Comparing three different modes of electroretinography in experimental glaucoma: diagnostic performance and correlation to structure

Effects of Optical Zone Variation of High-Addition Multifocal Contact Lenses on the Global Flash Multifocal Electroretinography

OBJECTIVES

To evaluate the retinal response to myopic defocus after the wear of soft multifocal contact lenses with high addition through electroretinography.

METHODS

Twenty-seven participants meeting inclusion criteria were enrolled. Tropicamide 1% drops (2) were instilled. Participants were then fitted with three different contact lenses: a single-vision spherical lens (SE +3.00 D), L1, serving as a control, and two soft multifocal lens designs (SE +3.00 D/add +10 D), one with a central distance zone of 4.0 mm (L2) and one with a central distance zone of 7.0 mm (L3). A global flash multifocal electroretinography was performed. Direct component (DC) amplitude, DC peak time, induced component (IC) amplitude, and IC peak time were recorded. Waveforms were grouped into five concentric areas, covering from 0° to 24° of retinal eccentricity. Differences of L2/L3 versus L1 were analyzed with t tests. Finally, correlations were calculated between the percentage of defocus in the pupil area versus the electroretinography results.

RESULTS

Results show that the DC amplitude, caused mainly by photoreceptors and bipolar cells, is not influenced by the design of the lenses. The IC amplitude, however, is significantly decreased when the lens with a smaller optical zone (L2) is worn. This significant difference only concerns the ring 5, which corresponds to a retinal eccentricity of 15.7° to 24.0°.

CONCLUSION

Soft multifocal lens designs influence the peripheral retinal reaction to defocus. A larger treatment zone seems to significantly impact the retinal response to defocus between 15.7° and 24.0° of eccentricity from the macula.

The diagnostic accuracy of photopic negative responses evoked by broadband and chromatic stimuli in a clinically heterogeneous population

PURPOSE

To compare the diagnostic accuracy of the photopic negative response (PhNR) elicited by red-blue (RB) and white-white (WW) stimuli, for detection of retinal ganglion cell (RGC) dysfunction in a heterogeneous clinical cohort.

METHODS

Adults referred for electrophysiological investigations were recruited consecutively for this single-centre, prospective, paired diagnostic accuracy study. PhNRs were recorded to red flashes (1.5 cd·s·m-2) on a blue background (10 cd·m-2) and to white flashes on a white background (the latter being the ISCEV standard LA 3 stimulus). PhNR results were compared with a reference test battery assessing RGC/optic nerve structure and function including optical coherence tomography (OCT) retinal nerve fibre layer thickness and mean RGC volume measurements, fundus photography, pattern electroretinography and visual evoked potentials. Primary outcome measures were differences in sensitivity and specificity of the two PhNR methods.

RESULTS

Two hundred and forty-three participants were initially enrolled, with 200 (median age 54; range 18-95; female 65%) meeting inclusion criteria. Sensitivity was 53% (95% confidence intervals [CI] 39% to 68%) and 62% (95% CI 48% to 76%), for WW and RB PhNRs, respectively. Specificity was 80% (95% CI 74% to 86%) and 78% (95% CI 72% to 85%), respectively. There was a statistically significant difference between sensitivities (p = 0.046) but not specificities (p = 0.08) of the two methods. Receiver operator characteristic (ROC) area under the curve (AUC) values were 0.73 for WW and 0.74 for RB PhNRs.

CONCLUSION

PhNRs to red flashes on a blue background may be more sensitive than white-on-white stimuli, but there is no significant difference between specificities. This study highlights the value and potential convenience of using white-on-white stimuli, already used widely for routine ERG assessment.

Utility of Light-Adapted Full-Field Electroretinogram ON and OFF Responses for Detecting Glaucomatous Functional Damage

Purpose

To compare parameters of electroretinogram (ERG) responses for their ability to detect functional loss in early stages of nonhuman primate (NHP) experimental glaucoma (EG), including photopic negative responses (PhNR) to a standard brief red flash on a blue background (R/B) and 200-ms-long R/B and white-on-white (W/W) flashes, to W/W flicker stimuli (5-50 Hz), and to a dark-adapted intensity series.

Methods

Light-adapted ERGs were recorded in 12 anesthetized monkeys with unilateral EG. Amplitudes and implicit times of the a-wave, b-wave, and d-wave were measured, as well as amplitudes of PhNRs and oscillatory potentials for flash onset and offset. Flicker ERGs were measured using peak-trough and fundamental frequency analyses. Dark-adapted ERG parameters were modeled by Naka-Rushton relationships.

Results

Only PhNR amplitudes were significantly reduced in EG eyes compared to fellow control (FC) eyes. The d-wave implicit time was delayed in EG versus FC eyes only for the W/W long flash, but in all eyes it was 10 to 20 ms slower for R/B versus the W/W condition. Flicker ERGs were <0.5 ms delayed in EG versus FC overall, but amplitudes were affected only at 5 Hz. The brief R/B PhNR amplitude had the highest sensitivity to detect EG and strongest correlation to parameters of structural damage.

Conclusions

The PhNR to the standard brief R/B stimulus was best for detecting and following early-stage functional loss in NHP EG.

Translational Relevance

These results suggest that there would be no benefit in using longer duration flashes to separate onset and offset responses for clinical management of glaucoma.

Silicone Oil-Induced Glaucomatous Neurodegeneration in Rhesus Macaques

Previously, we developed a simple procedure of intracameral injection of silicone oil (SO) into mouse eyes and established the mouse SOHU (SO-induced ocular hypertension under-detected) glaucoma model with reversible intraocular pressure (IOP) elevation and significant glaucomatous neurodegeneration. Because the anatomy of the non-human primate (NHP) visual system closely resembles that of humans, it is the most likely to predict human responses to diseases and therapies. Here we tried to replicate the mouse SOHU glaucoma model in rhesus macaque monkeys. All six animals that we tested showed significant retinal ganglion cell (RGC) death, optic nerve (ON) degeneration, and visual functional deficits at both 3 and 6 months. In contrast to the mouse SOHU model, however, IOP changed dynamically in these animals, probably due to individual differences in ciliary body tolerance capability. Further optimization of this model is needed to achieve consistent IOP elevation without permanent damage of the ciliary body. The current form of the NHP SOHU model recapitulates the severe degeneration of acute human glaucoma, and is therefore suitable for assessing experimental therapies for neuroprotection and regeneration, and therefore for translating relevant findings into novel and effective treatments for patients with glaucoma and other neurodegenerations.

Mimicking chronic glaucoma over 6 months with a single intracameral injection of dexamethasone/fibronectin-loaded PLGA microspheres

To create a chronic glaucoma animal model by a single intracameral injection of biodegradable poly lactic-co-glycolic acid (PLGA) microspheres (Ms) co-loaded with dexamethasone and fibronectin (MsDexaFibro). MsDexaFibro were prepared by a water-in-oil-in-water emulsion method including dexamethasone in the organic phase and fibronectin in the inner aqueous phase. To create the chronic glaucoma model, an interventionist and longitudinal animal study was performed using forty-five Long Evans rats (4-week-old). Rats received a single intracameral injection of MsDexafibro suspension (10%w/v) in the right eye. Ophthalmological parameters such as clinical signs, intraocular pressure (IOP), neuro-retinal functionality by electroretinography (ERG), retinal structural analysis by optical coherence tomography (OCT), and histology were evaluated up to six months. According to the results obtained, the model proposed was able to induce IOP increasing in both eyes over the study, higher in the injected eyes up to 6 weeks (p < 0.05), while preserving the ocular surface. OCT quantified progressive neuro-retinal degeneration (mainly in the retinal nerve fiber layer) in both eyes but higher in the injected eye. Ganglion cell functionality decreased in injected eyes, thus smaller amplitudes in PhNR were detected by ERG. In conclusion, a new chronic glaucoma animal model was created by a single injection of MsDexaFibro very similar to open-angle glaucoma occurring in humans. This model would impact in different fields such as ophthalmology, allowing long period of study of this pathology; pharmacology, evaluating the neuroprotective activity of active compounds; and pharmaceutical technology, allowing the correct evaluation of the efficacy of long-term sustained ocular drug delivery systems.

The p-ERG spatial acuity in the biomedical pig under physiological conditions

Pigs are becoming an important pre-clinical animal species for translational ophthalmology, due to similarities with humans in anatomical and physiological patterns. Different models of eye disorders have been proposed, and they are good candidates to assess biocompatibility/functionality of retinal prostheses. Electroretinography is a common tool allowing to gain information on retinal function, with several types of electroretinogram (ERG) been implemented including full field (ff-ERG), multifocal (mf-ERG) and pattern (p-ERG). p-ERG represents a valuable tool to monitor Retinal Ganglion Cells (RGCs) activity and can be used to calculate p-ERG spatial acuity. Unfortunately, scarce methodological data are available regarding recording/interpretation of p-ERG and retinal acuity in biomedical pigs yet enhancing knowledge regarding pig vision physiology will allow for more refined and responsible use of such species. Aim of this study was to record p-ERG in juvenile pigs to functionally assess visual acuity. Six female hybrid pigs underwent two p-ERG recording sessions at 16 and 19 weeks of age. Photopic ff-ERG were also recorded; optical coherence tomography (OCT) and histology were used to confirm retinal integrity. ff-ERG signals were repeatable within/across sessions. All p-ERG traces consistently displayed characterizing peaks, and the progressive decrease of amplitude in response to the increment of spatial frequency revealed the reliability of the method. Mean p-ERG spatial acuities were 5.7 ± 0.14 (16 weeks) and 6.2 ± 0.15 cpd (19 weeks). Overall, the p-ERG recordings described in the present work seem reliable and repeatable, and may represent an important tool when it comes to vision assessment in pigs.

Intereye structure-function relationship using photopic negative response in patients with glaucoma or glaucoma suspect

We evaluated the intereye structure–function relationship in glaucoma patients using photopic negative response in electroretinogram analysis. Patients with confirmed glaucoma (36 eyes, 36 patients) or suspected glaucoma (19 eyes, 19 patients) were included in this study. Electroretinogram (RETI-scan) was performed with red stimulus on blue background. Intereye comparison for 55 patients was performed between better eyes and worse eyes, which were divided based on average retinal nerve fiber layer (RNFL) thickness measured using spectral-domain optical coherence tomography. In the intereye analysis, PhNR amplitude was lower in worse eyes than in better eyes (P < 0.001). The intereye difference in PhNR amplitude was significantly correlated with intereye difference in average RNFL, as well as average or minimum ganglion cell-inner plexiform layer (GCIPL) thickness (P = 0.006, 0.044, 0.001). In patients with mean deviation ≥ − 6 dB of worse eyes, the intereye difference in PhNR amplitude was significantly associated with intereye difference in average RNFL thickness or minimum GCIPL thickness (P = 0.037, 0.007), but significant correlation was not found between mean sensitivity of visual field tests and structural parameters. In conclusion, PhNR performed well with regard to intereye structure–function association in glaucoma patients, especially at the early stage.

Photopic negative response recorded with RETeval system in eyes with optic nerve disorders

Electroretinography (ERG) is used to evaluate the physiological status of the retina and optic nerve. The purpose of this study was to determine the usefulness of ERGs recorded with the RETeval system in diagnosing optic nerve diseases. Forty-eight patients with optic nerve disorders, including optic neuritis, ischemic optic neuropathy, traumatic optic neuropathy, and dominant optic atrophy, and 36 normal control subjects were studied. The amplitudes of the photopic negative response (PhNR) were recorded with the RETeval system without mydriasis. The circumpapillary retinal nerve fiber layer thickness (cpRNFLT) was determined by optical coherence tomography (OCT). The significance of the correlations between the PhNR and cpRNFLT parameters were determined, and the receiver operating curve (ROC) analyses were performed for the PhNR and cpRNFLT. Patients with optic nerve disorders had significantly smaller PhNRs compared to the control subjects (P = 0.001). The ROC analyses indicated that both PhNR and cpRNFLT had comparable diagnostic abilities of detecting optic nerve disorders with PhNR at 0.857 and cpRNFLT at 0.764. The PhNR components recorded with the RETeval system have comparable diagnostic abilities as the cpRNFLT in diagnosing optic nerve disorders.

A Monoclonal Anti-HMGB1 Antibody Attenuates Neurodegeneration in an Experimental Animal Model of Glaucoma

Neuroinflammation is a crucial process for the loss of retinal ganglion cells (RGC), a major characteristic of glaucoma. High expression of high-mobility group box protein 1 (HMGB1) plays a detrimental role in inflammatory processes and is elevated in the retinas of glaucoma patients. Therefore, this study aimed to investigate the effects of the intravitreal injection of an anti-HMGB1 monoclonal antibody (anti-HMGB1 Ab) in an experimental animal model of glaucoma. Two groups of Spraque Dawley rats received episcleral vein occlusion to chronically elevate intraocular pressure (IOP): (1) the IgG group, intravitreal injection of an unspecific IgG as a control, n = 5, and (2) the HMGB1 group, intravitreal injection of an anti-HMGB1 Ab, n = 6. IOP, retinal nerve fiber layer thickness (RNFLT), and the retinal flash response were monitored longitudinally. Post-mortem examinations included immunohistochemistry, microarray, and mass spectrometric analysis. RNFLT was significantly increased in the HMGB1 group compared with the IgG group (p < 0.001). RGC density showed improved neuronal cell survival in the retina in HMGB1 compared with the IgG group (p < 0.01). Mass spectrometric proteomic analysis of retinal tissue showed an increased abundance of RNA metabolism-associated heterogeneous nuclear ribonucleoproteins (hnRNPs), such as hnRNP U, D, and H2, in animals injected with the anti-HMGB1 Ab, indicating that the application of the antibody may cause increased gene expression. Microarray analysis showed a significantly decreased expression of C-X-C motif chemokine ligand 8 (CXCL8, p < 0.05) and connective tissue growth factor (CTGF, p < 0.01) in the HMGB1 group. Thus, these data suggest that intravitreal injection of anti-HMGB1 Ab reduced HMGB1-dependent inflammatory signaling and mediated RGC neuroprotection.

Visual function tests for glaucoma practice - What is relevant?

Glaucoma represents one of the most important ocular diseases causing irreversible ganglion cell death. It is one of the most common causes of visual impairment and morbidity in the elderly population. There are various tests for measuring visual function in glaucoma. While visual field remains the undisputed method for screening, diagnosis, and monitoring disease progression, other tests have been studied for their utility in glaucoma practice. This review discusses some of the commonly used tests of visual function that can be routinely used in clinics for glaucoma management. Among the various modalities of testing visual function in glaucoma, this review highlights the tests that are most clinically relevant.

Temporal contrast adaptation in the analysis of visual function in primary open-angle glaucoma

PURPOSE

To explore the utility of the recovery time (RT) after temporal contrast adaptation in primary open-angle glaucoma (POAG) visual function analysis, especially in severe and end-stage glaucoma, by the Erlanger Flicker Test (EFT).

METHODS

This study included 80 POAG eyes (45 subjects) and 20 normal eyes (20 subjects). POAG eyes were divided into 5 groups. The diagnostic efficacy of the EFT was assessed, and the RT of POAG eyes at different stages was compared. The EFT results were compared with glaucomatous structure and function test results. A nomogram was developed to predict disease progression by the RT and structural indicators.

RESULTS

In the normal eyes, as the test contrast increased, the RT gradually decreased. The EFT test-retest reproducibility was good, with intraclass correlation coefficient values of 0.6 (P < 0.05) for each test contrast. At 12%, 25%, and 35% contrast, the RT in the severe and end-stage glaucoma eyes was significantly prolonged compared with the control group (P < 0.05). The RT at different contrasts was significantly correlated with visual acuity, mean defect, mean sensitivity, and general and individual quadrant optic nerve fiber layer thickness (P ≤ 0.001). The receiver operating curve indicated that RT_12% showed the best overall area under the curve (0.863). We included RT_25% and average optic nerve fiber layer thickness in constructing the nomogram. POAG eyes were further divided into 8 stages. According to the probability distribution, this model showed good performance for visual function analysis in advanced glaucoma.

CONCLUSIONS

Combined with traditional glaucomatous structural and functional parameters, the EFT can be used in the diagnosis and visual function analysis of POAG, especially for severe and end-stage glaucoma. It could be a potential test for disease staging in severe and end-stage glaucoma.

The role of pattern electroretinograms and optical coherence tomography angiography in the diagnosis of normal-tension glaucoma

In this study, we investigated the correlation between pattern electroretinogram (PERG) and optical coherence tomography angiography (OCTA) parameters for diagnosis in patients with normal-tension glaucoma (NTG). Forty-nine normal individuals (49 eyes) and 60 patients with NTG (60 eyes) were enrolled. OCTA and PERG parameters, such as macular vessel density (VD) and the amplitude of N35–P50 and P50–N95, were measured. Correlation analyses were performed between the parameters, and the area under the curve (AUC) was used to identify their diagnostic ability for NTG. Macular VD and the amplitude of N35–P50 and P50–N95 showed significant differences between the normal individuals and patients with NTG. Correlation between P50 and N95 amplitude and macular VD was significant in the normal and early glaucoma groups. Macular VD showed a higher AUC value (0.730) than that of P50–N95 amplitude (0.645) in the early glaucoma group. In the moderate to severe glaucoma group, the AUC value of the amplitude of P50–N95 (0.907) was higher than that of macular VD (0.876). The results indicate that PERG and OCTA parameters may identify glaucoma in its early stage, based on the severity of glaucomatous damage in patients with NTG.

Asymmetric Functional Impairment of ON and OFF Retinal Pathways in Glaucoma

Purpose

To investigate ON-pathway versus OFF-pathway dysfunction in glaucoma using handheld electroretinography (ERG) with a temporally modulated sinusoidal flicker stimulus.

Design

Cross-sectional study.

Participants

Fifty-nine participants accounting for 104 eyes, comprised of 19 control eyes, 26 glaucoma suspect eyes, and 59 glaucoma eyes.

Methods

Participants underwent portable ERG testing, which included the photopic flash, photopic flicker, photopic negative response stimulus, ON-OFF stimulus, and a custom-written sinusoidal flicker stimulus that was modulated from 50 to 0.3 Hz.

Main Outcome and Measures

The ERG response amplitudes were measured by the handheld ERG. For the custom-written sinusoidal flicker stimulus, we derived and compared the log10 first harmonic frequency response amplitudes. Patient discomfort and fatigue after ERG testing were rated on a scale from 1 to 5.

Results

Baseline demographics were not significantly different between groups, except for ocular characteristics. Analysis was performed adjusting for participant age, sex, race, and dilation status, and the sinusoidal frequency responses were stratified at 10 Hz because higher frequencies are associated with the OFF-pathway, whereas lower frequencies are associated with the ON-pathway. After stratification, glaucoma eyes showed an adjusted decrease of 32.1% at frequencies of more than 10 Hz (95% confidence interval [CI], -51.8% to -4.1%; P = 0.03). For 10 Hz stimulus frequencies or less, an adjusted 11.5% reduction was found (95% CI, -39.5% to 29.1%; P = 0.50). Glaucoma suspect eyes did show a decreased response, but this was not significant at either frequency range. When comparing handheld ERG with traditional visual field assessments, participants found the handheld ERG to result in much less discomfort and fatigue.

Conclusions

Our finding that glaucoma participants showed greater decreases in ERG response at higher frequencies supports the hypothesis that the OFF-pathway may be more vulnerable in human glaucoma. Using a handheld ERG device with a sinusoidal flicker stimulus may provide an objective assessment of visual function in glaucoma.

Comparison of the Humphrey Field Analyzer and Photopic Negative Response of Focal Macular Electroretinograms in the Evaluation of the Relationship Between Macula Structure and Function

Purpose: To investigate the association between macular inner retinal layer thickness and macula visual field (VF) mean deviation as measured by the Humphrey Field Analyzer (HFA) or macular function as measured by focal macular electroretinograms (ERGs) in patients with glaucoma.

Methods: The participants in this cross-sectional study were 71 patients with glaucoma and 10 healthy controls. Macular inner retinal layer thickness and function were measured in all participants using optical coherence tomography (OCT) and HFA or focal macular ERGs, respectively. Macular OCT images were segmented into the macular retinal nerve fiber layer (mRNFL), macular ganglion cell layer/inner plexiform layer (GCL/IPL), and ganglion cell complex (GCC). Spearman correlation analysis was used to assess the relationship between macular inner retinal layer thickness and function.

Results: Focal macular ERGs were composed of a negative wave (N1), a positive wave (P1), and a slow negative wave (N2). The N2 response density was significantly reduced in eyes with glaucoma, and was significantly associated with the thickness of the mRNFL (R = 0.317), GCL/IPL (R = 0.372), or GCC (R = 0.367). The observed structure–function relationship was also significantly correlated with the HFA VF mean deviation for each thickness [mRNFL (R = 0.728), GCL/IPL (R = 0.603), or GCC (R = 0.754)].

Conclusions: Although a significant correlation was found between the N2 response density and the thickness of the macular inner layer, the observed structure–function relationship with the mean deviation of the HFA VF was higher than that of the N2 response density.

A Topical Formulation of Melatoninergic Compounds Exerts Strong Hypotensive and Neuroprotective Effects in a Rat Model of Hypertensive Glaucoma

Melatonin is of great importance for regulating several eye processes, including pressure homeostasis. Melatonin in combination with agomelatine has been recently reported to reduce intraocular pressure (IOP) with higher efficacy than each compound alone. Here, we used the methylcellulose (MCE) rat model of hypertensive glaucoma, an optic neuropathy characterized by the apoptotic death of retinal ganglion cells (RGCs), to evaluate the hypotensive and neuroprotective efficacy of an eye drop nanomicellar formulation containing melatonin/agomelatine. Eye tissue distribution of melatonin/agomelatine in healthy rats was evaluated by HPLC/MS/MS. In the MCE model, we assessed by tonometry the hypotensive efficacy of melatonin/agomelatine. Neuroprotection was revealed by electroretinography; by levels of inflammatory and apoptotic markers; and by RGC density. The effects of melatonin/agomelatine were compared with those of timolol (a beta blocker with prevalent hypotensive activity) or brimonidine (an alpha 2 adrenergic agonist with potential neuroprotective efficacy), two drugs commonly used to treat glaucoma. Both melatonin and agomelatine penetrate the posterior segment of the eye. In the MCE model, IOP elevation was drastically reduced by melatonin/agomelatine with higher efficacy than that of timolol or brimonidine. Concomitantly, gliosis-related inflammation and the Bax-associated apoptosis were partially prevented, thus leading to RGC survival and recovered retinal dysfunction. We suggest that topical melatoninergic compounds might be beneficial for ocular health.

The photopic negative response (PhNR): measurement approaches and utility in glaucoma

Purpose

Visual electrophysiological testing continues to generate interest among glaucoma experts because of its potential help in clarifying disease pathophysiology and promoting early detection of glaucomatous damage. The photopic negative response (PhNR) is a slow negative component of the full-field electroretinogram that has been shown to provide specific information about retinal ganglion cells (RGCs) activity. The purpose of this article is to review the literature to explore the currently available measurement methods and the utility of PhNR in glaucoma diagnostic process.

Methods

We gathered publications related to the origins, types of stimuli used, measurements methods and applications of the PhNR of ERG in animal models and humans through a search of the literature cited in PubMed. Search terms were: “PhNR”, “photopic negative response”, “glaucoma”, “glaucomatous optic neuropathy”, “ERG”, “electroretinogram”.

Results

The most reliable PhNR measurements are obtained using a red stimulus on a blue background, without requiring refractive correction, fixation monitoring, or ocular media transparency. Given its direct correlation with RGCs response, the PhNR measured as baseline-to-trough (BT) represents the most reliable parameter of evaluation. Glaucoma patients with evident perimetric defects show pathologic PhNR values. Even though the PhNR is promising in detecting early RGCs impairment, distinguishing between healthy subjects and suspect patients at risk of developing glaucomatous damage still remains challenging.

Conclusion

The PhNR is a useful additional tool to explore disorders that affect the innermost retina, including glaucoma and other forms of optic neuropathy. In particular, comparing reports of the standard examinations (optic disc assessment, OCT RNFL measurement, standard automated perimetry) with the results of electrophysiological tests may be helpful in solving clinical diagnostic and management dilemmas. On the one hand, the PhNR of the ERG can examine the parvocellular pathways; on the other hand, the steady-state pattern ERG optimized for glaucoma screening (PERGLA) can explore the magnocellular pathways. This could give ophthalmologists a useful feedback to identify early RGCs alterations suggestive of glaucoma, stratify the risk and potentially monitor disease progression.

Electrophysiology in Glaucoma

OBJECTIVES

Electrophysiological testing of the visual system has been continuously used in studies involving the evaluation of retinal ganglion cells and the diagnosis of glaucoma. This study aims to review the results of recent studies regarding the clinical applicability of electrophysiological tests to glaucoma.

METHODS

A systematic review of the literature was carried out by 2 independent reviewers using the PubMed and EMBASE electronic databases, searching for articles published in English from January 1, 2014 to July 1, 2019 using a combination of the following keywords: ("glaucoma" OR "ocular hypertension") AND ("electrophysiolog" OR "electroretinogra" OR "ERG" OR "mfERG" OR "Pattern-reversal electroretinography" OR "PERG" OR "mfPERG" OR "photopic negative response" OR "pattern electroretinogram" OR "visual evoked potential" OR "multifocal electroretinography" OR "multifocal electroretinogram" OR "electro-oculography" OR "multifocal VEP" OR "mf-ERG"). A total of 38 studies were selected and the data of 30 of them were tabulated in this review.

RESULTS

Among the 30 studies selected, the photopic negative response and the reversal pattern electroretinogram were found to be the major methods used to record the electroretinographic responses generated by the retinal ganglion cell. Their multifocal versions and the multifocal visual evoked potential were also proposed during this period. In general, the results underscored a consistent but general correlation between the amplitude and latency measures and routine tests for glaucoma, such as perimetry and optical coherence tomography.

DISCUSSION

In agreement with previous reviews, clinical electrophysiological testing of the visual system reasonably matched with both the structural and functional analyses for glaucoma. No definitive indications of these tests have been established either at early detection or during follow-up of the disease, and easier protocols and better topographical correspondence with current glaucoma tests are warranted for their routine use.

Measurable Aspects of the Retinal Neurovascular Unit in Diabetes, Glaucoma, and Controls

PURPOSE

To study the structural and angiographic optical coherence tomography (OCT) data of the macula from controls, patients with diabetes, and patients with glaucoma to evaluate neurovascular and structural relationships.

METHODS

This was a retrospective study of 89 eyes from 49 patients in a community-based retinal referral practice with diabetes, glaucoma, and normal controls. The patients were evaluated with OCT to include retinal nerve fiber layer (RNFL) thickness measurement and ganglion cell layer (GCL) volume determination. The vascular density of the radial peripapillary capillary network and the vascular plexuses in the macula were evaluated with OCT angiography. The main outcome measures were the data obtained per disease state and the interrelationships the data displayed.

RESULTS

The mean GCL volumes were significantly lower than the control group in both the diabetic (P = .016) and glaucoma (P < .001) groups. The difference between the diabetic and glaucoma groups was not significant (P = .052). The mean global vascular density was greater in the control group than the diabetic group (P = .002) and the glaucoma group (P < .001). The mean RNFL thicknesses were lowest in the glaucoma group. Both the diabetic and glaucoma groups had significantly lower radial peripapillary network and deep vascular plexus density values compared to controls.

CONCLUSIONS

Although there are important differences in disease pathogenesis between diabetes and glaucoma, they share certain similarities in the structural and angiographic abnormalities eventually produced. This suggests that, in addition to canonical pathways of disease, a component of both could represent neurodegenerative disease, offering the possibility for the development of new treatments. NOTE: Publication of this article is sponsored by the American Ophthalmological Society.

Glaucoma - Next Generation Therapeutics: Impossible to Possible

The future of next generation therapeutics for glaucoma is strong. The recent approval of two novel intraocular pressure (IOP)-lowering drugs with distinct mechanisms of action is the first in over 20 years. However, these are still being administered as topical drops. Efforts are underway to increase patient compliance and greater therapeutic benefits with the development of sustained delivery technologies. Furthermore, innovations from biologics- and gene therapy-based therapeutics are being developed in the context of disease modification, which are expected to lead to more permanent therapies for patients. Neuroprotection, including the preservation of retinal ganglion cells (RGCs) and optic nerve is another area that is actively being explored for therapeutic options. With improvements in imaging technologies and determination of new surrogate clinical endpoints, the therapeutic potential for translation of neuroprotectants is coming close to clinical realization. This review summarizes the aforementioned topics and other related aspects.

iDrugs and iDevices Discovery Research: Preclinical Assays, Techniques, and Animal Model Studies for Ocular Hypotensives and Neuroprotectants

Discovery ophthalmic research is centered around delineating the molecular and cellular basis of ocular diseases and finding and exploiting molecular and genetic pathways associated with them. From such studies it is possible to determine suitable intervention points to address the disease process and hopefully to discover therapeutics to treat them. An investigational new drug (IND) filing for a new small-molecule drug, peptide, antibody, genetic treatment, or a device with global health authorities requires a number of preclinical studies to provide necessary safety and efficacy data. Specific regulatory elements needed for such IND-enabling studies are beyond the scope of this article. However, to enhance the overall data packages for such entities and permit high-quality foundation-building publications for medical affairs, additional research and development studies are always desirable. This review aims to provide examples of some target localization/verification, ocular drug discovery processes, and mechanistic and portfolio-enhancing exploratory investigations for candidate drugs and devices for the treatment of ocular hypertension and glaucomatous optic neuropathy (neurodegeneration of retinal ganglion cells and their axons). Examples of compound screening assays, use of various technologies and techniques, deployment of animal models, and data obtained from such studies are also presented.

Electroretinography in idiopathic intracranial hypertension: comparison of the pattern ERG and the photopic negative response

PURPOSE

To evaluate the relationship between electrophysiological measures of retinal ganglion cell (RGC) function in patients who have idiopathic intracranial hypertension (IIH).

METHODS

The pattern electroretinogram (pERG) and photopic negative response (PhNR) were recorded from 11 IIH patients and 11 age-similar controls. The pERG was elicited by a contrast-reversing checkerboard. The PhNR, a slow negative component following the flash ERG b-wave, was recorded in response to a long-wavelength flash presented against a short-wavelength adapting field. The PhNR was elicited using full-field (ffPhNR) and focal macular (fPhNR) stimuli. Additionally, Humphrey visual field mean deviation (HVF MD) was measured and ganglion cell complex volume (GCCV) was obtained by optical coherence tomography.

RESULTS

The ffPhNR, fPhNR, and pERG amplitudes were outside of the normal range in 45, 9, and 45% of IIH patients, respectively. However, only mean ffPhNR amplitude was reduced significantly in the patients compared to controls (p < 0.01). The pERG amplitude correlated significantly with HVF MD and GCCV (both r > 0.65, p < 0.05). There were associations between ffPhNR amplitude and HVF MD (r = 0.58, p = 0.06) and with GCCV (r = 0.52, p = 0.10), but these did not reach statistical significance. fPhNR amplitude was not correlated significantly with HVF MD or GCCV (both r < 0.40, p > 0.20).

CONCLUSIONS

Although the fPhNR is generally normal in IIH, other electrophysiological measures of RGC function, the ffPhNR and pERG, are abnormal in some patients. These measures provide complementary information regarding RGC dysfunction in these individuals.

The Small Heat Shock Protein α-Crystallin B Shows Neuroprotective Properties in a Glaucoma Animal Model

Glaucoma is a neurodegenerative disease that leads to irreversible retinal ganglion cell (RGC) loss and is one of the main causes of blindness worldwide. The pathogenesis of glaucoma remains unclear, and novel approaches for neuroprotective treatments are urgently needed. Previous studies have revealed significant down-regulation of α-crystallin B as an initial reaction to elevated intraocular pressure (IOP), followed by a clear but delayed up-regulation, suggesting that this small heat-shock protein plays a pathophysiological role in the disease. This study analyzed the neuroprotective effect of α-crystallin B in an experimental animal model of glaucoma. Significant IOP elevation induced by episcleral vein cauterization resulted in a considerable impairment of the RGCs and the retinal nerve fiber layer. An intravitreal injection of α-crystallin B at the time of the IOP increase was able to rescue the RGCs, as measured in a functional photopic electroretinogram, retinal nerve fiber layer thickness, and RGC counts. Mass-spectrometry-based proteomics and antibody-microarray measurements indicated that a α-crystallin injection distinctly up-regulated all of the subclasses (α, β, and γ) of the crystallin protein family. The creation of an interactive protein network revealed clear correlations between individual proteins, which showed a regulatory shift resulting from the crystallin injection. The neuroprotective properties of α-crystallin B further demonstrate the potential importance of crystallin proteins in developing therapeutic options for glaucoma.