Adaptation of the central retina for high acuity vision: cones, the fovea and the avascular zone

Delayed macular development in preterm infants with spontaneously regressed retinopathy of prematurity

PURPOSE

To evaluate the macular development in preterm infants with spontaneously regressed retinopathy of prematurity (ROP) utilizing handheld spectral domain optical coherence tomography (SD-OCT) during the early postnatal period.

DESIGN

A cross-sectional observational study.

METHODS

Using handheld SD-OCT, OCT images were acquired in non-sedated infants ages about 37 weeks(w) post-menstrual-age (PMA = gestational age in weeks + chronological age). Central foveal thickness (CFT), mean parafoveal thickness (PT, mean of the temporal and nasal-lateral retinal thickness 1000 μm from the foveal center), the thickness of inner retina layers (IRL) and outer retina layers (ORL) of the foveal center and parafoveal, the depth of the macular fovea (FD), and the angle of the macular fovea (FA) were measured and analyzed.

RESULTS

In contrast to the infants without ROP (group 1), OCT images of the infants with spontaneously regressed ROP (group 2) were more immature. The FD of Group 2 was shallower than Group 1 (P < 0.05); CFT and the foveal center IRL (FIRL) of Group 2 were thicker than Group 1 (P < 0.05); conversely, PT and the mean parafoveal IRL (PIRL) of Group 2 were thinner than Group 1 (P < 0.05); FA of Group 2 was bigger than Group 1 (P < 0.05); however, there was no significant difference in the foveal center ORL (FORL) and the mean parafoveal ORL (PORL) between Groups 1 and 2 (P > 0.05). Furthermore, in preterm infants, ROP was moderately correlated with FD, CFT, PT, FIRL, and PIRL (P < 0.05).

CONCLUSIONS

The spontaneously regressed ROP resulted in immature macular development in the early postnatal period. The inner retinal layers mainly contribute to this but not the outer retinal layers, indicating that the macular fovea's inner and outer retina layers developed asynchronously. ROP is an influential factor in macular development and maturation. This may be associated with the higher probability of visual impairment in children with a history of spontaneous regression of ROP at a prior time.

Mapping simulated visual field defects with movie-viewing pupil perimetry

PURPOSE

Assessing the quality of the visual field is important for the diagnosis of ophthalmic and neurological diseases and, consequently, for rehabilitation. Visual field defects (VFDs) are typically assessed using standard automated perimetry (SAP). However, SAP requires participants to understand instructions, maintain fixation and sustained attention, and provide overt responses. These aspects make SAP less suitable for very young or cognitively impaired populations. Here we investigate the feasibility of a new and less demanding form of perimetry. This method assesses visual sensitivity based on pupil responses while performing the perhaps simplest task imaginable: watching movies.

METHOD

We analyzed an existing dataset, with healthy participants (n = 70) freely watching movies with or without gaze-contingent simulated VFDs, either hemianopia (left- or right-sided) or glaucoma (large nasal arc, small nasal arc, and tunnel vision). Meanwhile, their gaze and pupil size were recorded. Using a recently published toolbox (Open-DPSM), we modeled the relative contribution of visual events to the pupil responses to indicate relative visual sensitivity across the visual field and to dissociate between conditions with and without simulated VFDs.

RESULT

Conditions with and without simulated VFDs could be dissociated, with an AUC ranging from 0.85 to 0.97, depending on the specific simulated VFD condition. In addition, the dissociation was better when including more movies in the modeling but the model with as few movies as 10 movies was sufficient for a good classification (AUC ranging from 0.84 to 0.96).

CONCLUSION

Movie-viewing pupil perimetry is promising in providing complementary information for the diagnosis of VFDs, especially for those who are unable to perform conventional perimetry.

Retinal ganglion cell circuits and glial interactions in humans and mice

Retinal ganglion cells (RGCs) are the brain's gateway for vision, and their degeneration underlies several blinding diseases. RGCs interact with other neuronal cell types, microglia, and astrocytes in the retina and in the brain. Much knowledge has been gained about RGCs and glia from mice and other model organisms, often with the assumption that certain aspects of their biology may be conserved in humans. However, RGCs vary considerably between species, which could affect how they interact with their neuronal and glial partners. This review details which RGC and glial features are conserved between mice, humans, and primates, and which differ. We also discuss experimental approaches for studying human and primate RGCs. These strategies will help to bridge the gap between rodent and human RGC studies and increase study translatability to guide future therapeutic strategies.

The macular microvascular changes in children with a history of retinopathy of prematurity treated with intravitreal Bevacizumab injection using optical coherence tomography angiography: a retrospective cohort

OBJECTIVE

Our study aims to evaluate and compare the macular microvascular condition of the intravitreal Bevacizumab (IVB)-treated retinopathy of prematurity (ROP) cases to the preterm cases without ROP and spontaneously regressed ROPs.

METHODS

It is a retrospective cohort of 50 premature neonates visited from 2016 to 2017 for ROP screening in Nikookari Eye Hospital and recalled for re-evaluation in 2022. These patients were classified into three groups based on their medical documents: 1. Preterm cases without ROP (PT), 2. Spontaneously regressed ROPs (SR), and 3. IVB-treated ROPs (IVB). All the included cases underwent a thorough ophthalmic exam, cyclo-refraction, Best-corrected visual acuity (BCVA) assessment, and macular optical coherence tomography angiography (OCTA). The foveal thickness, foveal avascular zone (FAZ) area, foveal, parafoveal, and perifoveal vascular density (VD) were evaluated as the quantitative variables.

RESULTS

Twenty-five male and 25 female cases with a median age of 5.0 entered the study. Twenty-six eyes were evaluated in the PT group, 50 in the SR group, and 24 in the IVB group. The SR group consisted of 25 zone-2 and 25 zone-3 ROPs. In comparison, the IVB group consisted of 9 zone-1 and 15 zone-2 ROPs (p: < 001). Also, zone-2 cases were more advanced in the IVB group. The IVB-treated eyes demonstrated a significantly higher foveal superficial capillary plexus (SCP) VD than the others (28.5% vs. 23.1 and 22.9, respectively, in PT and SR, p:0.008). However, the parafoveal deep capillary plexus (DCP) VD was lower than the PT cases (48.5% vs. 53.4, p:0.034). The FAZ area was also smaller than the PT cases (0.113 vs.0.219 mm2, p:0.032). The FAZ area was significantly positively correlated with the foveal SCP and DCP VD and negatively correlated with parafoveal DCP VD (CC: -0.770, -0.719, 0.377, respectively, p: < 0.001).

CONCLUSION

In the long term, although the IVB-treated ROP cases experience an excellent visual outcome comparable to those without ROP, they may show some macular microvascular changes. These changes might be related to the effect of IVB or the nature of more advanced stages of ROP.

Foveal thickness and vascular variables in adolescents born moderate-to-late preterm

PURPOSE

It is well established that children born very preterm are at increased risk for ocular abnormalities including altered foveal morphology. However, little is known about how children born moderate-to-late preterm (MLP), gestational age 32 + 0-36 + 6 weeks, are affected later in life. This study investigates foveal avascular zone (FAZ) area, vascular density (VD), central foveal thickness (CFT) and ganglion cell layer thickness (GCL++) of adolescents born MLP without history of retinopathy of prematurity and compare the results with full-term controls.

METHODS

In a prospective population-based cohort study, 50 adolescents (26 girls; mean age 16.5 years) born MLP were examined with optical coherence tomography (OCT) and OCT angiography (OCT-A). FAZ and VD were obtained from OCT-A scans and adjusted for ocular magnification. CFT and GCL++ were obtained from the OCT scans. The results from the MLP individuals were compared with the results from 49 healthy full-term controls (29 girls; mean age 16.7 years).

RESULTS

The results showed statistically significant differences in FAZ area (0.22 vs 0.28 mm2; p = 0.0032) and CFT (198.1 vs 187.1 μm; p = 0.0010) between the MLP group and controls. Strong correlations between FAZ area and CFT (r = -0.773, p < 0.0001) and GCL++ (r = -0.924, p < 0.0001) were found in the MLP group. There were no differences in VD.

CONCLUSIONS

Our results show that adolescents born MLP have a smaller FAZ area and an increased CFT compared with full-term controls. These results indicate that adolescents born MLP have similar parafoveal changes as children born extreme or very preterm.

A circuit motif for color in the human foveal retina

The neural pathways that start human color vision begin in the complex synaptic network of the foveal retina where signals originating in long (L), middle (M), and short (S) wavelength-sensitive cone photoreceptor types are compared through antagonistic interactions, referred to as opponency. In nonhuman primates, two cone opponent pathways are well established: an L vs. M cone circuit linked to the midget ganglion cell type, often called the red-green pathway, and an S vs. L + M cone circuit linked to the small bistratified ganglion cell type, often called the blue-yellow pathway. These pathways have been taken to correspond in human vision to cardinal directions in a trichromatic color space, providing the parallel inputs to higher-level color processing. Yet linking cone opponency in the nonhuman primate retina to color mechanisms in human vision has proven particularly difficult. Here, we apply connectomic reconstruction to the human foveal retina to trace parallel excitatory synaptic outputs from the S-ON (or "blue-cone") bipolar cell to the small bistratified cell and two additional ganglion cell types: a large bistratified ganglion cell and a subpopulation of ON-midget ganglion cells, whose synaptic connections suggest a significant and unique role in color vision. These two ganglion cell types are postsynaptic to both S-ON and L vs. M opponent midget bipolar cells and thus define excitatory pathways in the foveal retina that merge the cardinal red-green and blue-yellow circuits, with the potential for trichromatic cone opponency at the first stage of human vision.

Applications of Adaptive Optics Imaging for Studying Conditions Affecting the Fovea

The fovea is a highly specialized region of the central retina, defined by an absence of inner retinal layers and the accompanying vasculature, an increased density of cone photoreceptors, a near absence of rod photoreceptors, and unique private-line photoreceptor to midget ganglion cell circuitry. These anatomical specializations support high-acuity vision in humans. While direct study of foveal shape and size is routinely performed using optical coherence tomography, examination of the other anatomical specializations of the fovea has only recently become possible using an array of adaptive optics (AO)-based imaging tools. These devices correct for the eye's monochromatic aberrations and permit cellular-resolution imaging of the living retina. In this article, we review the application of AO-based imaging techniques to conditions affecting the fovea, with an emphasis on how imaging has advanced our understanding of pathophysiology.

Single cell dual-omic atlas of the human developing retina

The development of the retina is under tight temporal and spatial control. To gain insights into the molecular basis of this process, we generate a single-nuclei dual-omic atlas of the human developing retina with approximately 220,000 nuclei from 14 human embryos and fetuses aged between 8 and 23-weeks post-conception with matched macular and peripheral tissues. This atlas captures all major cell classes in the retina, along with a large proportion of progenitors and cell-type-specific precursors. Cell trajectory analysis reveals a transition from continuous progression in early progenitors to a hierarchical development during the later stages of cell type specification. Both known and unrecorded candidate transcription factors, along with gene regulatory networks that drive the transitions of various cell fates, are identified. Comparisons between the macular and peripheral retinae indicate a largely consistent yet distinct developmental pattern. This atlas offers unparalleled resolution into the transcriptional and chromatin accessibility landscapes during development, providing an invaluable resource for deeper insights into retinal development and associated diseases.

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.

Relationship between long-term visual function and the ratio of foveal avascular zone area in eyes with macular hole and healthy fellow eyes

PURPOSE

This study is to investigate the relationship between long-term changes in the foveal avascular zone (FAZ) and visual function of eyes with macular hole (MH) and compare the relationship between the FAZ of MH eyes and fellow eyes.

METHODS

This study included 31 patients with unilateral MH who underwent vitrectomy and their fellow eyes. Best-corrected visual acuity (BCVA) and metamorphopsia were measured preoperatively and at 1, 3, 6, and 12 months postoperatively. We evaluated retinal parameters using optical coherence tomography (OCT) and the superficial FAZ using OCT angiography. The FAZ ratio was defined as follows: (preoperative FAZ area of the MH eye)/(FAZ area of the fellow eye).

RESULTS

The preoperative FAZ area of MH eyes was 0.42 ± 0.08 mm2, which decreased to 0.24 ± 0.07 mm2 1 month postoperatively (p < 0.001) and slightly increased to 0.25 ± 0.06 mm2 12 months postoperatively (p = 1.000). The FAZ area did not differ significantly from that of fellow eyes (0.39 ± 0.06 mm2, p = 0.281). The FAZ area of MH eyes was not associated with visual function at any time point. The FAZ ratio showed a correlation with the preoperative, 6-month, and 12-month BCVA (r = 0.604, p < 0.001; r = 0.510, p = 0.003; and r = 0.475, p = 0.007, respectively).

CONCLUSIONS

A larger FAZ in the MH eye than that in the fellow eye is associated with poorer long-term visual acuity. The preoperative comparison of the FAZ of the MH eye with that of the fellow eye may be a biomarker for predicting long-term visual acuity.

Spatially resolved imaging of human macular capillaries using adaptive optics-enhanced optical coherence tomography angiography

Documenting the organization of the retinal capillaries is of importance to understand the visual consequences of vascular diseases which may differentially affect the microvascular layers. Here we detailed the spatial organization of the macular capillaries in ten healthy human subjects using a prototypic adaptive optics-enhanced optical coherence tomography angiography (AO-OCTA) system. Within the central 6° × 6°, the radial peripapillary capillaries and the superficial, intermediate and deep vascular plexuses (SVP, IVP and DVP, respectively) were consistently resolved. In 8 out of the 10 eyes, the capillary segments composing the perifoveal arcade (PFA) were perfused only by the SVP, while drainage of the PFA showed more variability, comprising a case in which the PFA was drained by the DVP. Around the center, a distinct central avascular zone could be documented for each layer in 7 of the 10 cases; in three eyes, the IVP and SVP merged tangentially around the center. In all eyes, the foveal avascular zone was larger in the DVP than in the SVP and IVP. In one eye with incomplete separation of the inner foveal layers, there was continuity of both the SVP and the IVP; a central avascular zone was only present in the DVP. The diversity of perfusion and drainage patterns supported a connectivity scheme combining parallel and serial organizations, the latter being the most commonly observed in perifoveal vessels. Our results thus help to further characterize the diversity of organization patterns of the macular capillaries and to robustly analyze the IVP, which will help to characterize early stages of microvascular diseases.

Multimodal phenotyping of foveal hypoplasia in albinism and albino-like conditions: a pediatric case series with adaptive optics insights

Aim of the present study is to evaluate the relationship between genetic and phenotypic data in a series of patients affected by grade I and II of foveal hypoplasia with stable fixation and good visual acuity using multimodal imaging techniques. All patients underwent complete clinical and instrumental assessment including structural Optical Coherence Tomography (OCT), OCT Angiography and Adaptive Optics (AO) imaging. Central macular thickness (CMT), inner nuclear layer (INL), vessel density in superficial capillary plexus were the main variables evaluated with OCT technology. Cone density, cone spacing, cone regularity, cone dispersion and angular density were the parameters evaluated with AO. Genetic evaluation and trio exome sequencing were performed in all affected individuals. Eight patients (3 males and 5 females) with a mean age of 12.62 years (range 8-18) were enrolled. The mean best corrected visual acuity (BCVA) was 0.18 ± 0.13 logMAR, mean CMT was 291.9 ± 16.6 µm and INL was 26.2 ± 4.6 µm. The absence of a foveal avascular zone (FAZ) was documented by examination of OCT-A in seven patients in the superficial capillary plexus. However, there was a partial FAZ in the deep plexus in patients P5 and P8. Of note, all the patients presented with major retinal vessels clearly crossing the foveal center. All individuals exhibited a grade I or II of foveal hypoplasia. In 5 patients molecular analyses showed an extremely mild form of albinism caused by compound heterozygosity of a TYR pathogenic variant and the hypomorphic p.[Ser192Tyr;Arg402Gln] haplotype. One patient had Waardenburg syndrome type 2A caused by a de novo variant in MITF. Two patients had inconclusive molecular analyses. All the patients displayed abnormalities on OCT-A. Photoreceptor count did not differ from normal subjects according to the current literature, but qualitative analysis of AO imaging showed distinctive features likely related to an abnormal pigment distribution in this subset of individuals. In patients with foveal hypoplasia, genetic and multimodal imaging data, including AO findings, can help understand the physiopathology of the foveal hypoplasia phenotype. This study confirms that cone density and visual function can both be preserved despite the absence of a pit.

Characterization of the development of the high-acuity area of the chick retina

The fovea is a small region within the central retina that is responsible for our high acuity daylight vision. Chickens also have a high acuity area (HAA), and are one of the few species that enables studies of the mechanisms of HAA development, due to accessible embryonic tissue and methods to readily perturb gene expression. To enable such studies, we characterized the development of the chick HAA using single molecule fluorescent in situ hybridization (smFISH), along with more classical methods. We found that Fgf8 provides a molecular marker for the HAA throughout development and into adult stages, allowing studies of the cellular composition of this area over time. The radial dimension of the ganglion cell layer (GCL) was seen to be the greatest at the HAA throughout development, beginning during the period of neurogenesis, suggesting that genesis, rather than cell death, creates a higher level of retinal ganglion cells (RGCs) in this area. In contrast, the HAA acquired its characteristic high density of cone photoreceptors post-hatching, which is well after the period of neurogenesis. We also confirmed that rod photoreceptors are not present in the HAA. Analyses of cell death in the developing photoreceptor layer, where rods would reside, did not show apoptotic cells, suggesting that lack of genesis, rather than death, created the "rod-free zone" (RFZ). Quantification of each cone photoreceptor subtype showed an ordered mosaic of most cone subtypes. The changes in cellular densities and cell subtypes between the developing and mature HAA provide some answers to the overarching strategy used by the retina to create this area and provide a framework for future studies of the mechanisms underlying its formation.

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.

Intensity-based optoretinography reveals sub-clinical deficits in cone function in retinitis pigmentosa

Introduction

Clinical tools have been widely used in the diagnosis, description, and monitoring the progression of retinitis pigmentosa (RP); however, many of these methods have inherently low sensitivity and specificity, and significant photoreceptor disruption can occur before RP progression has clinically manifest. Adaptive optics scanning light ophthalmoscopy (AOSLO) has shown promise as a powerful tool for assessing photoreceptor disruption both structurally and functionally due to its increased resolution.

Methods

Here we assess photoreceptor structure and function at the cellular level through AOSLO by acquiring intensity based optoretinography (iORG) in 15 individuals with no reported retinal pathology and 7 individuals with a prior clinical diagnosis of RP. Photoreceptor structure was quantified by calculating cone nearest neighbor distance (NND) across different retinal eccentricities from the AOSLO images. Cone outer segment length was measured across different retinal eccentricities using optical coherence tomography (OCT) derived longitudinal reflectivity profiles (LRPs). Finally, iORG measures of photoreceptor function were compared to retinal sensitivity as measured using the macular integrity assessment (MAIA) microperimeter.

Results

Broadly, participants with RP exhibited increasing cone nearest neighbor distances and decreasing cone outer segment length as a function of retinal eccentricity, consistent with prior reports for both controls and individuals with RP. Nearly all individuals with RP had reduced iORG amplitudes for all retinal eccentricities when compared to the control cohort, and the reduction was greater in eccentricities further from the fovea. Comparing iORG amplitudes to MAIA retinal sensitivity, we found that the iORG was more sensitive to early changes in photoreceptor function whereas MAIA was more sensitive to later stages of disease.

Discussion

This highlights the utility of iORG as a method to detect sub-clinical deficits in cone function in all stages of disease progression and supports the future use of iORG for identifying cells that are candidates for cellular based therapies.

Evolutionary and developmental specialization of foveal cell types in the marmoset

In primates, high-acuity vision is mediated by the fovea, a small specialized central region of the retina. The fovea, unique to the anthropoid lineage among mammals, undergoes notable neuronal morphological changes during postnatal maturation. However, the extent of cellular similarity across anthropoid foveas and the molecular underpinnings of foveal maturation remain unclear. Here, we used high-throughput single-cell RNA sequencing to profile retinal cells of the common marmoset (Callithrix jacchus), an early divergent in anthropoid evolution from humans, apes, and macaques. We generated atlases of the marmoset fovea and peripheral retina for both neonates and adults. Our comparative analysis revealed that marmosets share almost all their foveal types with both humans and macaques, highlighting a conserved cellular structure among primate foveas. Furthermore, by tracing the developmental trajectory of cell types in the foveal and peripheral retina, we found distinct maturation paths for each. In-depth analysis of gene expression differences demonstrated that cone photoreceptors and Müller glia (MG), among others, show the greatest molecular divergence between these two regions. Utilizing single-cell ATAC-seq and gene-regulatory network inference, we uncovered distinct transcriptional regulations differentiating foveal cones from their peripheral counterparts. Further analysis of predicted ligand-receptor interactions suggested a potential role for MG in supporting the maturation of foveal cones. Together, these results provide valuable insights into foveal development, structure, and evolution.

Smart Nanocarriers for the Treatment of Retinal Diseases

Retinal diseases, such as age-related macular degeneration, diabetic retinopathy, and retinoblastoma, stand as the leading causes of irreversible vision impairment and blindness worldwide. Effectively administering drugs for retinal diseases poses a formidable challenge due to the presence of complex ocular barriers and elimination mechanisms. Over time, various approaches have been developed to fabricate drug delivery systems for improving retinal therapy including virus vectors, lipid nanoparticles, and polymers. However, conventional nanocarriers encounter issues related to the controllability, efficiency, and safety in the retina. Therefore, the development of smart nanocarriers for effective or more invasive long-term treatment remains a desirable goal. Recently, approaches have surfaced for the intelligent design of nanocarriers, leveraging specific responses to external or internal triggers and enabling multiple functions for retinal therapy such as topical administration, prolonged drug release, and site-specific drug delivery. This Review provides an overview of prevalent retinal pathologies and related pharmacotherapies to enhance the understanding of retinal diseases. It also surveys recent developments and strategies employed in the intelligent design of nanocarriers for retinal disease. Finally, the challenges of smart nanocarriers in potential clinical retinal therapeutic applications are discussed to inspire the next generation of smart nanocarriers.

Sustained Retinal Defocus Increases the Effect of Induced Myopia on the Retinal Astrocyte Template

The aim of this article is to describe sustained myopic eye growth's effect on astrocyte cellular distribution and its association with inner retinal layer thicknesses. Astrocyte density and distribution, retinal nerve fiber layer (RNFL), ganglion cell layer, and inner plexiform layer (IPL) thicknesses were assessed using immunochemistry and spectral-domain optical coherence tomography on seventeen common marmoset retinas (Callithrix jacchus): six induced with myopia from 2 to 6 months of age (6-month-old myopes), three induced with myopia from 2 to 12 months of age (12-month-old myopes), five age-matched 6-month-old controls, and three age-matched 12-month-old controls. Untreated marmoset eyes grew normally, and both RNFL and IPL thicknesses did not change with age, with astrocyte numbers correlating to RNFL and IPL thicknesses in both control age groups. Myopic marmosets did not follow this trend and, instead, exhibited decreased astrocyte density, increased GFAP+ spatial coverage, and thinner RNFL and IPL, all of which worsened over time. Myopic changes in astrocyte density, GFAP+ spatial coverage and inner retinal layer thicknesses suggest astrocyte template reorganization during myopia development and progression which increased over time. Whether or not these changes are constructive or destructive to the retina still remains to be assessed.

Quantitative Foveal Structural Metrics as Predictors of Visual Acuity in Human Albinism

Purpose

To assess the degree to which quantitative foveal structural measurements account for variation in best-corrected visual acuity (BCVA) in human albinism.

Methods

BCVA was measured and spectral domain optical coherence tomography (SD-OCT) images were acquired for 74 individuals with albinism. Categorical foveal hypoplasia grades were assessed using the Leicester Grading System for Foveal Hypoplasia. Foveal anatomical specialization (foveal versus parafoveal value) was quantified for inner retinal layer (IRL) thickness, outer segment (OS) length, and outer nuclear layer (ONL) thickness. These metrics, participant sex, and age were used to build a multiple linear regression of BCVA. This combined linear model's predictive properties were compared to those of categorical foveal hypoplasia grading.

Results

The cohort included three participants with type 1a foveal hypoplasia, 23 participants with type 1b, 33 with type 2, ten with type 3, and five with type 4. BCVA ranged from 0.08 to 1.00 logMAR (mean ± SD: 0.53 ± 0.21). IRL ratio, OS ratio, and ONL ratio were measured in all participants and decreased with increasing severity of foveal hypoplasia. The best-fit combined linear model included all three quantitative metrics and participant age expressed as a binary variable (divided into 0-18 years and 19 years or older; adjusted R2 = 0.500). This model predicted BCVA more accurately than a categorical foveal hypoplasia model (adjusted R2 = 0.352).

Conclusions

A quantitative model of foveal specialization accounts for more variance in BCVA in albinism than categorical foveal hypoplasia grading. Other factors, such as optical aberrations and eye movements, may account for the remaining unexplained variance.

Age-Related Macular Degeneration, a Mathematically Tractable Disease

A progression sequence for age-related macular degeneration onset may be determinable with consensus neuroanatomical nomenclature augmented by drusen biology and eye-tracked clinical imaging. This narrative review proposes to supplement the Early Treatment of Diabetic Retinopathy Study (sETDRS) grid with a ring to capture high rod densities. Published photoreceptor and retinal pigment epithelium (RPE) densities in flat mounted aged-normal donor eyes were recomputed for sETDRS rings including near-periphery rich in rods and cumulatively for circular fovea-centered regions. Literature was reviewed for tissue-level studies of aging outer retina, population-level epidemiology studies regionally assessing risk, vision studies regionally assessing rod-mediated dark adaptation (RMDA), and impact of atrophy on photopic visual acuity. The 3 mm-diameter xanthophyll-rich macula lutea is rod-dominant and loses rods in aging whereas cone and RPE numbers are relatively stable. Across layers, the largest aging effects are accumulation of lipids prominent in drusen, loss of choriocapillary coverage of Bruch's membrane, and loss of rods. Epidemiology shows maximal risk for drusen-related progression in the central subfield with only one third of this risk level in the inner ring. RMDA studies report greatest slowing at the perimeter of this high-risk area. Vision declines precipitously when the cone-rich central subfield is invaded by geographic atrophy. Lifelong sustenance of foveal cone vision within the macula lutea leads to vulnerability in late adulthood that especially impacts rods at its perimeter. Adherence to an sETDRS grid and outer retinal cell populations within it will help dissect mechanisms, prioritize research, and assist in selecting patients for emerging treatments.

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.

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.

The Mongolian gerbil as an advanced model to study cone system physiology

In this work, we introduce a diurnal rodent, the Mongolian gerbil (Meriones unguiculatus) (MG) as an alternative to study retinal cone system physiology and pathophysiology in mice. The cone system is of particular importance, as it provides high-acuity and color vision and its impairment in retinal disorders is thus especially disabling. Despite their nocturnal lifestyle, mice are currently the most popular animals to study cone-related diseases due to the high availability of genetically modified models. However, the potential for successful translation of any cone-related results is limited due to the substantial differences in retinal organization between mice and humans. Alternatively, there are diurnal rodents such as the MG with a higher retinal proportion of cones and a macula-like specialized region for improved visual resolution, the visual streak. The focus of this work was the evaluation of the MG's cone system functionality using full-field electroretinography (ERG), together with a morphological assessment of its retinal/visual streak organization via angiography, optical coherence tomography (OCT), and photoreceptor immunohistochemistry. We found that rod system responses in MGs were comparable or slightly inferior to mice, while in contrast, cone system responses were much larger, more sensitive, and also faster than those in the murine counterparts, and in addition, it was possible to record sizeable ON and OFF ERG components. Morphologically, MG cone photoreceptor opsins were evenly distributed throughout the retina, while mice show a dorsoventral M- and S-opsin gradient. Additionally, each cone expressed a single opsin, in contrast to the typical co-expression of opsins in mice. Particular attention was given to the visual streak region, featuring a higher density of cones, elongated cone and rod outer segments (OSs), and an increased thickness of the inner and outer retinal layers in comparison to peripheral regions. In summary, our data render the MG a supreme model to investigate cone system physiology, pathophysiology, and to validate potential therapeutic strategies in that context.

Evolutionary and Developmental Specialization of Foveal Cell Types in the Marmoset

In primates, high-acuity vision is mediated by the fovea, a small specialized central region of the retina. The fovea, unique to the anthropoid lineage among mammals, undergoes notable neuronal morphological changes during postnatal maturation. However, the extent of cellular similarity across anthropoid foveas and the molecular underpinnings of foveal maturation remain unclear. Here, we used high throughput single cell RNA sequencing to profile retinal cells of the common marmoset ( Callithrix jacchus ), an early divergent in anthropoid evolution from humans, apes, and macaques. We generated atlases of the marmoset fovea and peripheral retina for both neonates and adults. Our comparative analysis revealed that marmosets share almost all its foveal types with both humans and macaques, highlighting a conserved cellular structure among primate foveas. Furthermore, by tracing the developmental trajectory of cell types in the foveal and peripheral retina, we found distinct maturation paths for each. In-depth analysis of gene expression differences demonstrated that cone photoreceptors and Müller glia, among others, show the greatest molecular divergence between these two regions. Utilizing single-cell ATAC-seq and gene-regulatory network inference, we uncovered distinct transcriptional regulations differentiating foveal cones from their peripheral counterparts. Further analysis of predicted ligand-receptor interactions suggested a potential role for Müller glia in supporting the maturation of foveal cones. Together, these results provide valuable insights into foveal development, structure, and evolution.

Significance statement

The sharpness of our eyesight hinges on a tiny retinal region known as the fovea. The fovea is pivotal for primate vision and is susceptible to diseases like age-related macular degeneration. We studied the fovea in the marmoset-a primate with ancient evolutionary ties. Our data illustrated the cellular and molecular composition of its fovea across different developmental ages. Our findings highlighted a profound cellular consistency among marmosets, humans, and macaques, emphasizing the value of marmosets in visual research and the study of visual diseases.

Cone Density Is Correlated to Outer Segment Length and Retinal Thickness in the Human Foveola

Purpose

Assessment of the relationship between in vivo foveolar cone density, cone outer segment length (OSL), and foveal retinal thickness (RT).

Methods

Foveolar cone density maps covering the central ±300 µm of the retina were derived from adaptive optics scanning laser ophthalmoscopy images. The corresponding maps of foveal cone OSL and RT were derived from high-resolution optical coherence tomography volume scans. Alignment of the two-dimensional maps containing OSL and RT with the cone density map was achieved by placing the location of maximum OSL on the cone density centroid (CDC).

Results

Across 10 participants (27 ± 9 years; 6 female), cone density at the CDC was found to be between 147,038 and 215,681 cones/mm². The maximum OSL and minimum RT were found to lie between 31 and 40, and 193 and 226 µm, respectively. A significant correlation was observed between cone density at the CDC and maximum OSL (P = 0.001), as well as the minimal RT (P < 0.05). Across all participants, the best fit for the relationship between normalized cone density and normalized OSL within the central 300 µm was given by a quadratic function.

Conclusions

Using optical coherence tomography-derived measurements of OSL enables to estimate CDC cone density and two-dimensional foveal cone density maps for example in patient eyes unsuitable for adaptive optics imaging. Furthermore, the observation of a fixed relationship between the normalized OSL and cone density points to a conserved mechanism shaping the foveal pit.

Nystagmus Characteristics in Albinism: Unveiling the Link to Foveal Hypoplasia and Visual Acuity

Purpose

The purpose of this study was to describe the association among nystagmus characteristics, foveal hypoplasia, and visual acuity in patients with albinism.

Methods

We studied nystagmus recordings of 50 patients with albinism. The nystagmus waveform was decomposed into two types: dominantly pendular and dominantly jerk. We correlated the nystagmus type, amplitude, frequency, and percentage of low velocity (PLOV) to Snellen visual acuity and foveal hypoplasia grades.

Results

The grade of foveal hypoplasia and visual acuity showed a strong correlation (r = 0.87, P < 0.0001). Nystagmus type and PLOV had the strongest significant (P < 0.0001) correlation with visual acuity (r = 0.70 and r = -0.56, respectively) and with foveal hypoplasia (r = 0.76 and r = -0.60, respectively). Patients with pendular nystagmus type had the lowest PLOV, and the highest grade of foveal hypoplasia (P < 0.0001). Severe foveal hypoplasia (grade 4), was almost invariably associated with pendular nystagmus (86%).

Conclusions

Foveal hypoplasia grade 4 is associated with pendular nystagmus, lower PLOV, and worse visual acuity. Based on these results, nystagmus recordings at a young age may contribute to predicting visual outcomes.

Visual Acuity-Related Outer Retinal Structural Parameters on Swept Source Optical Coherence Tomography and Angiography in XLRS Patients and Carriers

Purpose

To assess the quantitative differences in vessel density and retinal thickness of X-linked retinoschisis (XLRS) patients and RS1 mutation carriers, and the correlation with best-corrected visual acuity (BCVA) with swept source optical coherence tomography (SS-OCT) and OCT angiography (OCTA).

Methods

We analyzed the correlation between the BCVA of XLRS patients and the SS-OCT and OCTA findings including the detailed structural characteristics of XLRS patients.

Results

Besides the schitic changes in various retinal layers, the structural disturbance of outer retina was universally found. In 29 eyes included in the quantitative analysis, XLRS patients showed lower vessel density of the superficial capillary plexus, deep capillary plexus and lower thickness of the outer nuclear layer. BCVA was correlated with the thickness of the outer plexiform layer and outer nuclear layer and the thickness from the outer limiting membrane to the retinal pigment epithelium. Carriers showed higher thickness of outer plexiform layer and smaller foveal avascular zone area.

Conclusions

SS-OCT and OCTA could identify the pathological alterations of the individual retinal layers and capillaries, which could pinpoint the exact location of the damages related to visual impairment. In the carriers, the subtle alterations that can be detected with SS-OCT, despite their normal visual acuity, may be caused by the lyonization.

Translational Relevance

Swept source optical coherence tomography can be used as an efficient technique to expose the retinal damage related to visual impairment for prognosis and follow-up.

Optical coherence tomography angiography in diabetic retinopathy

There remain many unanswered questions on how to assess and treat the pathology and complications that arise from diabetic retinopathy (DR). Optical coherence tomography angiography (OCTA) is a novel and non-invasive three-dimensional imaging method that can visualize capillaries in all retinal layers. Numerous studies have confirmed that OCTA can identify early evidence of microvascular changes and provide quantitative assessment of the extent of diseases such as DR and its complications. A number of informative OCTA metrics could be used to assess DR in clinical trials, including measurements of the foveal avascular zone (FAZ; area, acircularity, 3D para-FAZ vessel density), vessel density, extrafoveal avascular zones, and neovascularization. Assessing patients with DR using a full-retinal slab OCTA image can limit segmentation errors and confounding factors such as those related to center-involved diabetic macular edema. Given emerging data suggesting the importance of the peripheral retinal vasculature in assessing and predicting DR progression, wide-field OCTA imaging should also be used. Finally, the use of automated methods and algorithms for OCTA image analysis, such as those that can distinguish between areas of true and false signals, reconstruct images, and produce quantitative metrics, such as FAZ area, will greatly improve the efficiency and standardization of results between studies. Most importantly, clinical trial protocols should account for the relatively high frequency of poor-quality data related to sub-optimal imaging conditions in DR and should incorporate time for assessing OCTA image quality and re-imaging patients where necessary.

Increased neuron density in the midbrain of a foveate bird, pigeon, results from profound change in tissue morphogenesis

The increase of brain neuron number in relation with brain size is currently considered to be the major evolutionary path to high cognitive power in amniotes. However, how changes in neuron density did contribute to the evolution of the information-processing capacity of the brain remains unanswered. High neuron densities are seen as the main reason why the fovea located at the visual center of the retina is responsible for sharp vision in birds and primates. The emergence of foveal vision is considered as a breakthrough innovation in visual system evolution. We found that neuron densities in the largest visual center of the midbrain - i.e., the optic tectum - are two to four times higher in modern birds with one or two foveae compared to birds deprived of this specialty. Interspecies comparisons enabled us to identify elements of a hitherto unknown developmental process set up by foveate birds for increasing neuron density in the upper layers of their optic tectum. The late progenitor cells that generate these neurons proliferate in a ventricular zone that can expand only radially. In this particular context, the number of cells in ontogenetic columns increases, thereby setting the conditions for higher cell densities in the upper layers once neurons did migrate.

Maturation and refinement of the maculae and foveae in the Anolis sagrei lizard

The fovea is a pit in the center of the macula, which is a region of the retina with a high concentration of photoreceptor cells, which accounts for a large degree of visual acuity in primates. The maturation of this primate visual acuity area is characterized by the shallowing and widening of the foveal pit, a decrease in the diameter of the rod-free zone, and an increase in photoreceptor cells packing after birth. Maturation occurs concurrently with progressing age, increasing eye size, and retinal length/area. These observations have led to the hypothesis that the maturation of the fovea might be a function of mechanical variables that remodel the retina. However, this has never been explored outside of primates. Here, we take advantage of the Anolis sagrei lizard, which has a bifoveated retina, to study maturation of the fovea and macula. Eyes were collected from male and female lizards-hatchling, 2-month, 4-month, 6-month, and adult. We found that Anolis maculae undergo a maturation process somewhat different than what has been observed in primates. Anole macular diameters actually increase in size and undergo minimal photoreceptor cell packing, possessing a near complete complement of these cells at the time of hatching. As the anole eye expands, foveal centers experience little change in overall retina cell density with most cell redistribution occurring at macular borders and peripheral retina areas. Gene editing technology has recently been developed in lizards; this study provides a baseline of normal retina maturation for future genetic manipulation studies in anoles.

Optical Coherence Tomography Angiography Assessment in Congenital Aniridia

PURPOSE

This study aims to characterize foveal vasculature assessed by optical coherence tomography angiography (OCT-A) in congenital aniridia which is hallmarked by foveal hypoplasia (FH).

DESIGN

Cross-sectional case-control analysis.

METHODS

At the National Referral Center for congenital aniridia, patients with confirmed PAX6-related aniridia and FH diagnosed on spectral-domain OCT (SD-OCT) with available OCT-A and matched control subjects were included. OCT-A was performed in patients with aniridia and control subjects. Foveal avascular zone (FAZ) and vessel density (VD) were collected. VD in the foveal and parafoveal areas at the level of the superficial and deep capillary plexi (SCP and DCP, respectively) were compared between the 2 groups. In patients with congenital aniridia, correlation between VD and the grading of FH was assessed.

RESULTS

Among 230 patients with confirmed PAX6-related aniridia, high-quality macular B-scans and OCT-A were available in 10 patients. On the foveal area, mean VD was higher in aniridia patients (41.10%, n = 10) than in control subjects (22.65%, n = 10) at the level of the SCP and the DCP (P = .0020 and P = .0273, respectively). On the parafoveal area, mean VD was lower in patients with aniridia (42.34%, n = 10) than in healthy subjects (49.24%, n = 10) at the level of both plexi (P = .0098 and P = .0371, respectively). In patients with congenital aniridia, a positive correlation was found between the grading of FH and the foveal VD at the SCP (r = 0.77, P = .0106).

CONCLUSIONS

Vasculature is altered in PAX6-related congenital aniridia, higher in foveal and lower in parafoveal areas, especially when FH is severe, which is consistent with the concept that the absence of retinal blood vessels is essential for foveal pit development.

A variation of foveal morphology in a group of children with hypermetropia

PURPOSE

During routine eye examinations, we noticed widened and flattened foveal pits with loss of normal V-shaped foveal profile and a pseudohole-like appearance in some otherwise healthy hypermetropic children. Our purpose was to describe clinical significance and multimodal imaging features of this incidental finding.

METHODS

Prospectively, 25 eyes of 13 hypermetropic children with these foveal changes and 36 eyes of 19 hypermetropic children with normal foveal appearance were enrolled. The macular thickness measurements and foveal parameters including pit diameter, depth, base, and area obtained by optical coherence tomography (OCT) (Heidelberg Spectralis, Heidelberg Engineering, Heidelberg, Germany), macular superficial and deep vessel density (VD) and foveal avascular zone values obtained by optical coherence tomography angiography (Avanti RTVue‑XR; Optovue, Fremont, CA, USA) were noted. The correlations of these parameters with visual function were evaluated.

RESULTS

In the study group, significantly widened and flattened pit contours with decreased central foveal thickness (p = 0.01), and increased distance between foveal edges (p < 0.001) were observed. While the whole image superficial macular VD was similar between the groups (p = 0.74), a significant decrease in deep macular VD was observed in the study group (p = 0.01). None of these changes were correlated with visual acuity.

CONCLUSION

Wider and flattened foveal pits described here represent a newly defined variation in healthy hypermetropic children. Although a correlation with visual acuity was not evident, these changes in foveal profile are shown to be related with macular microvascular changes in deep capillary plexus. Awareness of these morphologic changes will help clinicians in the differential diagnosis of macular pseudohole.

The Development of Retinal Function and Refractive Error in Children With Retinopathy of Prematurity

Purpose

The purpose of this study was to test the hypothesis that retinopathy of prematurity (ROP) prolongs development of rod-mediated thresholds for detection of stimuli at 10 degrees but not 30 degrees eccentricity. In addition, to evaluate the thresholds at each site for an association with visual acuity (VA) and spherical equivalent (SE).

Methods

We estimated rod-mediated dark-adapted thresholds (DATs) for the detection of 2 degree diameter, 50 ms, blue (λ < 510 nm) flashes at 10 degrees and 30 degrees eccentric in former preterm subjects (n = 111), stratified by ROP severity: None (n = 32), Mild (n = 66), and Severe (n = 13). We also tested Term-born (n = 28) controls. To determine the age at half-maximal sensitivity (Agehalf) for each group and eccentricity, we fit DATs to logistic growth curves. We obtained VA and SE for Preterm subjects and evaluated the course of threshold development at 10 degrees and 30 degrees for significant association with VA and SE predicted at age 10 years.

Results

DAT development at 10 degrees was significantly delayed in ROP (Mild and Severe); ROP did not significantly alter DAT development at 30 degrees. At age 10 years, among Preterm subjects, both VA and SE were significantly associated with group (None,Mild, and Severe). SE was predicted by the course of DAT development at 30 degrees. VA was not associated with the course of DAT development at 10 degrees.

Conclusions

At 10 degrees, ROP-whether mild or severe-is associated with significant delays in DAT development, evidence that the late-maturing central retina is vulnerable to ROP. The association of 30 degree threshold and myopia are evidence that more peripheral retina is important to refractive development.

Characterizing Foveal Hypoplasia Using Optical Coherence Tomography Angiography: Evaluation of Microvascular Abnormalities and Clinical Significance

This study aimed to evaluate foveal avascular zone (FAZ) features and macular flow density (FD) in various retinal layers in a cohort of patients with foveal hypoplasia (FH) using optical coherence tomography angiography (OCTA), in order to characterize microvascular abnormalities and explore their potential clinical significance. FAZ parameters and FD, as well as retinal thickness and volume values were analyzed and compared between patients with FH and an age- and gender-matched control cohort. Correlations between disease severity and visual acuity (VA), as well as between disease severity and FAZ features were evaluated. A total of 19 eyes with FH and 19 control eyes were included. The study group showed significantly higher FD values in the foveal sectors of the superficial and deep capillary plexus compared to controls. FAZ area, perimeter, and acircularity index (ACI) were noticeably altered in eyes with FH; however, they did not correlate with disease severity. Visual acuity was negatively correlated with disease severity. The results of this study provide evidence of altered microvasculature architecture specifically in the foveal sectors of patients with FH. The higher FD values in the foveal sectors of FH patients suggest a potential compensatory response of the retinal microvasculature. FAZ parameters and FD values of the foveal sectors could be used as part of an OCTA-based grading system in FH patients.

Functional Characteristics of Diverse PAX6 Mutations Associated with Isolated Foveal Hypoplasia

The human fovea is a specialized pit structure in the central retina. Foveal hypoplasia is a condition where the foveal pit does not fully develop, and it is associated with poor vision. Autosomal dominant isolated foveal hypoplasia (FVH1) is a rare condition of foveal hypoplasia (FH) that lacks any other ocular manifestations. FVH1 is associated with hypomorphic mutations in the PAX6 gene that encodes a sequence-specific DNA-binding transcription factor for morphogenesis and evolution of the eye. We report our findings in 17 patients with PAX6 mutations associated with FVH1 or FH with aniridia and corneal opacities. Patients with three mutations, p.V78E, p.V83F and p.R128H, in the C-terminal subdomain of the paired domain (CTS) consistently have severe FH. Luciferase assays for a single reporter containing a representative PAX6 binding site indicated that the transcriptional activities of these mutations were significantly reduced, comparable to that of the truncation mutation of p.G65Rfs*5. Patients with p.P20S in the N-terminal subdomain of the paired domain, and a patient with p.N365K in the proline-serine-threonine-rich domain (PSTD) had mild FH. A patient with p.Q255L in the homeodomain had severe FH. The P20S and Q255L mutants did not affect the transcriptional activity. Mutant N365K has a retained DNA-binding activity but a reduced transcriptional activity, due to a low PSTD transactivation. These findings demonstrated that mutations associated with FVH1 underlie a functional divergence between DNA-binding ability and transcriptional activity. We conclude that a wide range of mutations in the PAX6 gene is not limited to the CST region and are responsible for FVH1.

Congenital aniridia beyond black eyes: From phenotype and novel genetic mechanisms to innovative therapeutic approaches

Congenital PAX6-aniridia, initially characterized by the absence of the iris, has progressively been shown to be associated with other developmental ocular abnormalities and systemic features making congenital aniridia a complex syndromic disorder rather than a simple isolated disease of the iris. Moreover, foveal hypoplasia is now recognized as a more frequent feature than complete iris hypoplasia and a major visual prognosis determinant, reversing the classical clinical picture of this disease. Conversely, iris malformation is also a feature of various anterior segment dysgenesis disorders caused by PAX6-related developmental genes, adding a level of genetic complexity for accurate molecular diagnosis of aniridia. Therefore, the clinical recognition and differential genetic diagnosis of PAX6-related aniridia has been revealed to be much more challenging than initially thought, and still remains under-investigated. Here, we update specific clinical features of aniridia, with emphasis on their genotype correlations, as well as provide new knowledge regarding the PAX6 gene and its mutational spectrum, and highlight the beneficial utility of clinically implementing targeted Next-Generation Sequencing combined with Whole-Genome Sequencing to increase the genetic diagnostic yield of aniridia. We also present new molecular mechanisms underlying aniridia and aniridia-like phenotypes. Finally, we discuss the appropriate medical and surgical management of aniridic eyes, as well as innovative therapeutic options. Altogether, these combined clinical-genetic approaches will help to accelerate time to diagnosis, provide better determination of the disease prognosis and management, and confirm eligibility for future clinical trials or genetic-specific therapies.

Prevalence and severity of diabetic retinopathy at first presentation to vitreoretinal services in Bhutan: a 3-year national study

PURPOSE

To determine the prevalence and severity of diabetic retinopathy (DR) at first presentation among diabetic patients attending national vitreoretinal (VR) services in Bhutan STUDY DESIGN: Retrospective cross-sectional study METHODS: We included all diabetic patients in Bhutan who presented for retinal evaluation for the first time over a 3-year period (2013-2016). Data including demography, clinical details, diagnostic tests, and clinical staging of DR were analyzed.

RESULTS

A total of 843 diabetic patients, aged 57.2 ± 12.0 (range 18-86) years, were enrolled. The majority were male (452, 53.6%; cumulative frequency [cf] 391, 46.4%; P = .14) and from urban settings (570, 67.6%; cf 273; 32.4%) and did not have modern schooling (555, 65.8%). Hypertension was the most common systemic comorbidity (501, 59.4%). The prevalence of DR was 42.7%, with mild nonproliferative DR (NPDR) being the most common type (187, 51.9%), followed by moderate NPDR (88, 24.4%) and proliferative DR (45, 12.5%). In addition, 120 patients had clinically significant macular edema (CSME), with a prevalence of 14.2%. Best-corrected visual acuity (BCVA) of 6/60 or worse occurred in 231 eyes (13.7%), and 41 patients (4.86%) had BCVA of 6/60 or worse bilaterally due to DR/CSME. A logistic regression model indicated that the major determinant of DR was the duration of diabetes, the odds rising by 1.27× with each year of disease (P < .0001).

CONCLUSION

The prevalence of DR, including CSME, was high. Although a national DR screening program is established in Bhutan, there is a need to accelerate health education, community screening, and referral systems to reduce the prevalence of DR and CSME.

Foveal avascular zone in normal human eyes by optical coherence tomography angiography

OBJECTIVE

To analyze the influence factors of the area of superficial plexus foveal avascular zone (FAZ) and related indexes of fovea measured with optical coherence tomography angiography (OCT-A) in normal subjects.

METHODS

This was a cross-sectional study from November 2020 to May 2021 in the Inner Mongolia Autonomous Region, China. Each subject received related eye examination. The correlation between all the factors and superficial plexus FAZ were analyzed under univariable and multivariable linear regression analysis.

RESULTS

Finally, 239 subjects with sufficient data were recruited in the study, including 108 males and 131 females, aged 27.41±4.63 years. The area of superficial plexus FAZ was 0.33±0.16 mm². In the univariate regression, gender (β = 41.702, 95%CI: 9.152 to 74.253, P = 0.012), drinking (β = -66.074, 95%CI: -99.197 to -32.951, P = 0.001) and axial length (β = -15.874, 95%CI: -29.562 to -2.185, P = 0.023) were associated with superficial plexus FAZ area. In multivariate regression analysis results, drinking (β = -42.410, 95%CI = -79.388 to -5.432, P = 0.025) was significantly correlated with superficial plexus FAZ area.

CONCLUSION

The area of superficial plexus FAZ was not affected by age, gender, systematical and biochemical indicators, but related to the status of drinking.

The age-related pattern of inner retinal thickening is affected by myopia development and progression

The longitudinal effect of myopic eye growth on each individual retinal layer has not been described to date on an established non-human primate (NHP) model of myopia. We evaluated the changes experienced by the overall and individual central and mid-peripheral retinal thickness profiles in marmosets (Callithrix jacchus) induced with myopia continuously for 5.5 months compared to controls using spectral-domain optical coherence tomography. Cycloplegic refractive state (Rx), vitreous chamber depth (VCD) and retinal thickness were measured at baseline and after 3 and 5.5 months on thirteen marmosets: eight animals with lens-induced myopia and five untreated controls. The overall and individual retinal layer thickness in the central and mid-peripheral retina were obtained and compared between groups. Regression models were used to explore the extent to which VCD or Rx changes could predict the thickness changes observed. While the retinas of control marmosets thickened significantly over 5.5 months, marmosets with lens-induced myopia experienced less retinal thickening and thinning at times, mostly in the inner neuroretinal layers and the ganglion cell-inner plexiform layer. The regression models suggest that 90% of the growth and refractive changes observed could be predicted by the thickness changes in the near to mid peripheral retina. This study confirms the longitudinal effect that myopia has on the inner retina of a NHP model during the early stages of myopia development. The observed myopia-driven differences in inner retina thickness templates might represent early biomarkers of myopia progression and associated complications.

Foveal hypoplasia in parents of patients with albinism

BACKGROUND

Albinism is a group of genetic disorders characterized by general skin and retinal hypopigmentation. It is in most cases an autosomal recessive condition. Foveal hypoplasia (FH) is one of the main criteria for the diagnosis of albinism. The aim of this study was to analyze the macular profile of the parents of patients with albinism.

METHODS

This study included a case series of 27 patients with albinism seen in Rothschild Foundation between April 2017 and February 2020. Spectral-domain optical coherence tomography (SD-OCT) and OCT angiography (OCT-A) were performed in every patient when possible and in every available parents. FH was graded according to Thomas' classification based on OCT. Next generation sequencing-based gene panel testing was performed in parents and children when a FH was detected on OCT in a parent.

RESULTS

Twenty-seven patients with albinism were examined. Nine parents had FH based on the OCT B-scan (33%). In parents without FH based on the SD-OCT B-scan (67%), OCT-A showed a reduced avascular zone in the deep vascular plexus in 4 parents. Six parents carried variants that could explain their phenotype, including TYR R402Q hypomorphic alleles.

CONCLUSION

This study showed the presence of FH in parents of patients with albinism, and aimed to genetically explain this phenotype.

Generation of Lens Progenitor Cells and Lentoid Bodies from Pluripotent Stem Cells: Novel Tools for Human Lens Development and Ocular Disease Etiology

In vitro differentiation of human pluripotent stem cells (hPSCs) into specialized tissues and organs represents a powerful approach to gain insight into those cellular and molecular mechanisms regulating human development. Although normal embryonic eye development is a complex process, generation of ocular organoids and specific ocular tissues from pluripotent stem cells has provided invaluable insights into the formation of lineage-committed progenitor cell populations, signal transduction pathways, and self-organization principles. This review provides a comprehensive summary of recent advances in generation of adenohypophyseal, olfactory, and lens placodes, lens progenitor cells and three-dimensional (3D) primitive lenses, "lentoid bodies", and "micro-lenses". These cells are produced alone or "community-grown" with other ocular tissues. Lentoid bodies/micro-lenses generated from human patients carrying mutations in crystallin genes demonstrate proof-of-principle that these cells are suitable for mechanistic studies of cataractogenesis. Taken together, current and emerging advanced in vitro differentiation methods pave the road to understand molecular mechanisms of cataract formation caused by the entire spectrum of mutations in DNA-binding regulatory genes, such as PAX6, SOX2, FOXE3, MAF, PITX3, and HSF4, individual crystallins, and other genes such as BFSP1, BFSP2, EPHA2, GJA3, GJA8, LIM2, MIP, and TDRD7 represented in human cataract patients.

The retinal pigmentation pathway in human albinism: Not so black and white

Albinism is a pigment disorder affecting eye, skin and/or hair. Patients usually have decreased melanin in affected tissues and suffer from severe visual abnormalities, including foveal hypoplasia and chiasmal misrouting. Combining our data with those of the literature, we propose a single functional genetic retinal signalling pathway that includes all 22 currently known human albinism disease genes. We hypothesise that defects affecting the genesis or function of different intra-cellular organelles, including melanosomes, cause syndromic forms of albinism (Hermansky-Pudlak (HPS) and Chediak-Higashi syndrome (CHS)). We put forward that specific melanosome impairments cause different forms of oculocutaneous albinism (OCA1-8). Further, we incorporate GPR143 that has been implicated in ocular albinism (OA1), characterised by a phenotype limited to the eye. Finally, we include the SLC38A8-associated disorder FHONDA that causes an even more restricted "albinism-related" ocular phenotype with foveal hypoplasia and chiasmal misrouting but without pigmentation defects. We propose the following retinal pigmentation pathway, with increasingly specific genetic and cellular defects causing an increasingly specific ocular phenotype: (HPS1-11/CHS: syndromic forms of albinism)-(OCA1-8: OCA)-(GPR143: OA1)-(SLC38A8: FHONDA). Beyond disease genes involvement, we also evaluate a range of (candidate) regulatory and signalling mechanisms affecting the activity of the pathway in retinal development, retinal pigmentation and albinism. We further suggest that the proposed pigmentation pathway is also involved in other retinal disorders, such as age-related macular degeneration. The hypotheses put forward in this report provide a framework for further systematic studies in albinism and melanin pigmentation disorders.

Structure-function correlates of vision loss in neuromyelitis optica spectrum disorders

Optic neuritis (ON) in neuromyelitis optica spectrum disorders (NMOSD) regularly leads to more profound vision loss compared to multiple sclerosis (MS) and myelin-oligodendrocyte-glycoprotein-antibody associated disease (MOGAD). Here we investigate ON-related vision loss in NMOSD compared to MS and MOGAD in order to identify neuroaxonal and retinal contributors to visual dysfunction. In this retrospective study we included patients with aquaporin-4-antibody seropositive NMOSD (n = 28), MOGAD (n = 14), MS (n = 29) and controls (n = 14). We assessed optic nerve damage and fovea morphometry by optical coherence tomography. Visual function was assessed as high (HCVA) and low contrast visual acuity (LCVA), and visual fields' mean deviation (MD). In all diseases, lower visual function was associated with peripapillary retinal nerve fiber layer (pRNFL) and ganglion cell and inner plexiform layer (GCIP) thinning following a broken stick model, with pRNFL and GCIP cutoff point at ca. 60 µm. HCVA loss per µm pRNFL and GCIP thinning was stronger in NMOSD compared with MOGAD. Foveal inner rim volume contributed to MD and LCVA in NMOSD eyes, only. Together these data supports that visual dysfunction in NMOSD is associated with neuroaxonal damage beyond the effect seen in MS and MOGAD. A primary retinopathy, respectively Müller cell pathology, may contribute to this effect.

Structural impact of arrested foveal development in children born extremely preterm without ROP at 6.5 years of age

Objectives

To characterize changes of foveal topography and microstructure of persisting foveal immaturity at 6.5 years of age in children born extremely preterm without retinopathy of prematurity (EPT-NoROP).

Methods

Images from previous optical coherence tomography examinations of 37 EPT-NoROP and 92 control eyes were selected from a regional cohort of the EXPRESS (Extremely Preterm Infants in Sweden) study. Thickness of ganglion cell + inner plexiform layer (GCL+), outer nuclear layer (ONL), retinal thickness (RT) at the foveal centre (FC), foveal depth (FD) and RT at the foveal rim were evaluated.

Results

Layer thickness of GCL+, ONL and RT was increased at FC in the EPT-NoROP group. More than two-thirds had thickness values above the control limit (control mean +2 SD) at FC (GCL + 68%, ONL 76%, and RT 68%), and 50% had reduced FD compared to controls. All parameters showed a high correlation within the EPT-NoROP group, whereas no or weaker correlation was seen in control eyes. The EPT-NoROP sub-groups, divided based on the control limit, did not differ in terms of associated factors such as gestational age, birth weight, visual acuity, and refraction.

Conclusions

Extreme prematurity without impact of ROP is associated with increased GCL + , ONL, and RT thickness at FC as well as reduced FD compared to full-term controls at age 6.5. This indicates that prematurity per se may have a profound effect on foveal anatomical maturation during the first months after birth. Our results suggest RT at FC to be a simple and useful measure of foveal anatomical immaturity.

Insights into the developing fovea revealed by imaging

Early development of the fovea has been documented by histological studies over the past few decades. However, structural distortion due to sample processing and the paucity of high-quality post-mortem tissue has limited the effectiveness of this approach. With the continuous progress in high-resolution non-invasive imaging technology, most notably optical coherence tomography (OCT) and OCT angiography (OCT-A), in vivo visualization of the developing retina has become possible. Combining the information from histologic studies with this novel imaging information has provided a more complete and accurate picture of retinal development, and in particular the developing fovea. Advances in neonatal care have increased the survival rate of extremely premature infants. However, with enhanced survival there has been an attendant increase in retinal developmental complications. Several key abnormalities, including a thickening of the inner retina at the foveal center, a shallower foveal pit, a smaller foveal avascular zone, and delayed development of the photoreceptors have been described in preterm infants when compared to full-term infants. Notably these abnormalities, which are consistent with a partial arrest of foveal development, appear to persist into later childhood and adulthood in these eyes of individuals born prematurely. Understanding normal foveal development is vital to interpreting these pathologic findings associated with prematurity. In this review, we first discuss the various advanced imaging technologies that have been adapted for imaging the infant eye. We then review the key events and steps in the development of the normal structure of the fovea and contrast structural features in normal and preterm retina from infancy to childhood. Finally, we discuss the development of the perifoveal retinal microvasculature and highlight future opportunities to expand our understanding of the developing fovea.

Investigating Determinants and Evaluating Deep Learning Training Approaches for Visual Acuity in Foveal Hypoplasia

Purpose

To describe the relationships between foveal structure and visual function in a cohort of individuals with foveal hypoplasia (FH) and to estimate FH grade and visual acuity using a deep learning classifier.

Design

Retrospective cohort study and experimental study.

Participants

A total of 201 patients with FH were evaluated at the National Eye Institute from 2004 to 2018.

Methods

Structural components of foveal OCT scans and corresponding clinical data were analyzed to assess their contributions to visual acuity. To automate FH scoring and visual acuity correlations, we evaluated the following 3 inputs for training a neural network predictor: (1) OCT scans, (2) OCT scans and metadata, and (3) real OCT scans and fake OCT scans created from a generative adversarial network.

Main Outcome Measures

The relationships between visual acuity outcomes and determinants, such as foveal morphology, nystagmus, and refractive error.

Results

The mean subject age was 24.4 years (range, 1–73 years; standard deviation = 18.25 years) at the time of OCT imaging. The mean best-corrected visual acuity (n = 398 eyes) was equivalent to a logarithm of the minimal angle of resolution (LogMAR) value of 0.75 (Snellen 20/115). Spherical equivalent refractive error (SER) ranged from −20.25 diopters (D) to +13.63 D with a median of +0.50 D. The presence of nystagmus and a high-LogMAR value showed a statistically significant relationship (P < 0.0001). The participants whose SER values were farther from plano demonstrated higher LogMAR values (n = 382 eyes). The proportion of patients with nystagmus increased with a higher FH grade. Variability in SER with grade 4 (range, −20.25 D to +13.00 D) compared with grade 1 (range, −8.88 D to +8.50 D) was statistically significant (P < 0.0001). Our neural network predictors reliably estimated the FH grading and visual acuity (correlation to true value > 0.85 and > 0.70, respectively) for a test cohort of 37 individuals (98 OCT scans). Training the predictor on real OCT scans with metadata and fake OCT scans improved the accuracy over the model trained on real OCT scans alone.

Conclusions

Nystagmus and foveal anatomy impact visual outcomes in patients with FH, and computational algorithms reliably estimate FH grading and visual acuity.

HORNBILL: a phase I/IIa trial examining the safety, tolerability and early response of BI 764524 in patients with diabetic retinopathy and diabetic macular ischaemia-rationale, study design and protocol

Background

Diabetic macular ischaemia (DMI) is a complication of diabetic retinopathy that leads to irreversible vision loss. DMI is characterised by reduced retinal vessel density and enlargement of the foveal avascular zone (FAZ). Despite its clinical burden, there is no formal consensus on the definition of DMI, and no approved treatment. Semaphorin 3A (Sema3A) is an axonal guidance molecule that blocks revascularisation of the ischaemic retina. Sema3A modulation is therefore a promising mechanism of action for the treatment of ischaemic eye diseases. BI 764524 is an intravitreal anti-Sema3A ischaemia modulator agent.

Methods

HORNBILL (NCT04424290) is a phase I/IIa trial comprising a non-randomised, open-label, single rising dose (SRD) part and a randomised, masked, sham-controlled multiple dose (MD) part to investigate the safety, tolerability and early biological response of ischaemia modulator BI 764524 in adults (≥18 years) with DMI. DMI will be defined using optical coherence tomography angiography (OCTA) as either any degree of disruption in the retinal vascularity (SRD) or a FAZ of ≥0.5 mm² (MD). Subjects in the SRD part will receive 0.5, 1.0 or 2.5 mg of BI 764524; the maximum tolerated dose will then be used in the MD part. A minimum of 12 subjects will be enrolled into the SRD part; planned enrollment is 30 for the MD part. The primary endpoint of the SRD part is the number of subjects with dose-limiting adverse events (AEs) until day 8. The primary endpoint of the MD part is the number of subjects with drug-related AEs from baseline to end of study, and secondary endpoints include change from baseline in the size of the FAZ, best-corrected visual acuity and central retinal thickness.

Discussion

DMI is a poorly defined condition with no treatment options. HORNBILL is the first clinical trial to assess a treatment for DMI and to use OCTA as a means to define and examine DMI. The OCTA data generated in this trial could form the basis of formal diagnostic criteria for DMI. Furthermore, the novel mechanism of action (Sema3A modulation) explored in this trial has the potential to revolutionise the treatment landscape for patients with DMI.

Trial registration

ClinicalTrials.govNCT04424290; EudraCT 2019-004432-28. Registered on 9 June 2020

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-022-06527-y.

Living Without a Diagnosis: A Patient's Perspective on Diabetic Macular Ischemia

Diabetic macular ischemia (DMI) is a common complication of diabetic retinopathy (DR) that can result in progressive and irreversible vision loss. DMI is associated with damage in the vessels that supply blood to the retina and the enlargement of the foveal avascular zone. Currently, there are no approved treatments specifically for DMI. Furthermore, there is limited published information about the prognosis, prevalence or outcomes of DMI, and there is no consensus regarding diagnostic criteria. It is vital to ensure that there is sufficient, accessible and accurate information available to support patients, caregivers and physicians. To lay the foundation for more research into DMI and its impact on patients, we (a patient with DMI and an expert ophthalmologist) have worked together to interweave our personal perspectives and clinical experiences with a review of currently available literature on DMI. The development of a set of confirmed diagnostic criteria for DMI would assist both patients and physicians, allowing patients to access validated information about their condition and supporting the development of clinical trials for treatments of DMI. Training for physicians must continue to emphasise the importance of treating a patient holistically, rather than only treating their symptoms. Most importantly, developing trust and a healthy rapport between a patient and their physician is important in managing health anxiety and ensuring adherence to beneficial treatments or lifestyle adjustments; physicians must cultivate an open and flexible management approach with their patients. Finally, holistic educational programmes for patients, physicians and the general public around DMI and how it can affect daily functioning would facilitate general understanding and disease awareness.

Diabetic macular ischemia (DMI) is a common problem for patients with diabetic retinopathy that can lead to sight loss. There is very little information available about DMI, particularly from a patient’s point of view. To address the lack of information about DMI, we (a person with DMI and her eye doctor) have worked together to examine what it is like to live with DMI. It is important to provide clear and accessible information about diseases to patients and carers. The lack of information about DMI may be upsetting for some people, and should be addressed with more research. Developing of a set of confirmed signs and symptoms for the diagnosis of DMI would allow people to be more confident in the information that they receive about their disease, and support the development of treatments for DMI. The support of others is central to the wellbeing of people with vision loss. Although people with vision loss may also lose independence, care from loved ones can help to improve quality of life. Most importantly, developing trust between a patient and their doctor is central to managing people’s fears about their eyesight, and making sure that they follow helpful advice. Doctors must use an open and flexible approach with their patients, providing information in an honest and understandable way.