Clinical applications of photopic negative response (PhNR) for the treatment of glaucoma and diabetic retinopathy

Evaluation of inner retinal function at different stages of primary open angle glaucoma using the photopic negative response (PhNR) measured by RETeval electroretinography

PURPOSE

To investigate the objective function of the inner retinal layer in each stage of primary open angle glaucoma (POAG) using the photopic negative response (PhNR) measured by RETeval full-field electroretinography (ERG), and to identify which PhNR parameter is the most useful.

METHODS

Ninety eyes of 90 patients with POAG (30 with mild POAG (mean deviation (MD) ≥ -6 dB) and 60 with moderate-to-advanced POAG (MD < -6 dB)) and 76 eyes of 76 control cases were examined. We investigated six PhNR parameters and their relationships with the results of the Humphrey 30-2 visual field test and the thickness of the circumpapillary retinal nerve fiber layer (cpRNFL) obtained from optical coherence tomography. The following PhNR parameters were assessed: base-to-trough (BT), peak-to-trough (PT), 72msPhNR, the W-ratio, P-ratio, implicit time (IT), and a-wave and b-wave amplitudes on ERG.

RESULTS

All PhNR parameters other than IT significantly differed between the all POAG (all stages) and control groups and between the moderate-to-advanced POAG and control groups. BT and 72msPhNR in the mild POAG group, significantly differed from those in the control group. Regarding the relationships between PhNR parameters and the visual field and between these parameters and cpRNFL thickness, correlations were observed between all PhNR parameters, except PT and IT, and both the visual field and cpRNFL thickness in the all and moderate-to-advanced POAG groups. 72msPhNR correlated with cpRNFL thickness in the mild POAG group. The area under the receiver operating characteristic curve was greater for BT than for the other PhNR parameters in both the mild and moderate-to-advanced POAG groups. The discriminant linear function for examining the presence or absence of POAG and the threshold for diagnosis were quantitatively obtained as follows. Regarding BT: discriminant = 0.505 × BT + 2.017; threshold = positive for POAG, negative for no POAG; correct answer rate = 80.7%. Concerning 72msPhNR: discriminant = 0.533 × 72msPhNR + 1.553; threshold = positive for POAG and negative for no POAG; correct answer rate = 77.1%.

CONCLUSION

RETeval-measured PhNR parameters were useful for an objective evaluation of visual function in moderate-to-advanced POAG. BT appeared to be the most diagnostically useful parameter.

Structural and functional changes among diabetics with no diabetic retinopathy and mild non-proliferative diabetic retinopathy using swept-source optical coherence tomography angiography and photopic negative response

PURPOSE

To assess the structural and functional changes among diabetics with no diabetic retinopathy (NDR) and mild non-proliferative diabetic retinopathy (NPDR) using swept-source optical coherence tomography angiography (SSOCTA) and photopic negative response (PhNR) and to find the earliest changes.

METHODS

This was a prospective, cross-sectional, case-control study. Participants with minimum 5 years of diabetes mellitus (DM) were recruited and classified as NDR and mild NPDR based on fundus findings. Age-matched normals with nil ocular pathology were considered as controls. SSOCTA scan acquisition (6*6 mm angiography), followed by full field photopic electroretinography (FFERG) and red on blue PhNR (R/B PhNR) were done with complete pupillary dilatation.

RESULTS

A total of 88 participants were included with 35 controls, 39 NDR and 14 mild NPDR subjects. Vessel density of the superficial capillary plexus (SCP) and deep capillary plexus (DCP) of mild NPDR were significantly reduced compared to the controls (17.12 ± 2.65 mm^-1 vs. 18.75 ± 0.90 mm^-1, p = 0.025 and 7.96 ± 3.92 mm^-1 vs. 11.83 ± 3.05 mm^-1, p = 0.001 respectively). None of the parameters of controls had significant difference compared to NDR group (p > 0.05). The amplitudes of white on white (W/W) a-wave, W/W b-wave, red on blue (R/B) PhNR baseline to trough (BT) and R/B PhNR peak to trough in controls were significantly high compared to NDR and mild NPDR. Amplitude of R/B PhNR BT had the maximum area under the curve of 75.9% with a sensitivity and specificity of 94.3and 77.4%, respectively.

CONCLUSION

A significant decrease in functional changes as measured by ERG especially PhNR, is seen even among the NDR group compared to controls unlike SSOCTA parameters that measures very early vascular structural changes. PhNR is a sensitive test to identify early preclinical changes in DR when microvascular structural changes as determined by SSOCTA are normal.

[Electrophysiological and psychophysical studies in assessment of visual functions in patients with hereditary optic neuropathy]

PURPOSE

To study the capabilities of electrophysiological and psychophysical examination methods for assessment of the functional state of ganglion cells, retina and optic nerve in patients with hereditary optic neuropathy (HON).

MATERIAL AND METHODS

The study included 60 patients (118 eyes) with a genetically confirmed diagnosis of HON. All study patients underwent visual field test (VFT), spectral optical coherence tomography (OCT), flash and pattern visual evoked potentials (VEP) (Flash-VEP, FVEP; Pattern-VEP, PVEP), photopic electroretinography with photonegative response (PhNR) registration and the color vision test. In 24 patients (46 eyes), these parameters were assessed before the start of treatment and one year later. The treatment involved the mitochondria-targeted antioxidant SkQ1 - plastoquinonyl-decyl-triphenylphosphonium bromide (PDTP) in the form of eye drops.

RESULTS

The main PVEP components for 1.0° and 0.3° were registered in 20% and in 14% of patient eyes with HON and high visual functions, respectively. After one year of PDTP use, a significant decrease in P100 peak latency was found only in the group with disease duration of ≤1.5 years as of the time of treatment start (p<0.05). Significant differences were observed in the PhNR amplitude (p<0.004) between patients of the main and the control groups, as well as in the PhNR amplitude between patients with visual acuity of ≤0.1 and ≥0.13 (p<0.01). Patients with high visual functions were found to have a correlation between the PhNR amplitude, GCC thickness and the global loss index (GLV).

CONCLUSION

Along with VFT, OCT and color vision tests, electrophysiological studies are one of the main methods of examining patients with HON. After one year of PDTP use, there was a significant decrease in the FVEP P2 peak latency in the group with a disease duration of ≤1.5 years as of the time of treatment start. The PhNR amplitude in patients with high visual functions was found to correlate with structural changes in the ganglion cell layer and the retinal nerve fiber layer.

Comparison of broadband and monochromatic photopic negative response in eyes of patients with diabetes with no diabetic retinopathy and different stages of diabetic retinopathy

Purpose:

To evaluate the change in broadband (W/W), red on blue (R/B), and blue on yellow (B/Y) photopic negative response (PhNR) in patients with diabetes mellitus with no diabetic retinopathy (no DR) and different stages of DR and compare it with age-matched controls. This study was performed to provide a single PhNR protocol that can be used for early diagnosis of DR.

Methods:

It was a cross-sectional case-control study done in a hospital setup. Patients with diabetes with no DR and different stages of DR with no other associated ocular pathologies were included. Age-matched controls with no retinal pathologies were also included for comparison. All subjects underwent detailed ophthalmic examination and W/W, R/B, and B/Y electroretinography. Fifty control eyes and 52 treatment naïve eyes of 52 patients with diabetes [no DR = 11, mild nonproliferative diabetic retinopathy (NPDR) =11, moderate NPDR = 10, severe NPDR = 9, and proliferative DR = 11] were included in the study.

Results:

On comparing the ERG responses in patients with diabetes and age-matched controls, a significant reduction (P < 0.05) was noted in the amplitudes of a-wave (39.78 ± 11.34 μV vs. 67.28 ± 12.88 μV), b-wave (116.25 ± 45.25 vs. 134.39 ± 28.78 μV), W/W PhNR (33.86 ± 17.33 vs. 67.18 ± 15.99 μV), R/B PhNR (28.77 ± 15.85 vs. 53.48 ± 14.15 μV), and B/Y PhNR (55.04 ± 32.63 vs. 104.79 ± 24.37 μV). Posthoc analysis revealed that all the eyes in the diabetic group, including those with no DR, had a significantly reduced PhNR amplitude (P < 0.05) when compared with controls. PhNR was found to reduce in amplitude with increasing severity of DR (P < 0.05), with more significance in B/Y. Receiver operating characteristic showed highest area under the curve in B/Y PhNR (94%, P < 0.001), with maximum sensitivity and specificity of 88% and 87%, respectively.

Conclusion:

Changes in the amplitude and implicit time of ERG can reflect the severity of DR. PhNR amplitudes, especially B/Y PhNR, appear to be significantly reduced even in eyes with no DR.

Clinical electroretinography in diabetic retinopathy: a review

The electroretinogram (ERG) is a noninvasive, objective technique to evaluate retinal function that has become increasingly important in the study of diabetic retinopathy. We summarize the principles and rationale of the ERG, present findings from recent clinical studies that have used the full-field ERG, multifocal ERG, and pattern ERG to evaluate neural dysfunction in patients with diabetes, and weigh the strengths and limitations of the technique as it applies to clinical studies and management of patients with diabetic retinopathy. Taken together, ERG studies have provided convincing evidence for dysfunction of the neural retina in patients with diabetes, including those who have no clinically-apparent retinal vascular abnormalities. Recent full-field ERG findings have pointed to the intriguing possibility that photoreceptor function is abnormal in early-stage disease. Pattern ERG data, in conjunction with recently developed photopic negative response analyses, indicate inner retina dysfunction. In addition, multifocal ERG studies have shown spatially localized neural abnormalities that can predict the location of future microaneurysms. Given the insights provided by the ERG, it is likely to play a growing role in understanding the natural history of neural dysfunction in diabetes, as well as providing an attractive outcome measure for future clinical trials that target neural preservation in diabetic retinopathy.

Clinical electrophysiology of the optic nerve and retinal ganglion cells

Clinical electrophysiological assessment of optic nerve and retinal ganglion cell function can be performed using the Pattern Electroretinogram (PERG), Visual Evoked Potential (VEP) and the Photopic Negative Response (PhNR) amongst other more specialised techniques. In this review, we describe these electrophysiological techniques and their application in diseases affecting the optic nerve and retinal ganglion cells with the exception of glaucoma. The disease groups discussed include hereditary, compressive, toxic/nutritional, traumatic, vascular, inflammatory and intracranial causes for optic nerve or retinal ganglion cell dysfunction. The benefits of objective, electrophysiological measurement of the retinal ganglion cells and optic nerve are discussed, as are their applications in clinical diagnosis of disease, determining prognosis, monitoring progression and response to novel therapies.

Photopic negative response (PhNR) in the diagnosis and monitoring of raised intracranial pressure in children: a prospective cross-sectional and longitudinal protocol

INTRODUCTION

Raised intracranial pressure (rICP) can be a consequence of a variety of neurological disorders. A significant complication of rICP is visual impairment, due to retinal ganglion cell (RGC) dysfunction. In children, subjective measurements to monitor this, such as visual field examination, are challenging. Therefore, objective measurements offer promising alternatives for monitoring these effects. The photopic negative response (PhNR) is a component of the flash electroretinogram produced by RGCs; the cells directly affected in rICP-related vision loss. This project aims to assess the clinical feasibility and diagnostic efficacy of the PhNR in detecting and monitoring paediatric rICP.

METHODS AND ANALYSIS

Section 1 is a cross-sectional study; group 1 young persons with disorders associated with rICP and a comparator group 2 of age-matched children without rICP. Both groups will undergo a PhNR recording alongside a series of structural and functional ophthalmic investigations, with the rICP group also having measurement of intracranial pressure.Section 2 is a longitudinal study of the relationship between the PhNR and directly recorded intracranial pressure measurements, through repeated measures. PhNR amplitudes and peak times will be assessed against optical coherence tomography parameters, mean deviation of visual fields, other electrophysiology and ICP measurement through regression analyses.Group differences between PhNR measurements in the rICP and control groups will be performed to determine clinically relevant cut-off values and calculation of diagnostic accuracy. Longitudinal analysis will assess PhNR amplitude against ICP measurements through regression analysis. Feasibility and efficacy will be measured through acceptability, practicality and sensitivity outcomes.

ETHICS AND DISSEMINATION

Favourable opinion from a research ethics committee has been received and the study approved by Manchester Metropolitan University, the Health Research Authority and the Great Ormond Street Institute of Child Health (GOS-ICH) Research and Development office. This project is being undertaken as a doctoral award (ORM) with findings written for academic thesis submission, peer-reviewed journal and conference publications.

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.

Combined Intravitreal Dexamethasone Implant and Cataract Surgery in Patients with Diabetic Retinopathy: Effect on Retinal Morphology and Function

Introduction

Cataract surgery can be associated with vision-threatening complications in patients with diabetes. This study aimed to assess the functional and anatomic outcomes of the intravitreal dexamethasone (DEX) implant, administered at the time as cataract surgery, in patients with diabetic retinopathy and diabetic macular edema (DME).

Methods

This was a retrospective, observational, and single-center study. The primary endpoint was the mean change in central macular thickness (CMT) from baseline to month 1. Secondary endpoints included mean change in best corrected visual acuity (BCVA) from baseline to month 1 and 3, mean change in CMT from baseline to month 3, the photopic negative response (PhNR) and the b wave of flash full-field electroretinogram from baseline to month 1, and the incidence of adverse events.

Results

Twenty-four eyes of 21 patients were included in the study. The mean (range) age of patients was 69 (63–87) years and 13 (61.9%) were men. Mean (standard deviation) CMT significantly decreased from 447 (134) µm at baseline to 341 (134) µm at month 1 (mean difference − 106 ± 134 µm, 95% CI − 183.9 to − 28.1 µm; p = 0.0087). BCVA significantly improved from 46 (20) ETDRS letters at baseline to 59 (22) ETDRS letters at month 1 (mean difference 13 ± 21 letters, 95% CI 0.8–25.2 letters; p = 0.0375). Regarding electrophysiology, there was a statistically significant reduction in mean PhNR from 5.24 (1.67) µV at baseline to 3.73 (1.19) µV at month 1 (mean difference − 1.51 ± 0.42 µV, 95% CI − 2.4 to − 0.7 µV, p = 0.0008); whereas b wave amplitude did not change (12.69 ± 6.89 µV at baseline versus 12.29 ± 6.30 µV at month 1; p = 0.8347). Four (16.7%) eyes developed ocular hypertension over the course of follow-up, which was successfully controlled with topical hypotensive medication.

Conclusion

Perioperative DEX implant significantly improved both anatomic and functional outcomes in patients with DME who underwent cataract surgery.

Probing ON and OFF Retinal Pathways in Glaucoma Using Electroretinography

Glaucoma is a progressive neurodegenerative disease involving damage and eventually death of retinal ganglion cells (RGCs) that comprise the optic nerve. This review summarizes current understanding of specific RGC type vulnerability in glaucoma and how electroretinography (ERG) may provide an objective measure of these functional perturbations. There is building evidence to suggest that ON RGCs, which respond to light increments, may be more resilient to elevated intraocular pressure and glaucoma, whereas OFF RGCs, which respond to light decrements, may be more susceptible. ERG experiments in nonhuman primates and mice have also shown that the ON- and OFF-pathways can be separated using a variety of techniques such as pattern ERG and the photopic negative response. Another ERG paradigm of interest to separate the ON and OFF responses is a flicker stimulus at varying temporal frequencies. Response to lower temporal frequencies is associated with the ON-pathway, and ERG response to higher frequencies is associated with the OFF-pathway. In mice, experimental glaucoma models have shown greater decreases in ERG response at higher frequencies, suggesting that the OFF-pathway is more susceptible. We also summarize current clinical ERG protocols used for glaucoma and discuss innovations for developing new types of stimuli that can further separate the ON- and OFF-pathways. Applying these novel paradigms that distinguish ON- and OFF-pathways may ultimately improve glaucoma diagnostics and monitoring of glaucoma progression.

Functional evolution of visual involvement in experimental autoimmune encephalomyelitis

Background

Experimental autoimmune encephalomyelitis (EAE) is a common animal model of multiple sclerosis (MS). C57BL/6 mice immunized with myelin oligodendrocyte glycoprotein exhibit chronic disease course, together with optic neuritis, consisting of demyelination/axonal loss of the optic nerve.

Objectives

To characterize functional and structural visual damages in two different phases of EAE: pre- and post-motor onset.

Methods

Visual alterations were detected with Visual Evoked Potential (VEP), Electroretinogram (ERG) and Optical Coherence Tomography (OCT). Optic nerve histology was performed at 7 (pre-motor onset) or 37 (post-motor onset) days post-immunization (dpi).

Results

At 7 dpi, optic nerve inflammation was similar in EAE eyes with and without VEP latency delay. Demyelination was detected in EAE eyes with latency delay (p < 0.0001), while axonal loss (p < 0.0001) and ERG b-wave amplitude (p = 0.004) were decreased in EAE eyes without latency delay compared to Healthy controls. At 37 dpi, functional and structural optic nerve damage were comparable between EAE groups, while a decrease of ERG amplitude and NGCC thickness were found in EAE eyes with VEP latency delay detected post-motor onset.

Conclusions

Thanks to non-invasive methods, we studied the visual system in a MS model, which could be useful for developing specific therapeutic strategies to target different disease phases.

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.

Functional and Structural Changes of the Retinal Nerve Fiber Layer and Ganglion Cell Complex in Heavy Smokers

PURPOSE

To assess the functional and structural changes in the retinal nerve fiber layer (RNFL) and the ganglion cell complex (GCC) in heavy smokers using pattern electroretinogram (PERG), photopic negative response(PhNR) and spectral domain optical coherence tomography (SD-OCT).

PATIENTS AND METHODS

Sixty eyes of 30 heavy smokers (at least 15 cigarettes/day for 10 years) (study group) and 60 eyes of 30 age and gender-matched healthy non-smoker subjects (control group) were included. After full ophthalmologic examination (PERG), (PhNR) using RETI-port/scan 21 (Roland Consult, Brandenburg, Germany) and (SD-OCT using Topcon 3D OCT model 2000 FA version.8.30) were tested for all participants. Statistical analysis was performed to compare GCC, RNFL thicknesses, PERG and phNR values between groups.

RESULTS

The mean age was 36.67±4.13 years in the study group and 36.0±4.76 years in the control group. There were no statistical significant differences between the two groups regarding intraocular pressure (p=0.43), axial length (p=0.37), and central corneal thickness (p=0.86). There were significant differences of GCC thickness values between the study group (88.4±6.6 µm) and control group (94.83±5.25 µm) (p<0.001). The mean RNFL values of study and control groups were 97.87±5.88 and 106.43±6.59 µm, respectively (p<0.001). In the study group the superior and inferior quadrants of RNFL were significantly thinner, but there were no significant differences between the two groups in nasal and temporal quadrants. There were no significant differences of PERG-P50 amplitude (p=0.49) and latency (p=0.71); however, PERG-N95 amplitude and latency showed significant differences between the two groups (p<0.001).There were significant differences of phNR amplitude and latency between the two groups (p<0.001). Multiple regression analyses demonstrated that the PhNR, PERG amplitude and latency are the most important determinants for both RNFL and GCC thicknesses.

CONCLUSION

In heavy smokers RNFL thickness was decreased, the PhNR, PERG-N95 amplitudes were diminished and the implicit times were prolonged compared to non-smokers. PhNR and PERG reflect both dysfunction and loss of ganglion cells and their axons.

Comparison between broadband and monochromatic photopic negative response in full-field electroretinogram in controls and subjects with primary open-angle glaucoma

PURPOSE

A prospective, cross-sectional, case-control study was conducted to investigate the role of broadband and monochromatic photopic negative response (PhNR) of the full-field flash electroretinogram (ERG) in the evaluation of ganglion cell damage in primary open-angle glaucoma (POAG) subjects.

METHODS

Subjects with POAG and age-matched normal subjects were recruited from the outpatient department of a tertiary eye care center in South India. A total of 25 patients with POAG and 50 age-matched normal subjects were recruited. ERG was recorded using broadband (3.5 cd.s/m² white stimulus on 10 cd/m² white background) and monochromatic (3.5 cd.s/m² red stimulus on 10 cd/m² blue background and 1 cd.s/m² blue stimulus on 10 cd/m² yellow background) stimuli.

RESULTS

The reduction in PhNR amplitude in POAG compared to normal individuals was higher in red-on-blue PhNR [26.37 µV; p < 0.001, confidence interval (CI) 19.34 to 33.4] as compared to broadband stimuli (16.41 µV; p < 0.001, CI 8.68 to 24.13), and blue on yellow (21.96 µV; p < 0.001, CI 10.12 to 33.8). Red-on-blue PhNR amplitudes correlated better with mean deviation (MD; r = - 0.66, p < 0.05), pattern standard deviation (PSD; r = - 0.4, p = 0.04), visual field index (VFI; r = - 0.58, p < 0.05), and retinal nerve fiber layer thickness (r = - 0.67, p < 0.05) in comparison with broadband and monochromatic blue-on-yellow PhNR. Receiver operating characteristic curve revealed largest area under the curve (0.89) in red-on-blue PhNR compared to broadband (0.76) and blue on yellow (0.74). The sensitivity and specificity was also higher in red-on-blue PhNR (72% and 80%, respectively) as compared to the other stimuli (sensitivity and specificity of broadband 0.68 and 0.7, blue on yellow 0.64 and 0.7, respectively).

CONCLUSION

Correlation of PhNR with Humphrey visual field parameters and retinal nerve fiber layer thickness showed that red-on-blue PhNR can be a useful additional tool for clinical assessment of retinal ganglion cell dysfunction in glaucoma patients. Red-on-blue PhNR was more sensitive as compared to white-on-white and blue-on-yellow PhNR in identifying ganglion cell dysfunction and correlates well with other structural and functional tests for glaucoma such as MD, PSD, VFI, and RNFL thickness.

Optimizing a Portable ERG Device for Glaucoma Clinic: The Effect of Interstimulus Frequency on the Photopic Negative Response

Purpose

The purpose of this study was to investigate the effect of interstimulus frequency on the photopic negative response (PhNR) in the clinical electroretinogram (ERG) in glaucoma and healthy eyes.

Methods

Participants with open angle glaucoma (n = 15) and age-matched controls (n = 20) were recruited. Photopic ERGs were recorded in one eye using five frequencies (1-5 Hz) delivered in random order. ERGs were analyzed for changes to amplitude and timing between groups and interstimulus frequency. Coefficient of variation (CoV) was used to examine variability within recordings for each frequency.

Results

While the a-wave and b-wave showed minimal alteration, the PhNR was highly sensitive to changes in interstimulus frequency. The PhNR signal was largest at 1 Hz and steadily diminished with higher frequencies in both control and glaucoma groups. Significant differences in PhNR amplitude were found between controls and glaucoma groups at 2 and 3 Hz. While 1 Hz delivered the largest PhNR, it also showed a significantly greater CoV compared to other frequencies.

Conclusions

An interstimulus frequency of 2 Hz was optimal for recording the PhNR, creating a good balance between testing time and signal quality. A higher frequency could be used to further shorten clinical testing times; however, this may compromise its clinical utility by dampening the PhNR.

Translational Relevance

Here we show the importance of considering flash interstimulus frequency when designing ERG protocols for recording the PhNR as while higher frequencies can shorten test times, they also have considerable effects on the PhNR.

A Comparison of the RETeval Sensor Strip and DTL Electrode for Recording the Photopic Negative Response

PURPOSE

To compare the RETeval sensor strip and Dawson-Trick-Litzkow (DTL) electrodes for recording the photopic negative response (PhNR) using a portable electroretinogram (ERG) device in eyes with and without glaucoma.

METHODS

Twenty-six control and 31 glaucoma or glaucoma-suspect participants were recruited. Photopic ERGs were recorded with sensor strip and DTL electrodes in random order using the LKC RETeval device. Stimuli consisted of brief, red flashes (1.7 cd.s/m2) on a blue background (photopic 10 cd/m2). The PhNR amplitude was measured from baseline to trough and also expressed as a ratio over the b-wave amplitude.

RESULTS

The sensor strip-recorded PhNR amplitude was significantly attenuated (mean ± standard deviation [SD], 4.8 ± 2.1 vs. 12.7 ± 4.8 μV, P < 0.0001), with lower signal-to-noise ratio (SNR; 5.5 ± 2.1 vs. 8.1 ± 3.9, P < 0.0001), and a trend toward a larger PhNR/b-wave ratio compared with DTL electrodes. The PhNR amplitude, implicit time and PhNR/b-wave ratio correlated with visual field mean light sensitivity, although this fell short of significance for the sensor strip recorded PhNR amplitude. The electrodes demonstrated similar intersession repeatability with a coefficient of repeatability of ±27% and ±28% for the DTL and sensor strip, respectively.

CONCLUSIONS

Sensor strip electrodes are a viable alternative for recording reproducible PhNRs, especially when values are normalized to the b-wave. However, DTL electrodes should be considered in cases of attenuated PhNR, or in elevated noise levels, due to its better signal-to-noise quality.

TRANSLATIONAL RELEVANCE

Sensor strip electrodes can simplify PhNR recordings in the clinic, potentially eliminating the need for an experienced operator.

Electroretinographic evidence suggesting that the type 2 diabetic retinopathy of the sand rat Psammomys obesus is comparable to that of humans

Purpose

Type 2 diabetic retinopathy is the main cause of acquired blindness in adults. The aim of this work was to examine the retinal function of the sand rat Psammomys obesus as an animal model of diet-induced type 2 diabetes when subjected to a hypercaloric regimen.

Materials and methods

Hyperglycemia was induced in Psammomys obesus by high caloric diet (4 kcal/g). The visual function of control (n = 7) and diabetic (n = 7) adult rodents were followed up during 28 consecutive weeks with full-field electroretinogram(ERG) recordings evoked to flashes of white light according to the standard protocol of the International Society for Clinical Electrophysiology of Vision protocol (ISCEV).

Results

Twenty-eight weeks following the induction of diabetes, results revealed significantly reduced and delayed photopic and scotopic ERG responses in diabetic rats compared to control rats. More specifically, we noted a significant decrease in the amplitude of the dark-adapted 0.01ERG (62%), a- and b-wave amplitudes of the dark-adapted 3.0 ERG (33.6%, 55.1%) and the four major oscillatory potentials components (OP1-OP4) (39.0%, 75.2%, 54.8% and 53.7% respectively). In photopic conditions, diabetic rats showed a significant decrease in a- and b-wave (30.4%, 43.4%), photopic negative response (55.3%), 30 Hz flicker (63.7%), OP1-OP4(51.6%, 61.8%, 68.3% and 47.5% respectively) and S-cone (34.7%). Significantly delayed implicit times were observed for all ERG components in the diabetic animals. Results obtained are comparable to those characterizing the retinal function of patients affected with advanced stage of diabetic retinopathy.

Conclusion

Psammomys obesus is a useful translational model to study the pathophysiology of diabetic retinopathy in order to explore new therapeutic avenues in human patients.

Photopic negative response in diagnosis of glaucoma: an experimental study in glaucomatous rabbit model

AIM

To determine whether the photopic negative response (PhNR) elicited by transient white flash on white background is characterizing for glaucoma model in rabbits.

METHODS

Glaucoma was induced in twelve rabbits by subconjunctival injection of 0.05 mL of betamethasone in right eyes (each 1 mL contain betamethasone dipropionate 5 mg and betamethasone sodium phosphate 2 mg).The intraocular pressure (IOP), electroretinogram (ERG) and visual evoked potential (VEP) were measured successively prior and on the 3, 7d, two weeks and four weeks postglaucoma induction. After four weeks, the animals were sacrificed and the globes were histopathologically examined.

RESULTS

The IOP increased significantly after one week (P=0.0001), then it gradually returned to the control level. In ERG examination, the means of a and b wave amplitude and latency were not affected significantly. PhNR amplitude decreased significantly within one week (P=0.0001), but its latency was not affected significantly (P=0.132). The means of VEP latency and amplitude were significantly affected after two weeks and four weeks of glaucoma induction (P=0.0001 and 0.02, respectively). The histopathologic examination of the globes showed reduced number of cells in the retinal ganglion cell layer with multiple vacuoles in the retinal nerve fibre layer.There was significant positive correlation between ganglion cell layer cells and PhNR amplitude (r=0.8, P=0.002).

CONCLUSION

The rise in IOP resulted in irreversible changes or incomplete recovery of VEP and PhNR amplitude. Both PhNR and VEP represented good additional tools in early diagnosis of glaucoma.

Relationship among Photopic Negative Response, Retinal Nerve Fiber Layer Thickness, and Visual Field between Normal and POAG Eyes

Purpose. To determine the relationship among photopic negative response (PhNR) of the electroretinogram (ERG), retinal nerve fiber layer (RNFL) thickness, and the visual field in normal and glaucomatous patients. Methods. Thirty-eight normal volunteers and one hundred twenty-four patients with Primary open-angle glaucoma (POAG) were enrolled in the study. The PhNRs were elicited by white stimuli on a white background and red stimuli on a blue background. The visual field parameters were measured using the standard automated perimetry (SAP). The spectral domain optical coherence tomography (SD-OCT) was used to measure the retinal nerve fiber layer (RNFL) thickness around the optic disc. Results. The PhNR amplitude (W/W, B/R), MD, and mean RNFL thickness in POAG eyes were significantly lower than normal eyes (P = 0.001). The R value in Normal + Glaucomatous group was higher than that of the only glaucomatous group. The R values of PhNR amplitude (B/R) with MD and RNFL were higher than those of PhNR amplitude (W/W). Significant linear association was found in the relationship between RNFL thickness and PhNR amplitude (B/R) (R² = 0.5, P = 0.001). However, significant curve associations were found in the relationship between MD and PhNR amplitude (B/R) and RNFL thickness (R² = 0.525, 0.442, P = 0.001). Conclusions. The ganglion cell activity can be more efficiently evaluated with the PhNR elicited with a red than with a broadband stimulus. The linear relationship between the PhNR amplitude and RNFL thickness indicates that inner retinal function declines proportionately with neural loss in glaucomatous eyes. The PhNR and RNFLT are more objective tools to detect glaucomatous damage than visual field.