Müller glial cells of the primate foveola: An electron microscopical study

Unusual morphology of foveal Müller glia in an adult human born pre-term

The fovea of the human retina, a specialization for acute and color vision, features a high concentration of cone photoreceptors. A pit on the inner retinal aspect is created by the centrifugal migration of post-receptoral neurons. Foveal cells are specified early in fetal life, but the fovea reaches its final configuration postnatally. Pre-term birth retards migration resulting in a small pit, a small avascular zone, and nearly continuous inner retinal layers. To explore the involvement of Müller glia, we used serial-section electron microscopic reconstructions to examine the morphology and neural contacts of Müller glia contacting a single foveal cone in a 28-year-old male organ donor born at 28 weeks of gestation. A small non-descript foveal avascular zone contained massed glial processes that included a novel class of 'inner' Müller glia. Similar to classic 'outer' Müller glia that span the retina, inner Müller glia have bodies in the inner nuclear layer (INL). These cells are densely packed with intermediate filaments and insert processes between neurons. Unlike 'outer' Müller glia, 'inner' Müller glia do not reach the external limiting membrane but instead terminate at the outer plexiform layer. One completely reconstructed inner cell ensheathed cone pedicles and a cone-driven circuit of midget bipolar and ganglion cells. Inner Müller glia outnumber foveal cones by 1.8-fold in the outer nuclear layer (221,448 vs. 123,026 cells/mm2). Cell bodies of inner Müller glia outnumber those of outer Müller glia by 1.7-fold in the INL (41,872 vs. 24,631 cells/ mm2). Müller glia account for 95 and 80% of the volume of the foveal floor and Henle fiber layer, respectively. Determining whether inner cells are anomalies solely resulting from retarded lateral migration of inner retinal neurons in pre-term birth requires further research.

Current understanding of subclinical diabetic retinopathy informed by histology and high-resolution in vivo imaging

The escalating incidence of diabetes mellitus has amplified the global impact of diabetic retinopathy. There are known structural and functional changes in the diabetic retina that precede the fundus photography abnormalities which currently are used to diagnose clinical diabetic retinopathy. Understanding these subclinical alterations is important for effective disease management. Histology and high-resolution clinical imaging reveal that the entire neurovascular unit, comprised of retinal vasculature, neurons and glial cells, is affected in subclinical disease. Early functional manifestations are seen in the form of blood flow and electroretinography disturbances. Structurally, there are alterations in the cellular components of vasculature, glia and the neuronal network. On clinical imaging, changes to vessel density and thickness of neuronal layers are observed. How these subclinical disturbances interact and ultimately manifest as clinical disease remains elusive. However, this knowledge reveals potential early therapeutic targets and the need for imaging modalities that can detect subclinical changes in a clinical setting.

Müller Glial Cells in the Macula: Their Activation and Cell-Cell Interactions in Age-Related Macular Degeneration

Müller glia, the main glial cell of the retina, are critical for neuronal and vascular homeostasis in the retina. During age-related macular degeneration (AMD) pathogenesis, Müller glial activation, remodeling, and migrations are reported in the areas of retinal pigment epithelial (RPE) degeneration, photoreceptor loss, and choroidal neovascularization (CNV) lesions. Despite this evidence indicating glial activation localized to the regions of AMD pathogenesis, it is unclear whether these glial responses contribute to AMD pathology or occur merely as a bystander effect. In this review, we summarize how Müller glia are affected in AMD retinas and share a prospect on how Müller glial stress might directly contribute to the pathogenesis of AMD. The goal of this review is to highlight the need for future studies investigating the Müller cell's role in AMD. This may lead to a better understanding of AMD pathology, including the conversion from dry to wet AMD, which has no effective therapy currently and may shed light on drug intolerance and resistance to current treatments.

Myopic macular schisis: Insights into distinct morphological subtypes and novel biomechanical hypothesis

PURPOSE

To analyze the features of myopic macular schisis (MMS) in different retinal layers and to explore the role of Müller cells in the pathophysiology of such condition.

METHODS

Spectral-domain optical coherence tomography (SD-OCT) images of myopic eyes with staphyloma and macular schisis were reviewed. The morphological features of MMS were analyzed and correlated with their geographical location in the parafoveal and perifoveal region. A biomechanical model was adopted to explain MMS morphological differences. The effect of the different schisis subtypes with best corrected visual acuity (BCVA) was also explored.

RESULTS

A total of 36 eyes from 26 patients were included in this study. MMS was classified into inner, middle and outer retinal subtypes. The prevalence of middle retinal schisis was significantly lower in the parafovea, within a central 3 mm-diameter circle (p < 0.001) centered at the fovea . The prevalence of inner retinal schisis was significantly higher outside the central 3-mm diameter circle, in the perifoveal region (p < 0.001). No significant differences were noted in the prevalence of outer retinal schisis for these two locations (p = 0.475). The presence of middle retinal schisis within the central 3-mm diameter circle showed a weak association with lower BCVA (p = 0.058). The presence of outer retinal schisis within the central 3-mm diameter circle was significantly related with lower BCVA (p = 0.024).

CONCLUSION

Three major forms of MMS are distinguished: inner, middle and outer retinal schisis. This classification may have clinical importance as only the outer grade of schisis was associated with vision loss.

Evaluating Contrast Sensitivity in Early and Intermediate Age-Related Macular Degeneration With the Quick Contrast Sensitivity Function

Purpose

The purpose of this study was to describe, validate, and compare the contrast sensitivity functions (CSFs) acquired with the novel quick CSF (qCSF) method from patients with early and intermediate age-related macular degeneration (eAMD and iAMD) and healthy controls.

Methods

This is a cross-sectional analysis of contrast sensitivity (CS) and visual acuity (VA) baseline data from the prospective Multimodal Functional and Structural Visual System Characterization (MUMOVI) study. The qCSF testing was conducted with the manifold contrast vision meter (Adaptive Sensory Technology, San Diego, CA, USA). CS levels at spatial frequencies from 1 cycle per degree (CPD) to 18 CPD, the area underneath the logarithmic contrast sensitivity function (AULCSF), and contrast acuity (CA) were analyzed. The association of functional metrics with variables of interest was tested with linear models.

Results

Ninety-four study eyes from 94 study patients were included in the analysis (13 patients with eAMD, 33 patients with iAMD, and 48 healthy controls). Significant differences between the eAMD and the iAMD model estimates were only found for CS at 1 CPD (t value = -2.9, P value = 0.006) and CS at 1.5 CPD (-2.7, 0.01). A specific association between smoking years and CS at 1 CPD (P = 0.02) and CS at 1.5 CPD (P = 0.03) could be described in patients with AMD.

Conclusions

The qCSF testing allows the fast measurement of the whole CSF, enabling the integration into clinical routine. We showed that novel qCSF-derived metrics detect slight functional differences between AMD stages, which testing by Pelli-Robson charts or VA testing would miss. This study, therefore, yields novel qCSF-derived candidate metrics for therapeutic trials in AMD.

Presumed Müller Cell Activation in Multiple Evanescent White Dot Syndrome

Purpose

The purpose of this study was to investigate the foveal changes occurring in multiple evanescent white dot syndrome (MEWDS) using multimodal imaging techniques with a specific focus on hyper-reflective dots (HRDs).

Methods

This was a retro-prospective observational study including 35 eyes with active MEWDS. Structural and en face optical coherence tomography (OCT) was performed, with follow-up visits at 2 weeks, 6 weeks, and 2 months from baseline. HRD percentage area (HRD % area) was calculated in a 600 µm fovea centered circle on en face OCT, after background subtraction and image binarization. HRD % area was compared with 23 fellow control eyes. Longitudinal changes in the HRD % areas were assessed using repeated-measure statistics.

Results

HRDs were observed as scattered hyper-reflective spots on the vitreoretinal interface on en face OCT images, colocalizing with HRDs or vertical hyper-reflective lines on structural OCT images. The baseline evaluation showed a significantly higher HRD % area in MEWDS eyes compared to fellow eyes (0.10 ± 0.03 vs. 0.08 ± 0.04, P = 0.01). The HRD % area correlated positively with LogMAR visual acuity and inversely with the duration of symptoms. Longitudinal analysis revealed a significant reduction in the HRD % area over time. There was no significant interaction between the rate of HRD disappearance and clinical or demographic factors at baseline.

Conclusions

As HRD potentially represents the end-feet projections of activated Müller cells on the retinal surface, this study supports the involvement of Müller cells in the pathogenesis of the disease. The findings highlight the potential of en face OCT imaging for monitoring the progression of MEWDS.

Müller cell vulnerability in aging human retina: Implications on photoreceptor cell survival

Müller glial cells (MC) support various metabolic functions of the retinal neurons, and maintain the homeostasis. Oxidative stress is intensified with aging, and in human retina, MC and photoreceptors undergo lipid peroxidation and protein nitration. Information on how MC respond to oxidative stress is vital to understand the fate of aging retinal neurons. This study examined age-related changes in MC of donor human retina (age: 35-98 years; N = 18 donors). Ultrastructural and immunohistochemical observations indicate that MC undergo gliosis and increased lipid peroxidation, and show osmotic changes with advanced aging (>80 years). Photoreceptor cells also undergo oxidative-nitrosative stress with aging, and their synapses also show clear osmotic swelling. MC respond to oxidative stress via proliferation of smooth endoplasmic reticulum in their processes, and increased expression of aquaporin-4 in endfeet and outer retina. In advanced aged retinas (81-98 years), they showed mitochondrial disorganisation, accumulation of lipids and autophagosomes, lipofuscin granules and axonal remnants in phagolysosomes in their inner processes, suggesting a reduced phagocytotic potential in them with aging. Glutamine synthetase expression does not alter until advanced aging, when the retinas show its increased expression in endfeet and Henle fiber layer. It is evident that MC are vulnerable with normal aging and this could be a reason for photoreceptor cell abnormalities reported with aging of the human retina.

Dengue Virus Infection of Human Retinal Müller Glial Cells

Retinopathy is a recently recognized complication of dengue, affecting up to 10% of hospitalized patients. Research on the pathogenesis has focused largely on effects of dengue virus (DENV) at the blood-retinal barrier. Involvement of retinal Müller glial cells has received little attention, although this cell population contributes to the pathology of other intraocular infections. The goal of our work was to establish the susceptibility of Müller cells to infection with DENV and to identify characteristics of the cellular antiviral, inflammatory, and immunomodulatory responses to DENV infection in vitro. Primary human Müller cell isolates and the MIO-M1 human Müller cell line were infected with the laboratory-adapted Mon601 strain and DENV serotype 1 and 2 field isolates, and cell-DENV interactions were investigated by immunolabelling and quantitative real-time polymerase chain reaction. Müller cells were susceptible to DENV infection, but experiments involving primary cell isolates indicated inter-individual variation. Viral infection induced an inflammatory response (including tumour necrosis factor-α, interleukin [IL]-1β, and IL-6) and an immunomodulatory response (including programmed death-ligand [PD-L]1 and PD-L2). The type I interferon response was muted in the Müller cell line compared to primary cell isolates. The highest infectivity and cell responses were observed in the laboratory-adapted strain, and overall, infectivity and cell responses were stronger in DENV2 strains. This work demonstrates that Müller cells mount an antiviral and immune response to DENV infection, and that this response varies across cell isolates and DENV strain. The research provides a direction for future efforts to understand the role of human retinal Müller glial cells in dengue retinopathy.

Comparison of long-term visual and anatomical outcomes between internal limiting membrane flap and peeling techniques for macular holes with a propensity score analysis

OBJECTIVES

To compare visual and anatomical outcomes between internal limiting membrane (ILM) flap (IF) and peeling (IP) techniques for full-thickness macular holes (FTMHs).

METHODS

A retrospective case series with propensity-score matching (PSM). Patients with a minimum 12 months follow-up were divided into IF and IP groups and matched based on FTMH size and preoperative best-corrected visual acuity (BCVA). BCVA and optical coherence tomography (OCT) findings were obtained to assess outer retinal layer integrity, foveal thickness, and foveal displacement.

RESULTS

Twenty-six eyes were included in each group after PSM. The IF group showed significantly greater BCVA after 1 month, its corresponding change from preoperative BCVA, proportions of eyes with ellipsoid zone defects <250 μm after 1 month, and interdigitation zone restoration after 6 and 12 months (P = 0.007, 0.038, 0.048, 0.025, and 0.023, respectively), as well as less foveal gliosis after 1, 3, 6, and 12 months (P = 0.020, 0.017, 0.050, and 0.024, respectively). In the IP group, the mean outer nuclear layer thickness significantly decreased at 3 (P = 0.019) and 12 months (P = 0.016) compared to 1 month, and the foveal displacement toward the optic disc was significant after 1, 3, 6, and 12 months (P = 0.049, 0.006, 0.001, and <0.001, respectively).

CONCLUSIONS

Compared to IP, IF promoted faster recovery of BCVA and outer retinal layers and was more protective against postoperative foveal thinning and displacement; hence, it should be considered for small and large FTMHs.

EPIRETINAL MEMBRANE WITH FOVEAL HERNIATION: Visual and Surgical Outcomes

PURPOSE

Foveal herniation occurs when neuroretinal tissue protrudes through and above the level of an epiretinal membrane. This study describes the visual symptoms and spectral domain optical coherence tomography findings associated with foveal herniation and evaluates the postoperative visual, anatomical, and surgical outcomes.

METHODS

A multicenter retrospective review of patients diagnosed with epiretinal membrane identified 59 patients with preoperative foveal herniation on spectral domain optical coherence tomography. Data regarding visual symptoms, preoperative and postoperative best-corrected visual acuity (BCVA), central retinal thickness, macular volume, and size of foveal herniation were collected, and statistical analysis was performed.

RESULTS

A total of 58 of the 59 patients with foveal herniation underwent surgical epiretinal membrane peeling, with foveal contour restored in 53.5% of patients after surgery. Average BCVA improved from 20/80 to 20/40 Snellen equivalent at most-recent postoperative visit (P < 0.0001). The average central retinal thickness decreased from 632 µm to 432 µm (P < 0.0001) and the average macular volume decreased from 11.3 mm3 to 9.5 mm3 (P < 0.0001) at 3 months postoperatively. Preoperatively, greater herniation height was associated with worse BCVA (P = 0.008), greater central retinal thickness (P = 0.01), retinoschisis, cystoid macular edema, foveolar detachment, ellipsoid zone abnormality, and external limiting membrane abnormalities (P < 0.05). Postoperatively, there was a decrease in retinoschisis, cystoid macular edema, foveolar detachment, ellipsoid zone, and external limiting membrane abnormality (P < 0.05) on spectral domain optical coherence tomography.

CONCLUSION

Patients with larger foveal herniation height had greater preoperative central retinal thickness, worse preoperative and postoperative BCVA, and more intraretinal abnormalities on spectral domain optical coherence tomography. Surgical epiretinal membrane peeling in patients with foveal herniation resulted in a significant improvement in patients' BCVA and microstructural abnormalities.

Retinal regions shape human and murine Müller cell proteome profile and functionality

The human macula is a highly specialized retinal region with pit-like morphology and rich in cones. How Müller cells, the principal glial cell type in the retina, are adapted to this environment is still poorly understood. We compared proteomic data from cone- and rod-rich retinae from human and mice and identified different expression profiles of cone- and rod-associated Müller cells that converged on pathways representing extracellular matrix and cell adhesion. In particular, epiplakin (EPPK1), which is thought to play a role in intermediate filament organization, was highly expressed in macular Müller cells. Furthermore, EPPK1 knockout in a human Müller cell-derived cell line led to a decrease in traction forces as well as to changes in cell size, shape, and filopodia characteristics. We here identified EPPK1 as a central molecular player in the region-specific architecture of the human retina, which likely enables specific functions under the immense mechanical loads in vivo.

OUTER FOVEAL DEFECTS IN TYPE-2 MACULAR TELANGIECTASIA

PURPOSE

To report characteristics of outer foveal defects (OFDs) in type-2 macular telangiectasia (MacTel) on spectral domain optical coherence tomography.

METHODS

This was a single-center observational study. From a registry of 745 patients with MacTel, patients with OFDs were characterized. All patients underwent multimodal imaging including color fundus photography, confocal blue reflectance, fundus autofluorescence, and spectral domain optical coherence tomography. Staging of eyes was done using the Gass and Blodi classification. Spectral domain optical coherence tomography characteristics in the central 1 mm of the macula in eyes with OFD are reported.

RESULTS

Outer foveal defect was observed in 21 eyes of 15/745 (2%) patients with MacTel. These defects were bilateral in 6/15 (40%) patients and seen in stage 2 MacTel eyes. In order of prevalence, foveal parameters seen in OFD included hyper-reflective dots in outer retina in 19/21 (90%), ellipsoid zone loss in 18/21 (86%) eyes, interdigitation zone loss in 17/21 (81%) eyes, outer retinal hyporeflective cavitation in 14 (67%) eyes, hyporeflective cavitation at foveal pit in 8 (38%) eyes, and loss of external limiting membrane in 1 (5%) eye. The mean baseline length of the foveal ellipsoid zone loss was 240.17 ± 117.249 µm. The mean baseline central subfield thickness was 155.43 ± 17.215 µm. A total of 8/11 eyes (73%) showed an increase in size of OFD on follow-up.

CONCLUSION

Outer foveal defect in MacTel eyes is characterized predominantly by foveal loss of ellipsoid zone and interdigitation zone with relative preservation of external limiting membrane.

Non-vasogenic cystoid maculopathies

Besides cystoid macular edema due to a blood-retinal barrier breakdown, another type of macular cystoid spaces referred to as non-vasogenic cystoid maculopathies (NVCM) may be detected on optical coherence tomography but not on fluorescein angiography. Various causes may disrupt retinal cell cohesion or impair retinal pigment epithelium (RPE) and Müller cell functions in the maintenance of retinal dehydration, resulting in cystoid spaces formation. Tractional causes include vitreomacular traction, epiretinal membranes and myopic foveoschisis. Surgical treatment does not always allow cystoid space resorption. In inherited retinal dystrophies, cystoid spaces may be part of the disease as in X-linked retinoschisis or enhanced S-cone syndrome, or occur occasionally as in bestrophinopathies, retinitis pigmentosa and allied diseases, congenital microphthalmia, choroideremia, gyrate atrophy and Bietti crystalline dystrophy. In macular telangiectasia type 2, cystoid spaces and cavitations do not depend on the fluid leakage from telangiectasia. Various causes affecting RPE function may result in NVCM such as chronic central serous chorioretinopathy and paraneoplastic syndromes. Non-exudative age macular degeneration may also be complicated by intraretinal cystoid spaces in the absence of fluorescein leakage. In these diseases, cystoid spaces occur in a context of retinal cell loss. Various causes of optic atrophy, including open-angle glaucoma, result in microcystoid spaces in the inner nuclear layer due to a retrograde transsynaptic degeneration. Lastly, drug toxicity may also induce cystoid maculopathy. Identifying NVCM on multimodal imaging, including fluorescein angiography if needed, allows guiding the diagnosis of the causative disease and choosing adequate treatment when available.

Morphology of foveal hypoplasia: Hyporeflective zones in the Henle fiber layer of eyes with high-grade foveal hypoplasia

Background

Foveal hypoplasia is characterized by the persistance of inner retinal layers at the macular center. We evaluated using spectral-domain optical coherence tomography (SD-OCT) morphological parameters of the macular center of eyes with foveal hypoplasia and describe the presence of hyporeflective zones in the Henle fiber layer (HFL) of eyes with high-grade foveal hypoplasia.

Methods

Eyes with foveal hypoplasia were classified into two groups: high-grade foveal hypoplasia with thick inner retinal layers at the macular center (thickness above 100 μm; 16 eyes of 9 subjects) and low-grade foveal hypoplasia with thinner inner retinal layers at the macular center (thickness below 100 μm; 25 eyes of 13 subjects). As comparison, SD-OCT images of normal control eyes (n = 75) were investigated.

Results

Eyes with foveal hypoplasia displayed shorter central photoreceptor outer segments (POS), a thinner central myoid zone, and a thicker central HFL compared to control eyes. Eyes with high-grade foveal hypoplasia also displayed a thinner central outer nuclear layer (ONL) compared to eyes with low-grade foveal hypoplasia and control eyes. There was a negative correlation between the thicknesses of the central ONL and HFL in eyes with foveal hypoplasia; however, the total thickness of both ONL and HFL was similar in all eye populations investigated. Visual acuity of subjects with foveal hypoplasia was negatively correlated to the thickness of the central inner retinal layers and positively correlated to the length of central POS. In contrast to central POS, the length of paracentral POS (0.5 and 1.0 mm nasal from the macular center) was not different between the three eye populations investigated. The paracentral ONL was thickest in eyes with high-grade foveal hypoplasia and thinnest in control eyes. Hyporeflective zones in the HFL were observed on SD-OCT images of eyes with high-grade foveal hypoplasia, but not of eyes with low-grade foveal hypoplasia and control eyes. OCT angiography images recorded at the level of the HFL of eyes with high-grade foveal hypoplasia showed concentric rings of different reflectivity around the macular center; such rings were not observed on images of eyes with low-grade foveal hypoplasia and control eyes.

Conclusions

It is suggested that the hyporeflective zones in the HFL of eyes with high-grade foveal hypoplasia represent cystoid spaces which are surrounded by Henle fiber bundles. Cystoid spaces are likely formed because there are fewer Henle fibers and a thinner central ONL despite an unchanged thickness of both ONL and HFL. Cystoid spaces may cause the concentric rings of different reflectivity around the macular center in the HFL of eyes with high-grade foveal hypoplasia.

Contribution of Müller Cells in the Diabetic Retinopathy Development: Focus on Oxidative Stress and Inflammation

Diabetic retinopathy is a neurovascular complication of diabetes and the main cause of vision loss in adults. Glial cells have a key role in maintenance of central nervous system homeostasis. In the retina, the predominant element is the Müller cell, a specialized cell with radial morphology that spans all retinal layers and influences the function of the entire retinal circuitry. Müller cells provide metabolic support, regulation of extracellular composition, synaptic activity control, structural organization of the blood–retina barrier, antioxidant activity, and trophic support, among other roles. Therefore, impairments of Müller actions lead to retinal malfunctions. Accordingly, increasing evidence indicates that Müller cells are affected in diabetic retinopathy and may contribute to the severity of the disease. Here, we will survey recently described alterations in Müller cell functions and cellular events that contribute to diabetic retinopathy, especially related to oxidative stress and inflammation. This review sheds light on Müller cells as potential therapeutic targets of this disease.

ACUTE FOVEALITIS

PURPOSE

To describe the clinical, optical coherence tomography (OCT), and OCT angiography findings of a patient with a foveal disturbance from the acute phase to the resolution of the visual disturbances.

METHOD

The patient had a comprehensive ophthalmic examination to include OCT and OCT angiography.

RESULTS

A 36-year-old man presented with decreased vision and distortion in the right eye. The right eye showed yellow-white punctate opacities in the central fovea. OCT showed numerous, well-defined, globular, aggregated, hyperreflective lesions that corresponded to the visible opacities along with a focal discontinuity of the outer retinal layers. Over 3 weeks, the patient's findings resolved, and the VA improved to 20/20. No abnormalities of the choriocapillaris flow were detected using OCT angiography. The lesion resolved without pigmentary change.

CONCLUSION

The configuration of the hyperreflective deposits, the lack of pigmentary change, and the absence of OCT angiographic findings of flow problems in the choriocapillaris argue against a primary retinal pigment epithelial or choriocapillaris abnormality as the fundamental cause of the disease. The name acute fovealitis is suggested.

Macular pigment optical density assessed by heterochromatic flicker photometry in eyes affected by primary epiretinal membrane

PURPOSE

To compare macular pigment optical density (MPOD) in healthy eyes vs eyes affected by primary epiretinal membrane (ERM) in different stages and to assess the relation between MPOD and optical coherence tomography findings.

METHODS

Prospective cross-sectional study of 62 eyes from 62 patients affected by unilateral primary ERM. Contralateral healthy eyes from the same patients were used as a control group. Main outcome measures were MPOD, ERM stage, central foveal thickness (CFT), outer nuclear layer thickness (ONLT), integrity of outer retinal bands (ORB) and presence of Central Bouquet (CB) abnormalities.

RESULTS

In the study group mean CFT was 444±75 µm and mean ONLT was 245±40 µm, while in the control group mean CFT was 230±21 µm and mean ONLT was 102±14 µm (p<0.001). Mean MPOD was 0.86±0.07 in eyes with ERM and 0.48±0.09 in contralateral healthy eyes (p<0.001). MPOD was associated with CFT (p=0.006) and ONLT (p<0.001) while no significant associations were observed between MPOD and ORB integrity (p=0.14) and CB abnormalities (p=0.08).

CONCLUSIONS

MPOD increased in eyes affected by primary ERM proportionally to CFT and, especially, ONLT. Probably, centripetal forces exerted by ERM contraction on the retinal surface lead to a progressive foveal packing of foveal Muller cells.

Human Foveal Cone and Müller Cells Examined by Adaptive Optics Optical Coherence Tomography

Purpose

The purpose of this study was to image and investigate the foveal microstructure of human cone and Müller cells using adaptive optics-optical coherence tomography.

Methods

Six healthy subjects underwent the prototype adaptive optics-optical coherence tomography imaging, which allowed an axial resolution of 3.4 µm and a transverse resolution of approximately 3 µm. The morphological features of the individual retinal cells observed in the foveola were qualitatively and quantitatively evaluated.

Results

In the six healthy subjects, the image B-scans showed hyper-reflective dots that were densely packed in the outer nuclear layer. The mean number, diameter, and density of hyper-reflective dots in the foveola were 250.8 ± 59.6, 12.7 ± 59.6 µm, and 6966 ± 1833/mm2, respectively. These qualitative and quantitative findings regarding the hyper-reflective dots were markedly consistent with the morphological features of the foveal cone cell nuclei. Additionally, the images showed the funnel-shaped hyporeflective bodies running vertically and obliquely between the inner and external limiting membranes, illustrating the cell morphology of the foveal Müller cells.

Conclusions

Using adaptive optics, we succeeded in visualizing cross-sectional images of the individual cone and Müller cells of the human retina in vivo.

Translational Relevance

Adaptive optics-optical coherence tomography would help to improve our understanding of the pathogenesis of macular diseases.

En Face Optical Coherence Tomography Imaging of Foveal Dots in Eyes With Posterior Vitreous Detachment or Internal Limiting Membrane Peeling

Purpose

To analyze the morphology of foveal hyperreflective dots (HRD) identified with en face optical coherence tomography (OCT) and evaluate the effects of internal limiting membrane (ILM) peeling and posterior vitreous detachment (PVD) on the number of these lesions.

Methods

Retrospective cross-sectional study of patients with OCT angiography and en face OCT. Using en face OCT, superficial HRD lying on the foveal floor were measured and quantitated in eyes with ILM peel and in the fellow nonsurgical eyes. Eyes with foveal PVD were also compared to fellow eyes without foveal PVD. High-magnification en face OCT was also performed to better understand the morphology of HRD in the fovea.

Results

Eyes that underwent ILM peel (n = 10) displayed fewer HRD (P = 0.012) compared to control fellow nonoperated eyes. In eyes with foveal PVD, the mean number of HRD was numerically greater, but without statistical significance, compared to the contralateral eye without foveal PVD. High-magnification en face OCT illustrated HRD with irregular shapes and fine cilia-like or dendriform extensions. Average length of HRD was between 15 to 21 µm in all four groups.

Conclusions

HRD decreased in eyes with ILM peeling by en face OCT compared with fellow nonoperated eyes and exhibited a glial cell-like morphology and size closely resembling the white dot fovea described previously using scanning electron microscopy. HRD may represent processes of activated retinal glia, possibly Muller cells, that traverse defects in the ILM.

Determinants of vitreomacular traction width: associations with foveal floor width and vitreoretinal interface changes

To investigate the relationship between vitreomacular traction (VMT) width, foveal floor width (FFW) and other anatomical characteristics between eyes of patients with VMT. Retrospective observational study of unilateral and bilateral VMT cases from two specialist ophthalmic centres in the United Kingdom (UK) between 2016 and 2018. For unilateral VMT cases: VMT width in the affected eye and FFW in the non-affected fellow eye were measured. In bilateral VMT cases: VMT width in both eyes was measured. In all cases, the presence of any associated inner or outer retinal, and vitreoretinal interface (VRI) changes, including epiretinal membrane, was also documented. 88 patients fulfilled the study criteria: 57 having unilateral and 31 bilateral VMT. For unilateral VMT cases, log (VMT) width was significantly correlated with FFW (r = 0.347, p = 0.008). Using stepwise linear regression, FFW (p = 0.004) and VRI changes (p = 0.03) were both significantly associated with VMT width with a R² of 0.21. In bilateral VMT cases, there was strong positive correlation between log (VMT) width (r = 0.88, p < 0.001), and the presence of any VRI (r = 0.90, p < 0.001) or outer retinal changes (r = 0.50, p < 0.001) between the two eyes. These findings suggest that individual variations in foveal morphology as measured by the FFW, along with the presence of vitreoretinal interface changes, are associated with the extent of VMT width. VMT width, VRI and outer retinal changes were also highly correlated between eyes in bilateral VMT, suggesting that individual patient factors, which may be genetic or acquired, determine their presence and extent.

Topographic Distribution and Progression of Soft Drusen Volume in Age-Related Macular Degeneration Implicate Neurobiology of Fovea

Purpose

To refine estimates of macular soft drusen abundance in eyes with age-related macular degeneration (AMD) and evaluate hypotheses about drusen biogenesis, we investigated topographic distribution and growth rates of drusen by optical coherence tomography (OCT). We compared results to retinal features with similar topographies (cone density and macular pigment) in healthy eyes.

Methods

In a prospective study, distribution and growth rates of soft drusen in eyes with AMD were identified by human observers in OCT volumes and analyzed with computer-assistance. Published histologic data for macular cone densities (n = 12 eyes) and in vivo macular pigment optical density (MPOD) measurements in older adults with unremarkable maculae (n = 31; 62 paired eyes, averaged) were revisited. All values were normalized to Early Treatment Diabetic Retinopathy Study (ETDRS) subfield areas.

Results

Sixty-two eyes of 44 patients were imaged for periods up to 78 months. Soft drusen volume per unit volume at baseline is 24.6-fold and 2.3-fold higher in the central ETDRS subfield than in outer and inner rings, respectively, and grows most prominently there. Corresponding ratios (central versus inner and central versus outer) for cone density in donor eyes is 13.3-fold and 5.1-fold and for MPOD, 24.6 and 23.9-fold, and 3.6 and 3.6-fold.

Conclusions

Normalized soft drusen volume in AMD eyes as assessed by OCT is ≥ 20-fold higher in central ETDRS subfields than in outer rings, paralleling MPOD distribution in healthy eyes. Data on drusen volume support this metric for AMD risk assessment and clinical trial outcome measure. Alignment of different data modalities support the ETDRS grid for standardizing retinal topography in mechanistic studies of drusen biogenesis.

Foveal regeneration after resolution of cystoid macular edema without and with internal limiting membrane detachment: presumed role of glial cells for foveal structure stabilization

AIM

To document with spectral-domain optical coherence tomography the morphological regeneration of the fovea after resolution of cystoid macular edema (CME) without and with internal limiting membrane (ILM) detachment and to discuss the presumed role of the glial scaffold for foveal structure stabilization.

METHODS

A retrospective case series of 38 eyes of 35 patients is described. Of these, 17 eyes of 16 patients displayed foveal regeneration after resolution of CME, and 6 eyes of 6 patients displayed CME with ILM detachment. Eleven eyes of 9 patients displayed other kinds of foveal and retinal disorders associated with ILM detachment.

RESULTS

The pattern of edematous cyst distribution, with or without a large cyst in the foveola and preferred location of cysts in the inner nuclear layer or Henle fiber layer (HFL), may vary between different eyes with CME or in one eye during different CME episodes. Large cysts in the foveola may be associated with a tractional elevation of the inner foveal layers and the formation of a foveoschisis in the HFL. Edematous cysts are usually not formed in the ganglion cell layer. Eyes with CME and ILM detachment display a schisis between the detached ILM and nerve fiber layer (NFL) which is traversed by Müller cell trunks. ILM detachment was also found in single eyes with myopic traction maculopathy, macular pucker, full-thickness macular holes, outer lamellar holes, and glaucomatous parapapillary retinoschisis, and in 3 eyes with Müller cell sheen dystrophy (MCSD). As observed in eyes with MCSD, cellophane maculopathy, and macular pucker, respectively, fundus light reflections can be caused by different highly reflective membranes or layers: the thickened and tightened ILM which may or may not be detached from the NFL, the NFL, or idiopathic epiretinal membranes. In eyes with short single or multiple CME episodes, the central fovea regenerated either completely, which included the disappearance of irregularities of the photoreceptor layer lines and the reformation of a fovea externa, or with remaining irregularities of the photoreceptor layer lines.

CONCLUSION

The examples of a complete regeneration of the foveal morphology after transient CME show that the fovea may withstand even large tractional deformations and has a conspicuous capacity of structural regeneration as long as no cell degeneration occurs. It is suggested that the regenerative capacity depends on the integrity of the threedimensional glial scaffold for foveal structure stabilization composed of Müller cell and astrocyte processes. The glial scaffold may also maintain the retinal structure after loss of most retinal neurons as in late-stage MCSD.

Müller cells and astrocytes in tractional macular disorders

Tractional deformations of the fovea mainly arise from an anomalous posterior vitreous detachment and contraction of epiretinal membranes, and also occur in eyes with cystoid macular edema or high myopia. Traction to the fovea may cause partial- and full-thickness macular defects. Partial-thickness defects are foveal pseudocysts, macular pseudoholes, and tractional, degenerative, and outer lamellar holes. The morphology of the foveal defects can be partly explained by the shape of Müller cells and the location of tissue layer interfaces of low mechanical stability. Because Müller cells and astrocytes provide the structural scaffold of the fovea, they are active players in mediating tractional alterations of the fovea, in protecting the fovea from such alterations, and in the regeneration of the foveal structure. Tractional and degenerative lamellar holes are characterized by a disruption of the Müller cell cone in the foveola. After detachment or disruption of the cone, Müller cells of the foveal walls support the structural stability of the foveal center. After tractional elevation of the inner layers of the foveal walls, possibly resulting in foveoschisis, Müller cells transmit tractional forces from the inner to the outer retina leading to central photoreceptor layer defects and a detachment of the neuroretina from the retinal pigment epithelium. This mechanism plays a role in the widening of outer lameller and full-thickness macular holes, and contributes to visual impairment in eyes with macular disorders caused by conractile epiretinal membranes. Müller cells of the foveal walls may seal holes in the outer fovea and mediate the regeneration of the fovea after closure of full-thickness holes. The latter is mediated by the formation of temporary glial scars whereas persistent glial scars impede regular foveal regeneration. Further research is required to improve our understanding of the roles of glial cells in the pathogenesis and healing of tractional macular disorders.

High glucose treatment promotes extracellular matrix proteome remodeling in Mller glial cells

Background

The underlying pathomechanisms in diabetic retinopathy (DR) remain incompletely understood. The aim of this study was to add to the current knowledge about the particular role of retinal Mller glial cells (RMG) in the initial processes of DR.

Methods

Applying a quantitative proteomic workflow, we investigated changes of primary porcine RMG under short term high glucose treatment as well as glycolysis inhibition treatment.

Results

We revealed significant changes in RMG proteome primarily in proteins building the extracellular matrix (ECM) indicating fundamental remodeling processes of ECM as novel rapid response to high glucose treatment. Among others, Osteopontin (SPP1) as well as its interacting integrins were significantly downregulated and organotypic retinal explant culture confirmed the selective loss of SPP1 in RMG upon treatment. Since SPP1 in the retina has been described neuroprotective for photoreceptors and functions against experimentally induced cell swelling, its rapid loss under diabetic conditions may point to a direct involvement of RMG to the early neurodegenerative processes driving DR. Data are available via ProteomeXchange with identifier PXD015879.

Degenerative lamellar macular holes: tractional development and morphological alterations

Purpose

The development of degenerative lamellar macular holes (DLH) is largely unclear. This study was aimed at documenting with spectral-domain optical coherence tomography the tractional development and morphological alterations of DLH.

Methods

A retrospective case series of 44 eyes of 44 patients is described.

Results

The development of DLH is preceded for months or years by tractional deformations of the fovea due to the action of contractile epiretinal membranes (ERM) and/or the partially detached posterior hyaloid, or by cystoid macular edema (CME). DLH may develop after a tractional stretching and thickening of the foveal center, from a foveal pseudocyst, after a detachment of the foveola from the retinal pigment epithelium, a disruption of the foveal structure due to CME, and after surgical treatment of tractional lamellar or full-thickness macular holes (FTMH). The foveal configuration of a DLH can be spontaneously reestablished after short transient episodes of CME and a small FTMH. A DLH can evolve to a FTMH by traction of an ERM. Surgical treatment of a DLH may result in an irregular regeneration of the foveal center without photoreceptors.

Conclusions

Tractional forces play an important role in the development of DLH and in the further evolution to FTMH. It is suggested that a DLH is the result of a retinal wound repair process after a tractional disruption of the Müller cell cone and a degeneration of Henle fibers, to prevent a further increase in the degenerative cavitations.

Foveal crack sign as a predictive biomarker for development of macular hole in fellow eyes of patients with full-thickness macular holes

To investigate the prevalence and predictive value of the foveal crack sign (FCS) in fellow eyes of patients with full-thickness macular holes (FTMH) regarding future macular hole (MH) formation. In a retrospective observational case series, 113 fellow eyes of 113 patients with FTMH have been observed during a mean follow-up time of 21 months. According to baseline SD-OCT images, patients were divided into 4 separate groups: patients with FCS and vitreous adhesion, patients with FCS and vitreous detachment, patients without FCS with vitreous adhesion, patients without FCS with vitreous detachment. Progression rate to MH formation, predictive value of FCS and of vitreous interface status were calculated and compared across the four groups. FCS was observed in 19 of 113 fellow eyes (17%) of patients with FTMH, 10 of them with progression to MH during the mean follow up time of 21 months. 2 other eyes with progression to MH showed no FCS at baseline. Progression rate was shown to be 77% (10 of 13 eyes) in patients with FCS and vitreous adhesion, 0% (none of 6 eyes) in patients with FCS and vitreous detachment, 4% (2 of 48 eyes) in patients without FCS with vitreous adhesion, 0% (none of 46 eyes) in patients without FCS with vitreous detachment. FCS had sensitivity of 83.3% (95% CI 50.9–97.1%) and specificity of 91.1% (95% CI 83.3–95.6%) in predicting MH formation, positive predictive value of FCS was 52.6% (95% CI 29.5–74.8%) and negative predictive value 97.9% (95% CI 91.8–99.6%). Having simultaneously FCS and vitreous adhesion showed 83.3% (95% CI 50.9–97.1%) sensitivity and 97.1% (95% CI 91.1–99.2%) specificity in predicting macular hole formation; positive predictive value was 76.9% (95% CI 46.0–93.8%) and negative predictive value was 98.0% (95% CI 92.4–99.7%). Fellow eyes of patients with FTMH with foveal crack sign are at a very high risk (77%) of FTMH development, as long as posterior vitreous adhesion is present.

Hyperreflective Stress Lines and Macular Holes

Purpose

To determine the prevalence of a central hyperreflective line in eyes with full-thickness macular holes (FTMH) and lamellar macular holes (LMH) and to elucidate the pathoanatomic importance of this optical coherence tomography (OCT) sign.

Methods

This retrospective analysis evaluated patients with FTMH and LMH at the Stein Eye Institute. Clinical data was collected and SD-OCT volume scans were analyzed for the presence of a central vertical hyperreflective line in 3 separate cohorts: patients with SD-OCT preceding FTMH development, patients with SD-OCT after pars plana vitrectomy (PPVT) treatment for FTMH, and patients with SD-OCT of LMH.

Results

In total, 93 eyes with FTMH and 88 eyes with LMH were identified. Of the 93 FTMH eyes, SD-OCT volume scans were available before development of the FTMH in 12 eyes. Of these, 6 (50%) displayed a vertical hyperreflective line preceding the development of the FTMH. Fifty-one eyes underwent PPVT with resolution of the FTMH, and 26 displayed a hyperreflective line after resolution (51%). Of the 88 eyes with LMH, 22 displayed a hyperreflective line (25%). All hyperreflective lines were noted at the central fovea.

Conclusions

SD-OCT illustrated the presence of a central vertical hyperreflective line preceding FTMH and after resolution of FTMH after PPVT in approximately one-half of cases, and concurrent with LMH in 25% of cases. This vertical hyperreflective line may represent an early SD-OCT marker for the development of FTMH, and may be a sign of central foveal dehiscence owing to disruption of the Muller cell cone.

Morphology of partial-thickness macular defects: presumed roles of Müller cells and tissue layer interfaces of low mechanical stability

BACKGROUND

The pathogenesis of partial-thickness macular defects and the role of Müller glial cells in the development of such defects are not well understood. We document the morphological characteristics of various types of partial-thickness macular defects using spectral-domain optical coherence tomography, with the focus on tractional and degenerative lamellar holes, and discuss possible pathogenic mechanisms.

METHODS

A retrospective case series of 61 eyes of 61 patients with different types of partial-thickness macular defects is described.

RESULTS

Partial-thickness macular defects are caused by anteroposterior or tangential traction onto the fovea exerted by the partially detached posterior hyaloid and epiretinal membranes, respectively. Tractional elevation of the inner Müller cell layer of the foveola-without (outer lamellar holes, foveal pseudocysts) or with a disruption of this layer (tractional lamellar holes, macular pseudoholes)-produces an elevation of the inner layers of the foveal walls (nerve fiber layer to outer plexiform layer [OPL]) and a schisis between the OPL and Henle fiber layer (HFL). With the exception of outer lamellar holes, the (outer part of the) central outer nuclear layer and the external limiting membrane remain nondisrupted in the various types of partial-thickness defects. Degenerative lamellar holes are characterized by cavitations between the inner plexiform layer and HFL of the foveal walls; many cases have lamellar hole-associated epiretinal proliferation (LHEP). Proliferating cells of the disrupted Müller cell cone may contribute to the development of LHEP and fill the spaces left by degenerated photoreceptors in the foveal center.

CONCLUSIONS

It is suggested that morphological characteristics of partial-thickness macular defects can be explained by the disruption of the (stalk of the) Müller cell cone in the foveola and the location of tissue layer interfaces with low mechanical stability: the boundary with no cellular connections between both Müller cell populations in the foveola, and the interface between the OPL and HFL in the foveal walls and parafovea. We propose that the development of the cavitations in degenerative lamellar holes is initiated by traction which produces a schisis between the OPL and HFL, and enlarged by a slow and chronic degeneration of Henle fibers and bipolar cells.Trial registration retrospectively registered, #143/20-ek, 04/03/2020.

Two different populations of Müller cells stabilize the structure of the fovea: an optical coherence tomography study

PURPOSE

To document with spectral-domain optical coherence tomography the structural stabilization of the fovea and the sealing of outer macular defects by Müller cells.

METHODS

A retrospective case series of 45 eyes of 34 patients is described.

RESULTS

In cases of a cystic disruption of the foveola as in macular telangiectasia type 2 and vitreomacular traction, the Müller cell cone provides the structural stability of the fovea. In cases of a detachment or disruption of the Müller cell cone, e.g., in foveal pseudocysts, outer lamellar holes, and degenerative and tractional lamellar holes, Müller cells of the foveal walls may provide the structural stability of the fovea by the formation of a hyperreflective external limiting membrane (ELM) which bridges the holes in the central outer nuclear layer (ONL). Müller cells of the foveal walls and parafovea mediate the regeneration of the foveal architecture in cases of outer lamellar and full-thickness macular holes. The regeneration proceeds by a centripetal displacement of photoreceptor cell somata which closes the holes in the central ONL. The closure may be supported by the formation of a glial tissue band at the ELM which seals the hole.

CONCLUSIONS

The Müller cell cone provides the foveal stability in cases of a cystic disruption of the foveola. The structural stability of the outer foveal layers is mainly provided by the Müller cells of the foveal walls and parafovea; these cells also mediate the regeneration of the outer fovea in cases of a defect of the central ONL.

Spontaneous closure of small full-thickness macular holes: Presumed role of Müller cells

PURPOSE

To document with spectral domain optical coherence tomography the formation and spontaneous closure of small full-thickness macular holes and to propose the active role of Müller cells in macular hole closure.

METHODS

A retrospective case series of five patients with spontaneous closure of macular holes is reviewed. In one patient, foveal images were recorded over a period of 18 months.

RESULTS

In a 66-year-old man, vitreofoveal traction caused a detachment of the inner Müller cell layer of the foveola from the outer nuclear layer (ONL) which was associated with a large pseudocyst and a horizontal gap in the central ONL. The traction caused an elongation and subsequent disruption of the stalk of the Müller cell cone in the foveola. A small full-thickness macular hole developed when a portion of the inner Müller cell layer of the foveola was pulled out. After phacoemulsification and shortly before the subsequent spontaneous closure of the hole, there were rapid increases in the number and size of the cystic cavities in the foveal walls resulting in a narrowing of the hole. The hole closed by bridging the gap in the inner part of the central ONL; a new inner Müller cell layer of the foveola was formed, and the gap of the external limiting membrane (ELM) was closed. The cystic cavities in the foveal walls rapidly disappeared within 2 weeks after the closure of the hole. One to 2.5 months after hole closure, the thickness of the central ONL increased which decreased the distance between the central ELM and retinal pigment epithelium. In three of the four other patients, the hole also closed by bridging the gap in the inner part of the ONL.

CONCLUSION

It is suggested that the spontaneous closure of small macular holes and the subsequent reconstruction of the normal foveal structure are mediated by active mechanisms of Müller cells which resemble those involved in ontogenetic foveal development.

Functionally validated imaging endpoints in the Alabama study on early age-related macular degeneration 2 (ALSTAR2): design and methods

Background

Age-related macular degeneration (AMD), a leading cause of irreversible vision impairment in the United States and globally, is a disease of the photoreceptor support system involving the retinal pigment epithelium (RPE), Bruch’s membrane, and the choriocapillaris in the setting of characteristic extracellular deposits between outer retinal cells and their blood supply. Research has clearly documented the selective vulnerability of rod photoreceptors and rod-mediated (scotopic) vision in early AMD, including delayed rod-mediated dark adaptation (RMDA) and impaired rod-mediated light and pattern sensitivity. The unifying hypothesis of the Alabama Study on Early Macular Degeneration (ALSTAR2) is that early AMD is a disease of micronutrient deficiency and vascular insufficiency, due to detectable structural changes in the retinoid re-supply route from the choriocapillaris to the photoreceptors. Functionally this is manifest as delayed rod-mediated dark adaptation and eventually as rod-mediated visual dysfunction in general.

Methods

A cohort of 480 older adults either in normal macular health or with early AMD will be enrolled and followed for 3 years to examine cross-sectional and longitudinal associations between structural and functional characteristics of AMD. Using spectral domain optical coherence tomography, the association between (1) subretinal drusenoid deposits and drusen, (2) RPE cell bodies, and (3) the choriocapillaris’ vascular density and rod- and cone-mediated vision will be examined. An accurate map and timeline of structure-function relationships in aging and early AMD gained from ALSTAR2, especially the critical transition from aging to disease, will identify major characteristics relevant to future treatments and preventative measures.

Discussion

A major barrier to developing treatments and prevention strategies for early AMD is a limited understanding of the temporal interrelationships among structural and functional characteristics while transitioning from aging to early AMD. ALSTAR2 will enable the development of functionally valid, structural biomarkers for early AMD, suitable for use in forthcoming clinical trials as endpoint/outcome measures. The comprehensive dataset will also allow hypothesis-testing for mechanisms that underlie the transition from aging to AMD, one of which is a newly developed Center-Surround model of cone resilience and rod vulnerability.

Trial registration

ClinicalTrials.gov Identifier NCT04112667, October 7, 2019.

The Area and Number of Intraretinal Cystoid Spaces Predict the Visual Outcome after Ranibizumab Monotherapy in Diabetic Macular Edema

Visual outcomes in diabetic macular edema (DME) after anti-vascular endothelial growth factor therapy vary across individuals. We retrospectively reviewed the clinical records for 46 treatment-naive eyes of 46 patients with DME who underwent intravitreal ranibizumab (IVR) monotherapy with a pro re nata regimen for 12 months. Overall, mean best-corrected visual acuity (BCVA) improved. Multivariate analyses adjusted for age and baseline BCVA showed that the area ratio, compared with the retinal area, and the number of intraretinal cystoid spaces evaluated on OCT (optical coherence tomography) images at baseline positively correlated with LogMAR BCVA and the extents of ellipsoid zone and external limiting membrane disruption at 12 months, and negatively correlated with central retinal thickness at the time of edema resolution. Therefore, a high area ratio and large number of intraretinal cystoid spaces resulted in a disorganized outer retinal structure at 12 months, a thin and atrophic retina after edema resolution, and a worse visual outcome. The area ratio and number of intraretinal cystoid spaces on initial OCT images were predictors of the visual outcome after IVR therapy in DME irrespective of baseline age and BCVA. The factors were related to retinal neurodegenerative changes in DME and could help in obtaining proper informed consent before treatment.

Optical coherence tomography-based consensus definition for lamellar macular hole

BACKGROUND

A consensus on an optical coherence tomography definition of lamellar macular hole (LMH) and similar conditions is needed.

METHODS

The panel reviewed relevant peer-reviewed literature to reach an accord on LMH definition and to differentiate LMH from other similar conditions.

RESULTS

The panel reached a consensus on the definition of three clinical entities: LMH, epiretinal membrane (ERM) foveoschisis and macular pseudohole (MPH). LMH definition is based on three mandatory criteria and three optional anatomical features. The three mandatory criteria are the presence of irregular foveal contour, the presence of a foveal cavity with undermined edges and the apparent loss of foveal tissue. Optional anatomical features include the presence of epiretinal proliferation, the presence of a central foveal bump and the disruption of the ellipsoid zone. ERM foveoschisis definition is based on two mandatory criteria: the presence of ERM and the presence of schisis at the level of Henle's fibre layer. Three optional anatomical features can also be present: the presence of microcystoid spaces in the inner nuclear layer (INL), an increase of retinal thickness and the presence of retinal wrinkling. MPH definition is based on three mandatory criteria and two optional anatomical features. Mandatory criteria include the presence of a foveal sparing ERM, the presence of a steepened foveal profile and an increased central retinal thickness. Optional anatomical features are the presence of microcystoid spaces in the INL and a normal retinal thickness.

CONCLUSIONS

The use of the proposed definitions may provide uniform language for clinicians and future research.

Spatial distribution of macular pigment estimated by autofluorescence imaging in elderly Japanese individuals

PURPOSE

To determine the spatial distribution types of macular pigment (MP) in elderly Japanese individuals and to consider their origin.

STUDY DESIGN

Observational case series.

METHODS

Local MP optical density (MPOD) at some eccentricities and MP volume were measured using the MPOD module of a MultiColor Spectralis in 96 pseudophakic eyes of 96 participants (age range, 52-86 years; mean age, 72.8 ± 8.3 years). The MP distribution types were determined from the MP spatial profiles. The retinal thickness (RT) at the foveal center, at both 0.5° and 0.9° eccentricities, and the foveal width were measured using optical coherence tomography.

RESULTS

The mean local MPOD at the foveal center was 0.79. Spatial distribution was classified into four types: central peak (24.0%), ring-like (40.6%), intermediate (22.9%), and central dip (12.5%). The ring-like type was the most frequent in these Japanese participants. The central-peak type showed lower MPOD than did the other types in the area outside 0.9°. The ring-like type occurred frequently in eyes with small RT at 0.5° and wider foveal width. A rough contour of the Müller cell cone was found more frequently in the central-dip type than in the other types.

CONCLUSIONS

The present characteristics of the different distribution patterns could be explained by the hypothesis that MP presents mainly in the Müller cell cone within 0.5° and in Müller cells in the outer and inner plexiform layers in the area outside 0.5°. The anatomic characteristics of Müller cells at the fovea and parafovea likely affect the MP distribution.

Analysis of Hyperreflective Dots Within the Central Fovea in Healthy Eyes Using En Face Optical Coherence Tomography

Purpose

The purpose of this retrospective study was to describe and quantify superficial hyperreflective dots within the central fovea and correlate them with age, using en face and cross-sectional B-scan optical coherence tomography (OCT).

Methods

Healthy eyes, evaluated with a spectral domain instrument (primary cohort) at the Stein Eye Institute (UCLA) and with a swept source instrument (secondary cohort) at the Vitreous Retina Macula Consultants of New York, were included in this study. En face OCT images (3 × 3 mm) segmented at the level of the superior vascular plexus were acquired, and hyperreflective dots in the foveal avascular zone were quantified by two different methodologies. The threshold reflectivity methodology quantified these dots on a cropped en face OCT image using ellipsoid zone mean reflectivity as the threshold cutoff. The OCT B-scan methodology consisted of a manual count of elevated hyperreflective signals on B-scans that colocalized with the dots by en face OCT. Primary outcome was to quantify these dots and correlate them with age.

Results

A total of 44 healthy eyes were evaluated in the primary cohort, and 16 healthy eyes were evaluated in the secondary cohort. The hyperreflective dots steadily increased in number, especially in patients older than 50 years of age, with a strongly positive statistical significant correlation, using both quantitative strategies.

Conclusions

Remarkable superficial hyperreflective dots in the central fovea of healthy subjects are novel anatomical findings that may be readily identified with both en face and cross-sectional OCT and steadily increase in number with age. We propose that these dots may represent a normal anatomical landmark, such as Müller cell end feet or inner limiting membrane basal lamina.

Different modes of foveal regeneration after closure of full-thickness macular holes by (re)vitrectomy and autologous platelet concentrate

AIM

To describe using spectral-domain optical coherence tomography the regeneration of the foveal morphology after pars plana (re)vitrectomy surgery and gas tamponade combined with injection of autologous platelet concentrate to treat full-thickness macular holes, and to describe different anatomical outcome.

METHODS

A retrospective case series of 8 eyes of 8 patients was described.

RESULTS

In all cases investigated, the platelet-assisted closure of macular holes was associated with a rapid resolution of cystic cavities in the foveal walls. In two patients, there was a regular regeneration of the foveal morphology after hole closure; the regenerated central fovea had a regular structure with a foveola and photoreceptors. In three other patients, there was an irregular regeneration of the fovea; a foveola was not formed, photoreceptor cells were absent from the foveal center, and the center was composed of Müller and retinal pigment epithelial (RPE) cells. The foveal regeneration after hole closure may proceed with or without a temporary detachment of the foveal center from the RPE, and with or without a direct contact between the central outer nuclear layer (ONL) and the RPE. Contacts between the ONL and RPE were observed only in patients with an irregular foveal regeneration after hole closure.

CONCLUSION

The data show that there are different modes of foveal regeneration after closure of macular holes with (re)vitrectomy and platelet concentrate. It is suggested that the regular regeneration of the foveal morphology proceeds by Müller cell-mediated tissue movements without cell proliferation, whereas the irregular foveal regeneration proceeds in part by proliferation of Müller and RPE cells.

Glia of the human retina

The human retina contains three types of glial cells: microglia and two types of macroglia, astrocytes and Müller cells. Macroglia provide homeostatic and metabolic support to photoreceptors and neurons required for neuronal activity. The fovea, the site of the sharpest vision which is astrocyte- and microglia-free, contains two populations of Müller glia: cells which form the Müller cell cone in the foveola and z-shaped Müller cells of the foveal walls. Both populations are characterized by morphological and functional differences. Müller cells of the foveola do not support the activity of photoreceptors and neurons, but provide the structural stability of the foveal tissue and improve the light transmission through the tissue to the photoreceptors. This article gives overviews of the glia of the human retina and the structure and function of both Müller cell types in the fovea, and describes the contributions of astrocytes and Müller cells to the ontogenetic development of the fovea.

Foveal Abnormality associated with epiretinal Tissue of medium reflectivity and Increased blue-light fundus Autofluorescence Signal (FATIAS)

PURPOSE

To describe a distinct vitreomacular interface disorder (VMID) termed Foveal Abnormality associated with epiretinal Tissue of medium reflectivity and Increased blue-light fundus Autofluorescence Signal (FATIAS).

METHODS

A case series including forty-seven eyes of 47 patients. The included eyes must present an irregular foveal contour on optical coherence tomography (OCT) and a pathologically increased autofluorescent signal at the fovea on blue-light fundus autofluorescence (B-FAF). Main outcome measures were morphologic characteristics of the lesions, logarithm of minimum angle of resolution (logMAR) best-corrected visual acuity (BCVA), and central foveal thickness (CFT).

RESULTS

The following two types of FATIAS were identified: (1) the step type characterized by an asymmetric contour of the foveal pit and by a tissue of medium reflectivity on the foveal surface and (2) the rail type characterized by a shallow foveal pit and a rail of tissue of medium reflectivity on the foveal surface. The outer retinal bands were continuous in all cases. Both types presented with an area of increased B-FAF signal, usually bilobed in the step type and round and centered on the foveal pit in the rail type. LogMAR BCVA was 0.09 ± 0.1 and 0.1 ± 0.1 (P = 0.91), and CFT was 197.8 ± 9.7 and 202.2 ± 13.2 (P = 0.19) in the step and in the rail group, respectively.

CONCLUSIONS

We describe a distinct VMID named FATIAS. Two types of FATIAS may be appreciated with SD-OCT and B-FAF analyses, the step and the rail type. Both are characterized by abnormal foveal contour and autofluorescence signal.

The role of Müller cells in tractional macular disorders: an optical coherence tomography study and physical model of mechanical force transmission

BACKGROUND

To explore the role of foveal and parafoveal Müller cells in the morphology and pathophysiology of tractional macular disorders with a mathematical model of mechanical force transmission.

METHODS

In this retrospective observational study, spectral-domain optical coherence tomography images of tractional lamellar macular holes and patients with myopic foveoschisis were reviewed and analysed with a mathematical model of force transmission. Parafoveal z-shaped Müller cells were modelled as a structure composed of three rigid rods, named R1, R2 and R3. The angle formed between the rods was referred to as θ . R1, R2 and R3 lengths as well as the variation of the angle θ were measured and correlated with best corrected visual acuity (BCVA).

RESULTS

In tractional lamellar macular holes, there was a significant reduction of the angle θ towards the foveal centre (p<0.001). By contrast, there were no significant differences in θ in myopic foveoschisis (p=0.570). R2 segments were more vertical in myopic foveoschisis. There was a significant association between lower θ angles at 200 µm temporal and nasal to the fovea and lower BCVA (p<0.001 and p=0.005, respectively). The stiffness of parafoveal Müller cells was predicted to be function of the angle θ , and it grew very rapidly as the θ decreased.

CONCLUSION

Parafoveal Müller cells in the Henle fibre layer may guarantee structural stability of the parafovea by increasing retinal compliance and resistance to mechanical stress. Small values of the angle θ were related to worse BCVA possibly due to damage to Müller cell processes and photoreceptor's axons.

Immunohistological Study of Monkey Foveal Retina

The fovea centralis, an anatomically concave pit located at the center of the macula, is avascular, hypoxic, and characteristic of stem-cell niches of other tissues. We hypothesized that in the fovea, undifferentiated retinal-stem-cell-like cells may exist, and that neurogenesis may occur. Hence, we performed an immunohistological study using cynomolgus monkey retinas. After preparing frozen tissue sections of the retina including the foveal pit, immunostaining was performed for glial fibrillary acidic protein (GFAP), nestin, vimentin, neuron-specific class III β-tubulin (Tuj-1), arrestin 4, neurofilament, CD117, CD44, Ki67, and cellular retinaldehyde-binding protein (CRALBP), followed by fluorescence and/or confocal microscopy examinations. Immunostaining of the tissue sections enabled clear observation of strongly GFAP-positive cells that corresponded to the inner-half layer of the foveolar Müller cell cone. The surface layer of the foveal slope was partially costained with GFAP and vimentin. Tuj-1-positive cells were observed in the innermost layer of the foveolar retina, which spanned to the surrounding ganglion cell layer. Moreover, colocalization of Tuj-1 and GFAP was observed at the foveal pit. The coexpression of CD117 and CD44 was found in the interphotoreceptor matrix of the fovea. The foveolar cone stained positive for both nestin and arrestin 4, however, the photoreceptor layer outside of the foveola displayed weak staining for nestin. Colocalization of nestin and vimentin was observed in the inner half of the Henle layer, while colocalization of nestin and neurofilament was observed in the outer half, predominantly. Scattered Ki67-positive cells were observed in the cellular processes of the outer plexiform layer and the ganglion cell layer around the foveola. Immunostaining for CRALBP was negative in most parts of the GFAP-positive area. The Müller cell cone was divided into GFAP-strongly positive cells, presumably astrocytes, in the inner layer and nestin-positive/GFAP-weakly positive radial glia-like cells in the outer layer. These findings indicated that groups of such undifferentiated cells in the foveola might be involved in maintaining morphology and regeneration.

Fundus Autofluorescence in Lamellar Macular Holes and Pseudoholes: A Review

Macular pseudoholes (MPHs) and lamellar macular holes (LMHs) have been recently defined according to spectral domain optical coherence tomography (SD-OCT) criteria. A major feature for differentiating an MPH from an LMH remains the loss of foveal tissue. The anatomy of the foveola is peculiar with the macular pigment (MP) embedded in a very thin layer of tissue underlying the internal limiting membrane and mainly constituted of a specialized group of Müller cells and Henle's fibers. Despite the near microscopic resolution (≈5–7 μm) and the capability to visualize the outer retina in detail, SD-OCT may fail to ascertain whether a very small loss of this foveolar tissue has occurred. Blue-fundus autofluorescence (B-FAF) imaging is useful in this respect because even very small loss of MP can be identified, suggesting a corresponding localized loss of the innermost layers of the foveola. A definition of MP loss would help differentiating an LMH from an MPH where B-FAF imaging will be negative.

Morphology and Composition of the Inner Limiting Membrane: Species-Specific Variations and Relevance toward Drug Delivery Research

The inner limiting membrane (ILM) represents the structural boundary between the vitreous and the retina, and is suggested to act as a barrier for a wide range of retinal therapies. While it is widely acknowledged that the morphology of the human ILM exhibits regional variations and undergoes age-related changes, insight into its structure in laboratory animals is very limited. Besides presenting a detailed overview of the morphology and composition of the human ILM, this review specifically reflects on the species-specific differences in ILM structure. With these differences in mind, we furthermore summarize the most relevant reports on the barrier role of the ILM with regard to viral vectors, nanoparticles, anti-VEGF medication and stem cells. Overall, this review aims to deliberate on the impact of species-specific ILM variations on drug delivery research as well as to pinpoint knowledge gaps which future basic research should resolve.

Antecedents of Soft Drusen, the Specific Deposits of Age-Related Macular Degeneration, in the Biology of Human Macula

AMD pathobiology was irreversibly changed by the recent discovery of extracellular cholesterol-containing deposits in the subretinal space, between the photoreceptors and retinal pigment epithelium (RPE), called subretinal drusenoid deposits (SDDs). SDDs strikingly mirror the topography of rod photoreceptors in human macula, raising the question of whether an equivalent process results in a deposition related to foveal cones. Herein we propose that AMD's pathognomonic lesion-soft drusen and basal linear deposit (BLinD, same material, diffusely distributed)-is the leading candidate. Epidemiologic, clinical, and histologic data suggest that these deposits are most abundant in the central macula, under the fovea. Strong evidence presented in a companion article supports the idea that the dominant ultrastructural component is large apolipoprotein B,E-containing lipoproteins, constitutively secreted by RPE. Lipoprotein fatty acids are dominated by linoleate (implicating diet) rather than docosahexaenoate (implicating photoreceptors); we seek within the retina cellular relationships and dietary drivers to explain soft druse topography. The delivery of xanthophyll pigments to highly evolved and numerous Müller cells in the human fovea, through RPE, is one strong candidate, because Müller cells are the main reservoir of these pigments, which replenish from diet. We propose that the evolution of neuroglial relations and xanthophyll delivery that underlie exquisite human foveal vision came with a price, that is, soft drusen and sequela, long after our reproductive years.