Low-intensity far-red light inhibits early lesions that contribute to diabetic retinopathy: in vivo and in vitro

Changes in choroidal thickness and blood flow in response to form deprivation-induced myopia and repeated low-level red-light therapy in Guinea pigs

PURPOSE

To evaluate ocular refractive development, choroidal thickness (ChT) and changes in choroidal blood flow in form-deprived myopia (FDM) Guinea pigs treated with repeated low-level red-light (RLRL) therapy.

METHODS

Twenty-eight 3-week-old male tricolour Guinea pigs were randomised into three groups: normal controls (NC, n = 10), form-deprived (FD, n = 10) and red light treated with form-deprivation (RLFD, n = 8). Interocular refraction and axial length (AL) changes were monitored. Optical coherence tomography angiography (OCTA) measured choroidal thickness, vessel area density, vessel skeleton density and blood flow signal intensity (flux) in the choriocapillaris and medium-large vessel layers. The experimental intervention lasted 3 weeks.

RESULTS

At week 3, the FD group had higher myopia and longer axial length than the NC group (all p < 0.001). The RLFD group had higher hyperopia and shorter axial length than the FD group (all p < 0.001). At week 1, the NC group had a thicker choroidal thickness than the FD group (p < 0.05). At weeks 2 and 3, the RLFD group had a thicker choroidal thickness than the FD group (p = 0.002, p < 0.001, respectively). Additionally, the NC group had higher vessel area density, vessel skeleton density and flux in the choriocapillaris layer than the FD group at the three follow-up time points (all p < 0.05). At week 3, the vessel skeleton density and flux were higher in the RLFD group than in the FD group (all p < 0.05). Correlation analysis results showed that weekly changes in refraction and choroidal thickness were negatively correlated with changes in axial length (all p < 0.05). Choroidal thickness changes were positively correlated with alterations in the vessel area density, vessel skeleton density and flux in the choriocapillaris layer, as well as vessel skeleton density and flux changes in the medium-large vessel layers (all p < 0.05).

CONCLUSIONS

Repeated low-level red-light (RLRL) therapy retards FDM progression in Guinea pigs, potentially through increased choroidal blood flow in the choriocapillaris layer.

Prolonged Photobiomodulation with Deep Red Light Mitigates Incipient Retinal Deterioration in a Mouse Model of Type 2 Diabetes

Diabetic retinopathy is a prevalent complication of type 2 diabetes mellitus, characterized by progressive damage to the retinal structure and function. Photobiomodulation therapy, using red or near-infrared light, has been proposed as a non-invasive intervention to mitigate retinal damage, but has been tested generally with short-term stimuli. This study aimed to evaluate the effects of prolonged photobiomodulation with deep red light on retinal structure and function in a type 2 diabetes mouse model. Transgenic LepRdb/J (db/db) mice were exposed to photobiomodulation therapy via LED devices emitting 654 nm light for 12 h daily over ten weeks and compared to untreated mice. Retinal function was evaluated by flash electroretinography, while structural changes were assessed through histology and immunohistochemistry to detect astro- and microgliosis. At 33 weeks of age, db/db mice were obese and severely diabetic, but exhibited only incipient indicators of retinal deterioration. Electroretinogram b-wave peak latencies were prolonged at intermediate flash intensities, while the outer plexiform layer displayed significantly elevated IBA1 expression. Photobiomodulation therapy prevented these two markers of early retinal deterioration but had no effect on other morphological and functional parameters. Photobiomodulation is well-tolerated and maintains potential as a complementary treatment option for diabetic retinopathy but requires further optimization of therapeutic settings and combinatory treatment approaches.

The Effect of Repeated Low-Level Red-Light Therapy on Myopia Control and Choroid

Purpose

To investigate the long-term effects of repeated low-level red light (RLRL) therapy on the axial length (AL), spherical equivalent (SE), and choroidal parameters.

Methods

Two hundred eight myopic eyes were recruited. The RLRL group included 100 eyes, whereas the control group included 108 eyes. Throughout the one-year follow-up period, changes in AL and SE were recorded for both groups. The RLRL group underwent additional choroidal imaging, and changes in choroidal thickness (CT), choroidal vascularity (CV), and choriocapillaris luminal area (CLA) were assessed before and after RLRL therapy.

Results

During the follow-up period, the changing trends in AL and SE differed significantly between the RLRL and control groups. In the RLRL group, AL decreased at three and six months (both P < 0.05) and returned to pretreatment values at 12 months (P = 0.453). In contrast, AL increased significantly throughout the follow-up period (three, six, and 12 months) in the control group (all P < 0.001). The SE increased significantly during the entire follow-up period in the RLRL group (all P < 0.001), whereas it decreased significantly in the control group (all P < 0.05). Regarding choroidal parameters, significant improvements were observed in CT, CV and CLA throughout the follow-up period (all P < 0.05), and changes in most choroidal parameters were significantly correlated with changes in AL and SE during the follow-up period (all P < 0.05). Furthermore, AL, SE, and most choroidal parameters showed significant correlations between changes at three and 12 months (all P < 0.05).

Conclusions

RLRL therapy significantly improved choroidal blood perfusion and circulation, which may explain the observed slowing or reversal of myopia progression in the RLRL group. Thus RLRL therapy may be a novel and effective method for controlling myopia. Furthermore, the short-term effect of photobiomodulation therapy (i.e., changes at three months) can be used to predict the long-term effects (i.e., changes at 12 months).

Translational Relevance

In this study, RLRL therapy showed a significant control effect on the development of axial length and spherical equivalent. RLRL therapy also promoted the choroidal blood perfusion and circulation. RLRL therapy could be a novel and effective method for myopia control.

Photobiomodulation use in ophthalmology - an overview of translational research from bench to bedside

Photobiomodulation (PBM) refers to the process in which wavelengths of light are absorbed by intracellular photoacceptors, resulting in the activation of signaling pathways that culminate in biological changes within the cell. PBM is the result of low-intensity light-induced reactions in the cell in contrast to thermal photoablation produced by high-intensity lasers. PBM has been effectively used in the clinic to enhance wound healing and mitigate pain and inflammation in musculoskeletal conditions, sports injury, and dental applications for many decades. In the past 20 years, experimental evidence has shown the benefit of PBM in increasing numbers of retinal and ophthalmic conditions. More recently, preclinical findings in ocular models have been translated to the clinic with promising results. This review discusses the preclinical and clinical evidence of the effects of PBM in ophthalmology and provides recommendations of the clinical use of PBM in the management of ocular conditions.

Differences between long- and short-wavelength light-induced retinal damage and the role of PARP-1 in retinal injury induced by blue light

Photobiomodulation (PBM) therapy uses light of different wavelengths to treat various retinal degeneration diseases, but the potential damage to the retina caused by long-term light irradiation is still unclear. This study were designed to detect the difference between long- and short-wavelength light (650-nm red light and 450-nm blue light, 2.55 mW/cm2, reference intensity in PBM)-induced injury. In addition, a comparative study was conducted to investigate the differences in retinal light damage induced by different irradiation protocols (short periods of repeated irradiation and a long period of constant irradiation). Furthermore, the protective role of PARP-1 inhibition on the molecular mechanism of blue light-induced injury was confirmed by a gene knockdown technique or a specific inhibitor through in vitro and in vivo experiments. The results showed that the susceptibility to retinal damage caused by irradiation with long- and short-wavelength light is different. Shorter wavelength lights, such as blue light, induce more severe retinal damage, while the retina exhibits better resistance to longer wavelength lights, such as red light. In addition, repeated irradiation for short periods induces less retinal damage than constant exposure over a long period. PARP-1 plays a critical role in the molecular mechanism of blue light-induced damage in photoreceptors and retina, and inhibiting PARP-1 can significantly protect the retina against blue light damage. This study lays an experimental foundation for assessing the safety of phototherapy products and for developing target drugs to protect the retina from light damage.

Effects of slit lamp-delivered retinal laser photobiomodulation in a rat model of choroidal neovascularization

Neovascular age-related macular degeneration, also known as exudative or wet age-related macular degeneration, is the leading cause of blindness in the developed world. Photobiomodulation has the potential to target the up-stream hypoxic and pro-inflammatory drivers of choroidal neovascularization. This study investigated whether photobiomodulation attenuates characteristic pathological features of choroidal neovascularization in a rodent model. Experimental choroidal neovascularization was induced in Brown Norway rats with laser photocoagulation. A custom-designed, slit-lamp-mounted, 670 nm laser was used to administer retinal photobiomodulation every 3 days, beginning 6 days prior to choroidal neovascularization induction and continuing until the animals were killed 14 days later. The effect of photobiomodulation on the size of choroidal neovascular membranes was determined using isolectin-B4 immunohistochemistry and spectral domain-optical coherence tomography. Vascular leakage was determined with fluorescein angiography. The effect of treatment on levels of vascular endothelial growth factor expression was quantified with enzyme-linked immunosorbent assay. Treatment with photobiomodulation was associated with choroidal neovascular membranes that were smaller, had less fluorescein leakage, and a diminished presence of inflammatory cells as compared to sham eyes. These effects were not associated with a statistically significant difference in the level of vascular endothelial growth factor when compared to sham eyes. The data shown herein indicate that photobiomodulation attenuates pathological features of choroidal neovascularization in a rodent model by mechanisms that may be independent of vascular endothelial growth factor.

Safety of repeated low-level red-light therapy for children with myopia

BACKGROUD

To investigate the safety of repetitive low-level red-light therapy (RLRLT) in children with myopia.

METHODS

Children with myopia were assigned to the RLRL and control groups. Axial length (AL) and spherical equivalent refraction (SER) were followed up at 3-, 6-, and 12-month. To evaluate the safety of RLRLT, at 6 and 12 months in the RLRL group, multifocal electroretinography (mfERG) and contrast sensitivity were recorded. Furthermore, optical coherence tomography was used to measure the relative reflectance of the ellipsoid zone (rEZR), photoreceptor outer segment (rPOSR), and retinal pigment epithelium (rRPER).

RESULTS

A total of 108 children completed the trial (55 in the RLRL group and 53 in the control group). After 3, 6, and 12 months, AL was shorter and SER less myopic in the RLRL group than in the control group. Regarding the safety of the RLRLT, the response density and amplitude of the P1 wave of the first ring of the mfERG increased significantly at 6 months (P = 0.001 and P = 0.017, respectively). At 6 and 12 months, contrast sensitivity at the high spatial frequency increased. Moreover, the rEZR increased significantly at 6 months (P = 0.029), the rPOSR increased significantly at 6 and 12 months (both P < 0.001), and the increase in rPOSR was greater with greater AL regression.

CONCLUSIONS

Based on retinal function and structure follow-up, RLRLT was safe within 12 months. However, rEZR and rPOSR increased, the effects of this phenomenon requires further observation.

Diabetes in spotlight: current knowledge and perspectives of photobiomodulation utilization

Introduction

Diabetes is a global health concern characterized by chronic hyperglycemia resulting from insulinopenia and/or insulin resistance. The rising prevalence of diabetes and its associated complications (ulcers, periodontitis, healing of bone defect, neuropathy, retinopathy, cardiopathy and nephropathy) necessitate innovative therapeutic approaches. Photobiomodulation (PBM), involves exposing tissues and cells to low-energy light radiation, leading to biological effects, largely via mitochondrial activation.

Methods

This review evaluates preclinical and clinical studies exploring the potential of PBM in diabetes and its complications, as well all clinical trials, both planned and completed, available on ClinicalTrials database.

Results

This review highlights the variability in PBM parameters across studies, hindering consensus on optimal protocols. Standardization of treatment parameters and rigorous clinical trials are needed to unlock PBM's full therapeutic potential. 87 clinical trials were identified that investigated PBM in diabetes mellitus (with 5,837 patients planned to be treated with PBM). Clinical trials assessing PBM effects on diabetic neuropathy revealed pain reduction and potential quality of life improvement. Studies focusing on wound healing indicated encouraging results, with PBM enhancing angiogenesis, fibroblast proliferation, and collagen density. PBM's impact on diabetic retinopathy remains inconclusive however, requiring further investigation. In glycemic control, PBM exhibits positive effects on metabolic parameters, including glucose tolerance and insulin resistance.

Conclusion

Clinical studies have reported PBM-induced reductions in fasting and postprandial glycemia without an increased hypoglycemic risk. This impact of PBM may be related to its effects on the beta cells and islets in the pancreas. Notwithstanding challenges, PBM emerges as a promising adjunctive therapy for managing diabetic neuropathy, wound healing, and glycemic control. Further investigation into its impact on diabetic retinopathy and muscle recovery is warranted.

Photobiomodulation Using Light-Emitting Diode (LED) for Treatment of Retinal Diseases

Photobiomodulation (PBM) is a type of phototherapy that employs light-emitting diodes (LEDs) or low-power lasers to selectively administer specific wavelengths of visible light, ranging from 500 to 1000 nm, including near-infrared (NIR) wavelengths. LEDs are advantageous compared to lasers due to their ability to treat large areas at a lower cost, lack of tissue damage potential in humans, and reduced risk of eye-related accidents. The ophthalmology community has recently taken interest in PBM as a promising novel approach for managing various retinal conditions such as age-related macular degeneration, retinopathy of prematurity, retinitis pigmentosa, diabetic retinopathy, Leber's hereditary optic neuropathy, amblyopia, methanol-induced retinal damage, and potentially others. This review critically assesses the existing body of research on PBM applications in the retina, focusing on elucidating the underlying mechanisms of action and evaluating the clinical outcomes associated with this therapeutic modality.

Smart Contact Lenses as Wearable Ophthalmic Devices for Disease Monitoring and Health Management

The eye contains a complex network of physiological information and biomarkers for monitoring disease and managing health, and ocular devices can be used to effectively perform point-of-care diagnosis and disease management. This comprehensive review describes the target biomarkers and various diseases, including ophthalmic diseases, metabolic diseases, and neurological diseases, based on the physiological and anatomical background of the eye. This review also includes the recent technologies utilized in eye-wearable medical devices and the latest trends in wearable ophthalmic devices, specifically smart contact lenses for the purpose of disease management. After introducing other ocular devices such as the retinal prosthesis, we further discuss the current challenges and potential possibilities of smart contact lenses.

Evaluation of Photobiomodulation and Boldine as Alternative Treatment Options in Two Diabetic Retinopathy Models

Diabetic retinopathy causes progressive and irreversible damage to the retina through activation of inflammatory processes, overproduction of oxidative species, and glial reactivity, leading to changes in neuronal function and finally ischemia, edema, and hemorrhages. Current treatments are invasive and mostly applied at advanced stages, stressing the need for alternatives. To this end, we tested two unconventional and potentially complementary non-invasive treatment options: Photobiomodulation, the stimulation with near-infrared light, has shown promising results in ameliorating retinal pathologies and insults in several studies but remains controversial. Boldine, on the other hand, is a potent natural antioxidant and potentially useful to prevent free radical-induced oxidative stress. To establish a baseline, we first evaluated the effects of diabetic conditions on the retina with immunofluorescence, histological, and ultrastructural analysis in two diabetes model systems, obese LepR^db/db mice and organotypic retinal explants, and then tested the potential benefits of photobiomodulation and boldine treatment in vitro on retinal explants subjected to high glucose concentrations, mimicking diabetic conditions. Our results suggest that the principal subcellular structures affected by these conditions were mitochondria in the inner segment of photoreceptors, which displayed morphological changes in both model systems. In retinal explants, lactate metabolism, assayed as an indicator of mitochondrial function, was altered, and decreased photoreceptor viability was observed, presumably as a consequence of increased oxidative-nitrosative stress. The latter was reduced by boldine treatment in vitro, while photobiomodulation improved mitochondrial metabolism but was insufficient to prevent retinal structural damage caused by high glucose. These results warrant further research into alternative and complementary treatment options for diabetic retinopathy.

Smart Contact Lens Systems for Ocular Drug Delivery and Therapy

Ocular drug delivery and therapy systems have been extensively investigated with various methods including direct injections, eye drops and contact lenses. Nowadays, smart contact lens systems are attracting a lot of attention for ocular drug delivery and therapy due to their minimally invasive or non-invasive characteristics, highly enhanced drug permeation, high bioavailability, and on-demand drug delivery. Furthermore, smart contact lens systems can be used for direct light delivery into the eyes for biophotonic therapy replacing the use of drugs. Here, we review smart contact lens systems which can be classified into two groups of drug-eluting contact lens and ocular device contact lens. More specifically, this review covers smart contact lens systems with nanocomposite-laden systems, polymeric film-incorporated systems, micro and nanostructure systems, iontophoretic systems, electrochemical systems, and phototherapy systems for ocular drug delivery and therapy. After that, we discuss the future opportunities, challenges and perspectives of smart contact lens systems for ocular drug delivery and therapy.

Red light photobiomodulation rescues murine brain mitochondrial respiration after acute hypobaric hypoxia

Low-level laser therapy, or photobiomodulation, utilizes red or near-infrared light for the treatment of pathological conditions due to the presence of intracellular photoacceptors, such as mitochondrial cytochrome c oxidase, that serve as intermediates for the therapeutic effects. We present an in-detail analysis of the effect of low-intensity LED red light irradiation on the respiratory chain of brain mitochondria. We tested whether low-level laser therapy at 650 nm could alleviate the brain mitochondrial dysfunction in the model of acute hypobaric hypoxia in mice. The irradiation of the mitochondrial fraction of the left cerebral cortex with low-intensity LED red light rescued Complex I-supported respiration during oxidative phosphorylation, normalized the initial polarization of the inner mitochondrial membrane, but has not shown any significant effect on the activity of Complex IV. In comparison, the postponed effect (in 24 h) of the similar transcranial irradiation following hypoxic exposure led to a less pronounced improvement of the mitochondrial functional state, but normalized respiration related to ATP production and membrane polarization. In contrast, the similar irradiation of the mitochondria isolated from control healthy animals exerted an inhibitory effect on CI-supported respiration. The obtained results provide significant insight that can be beneficial for the development of non-invasive phototherapy.

Considerations for the Use of Photobiomodulation in the Treatment of Retinal Diseases

Photobiomodulation (PBM) refers to the beneficial effect produced from low-energy light irradiation on target cells or tissues. Increasing evidence in the literature suggests that PBM plays a positive role in the treatment of retinal diseases. However, there is great variation in the light sources and illumination parameters used in different studies, resulting in significantly different conclusions regarding PBM's therapeutic effects. In addition, the mechanism by which PBM improves retinal function has not been fully elucidated. In this study, we conducted a narrative review of the published literature on PBM for treating retinal diseases and summarized the key illumination parameters used in PBM. Furthermore, we explored the potential molecular mechanisms of PBM at the retinal cellular level with the goal of providing evidence for the improved utilization of PBM in the treatment of retinal diseases.

Effects of Photobiomodulation in Patients Presenting with Reticular Pseudodrusen: A Retrospective Observational Case Series Study

Background and Objectives: The purpose of this study is to describe the effects of photobiomodulation on drusen regression with patients presenting with reticular pseudodrusen (RPD). Materials and Methods: This study is a retrospective observational case series study including patients presenting with RPD who underwent treatment by photobiomodulation. All patients underwent a complete ophthalmic examination and multimodal imaging prior to treatment, including spectral-domain optical coherence tomography (SD-OCT). Eyes were treated two times per week for six consecutive weeks. Best corrected-visual acuity (BVCA) was measured prior and after treatment for all patients. The number of RPD on the SD-OCT scans centered on the macula and stages of RPD was noted at baseline and 6 months after the first treatment session. Results: Five eyes of five patients were included in the study. Mean BCVA did not change 6 months after treatment compared to baseline. Mean number of RPD per eye was 112.60 +/- 48.33 RPD at baseline and 111.6 +/- 49.29 in the same area 6 months after treatment. Changes in RPD distribution according to RPD classification were observed before and after treatment with photobiomodulation. Changes in distribution mostly concerned stages 1 and 3 RPD: Total number of stage 1 RPD was 289 and increased to 324 after treatment. Total number of stage 3 RPD was 97 at baseline and decreased to 67 6 months after treatment. Percentage of stage 1 RPD increased from 46% to 56% after treatment. Percentage of stage 3 RPD decreased from 20% to 13% after treatment. Conclusions: Changes in RPD distribution were observed before and after treatment with photobiomodulation. The number of stage 3 reticular pseudodrusen decreased while number of stage 1 reticular pseudodrusen increased after treatment.

Red light irradiation as an intervention for myopia

Myopia is one of the main causes of visual impairment worldwide. Preventing myopia and providing myopia-related interventions are of paramount importance. Based on a thorough review of the available literature, we conclude that red light irradiation can produce hyperopia, resulting in myopia prevention and control. Further, we suggest that red light irradiation may be a powerful tool for myopia prevention and control in the future. At the same time, red light has a protective effect on the cornea and retina at the cellular level, suggesting that red light irradiation may be a safe and effective modality for delaying myopia. Therefore, this form of irradiation is expected to play an important role in the prevention and control of myopia. However, more studies are needed to enhance the current state of knowledge and inform medical guidelines more comprehensively.

A preliminary observation on rod cell photobiomodulation in treating diabetic macular edema

Purpose

To evaluate the safety and effectiveness of photobiomodulation (PBM) in the treatment of diabetic macular edema (DME).

Methods

It was a single-center, self-controlled prospective study. The clinical records of 12 diabetic retinopathy patients (5 males and 7 females, 20 eyes in total) who were treated with PBM for DME at the Second Affiliated Hospital, Zhejiang University School of Medicine, were analyzed. The mean age was 56 (26-68) years. All the participants received PBM treatment during darkness at night in no less than 5 days per week and no less than 8 ​h per day. In the baseline check and follow-up checks (1, 2, 6, 10, and 12 months after the start of treatment), the best-corrected visual acuity, the thickness of the retina in the macula, and the changes of the fundus lesions were observed. Wilcoxon signed rank test was used to compare the results before and after treatment. P ​< ​0.05 was considered statistically significant.

Results

No fundus complication was observed during follow-up checks. In baseline and 12-month follow-up checks, the best-corrected visual acuity was 71.75 ​± ​12.47 and 79.50 ​± ​10.85, maximal retinal thickness in macular area was 390.95 ​± ​77.12 ​μm and 354.13 ​± ​55.03 ​μm, average retinal thickness in macular area was 334.25 ​± ​36.45 ​μm and 314.31 ​± ​33.28 ​μm, foveal thickness was 287.00 ​± ​46.79 ​μm and 265.63 ​± ​67.14 ​μm. The best-corrected visual acuity, average retinal thickness in macular area in consecutive follow-up results except that in the 1st month showed significant difference compared with baseline results. There were significant difference between every follow-up result and baseline result of maximal retinal thickness in macular area (P ​< ​0.05). All follow-up results of foveal thickness were not significantly different (P ​> ​0.05) from the baseline result, except that in the 6th month (P ​= ​0.049). Obvious improvement could be observed in retinal fundus fluorescein angiography images.

Conclusions

PBM is a safe and effective treatment of DME, which deserves further investigation.

Dose Response Effect of Photobiomodulation on Hemodynamic Responses and Glucose Levels in Men with Type 2 Diabetes: A Randomized, Crossover, Double-Blind, Sham-Controlled Trial

This study verifies the acute dose response effect of photobiomodulation (PBM) by light emitting diodes (LEDs) on hemodynamic and metabolic responses in individuals with type 2 diabetes mellitus (T2DM). Thirteen participants with T2DM (age 52 ± 7 years) received PBM by a light-emitting diode array (50 GaAIAs LEDs, 850 ± 20 nm, 75 mW per diode) on the rectus and oblique abdomen, quadriceps femoris, triceps surae, and hamstring muscle areas, bilaterally, using different energy treatments (sham, 75, 150, 300, 450, and 600 Joules) in random order with a washout of at least 15 days apart. The PBM by LEDs statistically decreased plasma glucose levels (primary outcome) in 15 min after application of the 75 and 450 J irradiation protocol, reduced blood lactate levels 15 min after application of the 75, 450, and 600 J irradiation protocol, increased cardiac output (Q˙) and cardiac index (CI) in the 1st minute after application of the 75 and 300 J irradiation protocol, and reduced Q˙ and heart rate (HR) in the 15 min after application of the 300 J and 600 J irradiation protocol, respectively. For hemodynamic variables, including Q˙, total peripheral resistance (TPR), and HR, we observed that the ideal therapeutic window ranged between 75 and 300 J, while for metabolic variables, glucose and lactate, the variation was between 450 and 600 J.

Unconventional avenues to decelerated diabetic retinopathy

Diabetic retinopathy (DR) is an important microvascular complication of diabetes mellitus (DM), causing significant visual impairment worldwide. Current gold standards for retarding the progress of DR include blood sugar control and regular fundus screening. Despite these measures, the incidence and prevalence of DR and vision-threatening DR remain high. Given its slowly progressive course and long latent period, opportunities to contain or slow DR before it threatens vision must be explored. This narrative review assesses the recently described unconventional strategies to retard DR progression. These include gut-ocular flow, gene therapy, mitochondrial dysfunction-oxidative stress, stem cell therapeutics, neurodegeneration, anti-inflammatory treatments, lifestyle modification, and usage of phytochemicals. These therapies impact DR directly, while some of them also influence DM control. Most of these strategies are currently in the preclinical stage, and clinical evidence remains low. Nevertheless, our review suggests that these approaches have the potential for human use to prevent the progression of DR.

The Molecular Mechanisms of Action of Photobiomodulation Against Neurodegenerative Diseases: A Systematic Review

Neurodegenerative diseases might be slow but relentless, as we continue to fail in treating or delaying their progression. Given the complexity in the pathogenesis of these diseases, a broad-acting approach like photobiomodulation can prove promising. Photobiomodulation (PBM) uses red and infrared light for therapeutic benefits, working by stimulating growth and proliferation. The implications of photobiomodulation have been studied in several neurodegenerative disease models. It has been shown to improve cell survival, decrease apoptosis, alleviate oxidative stress, suppress inflammation, and rescue mitochondrial function. In in vivo models, it has reportedly preserved motor and cognitive skills. Beyond mitochondrial stimulation, the molecular mechanisms by which photobiomodulation protects against neurodegeneration have not been very well studied. This review has systematically been undertaken to study the effects of photobiomodulation at a molecular level and identify the different biochemical pathways and molecular changes in the process. The data showed the involvement of pathways like extracellular signal-regulated kinase (ERK), mitogen-activated protein kinase (MAPK), and protein kinase B (Akt). In addition, the expression of several genes and proteins playing different roles in the disease mechanisms was found to be influenced by PBM, such as neurotrophic factors and secretases. Studying the literature indicated that PBM can be translated to a potential therapeutic tool, acting through a spectrum of mechanisms that work together to decelerate disease progression in the organism, which is difficult to achieve through pharmacological interventions.

A Randomized Trial of Photobiomodulation Therapy for Center-Involved Diabetic Macular Edema with Good Visual Acuity (Protocol AE)

PURPOSE

To determine if treatment with a photobiomodulation (PBM) device results in greater improvement in central subfield thickness (CST) than placebo in eyes with center-involved diabetic macular edema (CI-DME) and good vision.

DESIGN

Phase 2 randomized clinical trial.

PARTICIPANTS

Participants had CI-DME and visual acuity (VA) 20/25 or better in the study eye and were recruited from 23 clinical sites in the United States.

METHODS

One eye of each participant was randomly assigned 1:1 to a 670-nm light-emitting PBM eye patch or an identical device emitting broad-spectrum white light at low power. Treatment was applied for 90 seconds twice daily for 4 months.

MAIN OUTCOME MEASURES

Change in CST on spectral-domain OCT at 4 months.

RESULTS

From April 2019 to February 2020, 135 adults were randomly assigned to either PBM (n = 69) or placebo (n = 66); median age was 62 years, 37% were women, and 82% were White. The median device compliance was 92% with PBM and 95% with placebo. OCT CST increased from baseline to 4 months by a mean (SD) of 13 (53) μm in PBM eyes and 15 (57) μm in placebo eyes, with the mean difference (95% confidence interval [CI]) being -2 (-20 to 16) μm (P = 0.84). CI-DME, based on DRCR Retina Network sex- and machine-based thresholds, was present in 61 (90%) PBM eyes and 57 (86%) placebo eyes at 4 months (adjusted odds ratio [95% CI] = 1.30 (0.44-3.83); P = 0.63). VA decreased by a mean (SD) of -0.2 (5.5) letters and -0.6 (4.6) letters in the PBM and placebo groups, respectively (difference [95% CI] = 0.4 (-1.3 to 2.0) letters; P = 0.64). There were 8 adverse events possibly related to the PBM device and 2 adverse events possibly related to the placebo device. None were serious.

CONCLUSIONS

PBM as given in this study, although safe and well-tolerated, was not found to be effective for the treatment of CI-DME in eyes with good vision.

Smart Wireless Near-Infrared Light Emitting Contact Lens for the Treatment of Diabetic Retinopathy

Diabetic retinopathy is currently treated by highly invasive repeated therapeutic injections and surgical interventions without complete vision recovery. Here, a noninvasive smart wireless far red/near-infrared (NIR) light emitting contact lens developed successfully for the repeated treatment of diabetic retinopathy with significantly improved compliance. A far red/NIR light emitting diode (LED) is connected with an application-specific integrated circuit chip, wireless power, and communication systems on a PET film, which is embedded in a silicone elastomer contact lens by thermal crosslinking. After in vitro characterization, it is confirmed that the retinal vascular hyper-permeability induced by diabetic retinopathy in rabbits is reduced to a statistically significant level by simply repeated wearing of smart far red/NIR LED contact lens for 8 weeks with 120 µW light irradiation for 15 min thrice a week. Histological analysis exhibits the safety and feasibility of LED contact lenses for treating diabetic retinopathy. This platform technology for smart LED contact lens would be harnessed for various biomedical photonic applications.

670nm photobiomodulation modulates bioenergetics and oxidative stress, in rat Müller cells challenged with high glucose

Diabetic retinopathy (DR), the most common complication of diabetes mellitus, is associated with oxidative stress, nuclear factor-κB (NFκB) activation, and excess production of vascular endothelial growth factor (VEGF) and intracellular adhesion molecule-1 (ICAM-1). Muller glial cells, spanning the entirety of the retina, are involved in DR inflammation. Mitigation of DR pathology currently occurs via invasive, frequently ineffective therapies which can cause adverse effects. The application of far-red to near-infrared (NIR) light (630-1000nm) reduces oxidative stress and inflammation in vitro and in vivo. Thus, we hypothesize that 670nm light treatment will diminish oxidative stress preventing downstream inflammatory mechanisms associated with DR initiated by Muller cells. In this study, we used an in vitro model system of rat Müller glial cells grown under normal (5 mM) or high (25 mM) glucose conditions and treated with a 670 nm light emitting diode array (LED) (4.5 J/cm2) or no light (sham) daily. We report that a single 670 nm light treatment diminished reactive oxygen species (ROS) production and preserved mitochondrial integrity in this in vitro model of early DR. Furthermore, treatment for 3 days in culture reduced NFκB activity to levels observed in normal glucose and prevented the subsequent increase in ICAM-1. The ability of 670nm light treatment to prevent early molecular changes in this in vitro high glucose model system suggests light treatment could mitigate early deleterious effects modulating inflammatory signaling and diminishing oxidative stress.

Light-Emitting Diode Laser Therapy for Hyperoxia-Induced Retinal Abnormalities

Introduction: Hyperoxygenation is linked to numerous effects in a variety of organ systems. It can cause tissue damage by generating reactive oxygen species (ROS), increasing oxidative stress, and inducing cell death by apoptosis. The present study aimed to evaluate the effects of low-level laser therapy on the retina in response to acute hyperoxia in animals. Methods: A total of 70 Wistar albino rats were evaluated in the present study: 10 rats were designated as a control group, and the rest were exposed to hyperoxia (O2 , 90%) for 3 days, 1 week, and 2 weeks (20 rats each). Each group was divided into two subgroups (n=10), one of which was designated as hyperoxia only. The other was treated with a 670 nm light-emitting diode laser (2 sessions/one week, ~ 9.0 J/cm2 ) in each eye. The animals were euthanized, and their retinas were dissected for analysis of protein content, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), total antioxidant capacity (TAC), hydrogen peroxide (H2 O2 ), malondialdehyde (MDA), and histological examination. Results: We found that two weeks of hyperoxia induced an increase in retinal protein content (P<0.001), an alteration in the intensities and molecular weights of protein fractions, a significant decrease in the TAC level (P<0.01), and a noticeable increase in H2 O2 and MDA levels (P<0.001). Histological examination revealed fragmentation of the photoreceptors and neovascularization in the outer and inner plexiform layers. Furthermore, the data showed remarkable improvement in the retinal protein contents, oxidative state, and retinal structure after light-emitting diode laser therapy. Conclusion: Light-emitting diode laser therapy was found to be a useful treatment paradigm for reducing hyperoxia-induced retinal damage.

Photoreceptor Cell Calcium Dysregulation and Calpain Activation Promote Pathogenic Photoreceptor Oxidative Stress and Inflammation in Prodromal Diabetic Retinopathy

This study tested the hypothesis that diabetes promotes a greater than normal cytosolic calcium level in rod cells that activates a Ca2+-sensitive protease, calpain, resulting in oxidative stress and inflammation, two pathogenic factors of early diabetic retinopathy. Nondiabetic and 2-month diabetic C57Bl/6J and calpain1 knockout (Capn1-/-) mice were studied; subgroups were treated with a calpain inhibitor (CI). Ca2+ content was measured in photoreceptors using Fura-2. Retinal calpain expression was studied by quantitative RT-PCR and immunohistochemistry. Superoxide and expression of inflammatory proteins were measured using published methods. Proteomic analysis was conducted on photoreceptors isolated from untreated diabetic mice or treated daily with CI for 2 months. Cytosolic Ca2+ content was increased twofold in photoreceptors of diabetic mice as compared with nondiabetic mice. Capn1 expression increased fivefold in photoreceptor outer segments of diabetic mice. Pharmacologic inhibition or genetic deletion of Capn1 significantly suppressed diabetes-induced oxidative stress and expression of proinflammatory proteins in retina. Proteomics identified a protein (WW domain-containing oxidoreductase [WWOX]) whose expression was significantly increased in photoreceptors from mice diabetic for 2 months and was inhibited with CI. Knockdown of Wwox using specific siRNA in vitro inhibited increase in superoxide caused by the high glucose. These results suggest that reducing Ca2+ accumulation, suppressing calpain activation, and/or reducing Wwox up-regulation are novel targets for treating early diabetic retinopathy.

Photobiomodulation Therapy for Age-Related Macular Degeneration and Diabetic Retinopathy: A Review

Purpose

Photobiomodulation therapy (PBT) has emerged as a possible treatment for age-related macular degeneration (AMD) and diabetic retinopathy (DR). This review seeks to summarize the application of PBT in AMD and DR.

Methods

The National Clinical Trial (NCT) database and PubMed were queried using a literature search strategy and reviewed by the authors.

Results

Fourteen studies examining the application of PBT for AMD and nine studies examining the application of PBT for diabetic macular edema (DME) were extracted from 60 candidate publications.

Discussion

Despite notable methodological differences between studies, PBT has been reported to treat certain DR and AMD patients. DR patients with center involving DME and VA ≥ 20/25 have demonstrated response to treatment. AMD patients at Age-Related Eye Disease Study Stages 2–4 with VA ≥20/200 have also shown response to treatment. Results of major clinical trials are pending.

Conclusion

PBT remains an emergent therapy with possible applications in DR and AMD. Further, high powered studies monitored by a neutral party with standard devices, treatment delivery and treatment timing are needed.

Low-Level Laser Therapy with 670 nm Alleviates Diabetic Retinopathy in an Experimental Model

Purpose:

To evaluate the effects of low-level laser therapy (LLLT) on the retina with diabetic retinopathy (DR).

Methods:

Eight Wistar rats were used as a control group, and 64 rats were injected intraperitoneally with 55 mg/kg of streptozotocin to induce diabetes and served as a diabetic group. After the establishment of the DR, the rats were separated into (a) 32 rats with DR; did not receive any treatment, (b) 32 rats with DR were exposed to 670 nm LLLT for 6 successive weeks (2 sessions/week). The retinal protein was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, total antioxidant capacity (TAC), hydrogen peroxide (H₂O₂), and histological examination.

Results:

LLLT improved retinal proteins such as neurofilament (NF) proteins (200 KDa, 160 KDa, and 86 KDa), neuron-specific enolase (NSE) (46 KDa). Moreover, the percentage changes in TAC were 46.8% (P < 0.001), 14.5% (P < 0.01), 4.8% and 1.6% (P > 0.05), and in H₂O_2, they were 30% (P < 0.001), 25% (P < 0.001), 20% (P < 0.01), and 5% (P > 0.05) after 1, 2, 4, and 6 weeks, compared with the control. DR displayed swelling and disorganization in the retinal ganglion cells (RGCs) and photoreceptors, congestion of the capillaries in the nerve fiber layer, thickening of the endothelial cells’ capillaries, and edema of the outer segment of the photoreceptors layer. The improvement of the retinal structure was achieved after LLLT.

Conclusion:

LLLT could modulate retinal proteins such as NSE and NFs, improve the RGCs, photoreceptors, and reduce the oxidative stress that originated in the retina from diabetes-induced DR.

The Present and Future of Mitochondrial-Based Therapeutics for Eye Disease

Translational Relevance

Mitochondria are viable therapeutic targets for a broad spectrum of ocular diseases.

A DOUBLE-MASKED, RANDOMIZED, SHAM-CONTROLLED, SINGLE-CENTER STUDY WITH PHOTOBIOMODULATION FOR THE TREATMENT OF DRY AGE-RELATED MACULAR DEGENERATION

Photobiomodulation treatment in a randomized, sham-controlled, single-center, double-masked study conducted in 46 eyes of patients with dry age-related macular degeneration significantly improved functional (visual acuity and contrast sensitivity) and anatomical (drusen volume and central drusen thickness) outcomes. Patient improvements were reported in the VFQ-25 assessing activities of daily living.

Purpose:

The LIGHTSITE I study investigated the efficacy and safety of photobiomodulation (PBM) treatment in subjects with dry age-related macular degeneration.

Methods:

Thirty subjects (46 eyes) were treated with the Valeda Light Delivery System, wherein subjects underwent two series of treatments (3× per week for 3–4 weeks) over 1 year. Outcome measures included best-corrected visual acuity, contrast sensitivity, microperimetry, central drusen volume and drusen thickness, and quality of life assessments.

Results:

Photobiomodulation-treated subjects showed a best-corrected visual acuity mean letter score gain of 4 letters immediately after each treatment series at Month 1 (M1) and Month 7 (M7). Approximately 50% of PBM-treated subjects showed improvement of ≥5 letters versus 13.6% in sham-treated subjects at M1. High responding subjects (≥5-letter improvement) in the PBM-treated group showed a gain of 8 letters after initial treatment (P < 0.01) and exhibited earlier stages of age-related macular degeneration disease. Statistically significant improvements in contrast sensitivity, central drusen volume, central drusen thickness, and quality of life were observed (P < 0.05). No device-related adverse events were reported.

Conclusion:

Photobiomodulation treatment statistically improved clinical and anatomical outcomes with more robust benefits observed in subjects with earlier stages of dry age-related macular degeneration. Repeated PBM treatments are necessary to maintain benefits. These pilot findings support previous reports and suggest the utility of PBM as a safe and effective therapy in subjects with dry age-related macular degeneration.

A study of therapeutic effects of 670 nm irradiation in different types of diabetic macular edema

The purpose of this study was to investigate the therapeutic effects of 670 nm irradiation in patients with diabetic macular edema. In several studies, positive effects of red/near-infrared irradiation showed in a range of ocular diseases such as macular degeneration, macular edema, and retinitis pigmentosa. This study was conducted on forty five eyes of 26 diabetic patients with macular edema between the ages of 51 and 80.

Measurement of visual acuity and slit lamp examination, funduscopy, and optical coherence tomography were performed in all subjects. None of the patients had proliferative retinopathy. We used a portable LED device (Warp 10, Quantum Devices) for treatment. Patients held this device at a distance of 3 cm from their eyes for 240 seconds for three months. Full ophthalmic examinations were repeated 1, 2, and 3 months after treatment.

After 3 months, the mean visual acuity improved from 0.44 ± 0.38 log MAR to 0.27 ± 0.24 log MAR and vision increased by 1.52 ± 1.16 lines post treatment (р<0.001). The mean central macula thickness decreased from 381.49 ± 144.40 μm to 359.72 ± 128.84 μm (р=0.050). In patients with mild and moderate nonproliferative diabetic retinopathy, the mean central retinal thickness decreased 52.06 ± 67.78 μm and 39.27 ± 44.69 μm, respectively, but patients with severe type showed an increase of 34.93 ± 65.65 μm in the mean central retinal thickness (р<0.001). Also, the severity of macular edema had no effect on final outcomes (р>0.05). Photobiomodulation can positively affect diabetic macular edema, especially in patients with mild to moderate diabetic retinopathy.

Therapeutic Options Under Development for Nonneovascular Age-Related Macular Degeneration and Geographic Atrophy

Age-related macular degeneration (AMD) is a chronic, multifactorial disease and a leading cause of irreversible blindness in the elderly population in the Western Hemisphere. Among the two major subtypes of AMD, the prevalence of the nonneovascular (dry) type is approximately 85-90% and the neovascular (wet) type is 10-15%. Healthy lifestyle and nutritional supplements of anti-oxidative micronutrients have been shown to delay the progression of dry AMD and lower the risk of development of wet AMD, and anti-vascular endothelial growth factor (anti-VEGF) injections have been shown to improve visual acuity for wet AMD patients. However, to date, there is no approved treatment for geographic atrophy (GA), a debilitating late stage of dry AMD. Thus, this represents a large unmet need in this patient population. This review focuses on the current management and treatment of nonneovascular AMD, the drugs and devices that have been under investigation for the treatment of GA, and the latest clinical trial results. A few therapeutic options have shown initial promising clinical trial results, but failed to show efficacy in larger trials, while others are awaiting future clinical trial results and long-term follow-up to evaluate safety and efficacy.

The Molecular Mechanisms of Action of Photobiomodulation Against Neurodegenerative Diseases: A Systematic Review

Neurodegenerative diseases might be slow but relentless, as we continue to fail in treating or delaying their progression. Given the complexity in the pathogenesis of these diseases, a broad-acting approach like photobiomodulation can prove promising. Photobiomodulation (PBM) uses red and infrared light for therapeutic benefits, working by stimulating growth and proliferation. The implications of photobiomodulation have been studied in several neurodegenerative disease models. It has been shown to improve cell survival, decrease apoptosis, alleviate oxidative stress, suppress inflammation, and rescue mitochondrial function. In in vivo models, it has reportedly preserved motor and cognitive skills. Beyond mitochondrial stimulation, the molecular mechanisms by which photobiomodulation protects against neurodegeneration have not been very well studied. This review has systematically been undertaken to study the effects of photobiomodulation at a molecular level and identify the different biochemical pathways and molecular changes in the process. The data showed the involvement of pathways like extracellular signal-regulated kinase (ERK), mitogen-activated protein kinase (MAPK), and protein kinase B (Akt). In addition, the expression of several genes and proteins playing different roles in the disease mechanisms was found to be influenced by PBM, such as neurotrophic factors and secretases. Studying the literature indicated that PBM can be translated to a potential therapeutic tool, acting through a spectrum of mechanisms that work together to decelerate disease progression in the organism, which is difficult to achieve through pharmacological interventions.

Photobiomodulation preconditioned human semen protects sperm cells against detrimental effects of cryopreservation

The biological consequences of semen samples preconditioning with photobiomodulation (PBM) were studied on human sperm cells post cryopreservation. Donated semen samples were collected from 22 married men with normal sperm parameters according to World Health Organization (WHO) criteria. Included samples were divided into control and PBM-preconditioning (one session, 810 nm, diode laser, and 0.6 J/cm²) groups before cryopreservation procedure. Progressive sperm motility (PSM), morphology, viability, sperm mitochondrial membrane potential(MMP), intracellular reactive oxygen species (ROS) and lipid peroxidation of sperm cells were assessed post thawing. PBM preconditioning of cryopreserved semen samples most prominently increased the PSM percentage 30 min post thawing (p = 0.000).Application of PBM before cryopreservation significantly increased the number of viable spermatozoa (p = 0.000), increased significantly the number of spermatozoa with high MMP (p = 0.004) and decreased significantly the number of spermatozoa with low MMP post-thawing(P = 0. 007)compared to control group. Cryopreserved human sperm cells with PBM preconditioning showed significant decrease in the levels of intracellular ROS (47.66 ± 2.14 versus 60.42 ± 3.16, p = 0.002) and lipid peroxidation (3.06 ± 0.13 versus 3.68 ± 0.27, p = 0.05)compared to control group. Our findings, as the first evidence, indicated that PBM-preconditioning of human semen before cryopreservation provides a real and substantial advantage. This might lead to a novel strategy in improving PBM application in the procedures of assisted reproductive technologies.

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.

Successful induction of diabetes in mice demonstrates no gender difference in development of early diabetic retinopathy

Purpose

Female mice have been found to be resistant to streptozotocin (STZ)-induced diabetes, and pre-clinical research related to diabetic complications commonly omits females. The purpose of this study was to develop a method to induce diabetes in female mice, and to determine if retinas of diabetic female mice develop molecular changes and histopathological abnormalities comparable to those which develop in male diabetic mice.

Methods

To induce diabetes, animals of both sexes received daily intraperitoneal (i.p.) injection of STZ for 5 consecutive days at 55 mg/kg BW (a dose that is known to induce diabetes in male mice) or for females, 75 mg/kg BW of STZ. Retinal abnormalities that have been implicated in the development of the retinopathy (superoxide generation and expression of inflammatory proteins, iNOS and ICAM-1) were evaluated at 2 months of diabetes, and retinal capillary degeneration was evaluated at 8 months of diabetes.

Results

Daily i.p. injection of STZ for 5 consecutive days at a concentration of 55 mg/kg BW was sufficient to induce diabetes in 100% of male mice, but only 33% of female mice. However, females did become hyperglycemic when the dose of STZ administered was increased to 75 mg/kg BW. The resulting STZ-induced hyperglycemia in female and male mice was sustained for at least 8 months. After induction of the diabetes, both sexes responded similarly with respect to the oxidative stress, expression of iNOS, and degeneration of retinal capillaries, but differed in the limited population evaluated with respect to expression of ICAM-1.

Conclusions

The resistance of female mice to STZ-induced diabetes can be overcome by increasing the dose of STZ used. Female mice can, and should, be included in pre-clinical studies of diabetes and its complications.

Preclinical and clinical studies of photobiomodulation therapy for macular oedema

AIMS/HYPOTHESIS

Diabetic macular oedema (DME) is the leading cause of visual impairment in people with diabetes. Intravitreal injections of vascular endothelial growth factor inhibitors or corticosteroids prevent loss of vision by reducing DME, but the injections must be given frequently and usually for years. Here we report laboratory and clinical studies on the safety and efficacy of 670 nm photobiomodulation (PBM) for treatment of centre-involving DME.

METHODS

The therapeutic effect of PBM delivered via a light-emitting diode (LED) device was tested in transgenic mice in which induced Müller cell disruption led to photoreceptor degeneration and retinal vascular leakage. We also developed a purpose-built 670 nm retinal laser for PBM to treat DME in humans. The effect of laser-delivered PBM on improving mitochondrial function and protecting against oxidative stress was studied in cultured rat Müller cells and its safety was studied in pigmented and non-pigmented rat eyes. We then used the retinal laser to perform PBM in an open-label, dose-escalation Phase IIa clinical trial involving 21 patients with centre-involving DME. Patients received 12 sessions of PBM over 5 weeks for 90 s per treatment at a setting of 25, 100 or 200 mW/cm² for the three sequential cohorts of 6-8 patients each. Patients were recruited from the Sydney Eye Hospital, over the age of 18 and had centre-involving DME with central macular thickness (CMT) of >300 μm with visual acuity of 75-35 Log minimum angle of resolution (logMAR) letters (Snellen visual acuity equivalent of 20/30-20/200). The objective of this trial was to assess the safety and efficacy of laser-delivered PBM at 2 and 6 months. The primary efficacy outcome was change in CMT at 2 and 6 months.

RESULTS

LED-delivered PBM enhanced photoreceptor mitochondrial membrane potential, protected Müller cells and photoreceptors from damage and reduced retinal vascular leakage resulting from induced Müller cell disruption in transgenic mice. PBM delivered via the retinal laser enhanced mitochondrial function and protected against oxidative stress in cultured Müller cells. Laser-delivered PBM did not damage the retina in pigmented rat eyes at 100 mW/cm². The completed clinical trial found a significant reduction in CMT at 2 months by 59 ± 46 μm (p = 0.03 at 200 mW/cm²) and significant reduction at all three settings at 6 months (25 mW/cm²: 53 ± 24 μm, p = 0.04; 100 mW/cm²: 129 ± 51 μm, p < 0.01; 200 mW/cm²: 114 ± 60 μm, p < 0.01). Laser-delivered PBM was well tolerated in humans at settings up to 200 mW/cm² with no significant side effects.

CONCLUSIONS/INTERPRETATION

PBM results in anatomical improvement of DME over 6 months and may represent a safe and non-invasive treatment. Further testing is warranted in randomised clinical trials.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02181400 Graphical abstract.

A Pilot Study Evaluating the Effects of 670 nm Photobiomodulation in Healthy Ageing and Age-Related Macular Degeneration

Limited evidence suggests that the application of 670 nm of red light alters the course of aged decline. A previous report on 18 patients showed regression of drusen and improvement in visual functions in patients with intermediate age-related macular degeneration (AMD) by 12 months. We evaluated the functional and structural effects of applying 670 nm light to 31 patients with intermediate AMD and 11 people aged 55 years or above with normal retina. The study eyes were treated daily in the morning with a 670 nm hand-held light source housed in a torch-like tube that emitted energy equivalent to 40 mW/cm² or 4.8J/ cm² for 2 min at the viewing aperture. Visual function in terms of best-corrected visual acuity, low luminance visual acuity, scotopic thresholds and rod-intercept time were compared between baseline and 1, 3, 6 and 12 months. Structural changes on optical coherence tomography OCT and colour photographs were also assessed. Five withdrew consent voluntarily due to the intensity of the study visit assessments and two developed neovascular AMD and were excluded from further treatment and the analysis. In normal ageing, there was an improvement in scotopic thresholds in the group with no AMD by 1.77dB (p = 0.03) and no other parameters showed any clinically significant change. In eyes with intermediate AMD, there was no significant improvement in any functional or structural changes at any time point up to 12 months although the compliance was good. This pilot study shows that photobiomodulation with 670 nm has no effect in patients who have already progressed to intermediate AMD.

Photobiomodulation Mediates Neuroprotection against Blue Light Induced Retinal Photoreceptor Degeneration

Potent neuroprotective effects of photobiomodulation with 670 nm red light (RL) have been demonstrated in several models of retinal disease. RL improves mitochondrial metabolism, reduces retinal inflammation and oxidative cell stress, showing its ability to enhance visual function. However, the current knowledge is limited to the main hypothesis that the respiratory chain complex IV, cytochrome c oxidase, serves as the primary target of RL. Here, we demonstrate a comprehensive cellular, molecular, and functional characterization of neuroprotective effects of 670 nm RL and 810 nm near-infrared light (NIRL) on blue light damaged murine primary photoreceptors. We show that respiratory chain complexes I and II are additional PBM targets, besides complex IV, leading to enhanced mitochondrial energy metabolism. Accordingly, our study identified mitochondria related RL- and NIRL-triggered defense mechanisms promoting photoreceptor neuroprotection. The observed improvement of mitochondrial and extramitochondrial respiration in both inner and outer segments is linked with reduced oxidative stress including its cellular consequences and reduced mitochondria-induced apoptosis. Analysis of regulatory mechanisms using gene expression analysis identified upregulation α-crystallins that indicate enhanced production of proteins with protective functions that point to the rescued mitochondrial function. The results support the hypothesis that energy metabolism is a major target for retinal light therapy.

Cho S, Britton W, S. Kern T, Antonetti DA, Hellström A, E.H. Smith L. Targeting Neurovascular Interaction in Retinal Disorders

The tightly structured neural retina has a unique vascular network comprised of three interconnected plexuses in the inner retina (and choroid for outer retina), which provide oxygen and nutrients to neurons to maintain normal function. Clinical and experimental evidence suggests that neuronal metabolic needs control both normal retinal vascular development and pathological aberrant vascular growth. Particularly, photoreceptors, with the highest density of mitochondria in the body, regulate retinal vascular development by modulating angiogenic and inflammatory factors. Photoreceptor metabolic dysfunction, oxidative stress, and inflammation may cause adaptive but ultimately pathological retinal vascular responses, leading to blindness. Here we focus on the factors involved in neurovascular interactions, which are potential therapeutic targets to decrease energy demand and/or to increase energy production for neovascular retinal disorders.

Multifunctional materials for implantable and wearable photonic healthcare devices

Numerous light-based diagnostic and therapeutic devices are routinely used in the clinic. These devices have a familiar look as items plugged in the wall or placed at patients' bedsides, but recently, many new ideas have been proposed for the realization of implantable or wearable functional devices. Many advances are being fuelled by the development of multifunctional materials for photonic healthcare devices. However, the finite depth of light penetration in the body is still a serious constraint for their clinical applications. In this Review, we discuss the basic concepts and some examples of state-of-the-art implantable and wearable photonic healthcare devices for diagnostic and therapeutic applications. First, we describe emerging multifunctional materials critical to the advent of next-generation implantable and wearable photonic healthcare devices and discuss the path for their clinical translation. Then, we examine implantable photonic healthcare devices in terms of their properties and diagnostic and therapeutic functions. We next describe exemplary cases of noninvasive, wearable photonic healthcare devices across different anatomical applications. Finally, we discuss the future research directions for the field, in particular regarding mobile healthcare and personalized medicine.

Emerging Concepts in the Treatment of Diabetic Retinopathy

PURPOSE OF REVIEW

Diabetic retinopathy (DR) is the leading cause of vision loss in working-age adults in the developed world. This review discusses the current approach to managing the disease, such as glycemic and blood pressure control, as well as laser photocoagulation, as well as emerging concepts and controversies on novel therapies.

RECENT FINDINGS

In recent years, the rise of intraocular anti-angiogenesis treatments is changing the paradigm of classic laser photocoagulation in the management of DR, but its long-term benefits remain an area of controversy. We also discuss new targets including anti-inflammation, neuroprotection, and novel laser technologies. Finally, we discuss new advances in retinal imaging that has vastly improved the diagnosis and management of DR. Diagnosis and management of diabetic retinopathy is a rapidly progressing field. Emerging concepts in ophthalmic imaging, medical treatments, and surgical approaches provide insights into how DR management will evolve in the near future.

Chronic photodamage in the chicken retina using 650-nm semiconductor laser

AIM

To investigate the occurrence of chronic photodamage in the cone-based retina, following long-term exposure to a 650-nm semiconductor laser (power: 2 mW).

METHODS

Chickens fed for 1mo under natural light after hatching were irradiated with 650-nm laser light at different times each day. Fifteen animals were included in each group. Group A was a control group, irradiated with natural light during the entire study. Group B was irradiated with laser for 3 min/d. Group C was irradiated with laser for 6 min/d. Group D was irradiated with laser for 30 min/d. The duration of the light experiment was 6mo. We obtained data at 1, 3, and 6mo, including measuring the retinal thickness in vivo using optical coherence tomography, hematoxylin and eosin staining, TUNEL assay, apoptosis staining, malondialdehyde (MDA) content, superoxide dismutase (SOD) activity, and Western blotting to detect changes in L/M opsins and rhodopsin.

RESULTS

At 1mo, the MDA content in Group D was higher than that observed in Group A (P=0.019). At 3mo the MDA content in Groups C and D was higher than that reported in Group A (P=0.026, 0.003). At 6mo, the MDA content in Groups B, C, and D was higher than that observed in Group A (P=0.038, 0.032, 0.000, respectively). There was no difference in SOD activity, and L/M opsin and rhodopsin content between the groups at 1 and 3mo. The SOD activity in group D was significantly decreased at 6mo (P=0.000), as was the content of rhodopsin. There was no significant reduction observed in retinal thickness, abnormal cell arrangement, and positive staining of TUNEL in the groups during the 6-month study period.

CONCLUSION

Irradiation using a 650 nm semiconductor laser (power: 2 mW) for 6min per day over 6mo do not cause photodamage. Similarly, a 3-month exposure of 30min per day do not cause damage. However, irradiation for 6mo resulted in a significant increase in the content of free radicals and a decrease in the content of rhodopsin in the retina, suggesting the presence of photodamage.

Loss of CD40 attenuates experimental diabetes-induced retinal inflammation but does not protect mice from electroretinogram defects

Chronic low grade inflammation is considered to contribute to the development of experimental diabetic retinopathy (DR). We recently demonstrated that lack of CD40 in mice ameliorates the upregulation of inflammatory molecules in the diabetic retina and prevented capillary degeneration, a hallmark of experimental diabetic retinopathy. Herein, we investigated the contribution of CD40 to diabetes-induced reductions in retinal function via the electroretinogram (ERG) to determine if inflammation plays a role in the development of ERG defects associated with diabetes. We demonstrate that diabetic CD40-/- mice are not protected from reduction to the ERG b-wave despite failing to upregulate inflammatory molecules in the retina. Our data therefore supports the hypothesis that retinal dysfunction found in diabetics occurs independent of the induction of inflammatory processes.

Role of Inflammation in Diabetic Retinopathy

Diabetic retinopathy is a common complication of diabetes and remains the leading cause of blindness among the working-age population. For decades, diabetic retinopathy was considered only a microvascular complication, but the retinal microvasculature is intimately associated with and governed by neurons and glia, which are affected even prior to clinically detectable vascular lesions. While progress has been made to improve the vascular alterations, there is still no treatment to counteract the early neuro-glial perturbations in diabetic retinopathy. Diabetes is a complex metabolic disorder, characterized by chronic hyperglycemia along with dyslipidemia, hypoinsulinemia and hypertension. Increasing evidence points to inflammation as one key player in diabetes-associated retinal perturbations, however, the exact underlying molecular mechanisms are not yet fully understood. Interlinked molecular pathways, such as oxidative stress, formation of advanced glycation end-products and increased expression of vascular endothelial growth factor have received a lot of attention as they all contribute to the inflammatory response. In the current review, we focus on the involvement of inflammation in the pathophysiology of diabetic retinopathy with special emphasis on the functional relationships between glial cells and neurons. Finally, we summarize recent advances using novel targets to inhibit inflammation in diabetic retinopathy.

670nm light treatment following retinal injury modulates Müller cell gliosis: Evidence from in vivo and in vitro stress models

Photobiomodulation (PBM) with 670 nm light has been shown to accelerate wound healing in soft tissue injuries, and also to protect neuronal tissues. However, little data exist on its effects on the non-neuronal components of the retina, such as Müller cells (MCs), which are the principal macroglia of the retina that play a role in maintaining retinal homeostasis. The aim of this study was to explore the effects of 670 nm light on activated MCs using in vivo and in vitro stress models. Adult Sprague-Dawley rats were exposed to photo-oxidative damage (PD) for 24 h and treated with 670 nm light at 0, 3 and 14 days after PD. Tissue was collected at 30 days post-PD for analysis. Using the in vitro scratch model with a human MC line (MIO-M1), area coverage and cellular stress were analysed following treatment with 670 nm light. We showed that early treatment with 670 nm light after PD reduced MC activation, lowering the retinal expression of GFAP and FGF-2. 670 nm light treatment mitigated the production of MC-related pro-inflammatory cytokines (including IL-1β), and reduced microglia/macrophage (MG/MΦ) recruitment into the outer retina following PD. This subsequently decreased photoreceptor loss, slowing the progression of retinal degeneration. In vitro, we showed that 670 nm light directly modulated MC activation, reducing rates of area coverage by suppressing cellular proliferation and spreading. This study indicates that 670 nm light treatment post-injury may have therapeutic benefit when administered shortly after retinal damage, and could be useful for retinal degenerations where MC gliosis is a feature of disease progression.

Photobiomodulation Inhibits Long-term Structural and Functional Lesions of Diabetic Retinopathy

Previous studies demonstrated that brief (3 to 4 min) daily application of light at 670 nm to diabetic rodents inhibited molecular and pathophysiologic processes implicated in the pathogenesis of diabetic retinopathy (DR) and reversed diabetic macular edema in small numbers of patients studied. Whether or not this therapy would inhibit the neural and vascular lesions that characterize the early stages of the retinopathy was unknown. We administered photobiomodulation (PBM) therapy daily for 8 months to streptozotocin-diabetic mice and assessed effects of PBM on visual function, retinal capillary permeability, and capillary degeneration using published methods. Vitamin D receptor and Cyp24a1 transcripts were quantified by quantitative real-time PCR, and the abundance of c-Kit⁺ stem cells in blood and retina were assessed. Long-term daily administration of PBM significantly inhibited the diabetes-induced leakage and degeneration of retinal capillaries and also significantly inhibited the diabetes-induced reduction in visual function. PBM also inhibited diabetes-induced reductions in retinal Cyp24a1 mRNA levels and numbers of circulating stem cells (CD45^-/c-Kit⁺), but these effects may not account for the beneficial effects of PBM on the retinopathy. PBM significantly inhibits the functional and histopathologic features of early DR, and these effects likely are mediated via multiple mechanisms.

Retinal pigment epithelium in the pathogenesis of age-related macular degeneration and photobiomodulation as a potential therapy?

The retinal pigment epithelium (RPE) comprises a monolayer of cells located between the neuroretina and the choriocapillaries. The RPE serves several important functions in the eye: formation of the blood-retinal barrier, protection of the retina from oxidative stress, nutrient delivery and waste disposal, ionic homeostasis, phagocytosis of photoreceptor outer segments, synthesis and release of growth factors, reisomerization of all-trans-retinal during the visual cycle, and establishment of ocular immune privilege. Age-related macular degeneration (AMD) is the leading cause of blindness in developed countries. Dysfunction of the RPE has been associated with the pathogenesis of AMD in relation to increased oxidative stress, mitochondrial destabilization and complement dysregulation. Photobiomodulation or near infrared light therapy which refers to non-invasive irradiation of tissue with light in the far-red to near-infrared light spectrum (630-1000 nm), is an intervention that specifically targets key mechanisms of RPE dysfunction that are implicated in AMD pathogenesis. The current evidence for the efficacy of photobiomodulation in AMD is poor but its safety profile and proposed mechanisms of action motivate further research as a novel therapy for AMD.

Photobiomodulation with 670 nm light ameliorates Müller cell-mediated activation of microglia and macrophages in retinal degeneration

Müller cells, the supporting cells of the retina, play a key role in responding to retinal stress by releasing chemokines, including CCL2, to recruit microglia and macrophages (MG/MΦ) into the damaged retina. Photobiomodulation (PBM) with 670 nm light has been shown to reduce inflammation in models of retinal degeneration. In this study, we aimed to investigate whether 670 nm light had an effect on Müller cell-initiated inflammation under retinal photo-oxidative damage (PD) in vivo and in vitro. Sprague-Dawley rats were pre-treated with 670 nm light (9J/cm²) once daily over 5 days prior to PD. The expression of inflammatory genes including CCL2 and IL-1β was analysed in retinas. In vitro, primary Müller cells dissociated from neonatal rat retinas were co-cultured with 661W photoreceptor cells. Co-cultures were exposed to PD, followed by 670 nm light treatment to the Müller cells only, and Müller cell stress and inflammation were assessed. Primary MG/MΦ were incubated with supernatant from the co-cultures, and collected for analysis of inflammatory activation. To further understand the mechanism of 670 nm light, the expression of COX5a and mitochondrial membrane potential (ΔΨm) were measured in Müller cells. Following PD, 670 nm light-treated Müller cells had a reduced inflammatory activation, with lower levels of CCL2, IL-1β and IL-6. Supernatant from 670 nm light-treated co-cultures reduced activation of primary MG/MΦ, and lowered the expression of pro-inflammatory cytokines, compared to untreated PD controls. Additionally, 670 nm light-treated Müller cells had an increased expression of COX5a and an elevated ΔΨm following PD, suggesting that retrograde signaling plays a role in the effects of 670 nm light on Müller cell gene expression. Our data indicates that 670 nm light reduces Müller cell-mediated retinal inflammation, and offers a potential cellular mechanism for 670 nm light therapy in regulating inflammation associated with retinal degenerations.