The anatomy of the foveola reinvestigated

Aging of the eye: Lessons from cataracts and age-related macular degeneration

Aging is the greatest risk factor for chronic human diseases, including many eye diseases. Geroscience aims to understand the effects of the aging process on these diseases, including the genetic, molecular, and cellular mechanisms that underlie the increased risk of disease over the lifetime. Understanding of the aging eye increases general knowledge of the cellular physiology impacted by aging processes at various biological extremes. Two major diseases, age-related cataract and age-related macular degeneration (AMD) are caused by dysfunction of the lens and retina, respectively. Lens transparency and light refraction are mediated by lens fiber cells lacking nuclei and other organelles, which provides a unique opportunity to study a single aging hallmark, i.e., loss of proteostasis, within an environment of limited metabolism. In AMD, local dysfunction of the photoreceptors/retinal pigmented epithelium/Bruch's membrane/choriocapillaris complex in the macula leads to the loss of photoreceptors and eventually loss of central vision, and is driven by nearly all the hallmarks of aging and shares features with Alzheimer's disease, Parkinson's disease, cardiovascular disease, and diabetes. The aging eye can function as a model for studying basic mechanisms of aging and, vice versa, well-defined hallmarks of aging can be used as tools to understand age-related eye disease.

Blastocyst-like Structures in the Peripheral Retina of Young Adult Beagles

In this immunohistological study on the peripheral retina of 3-year-old beagle dogs, excised retina specimens were immunostained with antibodies against nestin, Oct4, Nanog, Sox2, CDX2, cytokeratin 18 (CK 18), RPE65, and YAP1, as well as hematoxylin and DAPI, two nuclear stains. Our findings revealed solitary cysts of various sizes in the inner retina. Intriguingly, a mass of small round cells with scant cytoplasms was observed in the cavity of small cysts, while many disorganized cells partially occupied the cavity of the large cysts. The small cysts were strongly positive for nestin, Oct4, Nanog, Sox2, CDX2, CK18, and YAP1. RPE65-positive cells were exclusively observed in the tissue surrounding the cysts. Since RPE65 is a specific marker of retinal pigment epithelial (RPE) cells, the surrounding cells of the peripheral cysts were presumably derived from RPE cells that migrated intraretinally. In the small cysts, intense positive staining for nestin, a marker of retinal stem cells, seemed to indicate that they were derived from retinal stem cells. The morphology and positive staining for markers of blastocyst and RPE cells indicated that the small cysts may have formed structures resembling the blastocyst, possibly caused by the interaction between retinal stem cells and migrated RPE cells.

Peak Cone Density Predicted from Outer Segment Length Measured on Optical Coherence Tomography

PURPOSE

To compare peak cone density predicted from outer segment length measured on optical coherence tomography with direct measures of peak cone density from adaptive optics scanning light ophthalmoscopy.

METHODS

Data from 42 healthy participants with direct peak cone density measures and optical coherence tomography line scans available were used in this study. Longitudinal reflectivity profiles were analyzed using two methods of identifying the boundaries of the ellipsoid and interdigitation zones to estimate maximum outer segment length: peak-to-peak and the slope method. These maximum outer segment length values were then used to predict peak cone density using a previously described geometrical model. A comparison between predicted and direct peak cone density measures was then performed.

RESULTS

The mean bias between observers for estimating maximum outer segment length across methods was less than 2 µm. Cone density predicted from the peak-to-peak method against direct cone density measures showed a mean bias of 6,812 cones/mm2 with 50% of participants displaying a 10% difference or less between predicted and direct cone density values. Cone density derived from the slope method showed a mean bias of -17,929 cones/mm2 relative to direct cone density measures, with only 41% of participants demonstrating less than a 10% difference between direct and predicted cone density values.

CONCLUSION

Predicted foveal cone density derived from peak-to-peak outer segment length measurements using commercial optical coherence tomography show modest agreement with direct measures of peak cone density from adaptive optics scanning light ophthalmoscopy. The methods used here are imperfect predictors of cone density, however, further exploration of this relationship could reveal a clinically relevant marker of cone structure.

TRPP2 is located in the primary cilia of human non-pigmented ciliary epithelial cells

PURPOSE

Mechanosensitive channels (MSCs) and primary cilium possess a possible relevance for the sensation of intraocular pressure (IOP). However, there is only limited data on their expression and localization in the ciliary body epithelium (CBE). The purpose of this study was to characterize the expression and localization of TRPP2 in a human non-pigmented ciliary epithelial cell (HNPCE) line.

METHODS

The expression of the TRPP2 was studied by quantitative (q)RT-PCR and in situ hybridization in rat and human tissue. Protein expression and distribution were studied by western blot analysis, immunohistochemistry, and immunoelectron microscopy. Cellular location of TRPP2 was determined in rat and human CBE by immunofluorescence and immunoblot analysis. Electron microscopy studies were conducted to evaluate where and with substructure TRPP2 is localized in the HNPCE cell line.

RESULTS

The expression of TRPP2 in rat and human non-pigmented ciliary epithelium was detected. TRPP2 was mainly located in nuclei, but also showed a punctate distribution pattern in the cytoplasm of HNPCE of the tissue and the cell line. In HNPCE cell culture, primary cilia did exhibit different length following serum starvation and hydrostatic pressure. TRPP2 was found to be colocalized with these cilia in HNPCE cells.

CONCLUSION

The expression of TRPP2 and the primary cilium in the CB may indicate a possible role, such as the sensing of hydrostatic pressure, for the regulation of IOP. Functional studies via patch clamp or pharmacological intervention have yet to clarify the relevance for the physiological situation or aqueous humor regulation.

Pupillometry to show stress release during equine sports massage therapy

Anecdotal reports state that wellness treatments for horses, such as massage therapy, relaxes the treated animal. Massage therapists and horse owners typically report an "improvement" without verifying or quantifying the treatment results. This paper shows that the effect of wellness treatment and stress release can be measured with pupillometry. One of the horse's pupils was photographed at the beginning and end of the treatment to determine the changes in the balance between the sympathetic and parasympathetic system activities. The owners assigned horses to two experimental groups: animals receiving a massage (N = 18) and horses standing with a person next to the horse for the time of a massage in the stable lane (N = 10). Six animals in the experimental group were excluded from the analysis because the pupils could not be traced. We opened the images of the pupil with Fiji (ImageJ) and used the elliptical selection tool to measure the pupils' and iris' areas. The ratio between the pupils' aperture and the iris' area was a normalized measure for pupil size. At the end of the experiment, we compared the normalized size of the pupils with a two-tailed paired t-test within groups and a two-tailed t-test between groups. For the experimental group, it was before and after the treatment, and for the control group, before and after the horse was placed in the stable lane. Comparisons between the experimental and control groups were made at the procedure's beginning and end. The treatment significantly decreased the normalized pupil area in the experimental group, on average, by a factor of 0.78 ± 0.15 (P = 0.042). For the horses in the control group, the pupil size increased, on average, by a factor of 1.14 ± 018. Changes were statistically not significant (P = 0.19). The initial pupil size of the horses in the experimental group was 1.88 times larger than that in the control group. After the treatment, the difference was reduced to a factor of 1.25. At the beginning of the experiment, the horses in the experimental group had, on average, larger pupil sizes than the horses in the control group, indicating that the horses in the experimental group were more stressed before the treatment than the control animals. The observed changes in pupil size in the experimental group likely resulted from enhanced parasympathetic and diminished sympathetic activity resulting from the treatment. Observed changes in pupil size agree with the anecdotal horse owner reports and the therapist's treatment notes.

Macular Anatomy Differs in Dyslexic Subjects

The macula, as the central part of the retina, plays an important role in the reading process. However, its morphology has not been previously studied in the context of dyslexia. In this research, we compared the thickness of the fovea, parafovea and perifovea between dyslexic subjects and normal controls, in 11 retinal segmentations obtained by optical coherence tomography (OCT). With this aim, we considered the nine sectors of the Early Treatment Diabetic Retinopathy Study (ETDRS) grid and also summarized data from sectors into inner ring subfield (parafovea) and outer ring subfield (perifovea). The thickness in all the four parafoveal sectors was significantly thicker in the complete retina, inner retina and middle retina of both eyes in the dyslexic group, as well as other macular sectors (fovea and perifovea) in the inner nuclear layer (INL), inner plexiform layer (IPL), IPL + INL and outer plexiform layer + outer nuclear layer (OPL + ONL). Additionally, the inner ring subfield (parafovea), but not the outer ring subfield (perifovea), was thicker in the complete retina, inner retina, middle retina (INL + OPL + ONL), OPL + ONL, IPL + INL and INL in the dyslexic group for both eyes. In contrast, no differences were found between the groups in any of the sectors or subfields of the outer retina, retinal nerve fiber layer, ganglion cell layer or ganglion cell complex in any eye. Thus, we conclude from this exploratory research that the macular morphology differs between dyslexic and normal control subjects, as measured by OCT, especially in the parafovea at middle retinal segmentations.

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.

Functional Optical Coherence Tomography for Intrinsic Signal Optoretinography: Recent Developments and Deployment Challenges

Intrinsic optical signal (IOS) imaging of the retina, also termed as optoretinogram or optoretinography (ORG), promises a non-invasive method for the objective assessment of retinal function. By providing the unparalleled capability to differentiate individual retinal layers, functional optical coherence tomography (OCT) has been actively investigated for intrinsic signal ORG measurements. However, clinical deployment of functional OCT for quantitative ORG is still challenging due to the lack of a standardized imaging protocol and the complication of IOS sources and mechanisms. This article aims to summarize recent developments of functional OCT for ORG measurement, OCT intensity- and phase-based IOS processing. Technical challenges and perspectives of quantitative IOS analysis and ORG interpretations are discussed.

Macrophage-Like Cell Density Is Increased in Proliferative Diabetic Retinopathy Characterized by Optical Coherence Tomography Angiography

Purpose

To quantitatively characterize macrophage-like cells (MLCs) at the vitreoretinal interface in different severity stages of diabetic retinopathy (DR) using optical coherence tomography angiography (OCTA).

Methods

The study included 72 eyes of 72 subjects: 18 healthy controls, 22 diabetes mellitus (DM) without DR, 17 nonproliferative DR (NPDR), and 15 proliferative DR (PDR). We obtained repeated (average, 6.5; range, 3-10) macular OCTA scans for each eye. We registered and averaged the 3-µm OCT slab above the vitreoretinal interface to visualize MLCs. Using a semiautomated method, we binarized and quantified MLCs and compared MLC densities among groups. We also evaluated MLC distribution relative to underlying superficial capillary plexus vasculature and quantified MLCs overlying blood vessels within the perivascular 30-µm watershed region and within ischemic zones (defined as >30 µm from the nearest vessel).

Results

MLC density was 2.8- to 3.8-fold higher in PDR compared with all other groups (P < 0.05 for all). MLC density in PDR was most increased in perivascular areas (3.3- to 4.2-fold; P < 0.05 vs. all) and on blood vessels (3.0- to 4.0-fold; P < 0.05 vs. all), and elevated to a lesser extent in ischemic areas (2.3- to 3.4-fold; P < 0.05 vs. all). MLCs were more likely to localize on blood vessels in DM without DR, NPDR, and PDR (P < 0.05 for all), but not healthy eyes.

Conclusions

MLC density was significantly increased in PDR. MLCs clustered on blood vessels in diabetic but not in healthy eyes. Further studies are needed to confirm the origin, identity, and function of MLCs during DR.

Spontaneous fundus lesions in elderly monkeys: An ideal model for age-related macular degeneration and high myopia clinical research

AIMS

Age-related macular degeneration (AMD) and high myopia are frequent causes of progressive visual impairment, so it is critical to identify animal models with resembling human retinal physiology, AMD and high myopia pathological features for therapeutic studies.

MAIN METHODS

We screened elderly cynomolgus monkeys for fundus lesions by slit-lamp biomicroscope combined with fundus pre-set lens and further examined positive cases by color fundus photography (CFP), optical coherence tomography (OCT), fundus fluorescein angiography (FFA), streak retinoscopy, and A-scan ultrasonography.

KEY FINDINGS

Among the 156 animals examined, 10 males and 5 females (30 eyes) exhibited fundus abnormalities (9.6% prevalence). Multi-modal imaging revealed drusen in 20 eyes of 11 animals (prevalence rate of 7.1%), tessellated fundus in 22 eyes of 11 animals, and myopia choroidal neovascularization (CNV) in 4 eyes of 3 animals.

SIGNIFICANCE

Aged cynomolgus monkeys exhibit spontaneous fundus lesions resembling human AMD and high myopia, which could be an ideal model for clinical research.

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.

Age-Related Macular Degeneration: Role of Oxidative Stress and Blood Vessels

Age-related macular degeneration (AMD) is a common irreversible ocular disease characterized by vision impairment among older people. Many risk factors are related to AMD and interact with each other in its pathogenesis. Notably, oxidative stress and choroidal vascular dysfunction were suggested to be critically involved in AMD pathogenesis. In this review, we give an overview on the factors contributing to the pathophysiology of this multifactorial disease and discuss the role of reactive oxygen species and vascular function in more detail. Moreover, we give an overview on therapeutic strategies for patients suffering from AMD.

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.

Evolution and visual outcomes of outer foveolar lucency after surgery for large idiopathic macular hole

PURPOSE

To explore the evolution of outer foveolar lucency (OFL) after vitrectomy and the correlation between OFL and visual acuity (VA) outcome in eyes with large idiopathic macular hole (IMH).

METHODS

In this retrospective study, 244 eyes of 233 subjects with large IMH (diameter > 400 μm), who underwent vitrectomy, were included. Preoperative clinical data, postoperative optical coherence tomography (OCT) images, and VA at 1-, 4-, and 10-month visits were documented. The prevalence, incidence, and width of OFL and their correlation with postoperative VA were analyzed.

RESULTS

The prevalence of OFL was 10.4% (24/231) at 1 month and significantly increased to 30.4% (55/181) at 4 months (P < 0.001) and 34.2% (25/73) at 10 months (P < 0.001). The incidence was 26.1% (40/153) and 22.0% (9/41) at 4 and 10 months, respectively. OFL appeared at 1 month while disappeared at 4 or 10 months in 8 eyes (50.0%). The presence of OFL at 1 month was negatively associated with IMH diameter (Nagelkerke R² = 0.06; P = 0.02). Eyes with OFL at 4 months had better VA at their 4-month visit than eyes without OFL (P = 0.02). Eyes with early-developed OFLs had better VA at 10 months than those with later-developed ones (P = 0.02). Width of OFL was not associated with postoperative VA at any point.

CONCLUSIONS

OFL is not rare in eyes with large IMH after surgery. It can occur gradually and remain during the 10-month follow-up. The presence of OFL appears to have no negative impact on the postoperative VA and it may represent the remodeling of foveal photoreceptors.

Reduced photoreceptor outer segment layer thickness in mild commotio retinae without ellipsoid zone disruption

PURPOSE

To quantitatively investigate the reflectivity and structure of the outer retinal layers on spectral-domain optical coherence tomography (SD-OCT) in commotio retinae.

METHODS

Nineteen patients with acute macular commotio retinae and 19 age-matched normal controls were examined using SD-OCT. Longitudinal reflectance profiles (LRP) were obtained using Image J. The reflectivity of outer retinal layers was measured at the fovea, 1 mm nasal to fovea and 1 mm temporal to fovea. The reflectivity ratios of outer retinal layers divided by the outer nuclear layer (ONL) were calculated for normalization. Photoreceptor outer segment layer thickness was also measured. The results were compared between the patients and controls.

RESULTS

The reflectivity ratio of ellipsoid zone/ONL and outer segment/ONL was higher in commotio retinae than in controls only at fovea (12.66 ± 4.73 vs 9.67 ± 3.34, p = 0.041; 7.70 ± 2.20 vs 3.73 ± 1.63, p < 0.001, respectively) but not at 1 mm nasal or temporal to the fovea. Photoreceptor outer segment layer thickness was significantly shorter in commotio retinae compared to controls at all three locations (19.64 ± 3.05 vs 25.16 ± 3.53, 16.95 ± 4.02 vs 20.00 ± 3.00, and 15.42 ± 3.22 vs 20.05 ± 2.48, respectively, all p < 0.05).

CONCLUSIONS

Quantitative measurement of SD-OCT images revealed that shortening of photoreceptor outer segment is an additional, and potentially better, biomarker for commotio retinae on top of increased reflectivity.

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.

Multimodal imaging including optical coherence tomography angiography in patients with type B Niemann-Pick disease

PURPOSE

To evaluate accumulation patterns of deposits in retinal layers of type B Niemann-Pick patients by multimodal imaging.

METHODS

Seven patients with type B Niemann-Pick disease were included in this study. All participants underwent a complete ophthalmologic evaluation, high-resolution digital colour imaging, spectral-domain optical coherence tomography, blue light fundus autofluorescence and optical coherence tomography angiography (OCTA).

RESULTS

We demonstrated different accumulation patterns in the retinal ganglion cell layer, the retinal nerve fibre layer and the subfoveolar region by multimodal imaging. Local retinal capillary nonflow areas in the superficial plexus, increased vascular tortuosity and deformed foveal avascular areas were shown in OCTA scans.

CONCLUSION

Multimodal imaging including OCTA is a useful technique for the identification of different types of accumulation patterns, diagnosis and follow-up of type B Niemann-Pick patients.

Data showing the shapes of cones and Müller cells within the fovea of monkeys reconstructed from serial sections and focused ion beam analysis

The data presented in this article are related to the research paper entitled “The anatomy of the foveola reinvestigated” (Tschulakow et al., 2018) [1]. Here we show the original aligned serial sections through the foveal centre of monkeys at different planes of section and 3 D models of central foveal cells.