Age-related changes in the flash electroretinogram and oscillatory potentials in individuals age 75 and older

Age-dependencies of the electroretinogram in healthy subjects

OBJECTIVE

The purpose of this study was to evaluate the age-dependency of amplitudes and implicit times in the electroretinograms (ERGs) of healthy individuals and provide clinicians and researchers with a reference for a variety of stimulus paradigms.

DESIGN AND METHODS

Full-field electroretinography was conducted on 73 healthy participants aged 14-73 using an extended ISCEV standard protocol that included an additional 9 Hz flicker stimulus for assessing rod function and special paradigms for isolated On-Off and S-cone responses. Correlation coefficients and best-fit regression models for each parameter's age-dependency were calculated.

RESULTS

Dark-adapted ERGs, in particular, displayed notable age-related alterations. The attenuation and delay of the b-wave with higher age were most significant in the dark-adapted, rod-driven 0.001 cd s/m2 flash ERG. The age-dependent reduction of the a-wave amplitude was strongest in the standard dark-adapted 3 cd s/m2 flash condition. Cone-driven, light-adapted responses to either flash or flicker stimuli displayed comparatively small alterations at higher age. S-cone function tended to diminish at an early age, but the effect was not significant in the whole population.

CONCLUSION

The results suggest that rod and cone function decline at different rates with age, with rods being generally more affected by aging. Nonetheless, response amplitudes displayed a wide variability across the whole sample.

The effects of time restricted feeding on age-related changes in the mouse retina

Dietary modifications such as caloric restriction (CR) and intermittent fasting (IF) have gained popularity due to their proven health benefits in aged populations. In time restricted feeding (TRF), a form of intermittent fasting, the amount of time for food intake is regulated without restricting the caloric intake. TRF is beneficial for the central nervous system to support brain health in the context of aging. Therefore, we here ask whether TRF also exerts beneficial effects in the aged retina. We compared aged mice (24 months) on a TRF paradigm (access to food for six hours per day) for either 6 or 12 months against young control mice (8 months) and aged control mice on an ad libitum diet. We examined changes in the retina at the functional (electroretinography), structural (histology and fluorescein angiograms) and molecular (gene expression) level. TRF treatment showed amelioration of age-related reductions in both scotopic and photopic b-wave amplitudes suggesting benefits for retinal interneuron signaling. TRF did not affect age-related signs of retinal inflammation or microglial activation at either the molecular or histological level. Our data indicate that TRF helps preserve some aspects of retinal function that are decreased with aging, adding to our understanding of the health benefits that altered feeding patterns may confer.

Full-field electroretinogram recorded with skin electrodes in 6- to 12-year-old children

PURPOSE

To determine the full-field electroretinogram (ffERG) parameters, including the light-adapted (LA) 3 ERG and the photopic negative response (PhNR), in 6- to 12-year-old children.

METHODS

ffERG data were obtained from 214 eyes of 214 healthy subjects. The amplitudes and peak time of the ffERG responses were obtained from children divided into 6- to 8-year-old and 9- to 12-year-old groups. Using a skin electrode, electrical signals were measured in response to white stimulating light and white background light (LA 3 ERG). A blue background light and red flashes were then used to elicit the PhNR.

RESULTS

The a-wave amplitude ranged from 0.40 to 9.20 μV, the b-wave ranged from 4.70 to 30.80 μV, and the PhNR ranged from 1.30 to 39.90 μV. The b-wave peak time (33.20 ms) of 6- to 8-year-old groups was slightly shorter than that of the 9- to 12-year-old groups (33.60 ms, P = 0.01), but no differences in amplitudes or in peak time of other components. There were significant correlations between the amplitudes (a-wave and b-wave: r = 0.43, p < 0.001; a-wave and PhNR: r = 0.25, p < 0.001; b-wave and PhNR: r = 0.45, p < 0.001). There was a moderate correlation between the a-wave and b-wave peak time (r = 0.31, P < 0.001).

CONCLUSIONS

We determined the largest dataset of the LA 3 ERG and PhNR parameters in a population of healthy children, aged 6-12 years, which may provide a useful reference value when evaluating children with potential retinal defects.

Flash Electroretinography as a Measure of Retinal Function in Myopia and Hyperopia: A Systematic Review

Refractive errors (myopia and hyperopia) are the most common visual disorders and are severe risk factors for secondary ocular pathologies. The development of refractive errors has been shown to be associated with changes in ocular axial length, suggested to be induced by outer retinal elements. Thus, the present study systematically reviewed the literature examining retinal function as assessed using global flash electroretinograms (gfERGs) in human clinical refractive error populations. Electronic database searching via Medline, PubMed, Web of Science, Embase, Psych INFO, and CINAHL retrieved 981 unique records (last searched on the 29 May 2022). Single case studies, samples with ocular comorbidities, drug trials, and reviews were excluded. Demographic characteristics, refractive state, gfERG protocol details, and waveform characteristics were extracted for the eight studies that met the inclusion criteria for the review and were judged to have acceptable risk of bias using the OHAT tool (total N = 552 participants; age 7 to 50). Study synthesis suggests that myopia in humans involves attenuation of gfERG photoreceptor (a-wave) and bipolar cell (b-wave) function, consistent with the animal literature. Meaningful interpretation of the overall findings for hyperopia was limited by inconsistent reporting, highlighting the need for future studies to report key aspects of gfERG research design and outcomes more consistently for myopic and hyperopic refractive errors.

Age and Sex-Related Changes in Retinal Function in the Vervet Monkey

Among the deficits in visual processing that accompany healthy aging, the earliest originate in the retina. Moreover, sex-related differences in retinal function have been increasingly recognized. To better understand the dynamics of the retinal aging trajectory, we used the light-adapted flicker electroretinogram (ERG) to functionally assess the state of the neuroretina in a large cohort of age- and sex-matched vervet monkeys (N = 35), aged 9 to 28 years old, with no signs of obvious ocular pathology. We primarily isolated the cone–bipolar axis by stimulating the retina with a standard intensity light flash (2.57 cd/s/m²) at eight different frequencies, ranging from 5 to 40 Hz. Sex-specific changes in the voltage and temporal characteristics of the flicker waveform were found in older individuals (21–28 years-old, N = 16), when compared to younger monkeys (9–20 years-old, N = 19), across all stimulus frequencies tested. Specifically, significantly prolonged implicit times were observed in older monkeys (p < 0.05), but a significant reduction of the amplitude of the response was only found in old male monkeys (p < 0.05). These changes might reflect ongoing degenerative processes targeting the retinal circuitry and the cone subsystem in particular. Altogether, our findings corroborate the existing literature in humans and other species, where aging detrimentally affects photopic retinal responses, and draw attention to the potential contribution of different hormonal environments.

An Analysis of Metabolic Changes in the Retina and Retinal Pigment Epithelium of Aging Mice

Purpose

The purpose of this study was to present our hypothesis that aging alters metabolic function in ocular tissues. We tested the hypothesis by measuring metabolism in aged murine tissues alongside retinal responses to light.

Methods

Scotopic and photopic electroretinogram (ERG) responses in young (3–6 months) and aged (23–26 months) C57Bl/6J mice were recorded. Metabolic flux in retina and eyecup explants was quantified using U-¹³C-glucose or U-¹³C-glutamine with gas chromatography-mass spectrometry (GC-MS), O₂ consumption rate (OCR) in a perifusion apparatus, and quantifying adenosine triphosphatase (ATP) with a bioluminescence assay.

Results

Scotopic and photopic ERG responses were reduced in aged mice. Glucose metabolism, glutamine metabolism, OCR, and ATP pools in retinal explants were mostly unaffected in aged mice. In eyecups, glutamine usage in the Krebs Cycle decreased while glucose metabolism, OCR, and ATP pools remained stable.

Conclusions

Our examination of metabolism showed negligible impact of age on retina and an impairment of glutamine anaplerosis in eyecups. The metabolic stability of these tissues ex vivo suggests age-related metabolic alterations may not be intrinsic. Future experiments should focus on determining whether external factors including nutrient supply, oxygen availability, or structural changes influence ocular metabolism in vivo.

Effects of DTL electrode position on the amplitude and implicit time of the electroretinogram

PURPOSE

This study sought to investigate whether there is an optimal position of the Dawson, Trick, and Litzkow (DTL) electrodes when measuring the full-field electroretinogram (ERG) for monitoring purposes.

METHODS

In 200 uveitis patients, an extended light-adapted (LA) ERG protocol was measured twice, incorporating the International Society for Clinical Electrophysiology of Vision standards. First, a LA ERG was measured with the DTL in the lower lid position (LLP) and thereafter in the fornix position. Differences in amplitudes and implicit times of a-waves, b-waves, and the 30 Hz peak were investigated. Intraclass correlation coefficients (ICCs) as well as coefficients of variation (CoV) were calculated, to assess both reliability and relative variability between the two DTL positions.

RESULTS

Implicit times showed no statistically significant differences between the two DTL positions. As expected, amplitudes at the different stimulus strengths were 1.12-1.19 higher in the LLP, but there were no significant differences in the CoV between the two DTL positions. The ICC was high for the b-wave and 30 Hz flicker response (0.842-0.979), but lower for the a-wave, especially for amplitudes (0.584-0.716).

CONCLUSIONS

For monitoring purposes in patients, we conclude that based on relative variability, no position is preferable above the other. However, because in most diseases amplitudes are decreased, the LLP may be chosen because it yields higher amplitudes. Whatever the choice, it is important to ensure that the DTL position remains stable during an ERG recording.

Assessing the Contribution of the Oscillatory Potentials to the Genesis of the Photopic ERG with the Discrete Wavelet Transform

The electroretinogram (ERG) is composed of slow (i.e., a-, b-waves) and fast (i.e., oscillatory potentials: OPs) components. OPs have been shown to be preferably affected in some diseases (such as diabetic retinopathy), while the a- and b-waves remain relatively intact. The purpose of this study was to determine the contribution of OPs to the building of the ERG and to examine whether a signal mostly composed of OPs could also exist. DWT analyses were performed on photopic ERGs (flash intensities: −2.23 to 2.64 log cd·s·m⁻² in 21 steps) obtained from normal subjects (n = 40) and patients (n = 21) affected with a retinopathy. In controls, the %OP value (i.e., OPs energy/ERG energy) is stimulus- and amplitude-independent (range: 56.6–61.6%; CV = 6.3%). In contrast, the %OPs measured from the ERGs of our patients varied significantly more (range: 35.4%–89.2%; p < 0.05) depending on the pathology, some presenting with ERGs that are almost solely composed of OPs. In conclusion, patients may present with a wide range of %OP values. Findings herein also support the hypothesis that, in certain conditions, the photopic ERG can be mostly composed of high-frequency components.

Variability of Normal Values of Electroretinogram Parameters Due to Aging in Healthy Individuals

Aim- To find normal values of implicit time and amplitudes of full-field electroretinogram and to determine their changes with age in healthy Romanian subjects. Material and Methods- The prospective study included 59 healthy subjects aged between 20 and 80 years old; in the end, we had valid ERG recordings for all tests from 54 subjects. All of the participants underwent full-field ERG, recorded with Metrovision MonPack One system. The implicit times and amplitudes were analyzed for a and b waves in dark-adapted 0.01 ERG, dark-adapted 3.0 ERG, dark-adapted oscillatory potentials, light-adapted 3.0 ERG, and 30Hz flicker ERG according to International Society for Clinical Electrophysiology of Vision (ISCEV) protocols. Results- ERG latency values were bigger in subjects above 50 years old than in younger subjects for b wave in dark adapted 0.01, dark adapted 3.0, light adapted 3.0 and dark adapted 3.0 flicker and for a wave in dark adapted 0.01 and dark adapted 3.0 ERG. There was no significant difference in latency values for dark adapted 3.0 oscillatory potentials between young and old subjects. Because of increased variability, we could not prove that observed differences for amplitudes held statistical significance. Conclusions- This study proves there is a major loss in retinal activity due to aging, most of it being caused by the rod cells delayed response. Also, oscillatory potentials do not seem to be affected by age, and could prove a valuable test to investigate for changes in patients with Diabetes mellitus.

Does pupil constriction under blue and green monochromatic light exposure change with age?

Many nonvisual functions are regulated by light through a photoreceptive system involving melanopsin-expressing retinal ganglion cells that are maximally sensitive to blue light. Several studies have suggested that the ability of light to modulate circadian entrainment and to induce acute effects on melatonin secretion, subjective alertness, and gene expression decreases during aging, particularly for blue light. This could contribute to the documented changes in sleep and circadian regulatory processes with aging. However, age-related modification in the impact of light on steady-state pupil constriction, which regulates the amount of light reaching the retina, is not demonstrated. We measured pupil size in 16 young (22.8±4 years) and 14 older (61±4.4 years) healthy subjects during 45-second exposures to blue (480 nm) and green (550 nm) monochromatic lights at low (7×10(12) photons/cm2/s), medium (3×10(13) photons/cm2/s), and high (10(14) photons/cm2/s) irradiance levels. Results showed that young subjects had consistently larger pupils than older subjects for dark adaptation and during all light exposures. Steady-state pupil constriction was greater under blue than green light exposure in both age groups and increased with increasing irradiance. Surprisingly, when expressed in relation to baseline pupil size, no significant age-related differences were observed in pupil constriction. The observed reduction in pupil size in older individuals, both in darkness and during light exposure, may reduce retinal illumination and consequently affect nonvisual responses to light. The absence of a significant difference between age groups for relative steady-state pupil constriction suggests that other factors such as tonic, sympathetic control of pupil dilation, rather than light sensitivity per se, account for the observed age difference in pupil size regulation. Compared to other nonvisual functions, the light sensitivity of steady-state pupil constriction appears to remain relatively intact and is not profoundly altered by age.

Differential changes in retina function with normal aging in humans

We evaluated the full field electroretinogram (ERG) to assess age-related changes in retina function in humans. ERG recordings were performed on healthy subjects with normal fundus appearance, lack of cataract and 20/20 acuity, aged 20-39 years (n = 27; mean age 25 ± 5, standard deviation), 40-59 years (n = 20; mean 53 ± 5), and 60-82 years (n = 18; mean 69 ± 5). Multiple ERG tests were applied, including light and dark-adapted stimulus-response function, dark adaptation and dynamic of recovery from a single bright flash under dark-adapted conditions. Changes in ERG properties were found in the oldest age group when compared with the two younger age groups. (1) The photopic hill effect was less pronounced. (2) Both photopic a-wave and b-wave amplitudes and implicit times were increased at high stimulus strengths. (3) Dark adaptation time was delayed for pure rod and L/M cone-driven responses, respectively. (4) Dark-adapted a-wave but not b-wave amplitudes were reduced, yielding higher B/A ratios. (5) Dark-adapted a- and b-waves implicit times were prolonged: there was a direct proportional correlation between minimal a-wave implicit times and age. (6) The dynamic of dark current recovery from a bright flash, under dark-adapted conditions, was transiently faster at intervals between 0.9 and 2 s. These results denote that aging of the healthy retina is accompanied by specific functional changes, which must be taken into account to optimally diagnose potential pathologies.

A negative electroretinogram (ERG) in a case of probable multiple system atrophy (MSA)

Recent articles have described negative ERGs in a small number of patients with cerebellar degeneration. Five of the previously reported seven cases were hereditary (2/5 had spinocerebellar ataxia-1 (SCA-1) gene mutations) and the other two were sporadic. We report a negative ERG in a case of cerebellar degeneration that differs significantly from earlier cases. The 65-year-old man had a 5-year history of ataxia, unsteady gait, orthostatic hypotension, and bladder and erectile dysfunction, with no family history of neurological or retinal disease. Visual acuity was 20/30 OD, 20/40 OS, but reportedly was never 20/20. His fundus exam showed optic nerve pallor, but otherwise was normal. Visual fields had enlarged blind spots but no central scotomas. Autofluorescence was normal. Photopic flash and 30-Hz ERG responses were normal. Rod b-waves were reduced and delayed. Standard flash a-waves were normal, but the b-waves were smaller than the a-waves. Blood tests were negative for Leber's hereditary optic neuropathy, dominant optic atrophy, and for expansions in SCA genes including SCA-1. This is only the third reported case of sporadic ataxia with a negative ERG. The patient's prominent autonomic dysfunction differs from the previous cases, and meets the clinical criteria for probable multiple system atrophy (MSA). This introduces another possible diagnosis in cases of negative ERGs with ataxia, and suggests that the visual system may be affected in MSA.

Neuronal adaptation in the human retina: a study of the single oscillatory response in dark adaptation and mesopic background illumination

PURPOSE

The single oscillatory response in complete dark adaptation (DA) and the effect of mesopic illumination were studied in order to investigate the behaviour of the neuronal adaptation system as reflected in the oscillatory potentials (OPs) of the electroretinogram (ERG).

METHODS

The rapid oscillatory and slow components (a- and b-waves) of single ERGs were simultaneously recorded in nine healthy, young subjects in response to first flash after both DA of 45 mins and light adaptation to a steady background light (BGL) of low mesopic intensity.

RESULTS

Two low-amplitude oscillatory peaks were present in the single response to the first flash recorded in DA. There was no increase in the summed amplitudes of the OPs (SOP) when recorded in the single response to the first flash in mesopic BGL. However, the morphology of the oscillatory response altered. The first OP was reduced and a third oscillatory peak appeared.

CONCLUSIONS

We conclude that early, scotopically related OPs may indeed be activated in the single response to the first flash in DA (i.e. without using conditioning flashes). Secondly, on its own, adaptation to mesopic BGL does not seem to trigger enhancement of the overall oscillatory response. The altered single oscillatory response to the first flash apparent in the mesopic BGL comprises a third cone-associated OP and seems to reflect a reorganization of the retinal microcircuitry from a predominantly rod-activated system to one of mixed rod/cone neuronal activity in the inner part of the retina at the level at which individual OPs have their respective origins.