The Effects of Diabetic Retinopathy and Pan-Retinal Photocoagulation on Photoreceptor Cell Function as Assessed by Dark Adaptometry

USP48 deubiquitination stabilizes SLC1A5 to inhibit retinal pigment epithelium cell inflammation, oxidative stress and ferroptosis in the progression of diabetic retinopathy

BACKGROUND

Diabetic retinopathy is one of the complications of diabetes mellitus. The aim of this study was to explore the effects of ubiquitin-specific protease 48 (USP48) and its underlying mechanisms in the development of diabetic retinopathy.

METHODS

CCK-8 assay, EdU assay, and flow cytometry were used to measure the proliferative ability and the apoptotic rate of ARPE-19 cells, respectively. ELISA kits were utilized to assess the levels of inflammatory cytokines. The levels of Fe2+, ROS and MDA were detected using the corresponding biochemical kits. The protein expression of USP48 and SLC1A5 was examined through western blot. The mRNA level of SLC1A5 was determined using RT-qPCR. The interaction relationship between USP48 and SLC1A5 was evaluated using Co-IP assay.

RESULTS

High glucose (HG) treatment significantly inhibited cell proliferation and elevated cell apoptosis, inflammation, ferroptosis and oxidative stress in ARPE-19 cells. HG treatment-caused cell damage was hindered by USP48 or SLC1A5 overexpression in ARPE-19 cells. Fer-1 treatment improved HG-caused cell damage in ARPE-19 cells, which was blocked by USP48 knockdown. Moreover, USP48 knockdown decreased SLC1A5 expression. SLC1A5 downregulation reversed the improvement effects of USP48 upregulation on cell damage in HG-treated ARPE-19 cells.

CONCLUSION

USP48 overexpression deubiquitinated SLC1A5 to elevate cell proliferation and suppress cell apoptosis, inflammation, ferroptosis and oxidative stress in HG-triggered ARPE-19 cells, thereby inhibiting the progression of diabetic retinopathy.

Reduced light exposure mitigates streptozotocin-induced vascular changes and gliosis in diabetic retina by an anti-inflammatory effect and increased retinal cholesterol turnover

Diabetic retinopathy is not cured efficiently and changes of lifestyle measures may delay early retinal injury in diabetes. The aim of our study was to investigate the effects of reduced daily light exposure on retinal vascular changes in streptozotocin (STZ)-induced model of DM with emphasis on inflammation, Aqp4 expression, visual cycle and cholesterol metabolism-related gene expression in rat retina and RPE. Male Wistar rats were divided into the following groups: 1. control; 2. diabetic group (DM) treated with streptozotocin (100 mg/kg); 3. group exposed to light/dark cycle 6/18 h (6/18); 4. diabetic group exposed to light/dark cycle 6/18 h (DM+6/18). Retinal vascular abnormalities were estimated based on lectin staining, while the expression of genes involved in the visual cycle, cholesterol metabolism, and inflammation was determined by qRT-PCR. Reduced light exposure alleviated vasculopathy, gliosis and the expression of IL-1 and TNF-α in the retina with increased perivascular Aqp4 expression. The expression of genes involved in visual cycle and cholesterol metabolism was significantly up-regulated in RPE in DM+6/18 vs. DM group. In the retina only the expression of APOE was significantly higher in DM+6/18 vs. DM group. Reduced light exposure mitigates vascular changes and gliosis in DM via its anti-inflammatory effect, increased retinal cholesterol turnover and perivascular Aqp4 expression.

Simultaneous alignment and surface regression using hybrid 2D-3D networks for 3D coherent layer segmentation of retinal OCT images with full and sparse annotations

Layer segmentation is important to quantitative analysis of retinal optical coherence tomography (OCT). Recently, deep learning based methods have been developed to automate this task and yield remarkable performance. However, due to the large spatial gap and potential mismatch between the B-scans of an OCT volume, all of them were based on 2D segmentation of individual B-scans, which may lose the continuity and diagnostic information of the retinal layers in 3D space. Besides, most of these methods required dense annotation of the OCT volumes, which is labor-intensive and expertise-demanding. This work presents a novel framework based on hybrid 2D-3D convolutional neural networks (CNNs) to obtain continuous 3D retinal layer surfaces from OCT volumes, which works well with both full and sparse annotations. The 2D features of individual B-scans are extracted by an encoder consisting of 2D convolutions. These 2D features are then used to produce the alignment displacement vectors and layer segmentation by two 3D decoders coupled via a spatial transformer module. Two losses are proposed to utilize the retinal layers' natural property of being smooth for B-scan alignment and layer segmentation, respectively, and are the key to the semi-supervised learning with sparse annotation. The entire framework is trained end-to-end. To the best of our knowledge, this is the first work that attempts 3D retinal layer segmentation in volumetric OCT images based on CNNs. Experiments on a synthetic dataset and three public clinical datasets show that our framework can effectively align the B-scans for potential motion correction, and achieves superior performance to state-of-the-art 2D deep learning methods in terms of both layer segmentation accuracy and cross-B-scan 3D continuity in both fully and semi-supervised settings, thus offering more clinical values than previous works.

Optical coherence tomography in healthy human subjects in the setting of prolonged dark adaptation

Human studies have established that short periods of dark adaptation can induce outer retinal thinning and various band intensity changes that can be detected with Optical Coherence Tomography (OCT). Similar findings were observed in mice, including a positive correlation between the degree of outer retinal changes and dark adaptation duration. We decided to assess potential retinal structural changes following prolonged dark adaptation in humans. 40 healthy subjects without any ocular diseases participated in this study. For each subject, one eye was covered for dark adaptation for four hours, and the other eye was left uncovered as a control. Before and after the dark adaptation period, both eyes were assessed with OCT. Using the Heidelberg Spectralis system, basic statistical functions, and qualitative and quantitative analysis, we were able to compare retinal layer thicknesses and band intensities between covered (dark adapted) versus uncovered (control) eyes. Prolonged dark adaptation did not induce any significant thickness, volume, or intensity changes in the outer retina or in the inner or overall retina. These observations thus alter our current understanding of the mechanisms underlying dark adaptation's neuroprotective effects in preventing blindness and require further study.

25-hydroxyvitamin D3 inhibits oxidative stress and ferroptosis in retinal microvascular endothelial cells induced by high glucose through down-regulation of miR-93

BACKGROUND

The decrease of vitamin D plays a critical role in diabetes mellitus (DM)-induced oxidative stress and vascular endothelial injury. Therefore, we investigated the effect and mechanism of 25-hydroxyvitamin D3 (25 (OH) D3) on oxidative stress and ferroptosis induced by high glucose in human retinal microvascular endothelial cells (hRMVECs). And the objective of this paper was to propose a new strategy for the prevention and treatment of diabetic retinopathy (DR).

METHODS

First, hRMVECs were transfected with mimics NC or miR-93. After that, cells were treated with 100 nM / 500 nM 25 (OH) D3 and then cultured in a high glucose (30 mM) environment. Subsequently, qRT-PCR was employed to detect the expression level of miR-93; CCK-8 for the proliferation of cells in each group; biochemical tests for the level of intracellular reactive oxygen species (ROS), malondialdehyde (MDA), reduced glutathione (GSH) and ferrous ion (Fe²⁺); and Western blot for the expression of ferroptosis-related proteins glutathione peroxidase 4 (GPX4) and SLC7A11).

RESULTS

Under a high glucose environment, 25 (OH) D3 at 100 nM/500 nM could significantly promote the proliferation of hRMVECs, remarkably decrease the level of intracellular ROS/MDA, and up-regulate the level of GSH. Besides, 25 (OH) D3 greatly reduced Fe²⁺ level in the cells while increased protein level of GPX4 and SLC7A11. Subsequently, we found that high glucose induced miR-93 expression, while 25 (OH) D3 markedly decreased high glucose-induced miR-93 overexpression. Furthermore, overexpression of miR-93 inhibited the functions of 25 (OH) D3 by activating ROS (ROS and MDA were up-regulated while GSH was down-regulated) and inducing Fe²⁺ (Fe²⁺ level was up-regulated while GPX4 and SLC7A11 level was down-regulated) in cells.

CONCLUSION

25 (OH) D3 may inhibit oxidative stress and ferroptosis in hRMVECs induced by high glucose via down-regulation of miR-93.

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

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

Dark Adaptation and Its Role in Age-Related Macular Degeneration

Dark adaptation (DA) refers to the slow recovery of visual sensitivity in darkness following exposure to intense or prolonged illumination, which bleaches a significant amount of the rhodopsin. This natural process also offers an opportunity to understand cellular function in the outer retina and evaluate for presence of disease. How our eyes adapt to darkness can be a key indicator of retinal health, which can be altered in the presence of certain diseases, such as age-related macular degeneration (AMD). A specific focus on clinical aspects of DA measurement and its significance to furthering our understanding of AMD has revealed essential findings underlying the pathobiology of the disease. The process of dark adaptation involves phototransduction taking place mainly between the photoreceptor outer segments and the retinal pigment epithelial (RPE) layer. DA occurs over a large range of luminance and is modulated by both cone and rod photoreceptors. In the photopic ranges, rods are saturated and cone cells adapt to the high luminance levels. However, under scotopic ranges, cones are unable to respond to the dim luminance and rods modulate the responses to lower levels of light as they can respond to even a single photon. Since the cone visual cycle is also based on the Muller cells, measuring the impairment in rod-based dark adaptation is thought to be particularly relevant to diseases such as AMD, which involves both photoreceptors and RPE. Dark adaptation parameters are metrics derived from curve-fitting dark adaptation sensitivities over time and can represent specific cellular function. Parameters such as the cone-rod break (CRB) and rod intercept time (RIT) are particularly sensitive to changes in the outer retina. There is some structural and functional continuum between normal aging and the AMD pathology. Many studies have shown an increase of the rod intercept time (RIT), i.e., delays in rod-mediated DA in AMD patients with increasing disease severity determined by increased drusen grade, pigment changes and the presence of subretinal drusenoid deposits (SDD) and association with certain morphological features in the peripheral retina. Specifications of spatial testing location, repeatability of the testing, ease and availability of the testing device in clinical settings, and test duration in elderly population are also important. We provide a detailed overview in light of all these factors.

Imaging retinal microvascular manifestations of carotid artery disease in older adults: from diagnosis of ocular complications to understanding microvascular contributions to cognitive impairment

Carotid artery stenosis (CAS) is a consequence of systemic atherosclerotic disease affecting the aging populations of the Western world. CAS is frequently associated with cognitive impairment. However, the mechanisms contributing to the development of vascular cognitive impairment (VCI) associated with CAS are multifaceted and not fully understood. In addition to embolization and decreased blood flow due to the atherosclerotic lesion in the carotid artery, microcirculatory dysfunction in the cerebral circulation also plays a critical role in CAS-related VCI. To better understand the microvascular contributions to cognitive decline associated with CAS and evaluate microvascular protective effects of therapeutic interventions, it is essential to examine the structural and functional changes of the microvessels in the central nervous system (CNS). However, there are some limitations of in vivo brain vascular imaging modalities. The retinal microvasculature provides a unique opportunity to study pathogenesis of cerebral small vessel disease and VCI, because the cerebral circulation and the retinal circulation share similar anatomy, physiology and embryology. Similar microvascular pathologies may manifest in the brain and the retina, thus ocular examination can be used as a noninvasive screening tool to investigate pathological changes in the CNS associated with CAS. In this review, ocular signs of CAS and the retinal manifestations of CAS-associated microvascular dysfunction are discussed. The advantages and limitation of methods that are capable of imaging the ocular circulation (including funduscopy, fluorescein angiography, Doppler sonography, optical coherence tomography [OCT] and optical coherence tomography angiography [OCTA]) are discussed. The potential use of dynamic retinal vessel analysis (DVA), which allows for direct visualization of neurovascular coupling responses in the CNS, for understanding microvascular contributions to cognitive decline in CAS patients is also considered.

Photoreceptor cells and RPE contribute to the development of diabetic retinopathy

Diabetic retinopathy (DR) is a leading cause of blindness. It has long been regarded as vascular disease, but work in the past years has shown abnormalities also in the neural retina. Unfortunately, research on the vascular and neural abnormalities have remained largely separate, instead of being integrated into a comprehensive view of DR that includes both the neural and vascular components. Recent evidence suggests that the most predominant neural cell in the retina (photoreceptors) and the adjacent retinal pigment epithelium (RPE) play an important role in the development of vascular lesions characteristic of DR. This review summarizes evidence that the outer retina is altered in diabetes, and that photoreceptors and RPE contribute to retinal vascular alterations in the early stages of the retinopathy. The possible molecular mechanisms by which cells of the outer retina might contribute to retinal vascular damage in diabetes also are discussed. Diabetes-induced alterations in the outer retina represent a novel therapeutic target to inhibit DR.

Looking Ahead: Visual and Anatomical Endpoints in Future Trials of Diabetic Macular Ischemia

Diabetic macular ischemia (DMI) is a common complication of diabetic retinopathy that can lead to progressive and irreversible visual loss. Despite substantial clinical burden, there are no treatments for DMI, no validated clinical trial endpoints, and few clinical trials focusing on DMI. Therefore, generating consensus on validated endpoints that can be used in DMI for the development of effective interventions is vital. In this review, we discuss potential endpoints appropriate for use in clinical trials of DMI, and consider the data required to establish acceptable and meaningful endpoints. A combination of anatomical, functional, and patient-reported outcome measures will provide the most complete picture of changes that occur during the progression of DMI. Potential endpoint measures include change in size of the foveal avascular zone measured by optical coherence tomography angiography and change over time in best-corrected visual acuity. However, these endpoints must be supported by further research. We also recommend studies to investigate the natural history and progression of DMI. In addition to improving understanding of how patient demographics and comorbidities such as diabetic macular edema affect clinical trial endpoints, these studies would help to build the consensus definition of DMI that is currently missing from clinical practice and research.

Diabetic Retinopathy: Important Biochemical Alterations and the Main Treatment Strategies

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by impaired glucose homeostasis, insulin resistance and hyperglycemia. Among its serious multisystemic complications is diabetic retinopathy (DR), which develops slowly and often insidiously. This disorder-the most common cause of vision loss in working-age adults-is characterized by functional and morphological changes in the retina. It results from the exacerbation of ischemic and inflammatory conditions prompted by alterations in the blood vessels, such as the development of leukostasis, thickening of the basement membrane, retinal neovascularization and fibrovascular tissue formation at the vitreoretinal interface. The pathogenic alterations are usually triggered at the biochemical level, involving a greater activity in 4 pathways: the polyol pathway, the hexosamine pathway, the formation of advanced glycation end-products and the activation of protein kinase C isoforms. When acting together, these pathways give rise to increased levels of reactive oxygen species and decreased levels of endogenous antioxidant agents, thus generating oxidative stress. All current therapies are aimed at the later stages of DR, and their application implies side effects. One possible strategy for preventing the complications of DM is to counteract the elevated superoxide production stemming from a high level of blood glucose. Accordingly, some treatments are under study for their capacity to reduce vascular leakage and avoid retinal ischemia, retinal neovascularization and macular edema. The present review summarizes the biochemical aspects of DR and the main approaches for treating it.

Diabetic photoreceptors: Mechanisms underlying changes in structure and function

Based on clinical findings, diabetic retinopathy (DR) has traditionally been defined as a retinal microvasculopathy. Retinal neuronal dysfunction is now recognized as an early event in the diabetic retina before development of overt DR. While detrimental effects of diabetes on the survival and function of inner retinal cells, such as retinal ganglion cells and amacrine cells, are widely recognized, evidence that photoreceptors in the outer retina undergo early alterations in diabetes has emerged more recently. We review data from preclinical and clinical studies demonstrating a conserved reduction of electrophysiological function in diabetic retinas, as well as evidence for photoreceptor loss. Complementing in vivo studies, we discuss the ex vivo electroretinography technique as a useful method to investigate photoreceptor function in isolated retinas from diabetic animal models. Finally, we consider the possibility that early photoreceptor pathology contributes to the progression of DR, and discuss possible mechanisms of photoreceptor damage in the diabetic retina, such as enhanced production of reactive oxygen species and other inflammatory factors whose detrimental effects may be augmented by phototransduction.

A critical review: Psychophysical assessments of diabetic retinopathy

Diabetic retinal disease remains a leading cause of vision loss despite currently available screening methods, ocular treatments, and efforts to control metabolic dysfunction. It is now understood that diabetes damages the entire retina and the cellular components of the neurovascular unit. Multiple studies have demonstrated impairment of various aspects of retinal function across the spectrum of retinopathy severity. Here we review these tests, the principles underlying their use, clinical data from multiple publications, the strengths and limitations of the studies, and prospects for their application to understand the pathophysiology of diabetic retinal disease and monitor its response to therapy. We focus on visual acuity, contrast sensitivity, color vision, visual field, and dark adaptation and their use to understand the pathophysiology of diabetic retinopathy and as potential endpoints for clinical trials.

Treated PDR Reveals Age-Appropriate Vision Deterioration But Distorted Retinal Organization

Purpose

We determined the progression of visual function, macular structure, and quality of life in patients with regressed proliferative diabetic retinopathy (PDR) after panretinal photocoagulation (PRP).

Methods

In this prospective study, 22 patients who underwent PRP for PDR and 11 age-matched control participants underwent examinations at baseline and after 5 years. Visual acuity, contrast sensitivity, reading acuity, frequency doubling perimetry, Humphrey field analyzer, and dark adaptation were measured. The Low Luminance Questionnaire and National Eye Institute Vision Function Questionnaire-25 were administered. Macular spectral-domain optical coherence tomography was taken.

Results

After 5 years, patients who had previously undergone PRP for PDR (18.4 ± 7.9 years previously) showed significant deterioration in contrast sensitivity, reading acuity, frequency doubling perimetry 24-2 pattern standard deviation, and Humphrey field analyzer 10-2 foveal sensitivity, which were equivalent to age-related decreases in control participants. They revealed no further impairment in vision-related activities on questionnaires. In contrast with controls, their maculas showed pathologic disorganization of the retinal layers, especially the nerve fiber layer, which were thicker and constituted a greater proportion of the overall retinal thickness than the norm and associated with impaired vision.

Conclusions

Patients with treated PDR had age-related decreases in vision, but stable quality of life. Prior injuries from the diabetes and, possibly, laser treatment led to substantial disruption in the retinal structure, which may explain the loss of vision.

Translational Relevance

Despite PRP treatment, patients with regressed PDR had pathologic progression of the nerve fiber layer; further investigation may identify a new therapeutic target to reverse the visual deficits.

DARK ADAPTATION IN MACULAR TELANGIECTASIA TYPE 2

PURPOSE

To evaluate dark adaptation (DA) in patients with macular telangiectasia Type 2 (MacTel).

METHODS

After a local photobleach (4 × 4° size, 83% bleach), DA was measured using a test stimulus (2° diameter) projected at 5° eccentricity horizontal from the foveal center within the temporal parafovea. Cone plateau, rod intercept time, and rod recovery rate (S2) were calculated from the resulting DA curves. Findings were correlated with disease stages (according to Gass and Blodi), the area of ellipsoid zone loss in optical coherence tomography, and macular pigment loss ("MP-Classes 1-3").

RESULTS

Fifty-nine eyes of 59 patients were compared with 18 eyes of 18 healthy controls. Dark adaptation was significantly impaired in patients with MacTel. Although differences were most pronounced for parameters indicating rod-mediated recovery, cone-mediated recovery was also decreased, yet to a lesser extent. Dark adaptation parameters were only weakly associated with disease stages and ellipsoid zone loss. A better association was found between rod-mediated recovery (S2 and rod intercept time) and macular pigment loss (Kendall's tau for rod intercept time: 0.69 and S2: -0.51; both P < 0.0001).

CONCLUSION

Dark adaptation is significantly impaired in patients with MacTel. Our results indicate an association of reduced macular pigment and rod dysfunction in MacTel.

Autophagy, lysosome dysfunction and mTOR inhibition in MNU-induced photoreceptor cell damage

Progressive photoreceptor death is the main cause of retinal degeneration diseases. Determining the underlying mechanism of this process is essential for therapy improvement. Autophagy has long been considered to be involved in neuronal degeneration diseases, and the regulation of autophagy is thought to have potential implications for neurodegenerative disease therapies. However, whether autophagy is protective or destructive varies among diseases and is controversial. In the present study, we established an N-methyl-N-nitrosourea (MNU)-induced photoreceptor cell damage model in vitro that faithfully replicated photoreceptor cell death in retinal degeneration diseases. Cell viability was tested by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxy-methoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assays. Reactive oxygen species (ROS) levels were assessed through 2,7-dichlorodihydrofluorescein diacetate (DCFH-DA) fluorescence. Autophagy was confirmed by observing autophagosomes using transmission electron microscopy (TEM). A lysosome tracker was used to identify acidic lysosomes in cells. We also measured the expression of some proteins related to autophagy, apoptosis and lysosomal degradation by western blot and immunofluorescence assays. We found that MNU could decrease photoreceptor cell viability in a time- and dose-dependent manner, and this change was accompanied by concomitant increases in ROS and the expression of the apoptosis-inducing protein cleaved caspase-3. Moreover, autophagy was activated by MNU treatment during this process. Inhibition of autophagy with 3-methyladenine accelerated cell damage. Lysosome dysfunction was confirmed by autophagosome enlargement and increased cathepsin expression, which was accompanied by mTOR dephosphorylation. In conclusion, autophagy was activated through inhibition of the PI3K/mTOR pathway in the context of MNU-induced photoreceptor cell death. Prolonged mTOR dephosphorylation and autophagy activation resulted in autophagic vacuole accumulation, as indicated by inefficient degradation in lysosomes, and further led to apoptosis.

Emerging Insights and Interventions for Diabetic Retinopathy

PURPOSE OF REVIEW

To introduce recent advances in the understanding of diabetic retinopathy and to summarize current and emerging strategies to treat this common and complex cause of vision loss.

RECENT FINDINGS

Advances in retinal imaging and functional analysis indicate that retinal vascular and neural pathologies exist long before the development of clinically visible retinopathy. Such diagnostics could facilitate risk stratification and selective early intervention in high-risk patients. Antagonists of the vascular endothelial growth factor pathway effectively reduce vision loss in diabetes and promote regression of disease severity. Promising new strategies to treat diabetic retinopathy involve novel systemic diabetes therapy and ocular therapies that antagonize angiogenic growth factor signaling, improve blood-retina barrier function and neurovascular coupling, modulate neuroretinal metabolism, or provide neuroprotection. Long considered a pure microvasculopathy, diabetic retinopathy in fact affects the neural and vascular retina as well as neurovascular communication. Emerging therapies include those that target neuroretinal dysfunction in addition to those modulating vascular biology.

Patient-Reported Outcomes Reveal Impairments Not Explained by Psychophysical Testing in Patients With Regressed PDR

Purpose

We evaluated the correlations between visual deficits and patient-reported symptoms in patients with regressed proliferative diabetic retinopathy (PDR) to determine whether there is a psychophysical basis for vision-related impairments.

Methods

Visual acuity, reading acuity, contrast sensitivity, frequency doubling perimetry (FDP), Humphrey field analyzer (HFA), and dark adaptation assessed visual function. The National Eye Institute Vision Function Questionnaire-25 (NEI VFQ-25) and Low Luminance Questionnaire (LLQ) assessed quality of life.

Results

We recruited 30 adults who received panretinal photocoagulation (PRP) for PDR and 15 control subjects; 22 diabetic and 11 control participants completed a second evaluation 5 years later. Visual acuity of the worse-seeing eyes tended to correlate better with NEI VFQ-25 and LLQ than did the acuity of the better-seeing eyes. Other vision measures were generally not associated with either questionnaire, especially responses related to driving ability and mental health. Visual acuity only detected subnormal performance in 43% to 45% of patients, while FDP 24-2, HFA 60-4, and LLQ detected abnormal performance in >80% of patients.

Conclusions

Poor visual acuity may explain some vision-related impairments in daily function. However, many patients with regressed PDR have normal acuity but reduced visual field and poor quality of life. In these patients, their reported symptoms were not fully explained by visual acuity or any psychophysical tests alone.

Translational Relevance

Visual acuity is a poor indicator of overall visual function in people with regressed PDR. In clinical settings, visual field tests and patient-reported outcomes may provide more comprehensive assessments of their functional deficits than visual acuity.

Correlation of retinal vascular perfusion density with dark adaptation in diabetic retinopathy

PURPOSE

To evaluate the anatomic versus functional changes in diabetic retinopathy (DR) by studying the correlation of retinal vascular perfusion density and dark adaptation (DA).

METHODS

Optical coherence tomography angiography (OCTA) and DA tests were performed in diabetic patients and nondiabetic controls. DA was measured using AdaptDx dark adaptometer and the rod intercept was recorded. Macular OCTA images were acquired using the RTVue XR Avanti with AngioVue.

RESULTS

Eighty-six eyes from 57 patients with diabetes (19 with no DR, 19 with non-proliferative DR [NPDR], and 19 with proliferative DR [PDR] who had undergone photocoagulation) and 10 eyes from 10 patients without diabetes were recruited. A significant decrease in vascular density and a prolonged rod intercept were found as DR progressed (P < .01). A negative trend was found between vascular density and the rod intercept. The negative trend in the deep layer (R² = 0.28) was more substantial than that in the superficial layer (R² = 0.14). A prolonged rod intercept was associated with elevated HbA1c (R² = 0.08).

CONCLUSIONS

The vascular density of the macula could be assessed by OCTA and the functional change in the outer retina could be measured non-invasively by DA. The severity of decreasing vascular density and prolongation of DA are proportional to progression of DR. Decreased deep retinal vascular perfusion density and impaired DA response are correlated and show a negative trend according to the severity of DR.

Layer boundary evolution method for macular OCT layer segmentation

Optical coherence tomography (OCT) is used to produce high resolution depth images of the retina and is now the standard of care for in-vivo ophthalmological assessment. It is also increasingly being used for evaluation of neurological disorders such as multiple sclerosis (MS). Automatic segmentation methods identify the retinal layers of the macular cube providing consistent results without intra- and inter-rater variation and is faster than manual segmentation. In this paper, we propose a fast multi-layer macular OCT segmentation method based on a fast level set method. Our framework uses contours in an optimized approach specifically for OCT layer segmentation over the whole macular cube. Our algorithm takes boundary probability maps from a trained random forest and iteratively refines the prediction to subvoxel precision. Evaluation on both healthy and multiple sclerosis subjects shows that our method is statistically better than a state-of-the-art graph-based method.

Abdominal obesity linked to a longer cone-mediated dark-adaptation recovery time in healthy eyes

Obesity has been associated with abnormal lipid metabolism and with tissue hypoxia. Human Bruch's membrane (BrM) lipid deposits have been proposed to create a diffusion barrier to metabolic exchange between the choroid and photoreceptors, delaying the regeneration of photopigments. The speed of retinal dark adaptation (DA) is dependent on the regeneration of these photopigments. While the retina is extremely sensitive to hypoxia, the inner retina, which encodes visual contrast, is more affected by hypoxia than the outer retina. This study examines the association between adiposity measures and the time course of DA measured psychophysically through contrast detection to test the functionality of both the outer and inner retina. Cone-mediated DA recovery of contrast threshold (CT) was measured following near-total photopigment bleach for 6 min in 52 healthy eyes of 52 individuals (42.6 ± 18.3 years). Stimuli were sine-wave gratings of low-spatial frequency (1 cycle-per-degree (cpd)) and low luminance (1 cd/m²) generated at the centre of a CRT monitor. CT recovery functions were fitted to an exponential decay model to determine the time constant (τ, seconds) of cone sensitivity recovery, final cone CT (CT_f) and CT elevation (CT₀). Weight, height and waist circumference (WC) were measured and body mass index (BMI) and waist-to-height ratio (WHtR) calculated. Relationships were examined through Spearman correlation and through multiple linear regression using age, optical and adiposity measures as independent variables. The repeatability of cone time constant measurements was estimated by the Bland-Altman method and reported as the coefficient of repeatability (CoR). Mean ± SD of time constant and CT_f were 57.3 ± 27.7 s and -1.78 ± 0.20 log₁₀ units respectively. Cone time constant showed positive Spearman correlation with WC (p = 0.008) and WHtR (p = 0.023) but not with BMI (p = 0.058). Only WHtR emerged as an independent predictor of time constant (p = 0.001). CT_f was not correlated with any adiposity measures. Mean cone time constant was 41 s slower in subjects (25%, n = 13) with abdominal obesity (WHtR≥0.5). Mean CT_f was not significantly different in subjects with or without abdominal obesity. CoR for cone time constant was ±16 s. In adult subjects, greater abdominal obesity (WHtR) was related to a longer contrast recovery time for cone-mediated DA (time to dark-adapt) suggesting outer retinal dysfunction. Final contrast threshold, preferentially processed by inner retinal cells, was unaffected by abdominal obesity.

Automatic segmentation of OCT retinal boundaries using recurrent neural networks and graph search

The manual segmentation of individual retinal layers within optical coherence tomography (OCT) images is a time-consuming task and is prone to errors. The investigation into automatic segmentation methods that are both efficient and accurate has seen a variety of methods proposed. In particular, recent machine learning approaches have focused on the use of convolutional neural networks (CNNs). Traditionally applied to sequential data, recurrent neural networks (RNNs) have recently demonstrated success in the area of image analysis, primarily due to their usefulness to extract temporal features from sequences of images or volumetric data. However, their potential use in OCT retinal layer segmentation has not previously been reported, and their direct application for extracting spatial features from individual 2D images has been limited. This paper proposes the use of a recurrent neural network trained as a patch-based image classifier (retinal boundary classifier) with a graph search (RNN-GS) to segment seven retinal layer boundaries in OCT images from healthy children and three retinal layer boundaries in OCT images from patients with age-related macular degeneration (AMD). The optimal architecture configuration to maximize classification performance is explored. The results demonstrate that a RNN is a viable alternative to a CNN for image classification tasks in the case where the images exhibit a clear sequential structure. Compared to a CNN, the RNN showed a slightly superior average generalization classification accuracy. Secondly, in terms of segmentation, the RNN-GS performed competitively against a previously proposed CNN based method (CNN-GS) with respect to both accuracy and consistency. These findings apply to both normal and AMD data. Overall, the RNN-GS method yielded superior mean absolute errors in terms of the boundary position with an average error of 0.53 pixels (normal) and 1.17 pixels (AMD). The methodology and results described in this paper may assist the future investigation of techniques within the area of OCT retinal segmentation and highlight the potential of RNN methods for OCT image analysis.

Automated segmentation of retinal layer boundaries and capillary plexuses in wide-field optical coherence tomographic angiography

Advances in the retinal layer segmentation of structural optical coherence tomography (OCT) images have allowed the separation of capillary plexuses in OCT angiography (OCTA). With the increased scanning speeds of OCT devices and wider field images (≥10 mm on fast-axis), greater retinal curvature and anatomic variations have introduced new challenges. In this study, we developed a novel automated method to segment seven retinal layer boundaries and two retinal plexuses in wide-field OCTA images. The algorithm was initialized by a series of points forming a guidance point array that estimates the location of retinal layer boundaries. A guided bidirectional graph search method consisting of an improvement of our previous segmentation algorithm was used to search for the precise boundaries. We validated the method on normal and diseased eyes, demonstrating subpixel accuracy for all groups. By allowing independent visualization of the superficial and deep plexuses, this method shows potential for the detection of plexus-specific peripheral vascular abnormalities.

HEALTH CONDITIONS LINKED TO AGE-RELATED MACULAR DEGENERATION ASSOCIATED WITH DARK ADAPTATION

PURPOSE

To determine the association between dark adaption (DA) and different health conditions linked with age-related macular degeneration (AMD).

METHODS

Cross-sectional study, including patients with AMD and a control group. Age-related macular degeneration was graded according to the Age-Related Eye Disease Study (AREDS) classification. We obtained data on medical history, medications, and lifestyle. Dark adaption was assessed with the extended protocol (20 minutes) of AdaptDx (MacuLogix). For analyses, the right eye or the eye with more advanced AMD was selected. Multivariate linear and logistic regressions were performed, accounting for age and AMD stage.

RESULTS

Seventy-eight subjects (75.6% AMD; 24.4% controls) were included. Multivariate assessments revealed that body mass index (BMI; β = 0.30, P = 0.045), taking AREDS vitamins (β = 5.51, P < 0.001), and family history of AMD (β = 2.68, P = 0.039) were significantly associated with worse rod intercept times. Abnormal DA (rod intercept time ≥ 6.5 minutes) was significantly associated with family history of AMD (β = 1.84, P = 0.006), taking AREDS supplements (β = 1.67, P = 0.021) and alcohol intake (β = 0.07, P = 0.017).

CONCLUSION

Besides age and AMD stage, a higher body mass index, higher alcohol intake, and a family history of AMD seem to impair DA. In this cohort, the use of AREDS vitamins was also statistically linked with impaired DA, most likely because of an increased severity of disease in subjects taking them.

Panretinal Photocoagulation: A Review of Complications

Panretinal photocoagulation (PRP) is a mainstay of therapy for retinal ischemic disease. The procedure involves creating thermal burns in the peripheral retina leading to tissue coagulation, the overall consequence of which is improved retinal oxygenation. While highly effective, there have been concerns historically regarding the anatomic effects and visual complications following PRP, the most common of which include choroidal effusions, exudative retinal detachments, macular edema, visual field deficits, and night vision defects. The occurrence of these complications is closely tied to laser parameters such as increased duration and power and intensive treatment in a single sitting, all of which cause increased dispersion of thermal energy within the retina and choroid. The advent of newer laser delivery systems, such as the multispot pattern laser, has greatly mitigated but not eliminated these issues. The following article reviews the most common complications following PRP treatment, including reported occurrences, inciting factors, and underlying pathophysiology.

Measurement of dark adaptometry during ISCEV standard flash electroretinography

PURPOSE

Dark adaptometry (DA) is a sensitive test for diagnosis of retinal disease. Patients requiring flash electroretinograms (ERGs) benefit from DA for proper diagnosis. Our purpose was to develop a DA test to be administered during the 20-min dark adaptation period of the flash ERG ( www.iscev.org ) using alternating red and blue stimuli to bias responses in favor of cones (red) and rods (blue).

METHODS

An ERG Ganzfeld was used to measure DA in 21 normal subjects and 21 patients with retinal disease. Subjects underwent 75 s of preadaptation followed by 20 min of DA using an adaptive staircase to detect alternating flashes of red and blue light. Normative red and blue DA was compared to patients at the 10-min midpoint and 20-min final threshold.

RESULTS

At 15 min, normals and patients showed asymptotic plateaus; hence, final thresholds were achieved within 15 min for parameters of this study. In RP and allied conditions (n = 11), 100% showed significantly elevated blue DA thresholds (> 2SD above normal) at 10 and 20 min. In cone diseases, 80% showed abnormal red DA at 10 min and 30% at 20 min, indicating that delayed adaptation is more typical of cone disease.

CONCLUSIONS

Two-color DA is expediently measured during the DA phase of ERGs providing clinical data which separate rod and cone dysfunction critical for accurate diagnosis of various retinal diseases. It provides an additional benchmark for monitoring function over time and invaluable guidance for patients functioning in dimly lit settings.

Automatic segmentation of nine retinal layer boundaries in OCT images of non-exudative AMD patients using deep learning and graph search

We present a novel framework combining convolutional neural networks (CNN) and graph search methods (termed as CNN-GS) for the automatic segmentation of nine layer boundaries on retinal optical coherence tomography (OCT) images. CNN-GS first utilizes a CNN to extract features of specific retinal layer boundaries and train a corresponding classifier to delineate a pilot estimate of the eight layers. Next, a graph search method uses the probability maps created from the CNN to find the final boundaries. We validated our proposed method on 60 volumes (2915 B-scans) from 20 human eyes with non-exudative age-related macular degeneration (AMD), which attested to effectiveness of our proposed technique.

Senescent Changes and Topography of the Dark-Adapted Multifocal Electroretinogram

Purpose

To investigate the topographic changes of the dark-adapted multifocal electroretinogram (mfERG) across adulthood in the central retina and compare the topography between macular versus extramacular, nasal versus temporal, and inferior versus superior retinal areas.

Methods

Sixty-five subjects (18–88 years) received a comprehensive dilated eye examination to ensure the health of their retina and were tested with a dark-adapted mfERG protocol using a 61-hexagon pattern. The lens absorption of each subject was also estimated using a heterochromatic flicker photometry (HFP) paradigm.

Results

The response amplitude and latency of the dark-adapted mfERG showed a significant change with age, which was best described with a linear model. All the retinal areas examined demonstrated similar aging effects. The extramacular and temporal retina showed higher response amplitude and faster response latency when compared with the macular and nasal retinae, respectively. No difference was found in response amplitude and latency between the inferior and superior retina. The HFP results also showed a significant correlation with age, consistent with senescent increases in short wavelength absorption by the crystalline lens. However, the change in lens absorption did not exceed the magnitude of the change in response amplitude and latency.

Discussion

Our results indicate that there is a decline in dark-adapted retinal activity as measured with the mfERG. These aging processes affect rods and rod-bipolar cells. Their decrease in response can be attributed to both optical and neural factors.

Retinal oxygen: from animals to humans

This article discusses retinal oxygenation and retinal metabolism by focusing on measurements made with two of the principal methods used to study O₂ in the retina: measurements of PO₂ with oxygen-sensitive microelectrodes in vivo in animals with a retinal circulation similar to that of humans, and oximetry, which can be used non-invasively in both animals and humans to measure O₂ concentration in retinal vessels. Microelectrodes uniquely have high spatial resolution, allowing the mapping of PO₂ in detail, and when combined with mathematical models of diffusion and consumption, they provide information about retinal metabolism. Mathematical models, grounded in experiments, can also be used to simulate situations that are not amenable to experimental study. New methods of oximetry, particularly photoacoustic ophthalmoscopy and visible light optical coherence tomography, provide depth-resolved methods that can separate signals from blood vessels and surrounding tissues, and can be combined with blood flow measures to determine metabolic rate. We discuss the effects on retinal oxygenation of illumination, hypoxia and hyperoxia, and describe retinal oxygenation in diabetes, retinal detachment, arterial occlusion, and macular degeneration. We explain how the metabolic measurements obtained from microelectrodes and imaging are different, and how they need to be brought together in the future. Finally, we argue for revisiting the clinical use of hyperoxia in ophthalmology, particularly in retinal arterial occlusions and retinal detachment, based on animal research and diffusion theory.