, which instead exhibited two types of collagen fibrils discriminated by size, and were absent in the human eyes investigated. In marmoset and human eyes, elastic components were detected in the transition zone that were absent in chickens. In summary, cellular/membrane specializations indicating a mechanical interaction at the choroid-sclera transition zone were not detected in chicken, non-human primate or human eyes. If mechanotransduction is necessary for scleral growth, matrix integrity or development, alternative structural arrangements might be required.

Choriocapillaris: Fundamentals and advancements

The choriocapillaris is the innermost structure of the choroid that directly nourishes the retinal pigment epithelium and photoreceptors. This article provides an overview of its hemovasculogenesis development to achieve its final architecture as a lobular vasculature, and also summarizes the current histological and molecular knowledge about choriocapillaris and its dysfunction. After describing the existing state-of-the-art tools to image the choriocapillaris, we report the findings in the choriocapillaris encountered in the most frequent retinochoroidal diseases including vascular diseases, inflammatory diseases, myopia, pachychoroid disease spectrum disorders, and glaucoma. The final section focuses on the development of imaging technology to optimize visualization of the choriocapillaris as well as current treatments of retinochoroidal disorders that specifically target the choriocapillaris. We conclude the article with pertinent unanswered questions and future directions in research for the choriocapillaris.

Nrf2 overexpression rescues the RPE in mouse models of retinitis pigmentosa

Nrf2, a transcription factor that regulates the response to oxidative stress, has been shown to rescue cone photoreceptors and slow vision loss in mouse models of retinal degeneration (rd). The retinal pigment epithelium (RPE) is damaged in these models, but whether it also could be rescued by Nrf2 has not been previously examined. We used an adeno-associated virus (AAV) with an RPE-specific (Best1) promoter to overexpress Nrf2 in the RPE of rd mice. Control rd mice showed disruption of the regular array of the RPE, as well as loss of RPE cells. Cones were lost in circumscribed regions within the cone photoreceptor layer. Overexpression of Nrf2 specifically in the RPE was sufficient to rescue the RPE, as well as the disruptions in the cone photoreceptor layer. Electron microscopy showed compromised apical microvilli in control rd mice but showed preserved microvilli in Best1-Nrf2–treated mice. The rd mice treated with Best1-Nrf2 had slightly better visual acuity. Transcriptome profiling showed that Nrf2 upregulates multiple oxidative defense pathways, reversing declines seen in the glutathione pathway in control rd mice. In summary, Nrf2 overexpression in the RPE preserves RPE morphology and survival in rd mice, and it is a potential therapeutic for diseases involving RPE degeneration, including age-related macular degeneration (AMD).

Effect of Choroidal Vessel Density on the Ellipsoid Zone and Visual Function in Retinitis Pigmentosa Using Optical Coherence Tomography Angiography

Purpose

We evaluate the effect of choroidal vessel density on the residual length of the ellipsoid zone (EZ) and visual function in patients with retinitis pigmentosa (RP) using optical coherence tomography angiography (OCTA).

Methods

Fifty-three patients with RP (n = 101 eyes) and 53 normal participants (n = 76 eyes) were enrolled in this study. Patients with RP were assigned to three groups according to their best-corrected visual acuity (BCVA). All patients underwent ophthalmologic examinations, including BCVA, fundus examination performed with a slit-lamp using an indirect 90 diopter (D) lens, OCTA, full-field electroretinogram (ERG), and visual field. The choroidal vessel density in the choriocapillaris-Sattler's layer (DC-S), Haller's layer (DH), horizontal length of the ellipsoid (HEL), and vertical length of the ellipsoid (VEL) were assessed using OCTA and Adobe Photoshop CS3 extended software.

Results

A significantly increasing impairment of choroidal vessel density (DC-S and DH) was characterized in the RP groups compared to those of the controls (P < 0.05 for all). The magnitude of the reduction in the DC-S and DH was much easier to identify for more severely impaired BCVA in the RP groups (P < 0.05 for all). The DC-S had the strongest correlation with the HEL, VEL, BCVA, visual field, and b-wave amplitude (r = 0.735, r = 0.753, r = -0.843, r = 0.579, and r = 0.671, respectively).

Conclusions

Using noninvasive OCTA, choroidal microcirculation, especially in the small/middle choroidal vessel layers, was a prominent factor affecting the EZ, visual acuity, visual field, and recordable ERG b-wave amplitude of patients with RP. This may provide new insights into the progress mechanism and treatment of RP.

Correlation between Visual Function and Structural Characteristics of the Macula in Advanced Retinitis Pigmentosa

We aimed to correlate the visual function and structural characteristics of the retina and choroid in advanced retinitis pigmentosa (RP) patients. A cross-sectional, retrospective review was conducted of medical records of 149 RP patients who reported visual field constriction on a central 30-2 Humphrey visual field chart. Using spectral domain-optical coherence tomography, central foveal thickness (CFT), ellipsoid zone (EZ) length, macular volume (MV), and submacular choroidal thickness (SMChT) were measured. A control cohort (68 eyes of 68 patients) was included for comparing the macular structure. Quantitative correlations between visual function indices [visual field index (VFI) and best-corrected visual acuity (BCVA)] and structural indices (CFT, EZ length, and SMChT) were evaluated. Mean age was 46.3 ± 15.5 years; mean illness duration was 60.7 ± 60.0 months. SMChT was thinner than that in normal controls. Per Pearson's correlation, BCVA and VFI exhibited a progressive worsening related to age and disease duration. In multivariate linear regression, BCVA and VFI were significantly correlated with CFT, EZ length, and MV at the central 1-mm area. Among RP patients with visual field constriction within 30°, VFI and BCVA closely correlate with the degree of retinal structural change, including the CFT, EZ length, and MV. SMChT uniformly decreased in this study population and exhibited no significant correlation with BCVA or VFI degree.

Retinal pigment epithelium-derived transforming growth factor-β2 inhibits the angiogenic response of endothelial cells by decreasing vascular endothelial growth factor receptor-2 expression

Transforming growth factor-β (TGF-β) is a multifunctional cytokine that is known to modulate various aspects of endothelial cell (EC) biology. Retinal pigment epithelium (RPE) is important for regulating angiogenesis of choriocapillaris and one of the main cell sources of TGF-β secretion, particularly TGF-β2. However, it is largely unclear whether and how TGF-β2 affects angiogenic responses of ECs. In the current study, we demonstrated that TGF-β2 reduces vascular endothelial growth factor receptor-2 (VEGFR-2) expression in ECs and thereby inhibits vascular endothelial growth factor (VEGF) signaling and VEGF-induced angiogenic responses such as EC migration and tube formation. We also demonstrated that the reduction of VEGFR-2 expression by TGF-β2 is due to the suppression of JNK signaling. In coculture of RPE cells and ECs, RPE cells decreased VEGFR-2 levels in ECs and EC migration. In addition, we showed that TGF-β2 derived from RPE cells is involved in the reduction of VEGFR-2 expression and inhibition of EC migration. These results suggest that TGF-β2 plays an important role in inhibiting the angiogenic responses of ECs during the interaction between RPE cells and ECs and that angiogenic responses of ECs may be amplified by a decrease in TGF-β2 expression in RPE cells under pathologic conditions.

CHOROIDAL AND RETINAL ATROPHY OF BIETTI CRYSTALLINE DYSTROPHY PATIENTS WITH CYP4V2 MUTATIONS COMPARED TO RETINITIS PIGMENTOSA PATIENTS WITH EYS MUTATIONS

PURPOSE

To compare atrophy of the choroid and retina between Bietti crystalline dystrophy (BCD) patients and EYS-related retinitis pigmentosa (RP) patients with a similar degree of central visual field defects, age, and axial length (AL).

METHODS

Nine eyes of nine BCD patients with CYP4V2 mutations (BCD group) were examined. Moreover, we selected 10 eyes of 10 RP patients with EYS mutations matched for age, axial length, and mean deviation (measured with the 10-2 SITA standard program; EYS-RP group), and 10 eyes of 10 normal volunteers matched for age and axial length (control group). Macular thicknesses of the choroid and retina were measured via swept-source optical coherence tomography.

RESULTS

The macular choroid was significantly thinner in the BCD group than in the EYS-RP and control groups, although the thickness did not significantly differ between the EYS-RP and control groups. The macular retina was significantly thinner in the BCD and EYS-RP groups than in the control group, although the thickness did not significantly differ between the BCD and EYS-RP groups at most sites.

CONCLUSION

Bietti crystalline dystrophy patients with CYP4V2 mutations showed more severe macular choroid atrophy as compared to EYS-related RP patients. These different damage patterns suggest differences in choroidal expression between CYP4V2 and EYS.

Enhanced depth imaging optical coherence tomography in patients with different phases of Behcet's panuveitis

OBJECTIVE

To evaluate the changes in choroidal thickness (CT) at 13 different points between "active," "remission," and "end-stage" phase of Behcet's panuveitis and compare this with the age, sex, and spherical equivalent matched healthy controls using enhanced depth imaging optical coherence tomography.

DESIGN

Prospective study.

PARTICIPANTS

Eighty-five eyes of 45 patients with Behcet's panuveitis (19 eyes with active phase, 48 eyes with remission phase, and 18 eyes with end-stage phase) and 84 eyes of 42 controls were enrolled in this study.

METHODS

CT measurements were obtained beneath the fovea and at 500-µm intervals for 3 mm nasal and temporal to the centre of the fovea. Correlation analyses were calculated to assess the relationship of the CT with age and disease duration.

RESULTS

At all 13 measurement points, CT was significantly thinnest in end-stage-phase eyes and thickest in active-phase eyes (p < 0.01). CT was thicker in remission-phase eyes compared with control eyes at foveal and perifoveal points, but the trend was not statistically significant. The mean CT at each of the 13 measured points showed a negative correlation with age and disease duration (p < 0.01).

CONCLUSIONS

Submacular CT, as measured by enhanced depth imaging optical coherence tomography, was significantly reduced in eyes with Behcet's panuveitis in the end-stage phase and increased in those in the active phase.

The Complement Regulatory Protein CD46 Deficient Mouse Spontaneously Develops Dry-Type Age-Related Macular Degeneration-Like Phenotype

In the mouse, membrane cofactor protein (CD46), a key regulator of the alternative pathway of the complement system, is only expressed in the eye and on the inner acrosomal membrane of spermatozoa. We noted that although Cd46(-/-) mice have normal systemic alternative pathway activating ability, lack of CD46 leads to dysregulated complement activation in the eye, as evidenced by increased deposition of C5b-9 in the retinal pigment epithelium (RPE) and choroid. A knockout of CD46 induced the following cardinal features of human dry age-related macular degeneration (AMD) in 12-month-old male and female mice: accumulation of autofluorescent material in and hypertrophy of the RPE, dense deposits in and thickening of Bruch's membrane, loss of photoreceptors, cells in subretinal space, and a reduction of choroidal vessels. Collectively, our results demonstrate spontaneous age-related degenerative changes in the retina, RPE, and choroid of Cd46(-/-) mice that are consistent with human dry AMD. These findings provide the exciting possibility of using Cd46(-/-) mice as a convenient and reliable animal model for dry AMD. Having such a relatively straight-forward model for dry AMD should provide valuable insights into pathogenesis and a test model system for novel drug targets. More important, tissue-specific expression of CD46 gives the Cd46(-/-) mouse model of dry AMD a unique advantage over other mouse models using knockout strains.

Morphology and Vascular Layers of the Choroid in Stargardt Disease Analyzed Using Spectral-Domain Optical Coherence Tomography

PURPOSE

To analyze total thickness, morphology and individual vascular layers of the choroid in eyes with Stargardt disease using spectral-domain optical coherence tomography (SD OCT).

DESIGN

Cross-sectional retrospective review.

METHODS

Twenty-eight patients with Stargardt disease (53 eyes) with a mean age of 46 (15-79) years and 30 healthy subjects (30 eyes) with a mean age of 49 (22-79) years who underwent 1-line raster scanning with SD OCT were identified. Diagnosis of Stargardt disease was based on ophthalmic history and complete ophthalmic evaluation. The healthy subjects had best-corrected visual acuity of 20/20 or better with no chorioretinal pathology. Two independent raters assessed the total thickness, morphology, and the individual vascular layers of the choroid.

RESULTS

The choroid was irregularly shaped in 26 of 41 eyes (64%) with Stargardt disease when compared to 0 of 30 healthy eyes (0%). Mean subfoveal total choroidal thickness and mean subfoveal large choroidal vessel layer thickness were significantly reduced in eyes with Stargardt disease when compared to healthy eyes (272.8 ± 32.8 μm vs 225.4 ± 69.9 μm; P = .03 and 219.5 ± 30.6 vs169.2 ± 70.1; P = .04, respectively). The maximal choroidal thickness was subfoveal in 9 of 41 eyes (22%), focal choroidal thinning was observed in 21 of 41 eyes (51%), and attenuation of large choroidal vessel layer was observed in 8 of 41 eyes (20%) with Stargardt disease. There was no association of the best-corrected visual acuity with any choroidal morphologic feature, except that it was better by a mean of 0.61 ± 0.21 in eyes that had preservation of large choroidal vessel layer (33 of 41, 80%) when compared to those that had attenuation of large choroidal vessel layer (P = .007).

CONCLUSION

This study shows alterations in the total thickness, morphology, and the individual vascular layers of the choroid in eyes with Stargardt disease on SD OCT. These findings may potentially contribute to the clinical staging and monitoring of Stargardt disease.

Restoration of Vision with Ectopic Expression of Human Rod Opsin

Many retinal dystrophies result in photoreceptor loss, but the inner retinal neurons can survive, making them potentially amenable to emerging optogenetic therapies. Here, we show that ectopically expressed human rod opsin, driven by either a non-selective or ON-bipolar cell-specific promoter, can function outside native photoreceptors and restore visual function in a mouse model of advanced retinal degeneration. Electrophysiological recordings from retinal explants and the visual thalamus revealed changes in firing (increases and decreases) induced by simple light pulses, luminance increases, and naturalistic movies in treated mice. These responses could be elicited at light intensities within the physiological range and substantially below those required by other optogenetic strategies. Mice with rod opsin expression driven by the ON-bipolar specific promoter displayed behavioral responses to increases in luminance, flicker, coarse spatial patterns, and elements of a natural movie at levels of contrast and illuminance (≈50–100 lux) typical of natural indoor environments. These data reveal that virally mediated ectopic expression of human rod opsin can restore vision under natural viewing conditions and at moderate light intensities. Given the inherent advantages in employing a human protein, the simplicity of this intervention, and the quality of vision restored, we suggest that rod opsin merits consideration as an optogenetic actuator for treating patients with advanced retinal degeneration.

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Ectopic human rod opsin restores visual functions in advanced retinal degeneration

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Rod opsin has greater sensitivity than current optogenetic strategies

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Rod opsin-treated animals respond to spatial stimuli, flicker, and natural scenes

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As a human protein ordinarily found in retinal tissue, barriers to clinic are minimized

ET-1 Plasma Levels, Aqueous Flare, and Choroidal Thickness in Patients with Retinitis Pigmentosa

Purpose. To assess endothelin-1 (ET-1) plasma levels, choroidal thickness, and aqueous flare in patients with early stage retinitis pigmentosa (RP) and to search for possible correlations. Methods. We compared 24 RP patients with 24 healthy controls. Choroidal thickness and aqueous flare were measured, respectively, by using a spectral domain optical coherence tomography and a laser flare-cell meter, whereas plasma samples were obtained from each patient to evaluate ET-1 plasma levels. Results. Notably, RP subjects showed significantly increased ET-1 plasma levels and reduced choroidal thickness compared with controls: 2.143 ± 0.258 versus 1.219 ± 0.236 pg/mL, P < 0.002, and 226.75 ± 76.37 versus 303.9 ± 39.87 μm, P < 0.03, respectively. Higher aqueous flare values were also demonstrated in RP compared to controls: in detail, 10.51 ± 3.97 versus 5.66 ± 1.29 photon counts/ms, P < 0.0001. Spearman's correlation test highlighted that the increase of ET-1 plasma levels was related with the decrease of choroidal thickness (r = -0.702; P < 0.023) and the increase of aqueous flare (r = 0.580; P < 0.007). Conclusions. Early stage RP patients show a breakdown of blood-ocular barrier and increased ET-1 plasma levels and these findings may contribute to the reduction of choroidal thickness.

Decreased retinal-choroidal blood flow in retinitis pigmentosa as measured by MRI

PURPOSE

To evaluate retinal and choroidal blood flow (BF) using high-resolution magnetic resonance imaging (MRI) as well as visual function measured by the electroretinogram (ERG) in patients with retinitis pigmentosa (RP).

METHODS

MRI studies were performed in 6 RP patients (29-67 years) and 5 healthy volunteers (29-64 years) on a 3-Tesla scanner with a custom-made surface coil. Quantitative BF was measured using the pseudo-continuous arterial spin-labeling technique at 0.5 × 0.8 × 6.0 mm. Full-field ERGs of all patients were recorded. Amplitudes and implicit times of standard ERGs were analyzed.

RESULTS

Basal BF in the posterior retinal-choroid was 142 ± 16 ml/100ml/min (or 1.14 ± 0.13 μl/mm(2)/min) in the control group and was 70 ±19 ml/100ml/min (or 0.56 ± 0.15 μl/mm(2)/min) in the RP group. Retinal-choroidal BF was significantly reduced by 52 ± 8 % in RP patients compared to controls (P<0.05). ERG a- and b-wave amplitudes of RP patients were reduced, and b-wave implicit times were delayed. There were statistically significant correlations between a-wave amplitude and BF value (r=0.9, P<0.05) but not between b-wave amplitude and BF value (r =0.7, P=0.2).

CONCLUSIONS

This study demonstrates a novel non-invasive MRI approach to measure quantitative retinal and choroidal BF in RP patients. We found that retinal-choroidal BF was markedly reduced and significantly correlated with reduced amplitudes of the a-wave of the standard combined ERG.

Layer-specific blood-flow MRI of retinitis pigmentosa in RCS rats

The Royal College of Surgeons (RCS) rat is an established animal model of retinitis pigmentosa, a family of inherited retinal diseases which starts with loss of peripheral vision and progresses to eventual blindness. Blood flow (BF), an important physiological parameter, is intricately coupled to metabolic function under normal physiological conditions and is perturbed in many neurological and retinal diseases. This study reports non-invasive high-resolution MRI (44 × 44 × 600 μm) to image quantitative retinal and choroidal BF and layer-specific retinal thicknesses in RCS rat retinas at different stages of retinal degeneration compared with age-matched controls. The unique ability to separate retinal and choroidal BF was made possible by the depth-resolved MRI technique. RBF decreased with progressive retinal degeneration, but ChBF did not change in RCS rats up to post-natal day 90. We concluded that choroidal and retinal circulations have different susceptibility to progressive retinal degeneration in RCS rats. Layer-specific retinal thickness became progressively thinner and was corroborated by histological analysis in the same animals. MRI can detect progressive anatomical and BF changes during retinal degeneration with laminar resolution.

Blood flow and anatomical MRI in a mouse model of retinitis pigmentosa

This study tested the sensitivity of an arterial spin labeling MRI method to image changes in retinal and choroidal blood flow (BF) and anatomical thickness of the retina in the rd10 mouse model of retinitis pigmentosa. High-resolution (42 × 42 μm) MRI was performed on rd10 mice and age-matched controls at 25, 35, and 60 days of age (n = 6 each group) on a 7-T scanner. Anatomical MRI was acquired, and quantitative BF was imaged using arterial spin labeling MRI with a separate cardiac labeling coil. Histology was obtained to confirm thickness changes in the retina. In control mice, the retinal and choroidal vascular layers were quantitatively resolved. In rd10 mice, retinal BF decreased progressively over time, while choroidal BF was unchanged. The rd10 retina became progressively thinner at later time points compared with age-matched controls by anatomical MRI and histology (P < 0.01). BF and anatomical MRI were capable of detecting decreased BF and thickness in the rd10 mouse retina. Because BF is tightly coupled to metabolic function, BF MRI has the potential to noninvasively assess retinal diseases in which metabolism and function are perturbed and to evaluate novel treatments, complementing existing retinal imaging techniques.

In vivo diffusion tensor MRI of the mouse retina: a noninvasive visualization of tissue organization

Diffusion tensor MRI (DTI) is a method for the noninvasive assessment of cellular organization and integrity in vivo. In this study, in vivo DTI was performed to demonstrate its ability to reflect photoreceptor cell alignment in adult C57BL/6 wild-type mice. Age-matched retinal degeneration 1 (rd1) mice were employed as a negative control, i.e. loss of the photoreceptor cell layer. In wild-type mice, DTI-estimated cell alignment suggests that the MR-detected outer retinal layer comprises cells aligning perpendicular to the retinal surface, consistent with the known organization of photoreceptor cells. The MR-detected outer retinal layer exhibits a lower apparent diffusion coefficient and higher fractional anisotropy than the other two MR-detected retinal layers (p < 0.05 for all comparisons). In rd1 mice, the remaining MR-detected retinal layer exhibits different cell alignment, apparent diffusion coefficient and fractional anisotropy from that of the MR-detected outer retinal layer in wild-type mice (p < 0.05 for all comparisons), reflecting the degeneration of photoreceptor cells in rd1 mouse retina. Overall, our findings suggest that in vivo DTI assessment of mouse retina with normal physiology or degenerative pathology is feasible.

Photoreceptor degeneration changes magnetic resonance imaging features in a mouse model of retinitis pigmentosa

Retinal degeneration-1 (rd1) mice are animal models of retinitis pigmentosa, a blinding disease caused by photoreceptor cell degeneration. This study aims to determine magnetic resonance imaging (MRI) changes in retinas of 1- and 3-month-old rd1 mice. Apparent diffusion coefficient in retina was measured using diffusion MRI. The blood-retinal barrier leakage was evaluated using gadolinium-diethylenetriaminepentaacetic acid-enhanced T(1)-weighted MRI before and after systemic gadolinium-diethylenetriaminepentaacetic acid injection. Photoreceptor degeneration in rd1 retina was apparent by decreased retinal thickness and loss of water diffusion anisotropy in both 1- and 3-month-old rd1 mice. Furthermore, statistically significant increase of mean retinal apparent diffusion coefficient and gadolinium-diethylenetriaminepentaacetic acid-enhanced T(1)-weighted MRI signals were observed in 3-month-old rd1 mice comparing with age-matched wild-type mice. Together, these data suggest that MRI parameter changes can signature common pathological changes in photoreceptor-degenerated eyes, particularly blood-retinal barrier leakage-induced retinal edema.

Choroidal imaging in inherited retinal disease using the technique of enhanced depth imaging optical coherence tomography

PURPOSE

The aim of this study is to image and describe the in vivo choroidal changes in various retinal dystrophies using the technique of enhanced depth imaging (EDI) optical coherence tomography (OCT) and to correlate these findings with the clinical appearance. Associations between choroidal change and genotype, visual acuity and results of retinal electrophysiology are also explored.

DESIGN

Retrospective observational case series.

METHODS

Twenty patients attending the medical retina clinics at Moorfields Eye Hospital underwent EDI OCT choroidal scans as part of the scanning protocol when they underwent OCT imaging with the Spectralis HRA and OCT. The choroidal images were obtained by moving the Spectralis camera close enough to obtain an inverted image of the retina. The scans were read by two experienced OCT readers assessing the choroidal thickness as well as the choroidal contour for focal areas of choroidal thinning corresponding to the areas of RPE/outer retinal atrophy. The spectrum of patients included those with Stargardt macular dystrophy, macular dystrophies secondary to known mutations such as peripherin/RDS, uncharacterised macular dystrophies, Best disease, bifocal chorioretinal atrophy, Bietti crystalline retinal dystrophy and choroideraemia.

RESULTS

The choroidal appearance was symmetrical in all patients who had both eyes scanned. Ten patients showed no choroidal thinning, five had focal mild to moderate choroidal thinning, three had focal severe choroidal thinning, and two patients had diffuse severe choroidal thinning. There was no association between choroidal thinning and visual acuity [Fisher's exact test, p = 0.350 (right eye), p = 1.000 (left eye)], or extent of retinal dysfunction on electrophysiology (Fisher's exact test, p = 1.000).

CONCLUSION

Enhanced depth imaging using spectral domain OCT can be used to identify choroidal changes in inherited retinal disease. The pattern of choroidal change correlates well with the clinical appearance. It appears that the extent and pattern of choroidal thinning is dependent on the stage of the disease in some cases, and in others the causative gene defect.

Photoreceptor degeneration, azoospermia, leukoencephalopathy, and abnormal RPE cell function in mice expressing an early stop mutation in CLCN2

PURPOSE

To determine the molecular basis and the pathologic consequences of a chemically induced mutation in a mouse model of photoreceptor degeneration, nmf240.

METHODS

Mice from a G3 N-ethyl-N-nitrosourea mutagenesis program were screened by indirect ophthalmoscopy for abnormal fundi. A chromosomal position for the recessive nmf240 mutation was determined by a genome-wide linkage analysis by use of simple sequence length polymorphic markers in an F2 intercross. The critical region was refined, and candidate genes were screened by direct sequencing. The nmf240 phenotype was characterized by histologic analysis of the retina, brain, and male reproductive organs and by electroretinogram (ERG)-based studies of the retina and retinal pigment epithelium (RPE).

RESULTS

Clinically, homozygous nmf240 mutants exhibit a grainy retina that progresses to panretinal patches of depigmentation. The mutation was localized to a region on chromosome 16 containing Clcn2, a gene associated with retinal degeneration. Sequencing identified a missense C-T mutation at nucleotide 1063 in Clcn2 that converts a glutamine to a stop codon. Mice homozygous for the Clcn2(nmf240) mutation experience a severe loss of photoreceptor cells at 14 days of age that is preceded by an elongation of RPE apical microvilli. Homozygous mutants also experience leukoencephalopathy in multiple brain areas and male sterility. Despite a normal retinal histology in nmf240 heterozygotes, the ERG light peak, generated by the RPE, is reduced.

CONCLUSIONS

The nmf240 phenotype closely resembles that reported for Clcn2 knockout mice. The observation that heterozygous nmf240 mice present with a reduced ERG light peak component suggests that CLCN2 is necessary for the generation of this response component.

Fibrae medullares in the retina of the RD mouse: a case report

PURPOSE

A rare finding of fibrae medullares in the mouse eye is presented in an animal suffering from retinal degeneration.

MATERIAL AND METHODS

Numerous eyes from different mouse strains were screened for myelinated fibres in the retina. Light and electron microscopy was used to document a single case in a rd mouse.

RESULTS

Myelinated fibres were found in the inner retina but not continuous with the optic nerve.

CONCLUSION

Even in this highly degenerated retina the potency of the optic nerve fibres to become myelinated still remained. The source of the appropriate glia cells is discussed.

Vascular changes in the posterior eye segment of secondary angle-closure glaucoma: cause or consequence?

BACKGROUND

To study the role of choroidal and retinal vessels in the pathology of secondary angle-closure glaucoma.

METHODS

DBA/2NNia and non-glaucomatous C57BL/6J mice over the age range 2-20 months were investigated. Corrosion cast preparations of the vasculature were studied using scanning electron microscopy. Whole mounts of the retina and choroid were stained enzyme-histochemically for NADPH diaphorase as an indicator for nitric oxide synthase activity. Semi- and ultra-thin sections of the posterior eye segment were performed and evaluated.

RESULTS

DBA/2NNia mice showed loss of choroidal pigmentation and a decrease in choriocapillary density already at 4 months of age. In animals 9 months and older, a decrease of choroidal NADPH-diaphorase positive nerve fibers was evident. The retinal vasculature showed only mild changes in NADPH-diaphorase staining, even in the oldest animals. The ultrastructural appearance of the retinal vessels was similar in both mouse strains and for all ages investigated.

CONCLUSIONS

Choroidal changes in the DBA/2NNia mouse are similar to that seen in other glaucoma models. The lack of retinal vasculature changes in adult and senescent DBA/2NNia mice suggests a normal blood supply of the retina during the progress of secondary angle-closure glaucoma in these animals.

Pigment epithelium-derived factor (PEDF) and vascular endothelial growth factor (VEGF) in aged human choroid and eyes with age-related macular degeneration

The purpose of this study was to examine the localization and relative levels of vascular endothelial growth factor (VEGF; an angiogenic factor) and pigment epithelium-derived factor (PEDF; an antiangiogenic factor) in aged human choroid and to determine if the localization or their relative levels changed in age-related macular degeneration (AMD). Ocular tissues were obtained from eight aged control donors (age range, 75-86 years; mean age, 79.8 years) with no evidence or history of chorioretinal disease and from 12 donors diagnosed with AMD (age range, 61-105 years; mean age, 83.9 years). Tissues were cryopreserved and streptavidin alkaline phosphatase immunohistochemistry was performed with rabbit polyclonal anti-human VEGF and rabbit polyclonal anti-human PEDF antibodies. Binding of the antibodies was blocked by preincubation of the antibody with an excess of recombinant human PEDF or VEGF peptide. Choroidal blood vessels were identified with mouse anti-human CD-34 antibody in adjacent tissue sections. Three independent observers graded the immunohistochemical reaction product. The most prominent sites of VEGF and PEDF localization in aged control choroid were RPE-Bruch's membrane-choriocapillaris complex including RPE basal lamina, intercapillary septa, and choroidal stroma. There was no significant difference in immunostaining intensity and localization of VEGF and PEDF in aged control choroids. The most intense VEGF immunoreactivity was observed in leukocytes within blood vessels. AMD choroid had a similar pattern and intensity of VEGF immunostaining to that observed in aged controls. However, PEDF immunoreactivity was significantly lower in RPE cells (p=0.0073), RPE basal lamina (p=0.0141), Bruch's membrane (p<0.0001), and choroidal stroma (p=0.0161) of AMD choroids. The most intense PEDF immunoreactivity was observed in disciform scars. Drusen and basal laminar deposits (BLDs) were positive for VEGF and PEDF. In aged control subjects, VEGF and PEDF immunostaining was the most intense in RPE-Bruch's membrane-choriocapillaris complex. In AMD, PEDF was significantly lower in RPE cells, RPE basal lamina, Bruch's membrane and choroidal stroma. These data suggest that a critical balance exists between PEDF and VEGF, and PEDF may counteract the angiogenic potential of VEGF. The decrease in PEDF may disrupt the balance and be permissive for the formation of choroidal neovascularization (CNV) in AMD.

Anatomical and functional evidence for progressive age-related decline in parasympathetic control of choroidal blood flow in pigeons

The choroid receives extensive parasympathetic innervation, which in birds arises largely from the ciliary ganglion (CG). Since age-related changes in parasympathetic regulation of choroidal blood flow (ChBF) could contribute to age-related retinal decline, we used anatomical and functional methods to determine if ChBF control by the CG shows age-related decline in pigeons. The efficacy of the choroidal vasodilatory response to activation of the CG preganglionic input from the medial subdivision of the nucleus of Edinger-Westphal (EWM) was assessed using laser Doppler flowmetry (LDF). The EWM receives bisynaptic retinal input, and electrical stimulation of EWM or light stimulation of the retina in young animals produces dramatic choroidal vasodilation. Transcleral LDF was therefore used to measure both basal ChBF and the increases in ChBF elicited by electrical stimulation of EWM or by retinal illumination in 0.5-18 year old pigeons. Fixed cryostat sections of the eye from 0.5 to 22 year old pigeons were immunolabeled for the 3A10 neurofilament-associated antigen to determine if intrachoroidal nerve fibers arising from CG exhibited age-related loss. We focused on superior choroid, since it is the primary target for CG nerve fibers. There was a marked age-related loss in the ChBF vasodilatory response elicited by either EWM stimulation or retinal illumination, as was also true for basal ChBF. A progressive decrease in choroidal nerve fibers of CG origin, to 17% of youthful abundance by 22 years of age, was also observed. The evoked ChBF increase, and basal ChBF, achieved 50% of their age-related decline between the ages of 3 and 4 years, while half the loss in CG innervation of choroid was later, occurring by 10 years. Age-related loss of choroidal nerve fibers occurs in parallel with but more slowly than the reduction in basal ChBF and the choroidal vasodilation that can be elicited via natural (light) or electrical activation of the central neural input to CG choroidal neurons. The prominent age-related decline in parasympathetic control of ChBF early in the pigeon life span could contribute to the age-related retinal decline observed in pigeons.

Pathomechanisms of Cystoid Macular Edema

Cystoid macular edema (CME) is a well-known endpoint of various ocular diseases, but the relative pathogenic impact of extra- and intracellular fluid accumulation within the retinal tissue still remains uncertain. While most authors favor an extracellular fluid accumulation as the main causative factor of cyst formation, there are indications that Müller cell swelling may also contribute to CME development (particularly in cases without significant angiographic vascular leakage). Vascular leakage occurs after a breakdown of the blood-retinal barrier during traumatic, vascular, and inflammatory ocular diseases, and allows the serum to get into the retinal interstitium. Since intraretinal fluid distribution is restricted by two diffusion barriers, the inner and outer plexiform layers, serum leakage from intraretinal vessels causes cysts mainly in the inner nuclear layer while leakage from choroid/pigment epithelium generates (in addition to subretinal fluid accumulation) cyst formation in the Henle fiber layer. In the normal healthy retina, the transretinal water fluxes are mediated by glial and pigment epithelial cells. These water fluxes are inevitably coupled to fluxes of osmolytes; in the case of glial (Müller) cells, to K(+) clearance currents. For this purpose, the cells express a complex, microtopographically optimized pattern of transporters and channels for osmolytes and water in their plasma membrane. Ischemic/hypoxic alterations of the retinal microvasculature result in gliotic responses which involve down-regulation of K(+) channels in the perivascular Müller cell end-feet. This means a closure of the main pathway which normally generates the osmotic drive for the redistribution of water from the inner retina into the blood. The result is an intracellular K(+) accumulation which, then, osmotically drives water from the blood into the glial cells (i.e., in the opposite direction) and causes glial cell swelling, edema, and cyst formation. While the underlying mechanisms await further research, it is expected that their improved knowledge will stimulate the development of novel therapeutic approaches to resolve edema in retinal tissue.

Ultrastructure of adult rd mouse retina

PURPOSE

To examine the ultrastructure of the adult rd mouse retina in order to determine what structures are altered or lost and thus to better interpret changes produced by photoreceptor and/or retinal transplantation in this model of retinal degeneration.

METHODS

rd mutant mice expressing a LacZ reporter gene in rod bipolars were used in order to identify these cells and their processes. Mice of age 6 weeks to 5 months were studied by electron microscopy, concentrating on the posterior pole where retinal transplants are usually placed.

RESULTS

The adult rd mouse retina contains degenerating cones, cone outer segments, cone synaptic pedicles with synaptic vesicles and post-synaptic contacts. The major abnormalities occur in the subretinal space where all traces of rods are gone and the main structures are inner segments of cones. These inner segments are smaller than normal, contain fewer and smaller mitochondria, have organized arrays of microtubules, resembling those in cone axonal processes, and are completely engulfed by massive proliferation of apical processes of the retinal epithelium. The subretinal space is well defined by the external limiting membrane vitreally and the retinal epithelium choroidally. Muller cells extend globular rather than filamentous processes into the subretinal space which contact the apical processes of the epithelium. Rod bipolar cells survive and retain processes in the external plexiform layer.

CONCLUSIONS

The adult rd mouse retains structural elements necessary for phototransduction and transmission of signals to the inner layers of the retina by the cone system. The major deficits are located in the subretinal space where all rods are lost and cone inner segments undergo a slow degeneration. Rod bipolar cells survive but appear to be de-afferented; there was no evidence that they contact residual cone processes in the external plexiform layer. The rd mouse is a logical model to study the effects of transplantation of photoreceptors because second- and third-order retinal neurons as well as degenerating cones survive in the adult retina.

Vascular endothelial growth factor upregulates pigment epithelium-derived factor expression via VEGFR-1 in human retinal pigment epithelial cells

We previously demonstrated that differentiated retinal pigment epithelial (RPE) cells express high levels of vascular endothelial growth factor (VEGF) and pigment epithelium-derived factor (PEDF), and a critical balance between VEGF and PEDF is important to prevent the development of choroidal neovascularization. We report here that VEGF secreted by RPE cells upregulates PEDF expression via VEGFR-1 in an autocrine manner. PEDF mRNA and protein expression was downregulated by neutralizing antibody against VEGF in differentiated human RPE cells. VEGFR-1 neutralization decreased PEDF mRNA and protein expression whereas anti-VEGFR-2 antibody had no effect. Addition of placenta growth factor (PlGF) restored PEDF expression in the presence of anti-VEGF antibody. These results demonstrate a regulatory interaction between angiogenesis stimulators and inhibitors to maintain homeostasis in normal human retina.

Photoreceptor layer reconstruction in a rodent model of retinal degeneration

We have examined the potential of retinal cell transplantation to dystrophic retinal degeneration mice as a way of replacing photoreceptors lost because of an intrinsic genetic defect. Early postnatal retinae which had been gently dissociated survived for at least 6 weeks after transplantation to the subretinal space. Over a significant area of distribution, transplanted cells formed outer segments which lay in close apposition to the host retinal pigment epithelial cell layer. The grafts integrated with the remaining host retina, sufficient at least to mediate a simple light-dark preference. A new synaptic layer was seen at the graft-host interface, which contained substantial numbers of photoreceptor synapses. This and the fact that the behavior could be elicited at low luminance levels argue for functional circuit reconstruction between grafted cells and host retina.