Outer Plexiform Layer Research Articles

Vascularized foveal zone: prevalence and structural characteristics

This study was performed to assess the prevalence of the vascularized foveal zone, including macular-foveal capillaries (MFC) and congenital retinal macrovessels (CRM), and to analyze the structural characteristics of the macular area in patients with MFC. The first phase of the study evaluated the prevalence of MFC and CRM. Optical coherence tomography angiography (OCT-A) was performed, and OCT-A images of the foveal avascular zone were analyzed. In the second phase, two groups were formed: the MFC group (12 eyes, 9 patients, mean age 43.8±10.7 years) and the control group (18 eyes, 17 patients, mean age 43.0±11.8 years). A comparative analysis was performed assessing central retinal thickness (CRT), thickness of retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), and foveal pit depth. MFCs were detected in 45 eyes from a total sample of 1031 eyes of 536 patients. The presence of CRM was recorded in three eyes of three patients. RNFL thickness was significantly higher in the MFC group in the inferior parafoveal sector (26.50 [26.00; 29.50] and 24.50 [21.75; 26.50] μm; p=0.022) and in the foveal zone (15.50 [14.00; 16.00] and 12.00 [11.00; 14.00] μm; p=0.017). Additionally, patients with MFC had a higher thickness of GCL and IPL in the fovea, inferior, nasal, and temporal parafoveal sectors. The depth of the foveal pit was significantly lower in the MFC group compared to the control group (83.0 [77.4; 101.6] and 128.0 [107.5; 147.05] μm; p=0.001). The prevalence of MFC was 4.36% (calculated per number of eyes), while the prevalence of CRM - 0.29%. The macular area in patients with MFC had increased thickness of the inner retinal layers and decreased depth of the foveal pit, suggesting potential disruption in the natural process of ganglion cell migration and apoptosis during embryogenesis.

Multimodal topographically oriented approach to the study of full-thickness macular holes

This article studies the relationship between structural changes according to the findings of optical coherence tomography (OCT) and OCT angiography (OCTA), microperimetry (MP), multifocal electroretinography (mfERG) parameters in topographically corresponding areas of the macular region in idiopathic full-thickness macular holes (FTMH). OCT, OCTA, MP and mfERG were performed in 14 eyes with FTMH stages I-IV according to Gass. In 13 points at a distance of 0-2.5°, 2.5-5.0°, and 5.0-10.0° from the fixation point, the light sensitivity (LS), amplitude and latency of the P1 component were compared with the size of the hole, the area of cystic changes (CC) at the level of the inner nuclear layer (INL) and the outer plexiform layer and Henle fiber layer complex (OPL+HFL), vessel density in the superficial and deep capillary plexus (SCP and DCP). LS and P1 component amplitude were significantly reduced at a distance of up to 5.0° from the fixation point. LS correlates with the apical and basal diameter of the hole (R> -0.53), the area of CC in the INL (R> -0.62) and the OPL+HFL complex (R> -0.55), the density of vessels in the SCP at a distance of up to 2.5° from the fixation point (R>0.51) and in the DCP at a distance of up to 5° from the fixation point (R>0.49). The P1 amplitude correlates with the basal diameter of the hole (R= -0.38), the area of CC in the INL and the OPL+HFL complex (R> -0.33) and vessel density in the SCP (R=0.37) at a distance of up to 2.5° from the fixation point, as well as vessel density in the DCP at a distance of up to 5° from the fixation point (R=0.47). Vessel density in the DCP is significantly lower in the presence of CC in the retina (p<0.001). In FTMH, there is a relationship between bioelectrical activity and LS, and structural disorders, capillary perfusion in different layers of the retina. A multimodal topographically oriented approach allows studying the relationship between structural and functional parameters in individual points of the retina and can be used in monitoring of FTMH after surgical treatment.

Macular edema in ocular inflammation

Aim of this paper is to present the pathophysiological processes and the ultrastructure of the retina, important for the formation and development of macular edema. Macular edema is defined as an abnormal leakage and fluid and/ protein accumulation in the external plexiform layer and inner nuclear layer (on/under the macula), as well as swelling of Muller cells that lead to its thickening and swelling. It occurs as consequence of increased leakage from the retinal perifoveal capillaries and consequential macular thickening that, if it lasts longer than 6 months, is seen as chronic in nature. Based on clinical and imaging techniques, macular edema is classified as ischemic and non-ischemic (cystoid or diffuse). Macular edema is not an isolated ocular disease but is rather a complication of an isolated ocular inflammation or of an ocular inflammation that's associated with systemic non-infectious (autoimmune) or infectious diseases. This paper, in addition to the pathogenesis and clinical manifestations of macular edema, also briefly covers imaging and treatment procedures and emphasizes the importance of treating the underlying inflammatory diseases that has led to the formation of the macular edema.

Rheumatic heart disease presenting with paracentral acute middle maculopathy (PAMM): A case report from rural India

A 38-year-old gentleman presented to us with disturbance in his superior field of view for 3 days. His visual acuity in both eyes was 6/6, N6. The macula of the left eye had a hypopigmented band. OCT demonstrated hyperreflectivity of the inner plexiform, inner nuclear, and outer plexiform layers of the retina, and perimetry showed a corresponding visual field defect. The patient revealed a history of heart surgery 26 years ago, and an echocardiogram revealed mitral valve abnormalities. The history and findings led to a diagnosis of paracentral acute middle maculopathy (PAMM) secondary to rheumatic heart disease. The patient was referred to a cardiologist and started on anti-platelet medications. Thus, we report an unusual case of PAMM due to chronic rheumatic heart disease in a young male from remote rural India. In our case, we made sure to start the patient on anti-platelet medications to prevent future adverse events.

Retinal neurotoxicity induced by inhalation of isopropyl nitrite

Purpose: Popper is a slang term given broadly to drugs of the chemical class called alkyl nitrites that are inhaled. Most widely sold products include the original isopropyl nitrite (IPN) a mix of isopropyl alcohol with nitrous acid and sulphuric acid. Multiple cases of retinopathy have been reported since 2001 that have been associated with the inhalation of poppers, predominantly in Europe. However, no clear information about the effect of these inhalant agents on retinal cells have been shown to date. Our work tries to address the neurotoxic effect of IPN on outer retinal cells evidenced by immunocytochemical technique on murine model.Methods: 8 Opn4‐KO mice were used, n:4 were treated with IPN using a aero chamber inhalator for 20 days (1 mL/5 s) and n:4 with oxygen (ctrl group). CARR antibody was used, encoded by the Arr3 gene in murine species. All the animals were supplied by the Animal Experimentation Center of the UAH. The euthanasia of the animals was carried out in accordance with RD 53/2013 Spanish regulations.Results: The sagittal sections of the Opn4 mouse retina taken with confocal microscopy at 40×, the expression of arrestin‐C can be observed, predominantly in the internal and external segments of the cones without disruption, the presence of CARR confirms the presence of cells of retinal cone in our CARR cuts (Cy5, red), The exposure parameters of the samples and image capture in the confocal microscope were taken based on the immunoreactivity in the Opn4 animal model, remaining stable for the rest of the photos. Labelling at the level of the outer plexiform layer is equally intense in Opn4 Ctrl and Opn4 to animals.Conclusions: The results failed to demonstrate morphological changes of clinical importance that could determine a neurotoxic role in the retina of IPN inhalation; however, we propose the existence of other factors and/or pharmacological interactions with the use of poppers in the aetiopathogenesis of this new ophthalmological disease.

Ultrastructural changes in the rat retina in the presence of long-term opioid exposure

Purpose: To determine the features of the untrastructural reorganization in the rat retina by the end of week 4 and week 6 of experimental opioid exposure. Material and Methods: Forty-eight adult male albino rats (weight, 200-250 g; age, 4.5 months) were used in this study. They received nalbuphine hydrochloride intramuscularly daily for 42 days. Particularly, the drug was administered daily at a dose of 0.212 mg/kg for weeks 1 and 2, 0.225 mg/kg for weeks 3 and 4, and 0.252 mg/kg for weeks 5 and 6. In this way, we experimentally created the conditions of chronic opioid exposure. Animals were divided into three groups. Group 1 (19 animals) received nalbuphine for 28 days, and group 2 (19 animals), for 42 days. Group 3 (control group) comprised 10 animals. Of these, 5 animals were treated with normal saline at a dose of 0.22 mg/kg intramuscularly daily for 28 days, and the rest were treated in a similar manner for 42 days. Transmission electron microscopy studies of the rat retina were conducted in a routine manner. Results: By the end of week 4 of experimental opioid exposure, there was an increase in the number of retinal microvessels with signs of hyperemia and degenerative changes in retinal pigment epithelium (RPE) cells, increase in the destruction of membranous discs of photoreceptor outer segments, necrobiotic changes in the nuclei of individual photoreceptors, axonal degeneration in the outer and inner plexiform layers, degenerative changes in retinal horizontal neurons, and the appearance of necrotic structural changes in the cytoplasm of bipolar and amacrine cells. By the end of week 6, there was a further increase in hyperemia of retinal vessels and degenerative and necrotic changes in individual RPE cells and photoreceptor outer segments. In addition, we observed destruction and shortening of mitochondrial cristae of photoreceptor inner segments, necrotic nuclear changes in individual photoreceptors, degeneration of axons of the outer and inner plexiform layers, degenerative and necrotic changes in bipolar and amacrine cells, hypertrophic Müller cell processes, degeneration of ganglion cells, and vascular hyperemia and moderate perivascular edema in the outer and inner plexiform layers. Conclusion: Therefore, in the current rat study, after a 4-week exposure to daily nalbuphine injections at a dose ranging 0.212 to 0.253 mg/kg, there was ultrastuctural evidence of destructive processes in the RPE and photoreceptor outer segments, axonal degeneration in the outer and inner plexiform layers, degenerative and necrotic changes in bipolar and amacrine cells, hypertrophic Müller cell processes, ganglion cell degeneration and hyperemia due to an impaired retinal microcirculatory ultrastructure. At week 6 of the experiment, there was evidence of increased destructive and degenerative processes in structural components of the retina.

Normative Database of the Superior-Inferior Thickness Asymmetry for All Inner and Outer Macular Layers of Adults for the Posterior Pole Algorithm of the Spectralis SD-OCT.

This study aims to establish a reference for the superior-inferior hemisphere asymmetry in thickness values for all macular layers for the posterior pole algorithm (PPA) available for the Spectralis SD-OCT device. We examined 300 eyes of 300 healthy Caucasian volunteers aged 18-84 years using the PPA, composed of a grid of 64 (8 × 8) cells, to analyze the thickness asymmetries of the following automatically segmented macular layers: retinal nerve fiber layer (RNFL); ganglion cell layer (GCL); inner plexiform layer (IPL); inner nuclear layer (INL); outer plexiform layer (OPL); outer nuclear layer (ONL); retinal pigment epithelium (RPE); inner retina; outer retina; complete retina. Mean ± standard deviation and the 2.5th and 97.5th percentiles of the thickness asymmetry values were obtained for all the corresponding cells. All the macular layers had significant superior-inferior thickness asymmetries. GCL, IPL, INL, ONL and RPE showed significantly greater thicknesses in the superior than the inferior hemisphere, whereas RNFL and OPL were thicker in the inferior hemisphere. The largest differences between hemispheres were for RNFL and ONL. This is the first normative database of macular thickness asymmetries for the PPA and should be considered to distinguish normal from pathological values when interpreting superior-inferior macular asymmetries.

Acute Macular Neuroretinopathy after SARS-CoV-2 Infection: An Analysis of Clinical and Multimodal Imaging Characteristics.

This study aimed to analyze clinical and multimodal imaging characteristics of acute macular neuroretinopathy (AMN) post-recent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Retrospective observational study. Medical records and multimodal imaging of 12 AMN eyes of eight patients (six female and two male) with recent SARS-CoV-2 infection were retrospectively analyzed. Four patients (50%) presented with bilateral AMN. Fundus ophthalmoscopy revealed a reddish-brown lesion around the macula, and two eyes had cotton-wool spots at the posterior pole. Three eyes showed mild hypo-autofluorescence. All FFA images (7 eyes) showed no abnormal signs. On OCT scans, all eyes showed outer nuclear layer (ONL) thinning, 8 eyes (66.7%) showed ONL hyperreflectivity, 5 eyes (41.7%) showed outer plexiform layer (OPL) hyperreflectivity, 8 eyes (66.7%) showed interdigitation zone (IZ) disruption, 11 eyes (91.6%) showed ellipsoid zone (EZ) disruption, 2 eyes (16.7%) showed cotton-wool spots and inner plexiform layer (IPL) hyperreflectivity, 1 eye (8.3%) had intraretinal cyst and 1 eye (8.3%) had inner nuclear layer (INL) thinning. Persistent scotoma, ONL hyperreflectivity and IZ/EZ disruption as well as recovery of OPL hyperreflectivity were reported after follow-up in three cases. AMN post-SARS-CoV-2 mostly affected young females and could present unilaterally or bilaterally. Dark lesions on IR reflectance and outer retinal hyperreflectivity on OCT are useful in diagnosing AMN. OPL/ONL hyperreflectivity on OCT could disappear after follow-up, but ONL thinning and IZ/EZ could persist.

Mouse model of radiation retinopathy reveals vascular and neuronal injury

PurposeTo characterize the neuronal and vascular pathology in vivo and in vitro in a mouse model of radiation retinopathy. MethodsC57Bl/6J mice underwent cranial irradiation with 12 Gy and in vivo imaging by optical coherence tomography and of relative blood flow velocity by laser speckle flowgraphy for up to 3–6 months after irradiation. Retinal architecture, vascular density and leakage and apoptosis were analyzed by histology and immunohistochemistry before irradiation or at 10, 30, 240, and 365 days after treatment. ResultsThe vascular density decreased in the plexiform layers starting at 30 days after irradiation. No impairment in retinal flow velocity was seen. Subtle perivascular leakage was present at 10 days, in particular in the outer plexiform layer. This corresponded to increased width of this layer. However, no significant change in the retinal thickness was detected by OCT-B scans. At 365 days after irradiation, the nuclear density was significantly reduced compared to baseline. Apoptosis was detected at 30 days and less prominent at 365 days. ConclusionsBy histology, vascular leakage at 10 days was followed by increased neuronal apoptosis and loss of neuronal and vascular density. However, in vivo imaging approaches that are commonly used in human patients did not detect pathology in mice.

Discovery of Novel Ophthalmic Imaging Biomarkers for Neurodegenerative Disease

AbstractBackgroundThe retina is increasingly investigated as a site of Alzheimer’s Disease (AD) manifestation, with amyloid β (Aβ) plaques being found in the retina of AD and mild cognitively impaired (MCI) patients, however functional changes in the retina are poorly understood. Retinal imaging techniques can be utilized for neurodegenerative biomarkers, since the retina is the only CNS organ available for noninvasive tracking.MethodRetinal imaging techniques were using to compare the retina of wild‐type (WT) or AD transgenic mice containing the APP: Swedish and Indiana mutation expressed under the prion promoter (TgCRND8) at 20 and 30 weeks of age (n = 10 mice per genotype). Optical coherence tomography (OCT) for retinal thickness assessment, Fundus Autofluorescence Imaging (FAF) for aggregate visualization, and electroretinogram (ERG) for retinal neuronal electrical activity were performed. Aβ ELISA was also performed on retina and cortex to evaluate amyloid burden correlation.ResultMean retinal insoluble Aβ 1‐42 was significantly elevated in TgCRND8 mice relative to WT at 23 weeks (35 vs 4.2 pg/mL, P&lt;0.05) and 42 weeks (77.9 vs 7.5 pg/mL, P&lt;0.05), and correlated with insoluble cortical brain Aβ 1‐42 (Pearson’s r = 0.847, P = 0.001). Total retinal thickness was significantly higher in TgCRND8 mice relative to WT (233 µm vs 225 µm, P&lt;0.01). Specifically, the retinal nerve fiber layer (RNFL) was thicker in TgCRND8 mice (28.5 vs 22.9 µm, P&lt;0.01). FAF imaging revealed significant autofluorescent aggregate detection in TgCRND8 mice both in the RNFL (94.3 vs 59.8 spots, P&lt;0.01) and outer plexiform layer (OPL) (87.8 vs 49.3 spots, P&lt;0.01). Lastly ERG revealed reduced b wave amplitude in TgCRND8 mice relative to WT (197.45 vs 457.9 µV, P&lt;0.001) and photopic negative response (PhNR) wave amplitude (8.2 µm vs 25.7 457.9 µV, P&lt;0.001). These values are indicative of dysfunctional bipolar and retinal ganglion cell electrical activity.ConclusionTgCRND8 mice have functional changes in retina thickness, FAF lipofuscin deposition, and ERG, which may prove invaluable as biomarkers for pre‐clinical AD diagnosis, monitoring and drug efficacy trials.

A retinal tauopathy with a characteristic molecular pattern points to the existence of a “Primary retinal tauopathy”

AbstractBackgroundPathogenic processes characteristic of neurodegenerative brain diseases, such as accumulation of phosphorylated Tau protein (pTau), can also be detected in the retina. Given the advanced state of retinal imaging technology and its potential to aid in the clinical diagnosis of Alzheimer’s disease (AD), it is imperative to investigate the part the retina plays in neurodegenerative diseases of the brain, as well as the associated eye‐specific degenerative processes.MethodsRetinas from 129 individuals who underwent eyeball resection/evisceration for severe ophthalmological conditions and from 35 post‐mortem donors with or without AD were analyzed. Paraffin‐embedded sections from cross‐sectioned retinas were stained with antibodies against different pTau species and Gallyas staining to detect neurofibrillary tangles. Retinal pTau accumulation, its distribution over the retinal layers, and molecular composition were determined neuropathologically and correlated with visual performance, age, and the presence of dementia.ResultsRetinal pTau pathology showed a consistent topographical expansion pattern that allowed distinguishing four stages: Stage 0: no pTau pathology; Stage 1: thread‐like pTau in the outer plexiform layer; Stage 2: additional cytoplasmic pTau in the inner nuclear layer; Stage 3: thread‐like pTau also in the inner plexiform layers. Antibodies against pTauS202/pT205 (AT8), pTauT231 (AT180), and anti‐MC‐1 Tau showed comparable results. Neurofibrillary tangles were not found. The stage of retinal tauopathy was correlated with age (r = 0.176, p = 0.024, n = 164), the underlying ophthalmologic diseases (p = 0.001; β = 0.292), and independently associated with vision impairment (p = 0.030; β = 0.192) in a linear regression model. Cases with a clinical diagnosis of dementia were associated with slightly higher stages of retinal tauopathy (binary logistic regression: p = 0.026; odds ratio (OR) = 1.685 [95% C.I.1.066‐2.664), although some demented cases were free of pTau pathology.ConclusionsThese results point towards the existence of a primary retinal tauopathy (PReT). It differs in its molecular composition from cerebral tauopathies by the lack of argyrophilic inclusions and the predominance of 3‐repeat Tau. However, PReT may be a prerequisite for developing AD pathology in the retina. Altogether, these findings support the presence of retinal neurodegenerative changes that may reflect changes in the brain.FundingSAO/FRA 2020/017

Association between retinal layer thickness and cerebral white matter hyperintensities in older adults

AbstractBackgroundThe brain and retina may share pathophysiological mechanisms in various central nervous system disorders, suggesting the potential associations between retinal layer thickness and cerebral white matter hyperintensities (WMH).MethodA total of 149 participants without dementia aged over 65 years (mean age: 75.4, SD: 5.4, range: 65‐91; male: 90 [60.4%]) from the randomly sampled community‐dwelling prospective cohort were included in the analysis. Using spectral‐domain optical coherence tomography, we assessed the thickness of 6 retinal layers in the macular region, the peripapillary retinal nerve fiber layers, and the subfoveal choroid. We classified WMH into 3 groups using the distance from the ventricle surface: juxtaventricular (JVWMH, &lt; 4mm), periventricular (PVWMH, &gt;4mm, &lt;14mm), and deep WMH (DWMH &gt; = 14mm). The associations between retinal layer thickness and WMH volume were examined using linear regression models adjusting age, sex, comorbid hypertension, and diabetes.ResultThe thicknesses of superior outer, inferior outer ganglion cell layers (GCL) and superior outer, inferior outer, total outer inner plexiform layers (IPL) were negatively associated with the total WMH, PVWMH, and DWMH volumes. Reduced thicknesses of total outer GCL and temporal outer inner nuclear layer (INL) were associated with higher total WMH and PVWMH volumes. Center GCL thickness was positively associated with JVWMH volume, and nasal outer GCL thickness was negatively associated with DWMH volume.ConclusionOuter GCL and IPL thicknesses may be associated with WMH volume in older adults. This study may also suggest differential associations based on etiology between retinal layer subfields and WMH subgroups.

Atlas of Retinal Imaging in Alzheimer’s Study (ARIAS): SD‐OCT in Preclinical Alzheimer’s disease

AbstractBackgroundARIAS is a preclinical Alzheimer’s disease (AD) cohort study, with the aim of following cognitively unimpaired (CU) older adults at high and low risk for AD and studying changes in retinal biomarkers over time. Here, we share baseline Spectral Domain Optical Coherence Tomography (SD‐OCT) data from ARIAS.MethodSD‐OCT was completed using the Heidelberg SPECTRALIS on 146 CU older adults (aged 55‐80), 83 high risk (APOE E4 carriers, first degree family history of AD), 63 low risk (APOE E4 non‐carriers, no first‐degree family history of AD). We took macular (30×25‐degree) and optic disc centered (radii of 3.5, 4.1, and 4.7 mm) SD‐OCT images. Vendor software was used to segment and compute average retinal thickness and volume in the 9 ETDRS maps for the macular and 7 glaucoma fields for the optic disk. ANCOVA (with age as a covariate) was used to compare retinal layer thickness and volume between the two groups. Bonferroni correction was used for multiple comparisons.ResultThe high risk group had significantly higher thickness/volume than the low risk group in the inner temporal quadrant of the ganglion cell layer (GCL, F(2, 144) = 3.67p&lt;.05), the central quadrant of the inner nuclear layer (INL, F(2, 144) = 3.48,p&lt;.05), the inner nasal quadrant of the outer plexiform layer (OPL, F(2, 144) = 7.35,p&lt;.05). The peripapillary retinal nerve fiber layer (pRNFL) showed increased global thickness (F(2, 144) = 4.30, p&lt;.05), and thickness in the nasal (F(2, 144) = 4.23, p&lt;.05), nasal inferior (F(2, 144) = 3.34, p&lt;.05), and temporal inferior (F(2, 144) = 3.61,p&lt;.05) quadrants in the high risk group compared to the low risk group.ConclusionSD‐OCT can be applied to examine retinal thickness in preclinical AD. Thickness/volume of specific quadrants of the GCL, INL, and OPL differentiated high risk CU older adults from low risk CU older adults in a large preclinical cohort. pRNFL global thickness, and thickness in the nasal, nasal inferior, and temporal inferior quadrants, was increased in the high risk group. These results confirm and extend our prior findings of increased retinal layer thickness in preclinical AD. Longitudinal data will confirm whether these layers change over time in preclinical AD.

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

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). 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. 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. 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. 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.

The Role of Sphingosine-1-Phosphate Receptor 2 in Mouse Retina Light Responses.

The bioactive sphingolipid sphingosine-1-phosphate (S1P) acts as a ligand for a family of G protein-coupled S1P receptors (S1PR1-5) to participate in a variety of signaling pathways. However, their specific roles in the neural retina remain unclear. We previously showed that S1P receptor subtype 2 (S1PR2) is expressed in murine retinas, primarily in photoreceptors and bipolar cells, and its expression is altered by retinal stress. This study aims to elucidate the role of S1PR2 in the mouse retina. We examined light responses by electroretinography (ERG), structural differences by optical coherence tomography (OCT), and protein levels by immunohistochemistry (IHC) in wild-type (WT) and S1PR2 knockout (KO) mice at various ages between 3 and 6 months. We found that a- and b-wave responses significantly increased at flash intensities between 400~2000 and 4~2000 cd.s/m2, respectively, in S1PR2 KO mice relative to those of WT controls at baseline. S1PR2 KO mice also exhibited significantly increased retinal nerve fiber layer (RNFL) and outer plexiform layer (OPL) thickness by OCT relative to the WT. Finally, in S1PR2 KO mice, we observed differential labeling of synaptic markers by immunohistochemistry (IHC) and quantitative reverse transcription polymerase chain reaction (RT-qPCR). These results suggest a specific involvement of S1PR2 in the structure and synaptic organization of the retina and a potential role in light-mediated functioning of the retina.

Microstructural and hemodynamic changes in the fundus after pars plana vitrectomy for different vitreoretinal diseases.

Pars plana vitrectomy is the standard treatment for several vitreoretinal diseases. Continuous improvements in ophthalmic surgical techniques have led to excellent postoperative recovery of the anatomic structure of the fundus. However, postoperative visual outcomes are not always satisfactory. A literature search of articles published before 31 December 2022 was conducted on PubMed using the following keywords: "diabetic retinopathy," "rhegmatogenous retinal detachment," "idiopathic epiretinal membrane," "idiopathic macular hole," "vitrectomy," "optical coherence tomography," "optical coherence tomography angiography," "microstructure," "microstructural," "hemodynamic," "hemodynamics," and "microcirculation." Additional studies were identified by hand-searching references for relevant studies. Articles were screened for language, repetition, and relevance to the direction of study. Studies with a sample size ≥ 7 and the final follow-up time ≥ 4weeks after vitrectomy were included in this review. Only articles published in English were included. Articles not related to our topic were excluded. Reviews and single case reports were excluded. We structured this review by disease category. The thickness of the retina and choroid, the area of the foveal avascular zone, the vessel density of the retinal and choroidal capillary plexus, and the potential association of related parameters with postoperative visual outcomes are the main outcome measures of studies included in this review. A total of 48 studies were included in this review. There were contradictory results regarding the association between postoperative microcirculatory parameters and visual acuity in patients with diabetic macular edema, with some studies concluding that improvement in perimacular microcirculation may be an important factor that affects visual acuity, and others concluded that postoperative improvement in visual acuity was not related to changes in macular blood flow. The results of studies on the relationship between postoperative microstructural and microcirculatory parameters and visual acuity in rhegmatogenous retinal detachment, idiopathic epiretinal membrane, and idiopathic macular hole eyes have been inconsistent. In gas tamponade macula-off rhegmatogenous retinal detachment eyes, postoperative best-corrected visual acuity has been reported to correlate positively with vessel density of deep capillary plexus and negatively with foveal avascular zone area of superficial capillary plexus and deep capillary plexus. In silicone oil tamponade macula-off rhegmatogenous retinal detachment eyes, best-corrected visual acuity has been reported to be positively correlated with the retinal thickness of the parafoveal 3mm temporal quadrant and positively correlated with the vessel density of the superficial capillary plexus in the foveal, parafoveal, and perifoveal area. In addition, best-corrected visual acuity was worse and associated with reduced thickness of the inner retina, ganglion cell layer, outer plexiform layer, and outer nuclear layer in silicone oil tamponade rhegmatogenous retinal detachment eyes compared to gas tamponade. Postoperative best-corrected visual acuity in idiopathic epiretinal membrane eyes was positively correlated with the foveal avascular zone area but negatively correlated with full retinal thickness and inner retinal thickness in the foveal and parafoveal areas. Improvement in postoperative best-corrected visual acuity in idiopathic macular hole eyes was associated with reduced inner retinal thickness and reduced foveal avascular zone area. Microstructural and hemodynamic changes are involved in the recovery process after PPV for different vitreoretinal diseases. The thickness of each retinal layer in different regions of the macula, foveal avascular zone area, and vessel density of different retinal capillary plexuses in different macular regions may be potential prognostic factors for postoperative visual recovery. However, the results of the existing literature are inconsistent and require further study.

Dye coupling of horizontal cells in the primate retina.

In the monkey retina, there are two distinct types of axon-bearing horizontal cells, known as H1 and H2 horizontal cells (HCs). In this study, cell bodies were prelabled using 4',6-diamidino-2-phenylindole (DAPI), and both H1 and H2 horizontal cells were filled with Neurobiotin™ to reveal their coupling, cellular details, and photoreceptor contacts. The confocal analysis of H1 and H2 HCs was used to assess the colocalization of terminal dendrites with glutamate receptors at cone pedicles. After filling H1 somas, a large coupled mosaic of H1 cells was labeled. The dendritic terminals of H1 cells contacted red/green cone pedicles, with the occasional sparse contact with blue cone pedicles observed. The H2 cells were also dye-coupled. They had larger dendritic fields and lower densities. The dendritic terminals of H2 cells preferentially contacted blue cone pedicles, but additional contacts with nearly all cones within the dendritic field were still observed. The red/green cones constitute 99% of the input to H1 HCs, whereas H2 HCs receive a more balanced input, which is composed of 58% red/green cones and 42% blue cones. These observations confirm those made in earlier studies on primate horizontal cells by Dacey and Goodchild in 1996. Both H1 and H2 HCs were axon-bearing. H1 axon terminals (H1 ATs) were independently coupled and contacted rod spherules exclusively. In contrast, the H2 axon terminals contacted cones, with some preference for blue cone pedicles, as reported by Chan and Grünert in 1998. The primate retina contains three independently coupled HC networks in the outer plexiform layer (OPL), identified as H1 and H2 somatic dendrites, and H1 ATs. At each cone pedicle, the colocalization of both H1 and H2 dendritic tips with GluA4 subunits close to the cone synaptic ribbons indicates that glutamate signaling from the cones to H1 and H2 horizontal cells is mediated by α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors.

Automated quantification of macular edema in patients with diabetic macular edema and their response to anti-VEGF: A study protocol

Diabetes mellitus type 2 (T2DM) is the fastest-growing chronic condition. Diabetes mellitus can lead to a variety of complications, all of which have a significant impact on medical care expenditures as well as patient life span and wellbeing. The most prevalent microvascular ocular sequel of diabetes is diabetic retinopathy (DR), causing diffuse retinal edema from extensive capillary leakage and localized edema from microaneurysm leakage. A dilated capillary segment is also seen. It has been observed that the fluid first accumulates between the inner nuclear layers and the outer plexiform layer. Later, it may infiltrate the inner plexiform and nerve fiber layers, causing edema and affecting the retina’s total thickness. The fovea takes on a cystoid appearance on optical coherence tomography due to central fluid accumulation, and cystoid macular edema can be seen. Anti-vascular endothelial growth factor (anti-VEGF) medication is a cornerstone of DME treatment. Research has shown that drugs that attach to soluble VEGF can repair the blood-retinal barrier, alleviate macular edema, and enhance vision for the majority of DME patients. Ranibizumab is the only FDA-approved drug for DME, but bevacizumab is often used off-label and an FDA request for aflibercept is still pending. Regular injections are necessary for effective treatment, but new findings suggest that this requirement lessens after a year. The study aims to evaluate the impact of intravitreal Anti-VEGF injection by measuring the alterations in macular edema and relating it to the visual results. CTRI reference Number – REF/2023/07/071019

Functional Evaluation of Retinal Pigment Epithelium and Outer Retinal Atrophy by High-Density Targeted Microperimetry Testing

Complete retinal pigment epithelium (RPE) and outer retinal atrophy (cRORA) on OCT imaging has recently been proposed to describe end-stage atrophy in age-related macular degeneration (AMD) by international consensus and expected to be associated with a dense scotoma, but such functional evidence is lacking. This study sought to examine the visual sensitivity defects associated with cRORA and to determine OCT features associated with deep defects. Observational study. Sixty eyes from 53 participants, including 342 microperimetry tests over 171 study visits. Participants underwent targeted high-density threshold-based microperimetry testing of atrophic lesions (with at least incomplete RPE and outer retinal atrophy [iRORA]) with a 3.5° diameter grid. The maximum extent of signs of atrophy for all lesions was graded on OCT imaging. Number of deep visual sensitivity defects (threshold ≤ 10decibels [dB]). Presence of choroidal signal hypertransmission ≥ 500 μm, complete RPE loss ≥250 μm, and inner nuclear layer and outer plexiform layer subsidence, and hyporeflective wedge-shaped band (defined as nascent geographic atrophy [nGA]) ≥ 500 μm (P ≤ 0.020), but not RPE attenuation or disruption (P ≥ 0.192), were all independently associated with a significant increase in the number of deep visual sensitivity defects ≤ 10 dB. Only cRORA lesions with hypertransmission ≥ 500 μm or complete RPE loss ≥ 250 μm, or with both of these features (P < 0.001), but not lesions with only hypertransmission 250-499 μm (P = 0.303), had significantly more deep visual sensitivity defects ≤ 10 dB compared with iRORA lesions. Lesions with nGA ≥ 500 μm, irrespective of the presence of hypertransmission ≥ 500 μm and/or complete RPE loss ≥ 250 μm, also showed a higher number of deep visual sensitivity defects ≤ 10 dB compared with lesions without nGA ≥ 500 μm (P≤0.011). Not all cRORA lesions show a difference in the number of deep visual sensitivity defects compared with iRORA. Instead, hypertransmission ≥ 500 μm, complete RPE loss ≥ 250 μm, and nGA ≥ 500 μm are all OCT features independently associated with deep visual sensitivity detects that could help inform the definition of end-stage atrophy on OCT imaging. Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Prph2 knock-in mice recapitulate human central areolar choroidal dystrophy retinal degeneration and exhibit aberrant synaptic remodeling and microglial activation.

Central areolar choroidal dystrophy is an inherited disorder characterized by progressive choriocapillaris atrophy and retinal degeneration and is usually associated with mutations in the PRPH2 gene. We aimed to generate and characterize a mouse model with the p.Arg195Leu mutation previously described in patients. Heterozygous (Prph2WT/KI) and homozygous (Prph2KI/KI) mice were generated using the CRISPR/Cas9 system to introduce the p.Arg195Leu mutation. Retinal function was assessed by electroretinography and optomotor tests at 1, 3, 6, 9, 12, and 20 months of age. The structural integrity of the retinas was evaluated at the same ages using optical coherence tomography. Immunofluorescence and transmission electron microscopy images of the retina were also analyzed. Genetic sequencing confirmed that both Prph2WT/KI and Prph2KI/KI mice presented the p.Arg195Leu mutation. A progressive loss of retinal function was found in both mutant groups, with significantly reduced visual acuity from 3 months of age in Prph2KI/KI mice and from 6 months of age in Prph2WT/KI mice. Decreased amplitudes in the electroretinography responses were observed from 1 month of age in Prph2KI/KI mice and from 6 months of age in Prph2WT/KI mice. Morphological analysis of the retinas correlated with functional findings, showing a progressive decrease in retinal thickness of mutant mice, with earlier and more severe changes in the homozygous mutant mice. We corroborated the alteration of the outer segment structure, and we found changes in the synaptic connectivity in the outer plexiform layer as well as gliosis and signs of microglial activation. The new Prph2WT/KI and Prph2KI/KI murine models show a pattern of retinal degeneration similar to that described in human patients with central areolar choroidal dystrophy and appear to be good models to study the mechanisms involved in the onset and progression of the disease, as well as to test the efficacy of new therapeutic strategies.