Internal limiting membrane peeling in rhegmatogenous retinal detachment: A meta-analysis

PURPOSE

To determine whether pars plana vitrectomy (PPV) with internal limiting membrane (ILM) peeling for rhegmatogenous retinal detachment (RRD) could get better functional and anatomical outcomes.

METHODS

A comprehensive literature search was performed to find relevant studies. A meta-analysis was conducted by comparing the weighted mean differences (WMD) in the mean change of best corrected visual acuity (BCVA) from baseline and calculating the odd ratios (OR) for rates of epiretinal membrane (ERM) formation and recurrence of retinal detachment (RD).

RESULTS

Fourteen studies were selected, including 2259 eyes (825 eyes in the ILM peeling group and 1434 eyes in the non-ILM peeling group). There was no significant difference in terms of mean change in BCVA from baseline and the rate of RD recurrence (WMD = 0.02, 95% CI, -0.20 to 0.24, P = 0.86, and OR = 0.55, 95% CI, 0.24 to 1.26, P = 0.16), but ILM peeling was associated with a significantly lower frequency of postoperative ERM formation (OR = 0.13, 95% CI, 0.06 to 0.26, P<0.00001). Similar results were obtained in a sub-analysis based on macula-off RRD.

CONCLUSION

ILM peeling results in similar BCVA, with same rate of RD recurrence, but lower rate of postoperative ERM development. ILM peeling could be considered in selected cases with risk factors that are likely to develop an ERM.

Pre-stimulus bioelectrical activity in light-adapted ERG under blue versus white background

To compare the baseline signal between two conditions used to generate the photopic negative response (PhNR) of the full-field electroretinogram (ERG): red flash on a blue background (RoB) and white flash on a white background (LA3). The secondary purpose is to identify how the level of pre-stimulus signal affects obtaining an unambiguous PhNR component. A retrospective chart review was conducted on four cohorts of patients undergoing routine ERG testing. In each group, LA3 was recorded the same way while RoB was generated differently using various luminances of red and blue light. The background bioelectrical activity 30 ms before the flash was extracted, and the root mean square (RMS) of the signal was calculated and compared between RoB and LA3 using Wilcoxon test. Pre-stimulus noise was significantly higher under RoB stimulation versus LA3 in all four conditions for both right and left eyes (ratio RoB/LA3 RMS 1.70 and 1.57 respectively, p < 0.033). There was also no significant difference between the RMS of either LA3 or RoB across protocols, indicating that the baseline noise across cohorts were comparable. Additionally, pre-stimulus noise was higher in signals where PhNR was not clearly identifiable as an ERG component versus signals with the presence of unambiguous PhNR component under RoB in all four groups for both eyes (p < 0.05), whereas the difference under LA3 was less pronounced. Our study suggests that LA3 produces less background bioelectrical activity, likely due to decreased facial muscle activity. As it seems that the pre-stimulus signal level affects PhNR recordability, LA3 may also produce a better-quality signal compared to RoB. Therefore, until conditions for a comparable bioelectrical activity under RoB are established, we believe that LA3 should be considered at least as a supplementary method to evaluate retinal ganglion cell function by ERG.

Fenofibrate Ameliorates Retinal Pigment Epithelium Injury Induced by Excessive Fat Through Upregulation of PI3K/AKT Signaling

Purpose

This study aimed to determine the effect and its mechanism of fenofibrate on retinal pigment epithelium (RPE) injury induced by excessive fat in vitro and in vivo.

Methods

ARPE-19 cells were co-incubated with palmitic acid (PA) and fenofibric acid (the active form of fenofibrate after metabolism in vivo) and mice fed with high-fat diet (HFD) were supplemented with fenofibrate. The following methods were used: Western blot and immunofluorescent staining to determine expressions of reactive oxygen species (ROS)-associated factors and proinflammatory cytokines; electroretinogram (ERG) c-wave to evaluate RPE function; TUNEL staining to detect the apoptotic cell in RPE tissue. Additionally, ARPE19 cells were treated with PI3K/AKT inhibitor or agonist to investigate the mechanism of fenofibric acid inhibiting PA-induced RPE damage.

Results

We found that the application of PA inhibited RPE cell viability in a dose-dependent manner, and increased the levels of NAPDH oxidase 4 (NOX4), 3-nitrotyrosin (3-NT), intracellular adhesion molecule-1(ICAM1), tumor necrosis factor alpha (TNFα) and vascular endothelial growth factor (VEGF) at 400μM. The application of fenofibric acid resulted in the inhibition of NOX4, 3-NT, TNFα, ICAM1 and VEGF expression in ARPE-19 cells treated with PA. Moreover, wortmannin, as a selective inhibitor of PI3K/AKT pathway, abolished the effects of fenofibrate on the oxidative stress and inflammation in ARPE-19 cells. In addition, 740Y-P, a selective agonist of PI3K/AKT pathway, enhanced the protective action of fenofibrate. Meanwhile, in vivo dosing of fenofibrate ameliorated the downregulated amplitudes of ERG c-wave in HFD-fed mice and suppressed the HFD-induced oxidative injury and inflammatory response in RPE tissues.

Conclusion

Our results suggested that fenofibrate ameliorated RPE cell damage induced by excessive fat in vitro and in vivo, in part, through activation of the PI3K/AKT signaling pathway.

Postoperative Outcome of Combined Phacovitrectomy in Eyes with Excessive Myopia (>-30 D)

Background

To report the outcomes of phacoemulsification combined with vitrectomy in eyes with extreme myopia (-30 diopters or more). Case Presentation. Three patients with cataract, vitreous opacities, and extreme myopia of more than -30 diopters underwent a combined surgical procedure of cataract extraction combined with vitrectomy. Postoperative refractive correction of the three cases ranged from -1.0 D to -2.5 D spherical equivalent. There was an obvious hyperopic shift of all cases. All patients noted a significant improvement in uncorrected and best-corrected visual acuity from 0.4 to 0.8 in case 1, from CF/70 cm to 1.0 in case 2, and from 0.12 to 0.5 in the right eye and 0.15 to 0.2 in the left eye in case 3. Vitreous floaters disappeared in all cases. No complications were noted during follow-up.

Conclusions

To the best of the authors' knowledge, these represent the first reported clinical cases of combined cataract extraction+vitrectomy surgery in eyes with extreme (>-30 D) myopia. Our results support the notion that phacoemulsification combined with vitrectomy may be a good therapeutic option for cataracts and vitreous floaters in cases with extreme myopia.

Hydrogen peroxide-induced oxidative damage and protective role of peroxiredoxin 6 protein via EGFR/ERK signaling pathway in RPE cells

Introduction

Damage to retinal pigment epithelium (RPE) cells caused by oxidative stress is closely related to the pathogenesis of several blinding retinal diseases, such as age-related macular degeneration (AMD), retinitis pigmentosa, and other inherited retinal degenerative conditions. However, the mechanisms of this process are poorly understood. Hence, the goal of this study was to investigate hydrogen peroxide (H₂O₂)-induced oxidative damage and protective role of peroxiredoxin 6 (PRDX6) protein via EGFR/ERK signaling pathway in RPE cells.

Methods

Cells from a human RPE cell line (ARPE-19 cells) were treated with H₂O₂, and then cell viability was assessed using the methyl thiazolyl tetrazolium assay. Cell death and reactive oxygen species (ROS) were detected by flow cytometry. The levels of PRDX6, epidermal growth factor receptor (EGFR), P38 mitogen-activated protein kinase (P38MAPK), c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK) were detected by Western blot assay. PRDX6 and EGFR were also detected via immunofluorescence staining.

Results

Our results show that H₂O₂ inhibited cell viability, induced cell death, and increased ROS levels in ARPE-19 cells. It was also found that H₂O₂ decreased the levels of PRDX6, EGFR, and phosphorylated ERK but increased the levels of phosphorylated P38MAPK and JNK. PRDX6 overexpression was found to attenuate H₂O₂-induced inhibition of cell viability and increased cell death and ROS production in ARPE-19 cells. PRDX6 overexpression also increased the expression of EGFR and alleviated the H₂O₂-induced decrease in EGFR and phosphorylated ERK. Moreover, inhibition of epidermal growth factor-induced EGFR and ERK signaling in oxidative stress was partially blocked by PRDX6 overexpression.

Discussion

Our findings indicate that PRDX6 overexpression protects RPE cells from oxidative stress damage caused by decreasing ROS production and partially blocking the inhibition of the EGFR/ERK signaling pathway induced by oxidative stress. Therefore, PRDX6 shows promise as a therapeutic target for the prevention of RPE cell damage caused by oxidative stress associated with retinal diseases.

Human amnionic progenitor cell secretome mitigates the consequence of traumatic optic neuropathy in a mouse model

Traumatic optic neuropathy (TON) is a condition in which acute injury to the optic nerve from direct or indirect trauma results in vision loss. The most common cause of TON is indirect injury to the optic nerve caused by concussive forces that are transmitted to the optic nerve. TON occurs in up to 5% of closed-head trauma patients and there is currently no known effective treatment. One potential treatment option for TON is ST266, a cell-free biological solution containing the secretome of amnion-derived multipotent progenitor (AMP) cells. We investigated the efficacy of intranasal ST266 in a mouse model of TON induced by blunt head trauma. Injured mice treated with a 10-day regimen of ST266 showed an improvement in spatial memory and learning, a significant preservation of retinal ganglion cells, and a decrease in neuropathological markers in the optic nerve, optic tract, and dorsal lateral geniculate nucleus. ST266 treatment effectively downregulated the NLRP3 inflammasome-mediated neuroinflammation pathway after blunt trauma. Overall, treatment with ST266 was shown to improve functional and pathological outcomes in a mouse model of TON, warranting future exploration of ST266 as a cell-free therapeutic candidate for testing in all optic neuropathies.

Electroretinographic Findings in Melanoma-Associated Retinopathy Treated by Intravitreal Dexamethasone Implant

A 63-year-old male with a history of bladder cancer in remission presented with progressive vision loss during a period of 2 years. Slit-lamp and funduscopic examination were unremarkable. Electroretinogram (ERG) revealed an unrecordable scotopic response and a moderately decreased photopic response. Computed tomography of the chest, abdomen, and pelvis showed a new duodenal mass. Subsequent biopsy disclosed malignant melanoma, and a diagnosis of melanoma-associated retinopathy (MAR) was made. The patient was then treated with a dexamethasone intravitreal implant 0.7 mg in his left eye. Two months after the implant, the patient reported a mild symptomatic improvement in his left eye, and ERG testing performed after the implant insertion revealed partial improvement in several scotopic and photopic ERG parameters. Repeat spectral-domain optical coherence tomography disclosed an improvement in retinal thickening. To the best of the authors' knowledge, this is the first report illustrating potential subjective visual improvement, improvement in retinal thickening, and ERG changes following treatment by intravitreal dexamethasone implant for MAR. [Ophthalmic Surg Lasers Imaging Retina. 2021;52:454-456.].

Volumetric histological characterization of optic nerve degeneration using tissue clearing: literature review and practical study

Tissue clearing technologies can greatly improve the depth and accuracy with which the three-dimensional structure of tissues, especially those of the nervous system, can be visualized. A review of the present literature suggests that the growing diversity and sophistication of various approaches have contributed to the expansion of this method to a greater variety of tissue types, experimental conditions, and imaging modalities. In the proof-of-concept study presented in this paper, a simplified and modified version of the tissue clearing method CUBIC (clear, unobstructed brain imaging cocktails and computational analysis) was used in conjunction with fluorescent staining and immunohistochemistry to illustrate the three-dimensional structure and molecular characteristics of inflammatory and degenerative activity in the mouse optic nerve. Based on the studies summarized in this mini-review, and our impression from using the mCUBIC method, it appears that tissue clearing could be a viable approach revealing three-dimensional histological features of myelin-rich tissues under normal conditions and after injury.

Carbon Dots Fabrication: Ocular Imaging and Therapeutic Potential

Vision loss is a major complication in common ocular infections and diseases such as bacterial keratitis, age-related macular degeneration (AMD) and diabetic retinopathy (DR). The prevalence of such ophthalmic diseases represents an urgent need to develop safe, effective, and long-term treatments. Current therapies are riddled with drawbacks and limitations which calls for the exploration of alternative drug delivery mechanisms. Toxicity of the inorganic metals and metal oxides used for drug delivery raise safety concerns that are alleviated with the alternate use of, a natural and organic polymer which is both biocompatible and environmentally friendly. Carbon dots (CDs) represent a great potential in novel biomedical applications due to their tunable fluorescence, biocompatibility, and ability to be conjugated with diverse therapeutic materials. There is a growing interest on the exploitation of these properties for drug delivery with enhanced bio-imaging. However, there are limited reports of CD applications for ophthalmic indications. In this review, we focus on the CD potential and the development of translational therapies for ophthalmic diseases. The current review presents better understanding of fabrication of CDs and how it may be useful in delivering anti-bacterial agents, anti-VEGF molecules as well as imaging for ophthalmic applications.

Natural protection of ocular surface from viral infections - A hypothesis

A pandemic outbreak of a viral respiratory infection (COVID-19) caused by a coronavirus (SARS-CoV-2) prompted a multitude of research focused on various aspects of this disease. One of the interesting aspects of the clinical manifestation of the infection is an accompanying ocular surface viral infection, viral conjunctivitis. Although occasional reports of viral conjunctivitis caused by this and the related SARS-CoV virus (causing the SARS outbreak in the early 2000s) are available, the prevalence of this complication among infected people appears low (~1%). This is surprising, considering the recent discovery of the presence of viral receptors (ACE2 and TMPRSS2) in ocular surface tissue. The discrepancy between the theoretically expected high rate of concurrence of viral ocular surface inflammation and the observed relatively low occurrence can be explained by several factors. In this work, we discuss the significance of natural protective factors related to anatomical and physiological properties of the eyes and preventing the deposition of large number of virus-loaded particles on the ocular surface. Specifically, we advance the hypothesis that the standing potential of the eye plays an important role in repelling aerosol particles (microdroplets) from the surface of the eye and discuss factors associated with this hypothesis, possible ways to test it and its implications in terms of prevention of ocular infections.

A New Two-Step Anesthesia for 23- or 25-Gauge Vitrectomy Surgery: A Prospective, Randomized Clinical Trial

OBJECTIVE

To investigate the safety and efficacy of topical anesthesia combined with subconjunctival anesthesia (termed two-step anesthesia) for 23- or 25-gauge pars plana vitrectomy or other posterior segment surgery.

METHODS

Patients (n = 90) requiring 23-/25-gauge vitrectomy or other posterior segment surgery were randomized into 3 groups. Group 1 received peribulbar anesthesia, group 2 received retrobulbar anesthesia and group 3 received two-step anesthesia. A 5-point visual analog pain scale (VAPS) was used to measure self-report of patient pain. Complications were recorded for subsequent analysis.

RESULTS

VAPS scores for overall intraoperative pain ranged from 0 to 3 (1.07 ± 1.07) in group 1, from 0 to 2 (0.69 ± 0.93) in group 2 and from 0 to 3 (1.06 ± 0.98) in group 3. Assessment of surgeon discomfort score ranged from 0 to 2 (0.31 ± 0.66) in group 1, from 0 to 3 (0.38 ± 0.82) in group 2 and from 0 to 2 (0.47 ± 0.62) in group 3. Both scores reveal no significant difference among the 3 groups. While there were no complications noted in group 1, there was an ocular perforation in group 2. Additionally, there were no complications in group 3 related to the anesthetic technique.

CONCLUSIONS

Results suggest that two-step anesthesia is a safe and effective anesthetic approach for selected patients undergoing 23- or 25-gauge pars plana vitrectomy or other posterior segment surgeries. It may offer a viable alternative to peribulbar anesthesia and retrobulbar anesthesia for carefully selected 23- or 25-gauge cannular-access ocular surgeries.

ISCEV extended protocol for derivation and analysis of the strong flash rod-isolated ERG a-wave

The International Society for the Clinical Electrophysiology of Vision (ISCEV) standard for full-field electroretinography (ERG) describes a minimum set of tests, but encourages the use of additional protocols for clinical ERG testing. This extended protocol describes recording methods and derivations that will allow analysis of rod-driven components of the dark-adapted (DA) strong flash ERG a-wave, more closely related to rod phototransduction than ISCEV standard DA ERGs. The method involves recording ERGs to a flash strength equivalent to 30 cd s m2 under conditions of dark adaptation and additionally to the same stimulus following light adaptation (LA) and in the presence of a standard photopic background luminance of 30 cd m−2. The isolated rod-driven ERG a-wave is derived by subtracting the LA response from the DA ERG. The method is likely to be of value in the characterization of retinal disorders which affect rod quantal catch, diseases that affect the dynamics of any component of the activation phase of rod phototransduction, or those affecting total numbers of rod photoreceptors.

CCL20-CCR6 axis modulated traumatic brain injury-induced visual pathologies

BACKGROUND

Traumatic brain injury (TBI) is a major cause of death and disability in the USA and the world; it constitutes 30% of injury-related deaths (Taylor et al., MMWR Surveill Summ 66:1-16, 2017). Contact sports athletes often experience repetitive TBI (rTBI), which exerts a cumulative effect later in life. Visual impairment is a common after-effect of TBI. Previously, we have shown that C-C chemokine 20 (CCL20) plays a critical role in neurodegeneration and inflammation following TBI (Das et al., J Neuroinflammation 8:148, 2011). C-C chemokine receptor 6 (CCR6) is the only receptor that CCL20 interacts with. The objective of the present study was to investigate the role of CCL20-CCR6 axis in mediating rTBI-induced visual dysfunction (TVD).

METHODS

Wild type (WT) or CCR6 knock out (CCR6-/-) mice were subjected to closed head rTBI. Pioglitazone (PG) is a peroxisome proliferator-activated receptor γ (PPARγ) agonist which downregulates CCL20 production. Subsets of WT mice were treated with PG following final rTBI. A subset of mice was also treated with anti-CCL20 antibody to neutralize the CCL20 produced after rTBI. Histopathological assessments were performed to show cerebral pathologies, retinal pathologies, and inflammatory changes induced by rTBI.

RESULTS

rTBI induced cerebral neurodegeneration, retinal degeneration, microgliosis, astrogliosis, and CCL20 expression. CCR6-/- mice showed reduced retinal degeneration, microgliosis, and inflammation. Treatment with CCL20 neutralization antibody or PG showed reduced CCL20 expression along with reduced retinal degeneration and inflammation. rTBI-induced GFAP-positive glial activation in the optic nerve was not affected by knocking out CCR6.

CONCLUSION

The present data indicate that rTBI-induced retinal pathology is mediated at least in part by CCL20 in a CCR6-dependent manner.

Iatrogenic retinal breaks and postoperative retinal detachments in microincision vitrectomy surgery compared with conventional 20-gauge vitrectomy: a meta-analysis

PURPOSE

To assess the incidence of iatrogenic retinal breaks (IRBs) and postoperative retinal detachments (RDs) in microincision vitrectomy surgery (MIVS) compared with 20-gauge (20 G) vitrectomy.

METHODS

A comprehensive literature search was performed to find relevant studies and a meta-analysis of the IRBs and postoperative RDs rates after 20 G vitrectomy versus MIVS was conducted.

RESULTS

Thirty-two studies were selected, including 14,373 eyes (6932 eyes in the 20 G group, 7441 eyes in the MIVS group). The meta-analysis demonstrated that the incidence of IRBs was significantly higher in 20 G vitrectomy vs. MIVS (OR = 2.22, 95% CI, 1.93-2.57, P < 0.00001) and in a subanalysis vs. 23 G MIVS (OR = 2.19, 95% CI, 1.87-2.56, P < 0.00001) and vs. 25 G MIVS (OR = 2.27, 95% CI, 1.62-3.18, P < 0.00001). Similar result was obtained in a subanalysis for macular surgery (OR = 2.44, 95% CI, 1.99-2.99, P < 0.00001), and also for sclerotomy-related IRBs (OR = 3.73, 95% CI, 2.55-5.44, P < 0.00001), but not for surgically induced posterior vitreous detachment-related IRBs (OR = 1.59, 95% CI, 0.89-2.84, P = 0.12). The incidence of postoperative RDs in 20 G vitrectomy was significantly higher compared to MIVS (OR = 1.72, 95% CI, 1.21-2.46, P = 0.003) and in a subanalysis vs. 23 G MIVS (OR = 2.45, 95% CI, 1.50-4.00, P = 0.0003), but not for 25 G MIVS (OR = 1.01, 95% CI, 0.63-1.64, P = 0.96). Similar result was obtained in a subanalysis for macular surgery (OR = 1.89, 95% CI, 1.26-2.85, P = 0.002).

CONCLUSION

This meta-analysis demonstrated that MIVS is associated with a lower risk of IRBs and postoperative RDs compared to 20 G vitrectomy.

ISCEV extended protocol for the photopic negative response (PhNR) of the full-field electroretinogram

The International Society for Clinical Electrophysiology of Vision (ISCEV) Standard for full-field electroretinography (ERG) describes a minimum procedure, but encourages more extensive testing. This ISCEV extended protocol describes an extension to the ERG Standard, namely the photopic negative response (PhNR) of the light-adapted flash ERG, as a well-established technique that is broadly accepted by experts in the field. The PhNR is a slow negative-going wave after the b-wave that provides information about the function of retinal ganglion cells and their axons. The PhNR can be reduced in disorders that affect the innermost retina, including glaucoma and other forms of optic neuropathy. This document, based on existing literature, provides a protocol for recording and analyzing the PhNR in response to a brief flash. The protocol includes full-field stimulation, a frequency bandwidth of the recording in which the lower limit does not exceed 0.3 Hz, and a spectrally narrowband stimulus, specifically, a red flash on a rod saturating blue background. Suggested flash strengths cover a range up to and including the minimum required to elicit a maximum amplitude PhNR. This extended protocol for recording the PhNR provides a simple test of generalized retinal ganglion cell function that could be added to standard ERG testing.

Inhibition or Stimulation of Autophagy Affects Early Formation of Lipofuscin-Like Autofluorescence in the Retinal Pigment Epithelium Cell

The accumulation of lipofuscin in the retinal pigment epithelium (RPE) is dependent on the effectiveness of photoreceptor outer segment material degradation. This study explored the role of autophagy in the fate of RPE lipofuscin degradation. After seven days of feeding with either native or modified rod outer segments, ARPE-19 cells were treated with enhancers or inhibitors of autophagy and the autofluorescence was detected by fluorescence-activated cell sorting. Supplementation with different types of rod outer segments increased lipofuscin-like autofluorescence (LLAF) after the inhibition of autophagy, while the induction of autophagy (e.g., application of rapamycin) decreased LLAF. The effects of autophagy induction were further confirmed by Western blotting, which showed the conversion of LC3-I to LC3-II, and by immunofluorescence microscopy, which detected the lysosomal activity of the autophagy inducers. We also monitored LLAF after the application of several autophagy inhibitors by RNA-interference and confocal microscopy. The results showed that, in general, the inhibition of the autophagy-related proteins resulted in an increase in LLAF when cells were fed with rod outer segments, which further confirms the effect of autophagy in the fate of RPE lipofuscin degradation. These results emphasize the complex role of autophagy in modulating RPE autofluorescence and confirm the possibility of the pharmacological clearance of RPE lipofuscin by small molecules.

Subfoveal Choroidal Thickness in Central Serous Chorioretinopathy: A Meta-Analysis

Purpose

To evaluate the relationship between subfoveal choroidal thickness (SFCT) and eyes with central serous chorioretinopathy (CSC) versus fellow or control eyes.

Methods

We performed a meta-analysis using databases including PubMed, Embase and ISI Web of Science to find relevant studies. Weighted mean difference (WMD) was calculated for the SFCT in CSC eyes, the unaffected fellow eyes and normal controls.

Results

Twelve studies were selected for this meta-analysis, including 1108 eyes (397 CSC eyes, 228 unaffected fellow eyes and 483 eyes of normal controls). The meta-analysis clearly demonstrated that the subfoveal choiroid of eyes with a clinical presentation of CSC was thickened compared to unaffected fellow eyes (WMD = 52.81, 95% confidence interval (CI), 39.13–66.49, P<0.00001) and was thickened compared to control eyes (WMD = 145.03, 95%CI, 121.33–168.73, P<0.00001). The mean SFCT measurement of the unaffected fellow eyes showed also significantly increased choroidal thickness compared to that of normal control eyes (WMD = 77.20, 95% CI, 44.98–109.42, P<0.00001). Similar results were obtained in a sub-analysis based on the same instrument.

Conclusion

It is demonstrated that SFCT is significantly increased in eyes with clinical manifestation of CSC, and in the clinically non-manifested fellow eyes. These results support the hypothesis that CSC is a bilateral disorder with an initial unilateral clinical presentation.

Retinal cross talk in the mammalian visual system

The existence and functional relevance of efferent optic nerve fibers in mammals have long been debated. While anatomical evidence for cortico-retinal and retino-retinal projections is substantial, physiological evidence is lacking, as efferent fibers are few in number and are severed in studies of excised retinal tissue. Here we show that interocular connections contribute to retinal bioelectrical activity in adult mammals. Full-field flash electroretinograms (ERGs) were recorded from one or both eyes of Brown-Norway rats under dark-adapted (n = 16) and light-adapted (n = 11) conditions. Flashes were confined to each eye by an opaque tube that blocked stray light. Monocular flashes evoked a small (5-15 μV) signal in the nonilluminated eye, which was named "crossed ERG" (xERG). The xERG began under dark-adapted conditions with a positive (xP1) wave that peaked at 70-90 ms and ended with slower negative (xN1) and positive (xP2) waves from 200 to 400 ms. xN1 was absent under light-adapted conditions. Injection of tetrodotoxin in either eye (n = 15) eliminated the xERG. Intraocular pressure elevation of the illuminated eye (n = 6) had the same effect. The treatments also altered the ERG b-wave in both eyes, and the alterations correlated with xERG disappearance. Optic nerve stimulation (n = 3) elicited a biphasic compound action potential in the nonstimulated nerve with 10- to 13-ms latency, implying that the xERG comes from slow-conducting (W type) fibers. Monocular dye application (n = 7) confirmed the presence of retino-retinal ganglion cells in adult rats. We conclude that mammalian eyes communicate directly with each other via a handful of optic nerve fibers. The cross talk alters retinal activity in rats, and perhaps other animals.

Pharmacogenetics of Complement Factor H Y402H Polymorphism and Treatment of Neovascular AMD with Anti-VEGF Agents: A Meta-Analysis

The purpose of this study is to investigate whether the Y402H polymorphism (rs1061170, a T-to-C transition at amino acid position 402) in the complement factor H (CFH) gene have a pharmacogenetics effect on the anti-vascular endothelial growth factor (VEGF) treatment for neovascular age-related macular degeneration (AMD). We performed a meta-analysis using databases including PubMed and EMBASE to find relevant studies. 13 published association studies were selected for this meta-analysis, including 2704 patients. For the CFH Y402H polymorphism, anti-VEGF treatment was much less effective in AMD patients with the CFH CC genotype (CC versus TT: odds ratio (OR) = 55, 95% confidence interval (CI), 0.31 to 0.95, P = 0.03; CC versus CT: OR = 0.60, 95% CI, 0.40 to 0.91, P = 0.02; and CC versus CT + TT: OR = 0.59, 95% CI, 0.38 to 0.90, P = 0.02, respectively). In subgroup analysis, CFH Y402H polymorphism was more likely to be a predictor of response for Caucasians (CC versus CT+TT: OR = 0.63, 95% CI, 0.42 to 0.95, P = 0.03). In conclusion, pharmacogenetics of CFH Y402H polymorphism may play a role in response to anti-VEGF treatment for neovascular AMD, especially for Caucasians.

Ranibizumab monotherapy or combined with laser versus laser monotherapy for diabetic macular edema: a meta-analysis of randomized controlled trials

Objective

To evaluate the relative efficacy of ranibizumab (RBZ) monotherapy or combined with laser (RBZ + Laser) versus laser monotherapy for the treatment of diabetic macular edema (DME).

Methods

A comprehensive literature search using PUBMED, ClinicalTrials.gov, and the Cochrane Library to identify randomized controlled trials (RCTs) comparing RBZ or RBZ + Laser to laser monotherapy in patients with DME. Efficacy estimates were determined by comparing weighted mean differences (WMD) in the change of best corrected visual acuity (BCVA) and central macular thickness (CMT) from baseline, and the risk ratios (RR) for the proportions of patients with at least 15 letters change from baseline. Safety analysis estimated the RR of cardiac disorders at 6 to 12 months in RBZ therapy vs. laser monotherapy. Statistical analysis was performed using the RevMan 5.1 software.

Results

Seven RCTs were selected for this meta-analysis, including 1749 patients (394 patients in the RBZ group, 642 patients in the RBZ + Laser group, and 713 patients in the laser group). RBZ and RBZ + Laser were superior to laser monotherapy in the mean change of BCVA and CMT from baseline (WMD = 5.65, 95% confidence interval (CI), 4.44–6.87, P<0.00001; WMD  = 5.02, 95% CI, 3.83–6.20, P<0.00001, and WMD  = −57.91, 95% CI, −77.62 to −38.20, P<0.00001; WMD  = −56.63, 95% CI, −104.81 to −8.44, P = 0.02, respectively). The pooled RR comparing the proportions of patients with at least 15 letters improvement or deterioration were also in favor of RBZ and RBZ + Laser (RR = 2.94, 95% CI, 1.82–4.77, P<0.00001; RR = 2.04, 95% CI, 1.50–2.78, P<0.00001, and RR = 0.21, 95% CI, 0.06–0.71, P = 0.01; RR = 0.52, 95% CI, 0.29–0.95, P = 0.03, respectively). There were no significant differences between RBZ and RBZ + Laser for any of the parameters. There were no difference in the safety profile between RBZ and laser.

Conclusion

RBZ and RBZ + Laser had better visual and anatomic outcomes than laser monotherapy in the treatment of DME. RBZ + Laser seemed to be equivalent to RBZ.

Formation of lipofuscin-like material in the RPE Cell by different components of rod outer segments

The mechanisms that control the natural rate of lipofuscin accumulation in the retinal pigment epithelial (RPE) cell and its stability over time are not well understood. Similarly, the contributions of retinoids, phospholipids and oxidation to the rate of accumulation of lipofuscin are uncertain. The experiments in this study were conducted to explore the individual contribution of rod outer segments (ROS) components to lipofuscin formation and its accumulation and stability over time. During the period of 14 days incubation of ROS, lipofuscin-like autofluorescence (LLAF) determined at two wavelengths (530 and 585 nm) by fluorescence-activated cell sorting (FACS) was measured from RPE cells. The autofluorescence increased in an exponential manner with a strong linear component between days 1 and 7. The magnitude of the increase was larger in cells incubated with 4-hydroxynonenal (HNE-ROS) compared with cells incubated with either bleached or unbleached ROS, but with a different spectral profile. A small (10-15%) decrease in LLAF was observed after stopping the ROS feeding for 14 days. The phagocytosis rate of HNE-ROS was higher than that of either bleached or unbleached ROS during the first 24 h of supplementation. Among the different ROS components, the increase of LLAF was highest in cells incubated with all-trans-retinal. Surprisingly, incubation with 11-cis-retinal and 9-cis-retinal also resulted in strong LLAF increase, comparable to the increase induced by all-trans-retinal. Supplementation with liposomes containing phosphatidylethanolamine (22: 6-PE) and phosphatidylcholine (18:1-PC) also increased LLAF, while incubation with opsin had little effect. Cells incubated with retinoids demonstrated strong dose-dependence in LLAF increase, and the magnitude of the increase was 2-3 times higher at 585 nm compared to 530 nm, while cells incubated with liposomes showed little dose-dependence and similar increase at both wavelengths. Very little difference in LLAF was noted between cells incubated with either unbleached or bleached ROS under any conditions. In summary, results from this study suggest that supplementation with various ROS components can lead to an increase in LLAF, although the autofluorescence generated by the different classes of components has distinct spectral profiles, where the autofluorescence induced by retinoids results in a spectral profile closest to the one observed from human lipofuscin. Future fluorescence characterization of LLAF in vitro would benefit from an analysis of multiple wavelengths to better match the spectral characteristics of lipofuscin in vivo.

Differential proteomics and functional research following gene therapy in a mouse model of Leber congenital amaurosis

Leber congenital amaurosis (LCA) is one of the most severe forms of inherited retinal degeneration and can be caused by mutations in at least 15 different genes. To clarify the proteomic differences in LCA eyes, a cohort of retinal degeneration 12 (rd12) mice, an LCA2 model caused by a mutation in the RPE65 gene, were injected subretinally with an AAV vector (scAAV5-smCBA-hRPE65) in one eye, while the contralateral eye served as a control. Proteomics were compared between untreated rd12 and normal control retinas on P14 and P21, and among treated and untreated rd12 retinas and control retinas on P42. Gene therapy in rd12 mice restored retinal function in treated eyes, which was demonstrated by electroretinography (ERG). Proteomic analysis successfully identified 39 proteins expressed differently among the 3 groups. The expression of 3 proteins involved in regulation of apoptosis and neuroptotection (alpha A crystallin, heat shock protein 70 and peroxiredoxin 6) were investigated further. Immunofluorescence, Western blot and real-time PCR confirmed the quantitative changes in their expression. Furthermore, cell culture studies suggested that peroxiredoxin 6 could act in an antioxidant role in rd12 mice. Our findings support the feasibility of gene therapy in LCA2 patients and support a role for alpha A crystallin, heat shock protein 70 and peroxiredoxin 6 in the pathogenetic mechanisms involved in LCA2 disease process.

Accumulation and autofluorescence of phagocytized rod outer segment material in macrophages and microglial cells

PURPOSE

To explore the ability of macrophages and microglial cells to phagocytize rod outer segments (ROSs) in a cell culture and characterize the resulting lipofuscin-like autofluorescence (LLAF).

METHODS

Either regular or modified ROSs or ROS components (11-cis-retinal, all-trans-retinal, lipids) were fed to macrophages and microglial cells for 4 days. Afterwards, autofluorescence was detected by fluorescence-activated cell sorting (FACS) at two different wavelengths (533 nm and 585 nm), and the cells were imaged by confocal and electron microscopy. Fluorescein isothiocyanate (FITC)-labeled ROSs were added to macrophage and microglial cell cultures for 1-24 h to determine the kinetics of phagocytosis in these cell lines.

RESULTS

Feeding with different ROSs or ROS components led to a significant increase in LLAF in both microglia and macrophages. The 4-hydroxynonenal (HNE)-modified ROSs gave rise to the highest increase in LLAF at both 533 nm and 585 nm. Application of 11-cis-retinal or all-trans-retinal resulted in higher LLAF at 585 nm, compared to application of 9-cis-retinal or liposomes. Fluorescein isothiocyanate-labeled ROSs co-localized well with lysosomes in both types of cells. HNE-modified ROSs were phagocytized more rapidly by both types of cells, compared to unmodified ROSs. Electron microscopy demonstrated inclusion bodies containing whorls of membranes in all types of cells fed with ROSs.

CONCLUSIONS

Both macrophages and microglia have the ability to phagocytize ROSs, and this results in increased autofluorescence. Oxidation of ROSs results in faster phagocytosis, higher levels of LLAF, and the appearance of more inclusion bodies inside the cells. Results from the present study suggest that both types of cells accumulate lipofuscin-like material under physiologically relevant conditions. Such accumulation could interfere with their ability to clear cellular debris and could be part of the pathogenetic mechanism for age-related macular degeneration and other lipofuscinopathies.

Protein misfolding and retinal degeneration

The retina is a highly complex and specialized organ that performs preliminary analysis of visual information. Composed of highly metabolically active tissue, the retina requires a precise and well-balanced means of maintaining its functional activity during extended periods of time. Maintenance and regulation of a vast array of different structural and functional proteins is required for normal function of the retina. This process is referred to as protein homeostasis and involves a variety of activities, including protein synthesis, folding, transport, degradation, elimination, and recycling. Deregulation of any of these activities can lead to malfunctioning of the retina, from subtle subclinical signs to severe retinal degenerative diseases leading to blindness. Examples of retinal degenerative diseases caused by disruption of protein homeostasis include retinitis pigmentosa and Stargardt's disease. A detailed discussion of the role of disruption in protein homeostasis in these and other retinal diseases is presented, followed by examples of some existing and potential treatments.

Therapeutic potential of valproic acid for retinitis pigmentosa

BACKGROUND/AIM

To examine the efficacy and safety of valproic acid (VPA) in patients with retinitis pigmentosa (RP).

METHODS

Thirteen eyes were examined before and after brief treatment (average 4 months) with VPA. Visual fields (VF) for each eye were defined using digitised Goldmann Kinetic Perimetry tracings. VF areas were log-transformed and VF loss/gain relative to baseline was calculated. Visual acuity was measured using a Snellen chart at a distance of 20&emsp14;feet (6.1 m). Values were converted to the logarithm of the minimum angle of resolution (logMAR) score.

RESULTS

Nine eyes had improved VF with treatment, two eyes had decreased VF and two eyes experienced no change, with an overall average increase of 11%. Assuming typical loss in VF area without treatment, this increase in VF was statistically significant (p<0.02). An average decrease (0.172) in the logMAR scores was seen in these 13 eyes, which translates to a positive change in Snellen score of approximately 20/47 to 20/32, which was significant (p<0.02) assuming no loss in acuity without treatment. Side effects were mild and well tolerated.

CONCLUSION

Treatment with VPA is suggestive of a therapeutic benefit to patients with RP. A placebo-controlled clinical trial will be necessary to assess the efficacy and safety of VPA for RP rigorously.

Visual cycle modulation in neurovascular retinopathy

Rats with oxygen-induced retinopathy (OIR) model the pediatric retinal disease retinopathy of prematurity (ROP). Recent findings in OIR rats imply a causal role for the rods in the ROP disease process, although only experimental manipulation of rod function can establish this role conclusively. Accordingly, a visual cycle modulator (VCM) - with no known direct effect on retinal vasculature - was administered to "50/10 model" OIR Sprague-Dawley rats to test the hypotheses that it would 1) alter rod function and 2) consequently alter vascular outcome. Four litters of pups (N=46) were studied. For two weeks, beginning on postnatal day (P) 7, the first and fourth litters were administered 6 mg kg(-1) N-retinylacetamide (the VCM) intraperitoneally; the second and third litters received vehicle (DMSO) alone. Following a longitudinal design, retinal function was assessed by electroretinography (ERG) and the status of the retinal vessels was monitored using computerized fundus photograph analysis. Rod photoreceptor and post-receptor response amplitudes were significantly higher in VCM-treated than in vehicle-treated rats; deactivation of phototransduction was also significantly more rapid. Notably, the arterioles of VCM-treated rats showed significantly greater recovery from OIR. Presuming that the VCM did not directly affect the retinal vessels, a causal role for the neural retina - particularly the rod photoreceptors - in OIR was confirmed. There was no evidence of negative alteration of photoreceptor function consequent to VCM treatment. This finding implicates the rods as a possible therapeutic target in neurovascular diseases such as ROP.

Ocular Changes after Photodynamic Therapy

PURPOSE

The aim of this study was to identify the changes in the primate visual system after a single session of photodynamic therapy (PDT) in an intact nonhuman primate retina.

METHODS

As part of a larger study, PDT (wavelength 689 nm, 50 J/cm2, 600 mW/cm2, 83 seconds, 4-mm spot size) with verteporfin (6 mg/m2 intravenous infusion) was performed in one eye each of two cynomolgus monkeys. Fundus photography, fluorescein angiography (FA), indocyanine green angiography (ICG), optical coherence tomography (OCT), and multifocal electroretinography (mfERG) were performed at baseline and 12 time points (1-283 days) after PDT. In addition, retinal histopathologic findings were evaluated at 9 months.

RESULTS

Various morphologic changes, including whitening of the treated area, RPE proliferation, closure of the choroidal vasculature, and subretinal edema (followed by foveolar thinning) were observed. Most of the changes persisted and were detectable in histopathologic evaluation at 9 months. Reductions of the mfERG amplitude, followed by varying degrees of recovery from the treated and the border regions, were observed. This was accompanied by progressive delay of P1 peak time up to 3 months after treatment, followed by complete recovery at 9 months. In addition, the nontreated area showed amplitude and timing mfERG deficits, which underwent gradual (but not complete) recovery.

CONCLUSIONS

In a primate model, under standard clinical parameters, a single PDT treatment resulted in various dynamic morphologic and functional retinal changes detectable for up to 9 months after treatment. The significance of the observed changes and possible ways of pharmacologic interference with PDT adverse effects are discussed.

An Overview of Drug Development with Special Emphasis on the Role of Visual Electrophysiological Testing

Visual electrophysiological techniques, such as electroretinography (ERG) and visual evoked potentials (VEP) can provide useful information on the safety, efficacy, and proper dosing of chemical entities under development as new drug therapies. During post-marketing safety surveillance, a variety of visual electrophysiological measures can be used to objectively assess and document individual patient response to ophthalmic drugs and ocular or visual system side effects of non-ophthalmic drugs. In this paper, the discovery, exploratory development, full-development and post-marketing stages of drug development are briefly outlined. The potential role of visual electrophysiological techniques in each of these stages is described and discussed.

Ocular Toxicity Due to Chloroquine and Hydroxychloroquine: Electrophysiological and Visual Function Correlates

Chloroquine (CQ) and hydroxycholorquine (HCQ) have been used widely for the treatment of rheumatoid arthritis and other similar inflammatory diseases since the early 50s. They remain the treatment of choice for many patients even today. Significant, either reversible or irreversible central visual loss associated with the drugs is very rare, but an important side effect that can warrant discontinuation of therapy. Early diagnosis of toxicity and evaluation of the visual function are, therefore, important parts of the treatment process. Various electrophysiological and psychophysical tests have been and are used for the detection, follow-up and prognosis of drug-associated central visual loss. A summary and comment on the tests, with emphasis on the use of more recently developed methods, such as the multifocal electroretinography (mfERG), are presented in this review.

Comparison of conventional ERG parameters and high-intensity A-wave analysis in a clinical setting

Computational analysis of high-intensity a-waves yields direct information about the rod and cone receptor potential. However, it is not clear whether such information adds materially to the diagnostic value of the standard ERG in a routine clinical setting. We recorded both conventional ISCEV standard and computational high intensity ERG parameters from 38 patients referred to a clinical laboratory for ERG testing, and also from eight normal volunteers. The patients were grouped as: (1) macular dysfunction; (2) diffuse cone dysfunction; (3) diffuse rod-cone dysfunction. The results showed moderate variation in both conventional and computational parameters, but in general a similar pattern of normality or abnormality for both among the disease groups. There were only a few outlying subjects for which one or the other approach seemed more sensitive. We conclude that a-wave analysis is an important tool for clinical research and the study of special patients, but adding it to the standard ERG protocol does not, at our present state of knowledge, add markedly to clinical evaluations in a routine clinical setting.

The lens-coating agent and the electroretinogram

PURPOSE

To investigate the effects of 0.5, 1.0 and 2.5% methylcellulose coating agents on the ERG in normals.

METHODS

A total of 15 healthy volunteers underwent photopic ERG recordings in three experimental protocols comparing 0.5, 1.0 and 2.5% methylcellulose solutions. The conductivity of the solutions was measured.

RESULTS

The difference between 0.5 and 1.0% solutions showed significant changes (p < 0.05) in ERG amplitudes. The 0.5% solution produced approximately 15% higher ERG amplitudes than the 1.0% solution. Comparison between 1.0 and 2.5% solutions did not show significant changes in ERG amplitudes. The conductivity was essentially the same for 0.5 and 1.0% solutions, but conductivity of the 2.5% solution was roughly half of that of the other two solutions.

CONCLUSIONS

Although the 0.5% solution did yield significantly higher ERG values than the 1.0% and 2.5% solutions, the exact mechanism by which this occurs is not known. The source of these differences could arise from a combination of factors such as conductivity, viscosity, or other unknown components of the solutions. ERG laboratories should be consistent in the use of coating agents, and be aware that any change in solution might alter normative values by a modest percentage.

Spectral sensitivity of the visual system as revealed by evoked potentials in normal and anomalous trichomats

The spectral sensitivity of the visual system upon adaptation by white light at intensity of 10,500 td was studied in Maxwellian view. The monochromatic stimuli had a size of 8 degrees and duration of 700 ms. They were superimposed on an adaptation field of 14 degrees. The spectral sensitivity was determined by the off-VEP amplitude measured from the negative peak with a latency of 75-80 ms to the positive peak with a latency of 100-110 ms. The EEG was led off monopolarly from the occipital scalp area. Eight normal trichomats, 2 protanomalous and 2 deuteranomalous subjects were investigated. Some specificity of the spectral sensitivity curve, determined by the VEP amplitude, were studied. Special attention was placed on the sensitivity decrease between lambda = 550 nm and lambda = 590 nm, which was much pronounced in the normal trichomats. Maximum sensitivity was observed at lambda = 527 nm. The sensitivity at lambda = 578 nm was lower than the maximum one by 0.8 logarithmic units or more. It is assumed that this sensitivity decrease is a manifestation of opponency between the middle wavelength and long wavelength mechanisms. In the anomalous trichomats the sensitivity decrease between lambda = 550 nm and lambda = 590 nm was much less pronounced. Maximum sensitivity was obtained at lambda = 551 nm. In the long wavelength range of the spectrum the deuteranomalous subjects showed a higher sensitivity as compared to the protanomalous ones. The obtained results suggest disturbances of color opponency in the anomalous trichomats.

The electroretinogram in diabetic retinopathy

Electroretinography (ERG) is an objective method of evaluating retinal function. Since its introduction to clinical practice in the 1940s, it has become a useful and routine diagnostic clinical tool in ophthalmology. This review summarizes the role of ERG as a clinical technique for evaluating the progression of diabetic retinopathy and as a research tool for increasing our understanding of the pathophysiology of diabetic retinopathy. Most studies show unequivocally that the different types of ERG tests detect local abnormalities or widespread pathology, even in very early stages of the disease. It seems plausible that measurements from ERG recordings, particularly the oscillatory potentials, may be useful for predicting progression from nonproliferative to the more sight-threatening stages--preproliferative or proliferative--of diabetic retinopathy. Some recent work implies that the ERG can also be a useful diagnostic method for discriminating between eyes with diabetic retinopathy and those without the condition.

S-cone ERGs elicited by a simple technique in normals and in tritanopes

PURPOSE

To measure changes in the relative spectral sensitivities of the dark adapted and light adapted ERG and thus to establish the possible contribution of rods to the 'blue cone' ERG elicited by flashes of blue light.

BACKGROUND

Short wavelength stimuli in the light-adapted eye evoke small rounded b-waves which have been considered to be S-cone responses. We have recorded such responses from tritanopes, which called the assumptions into question.

METHODS

Small ERGs were recorded to blue and green flashes. The stimulus was a Ganzfeld which employed light emitting diodes. ERGs were obtained in both the dark-adapted eye and after light adaptation to intense orange light (peak wavelength 610 nm). The change in sensitivity with light adaptation and the relative spectral sensitivity was determined from the voltage/log light intensity functions, using a 10 microV criterion.

RESULTS

(1) peak times and changes in sensitivity did not help distinguish light-adapted rod from possible S-cone responses; (2) analysis of the change in the ratio of blue:green sensitivity from darkness to 4.4 log Td. 610 nm background suggests that in seven normal subjects, 90% or more of the ERG evoked by 440 nm flashes is generated by S-cones; (3) three tritanopes have insignificantly reduced S-cone responses.

CONCLUSIONS

(1) clinical techniques used to isolate S-cone ERGs are appropriate; (2) there are at least two types of tritanope and in those we investigated, functional S-cones are probably displaced into the retinal periphery.