The human pattern ERG: alteration of response properties with aging

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.

Alterations in Retinal Signaling Across Age and Sex in 3xTg Alzheimer’s Disease Mice

Background:

Visual disturbances often precede cognitive dysfunction in patients with Alzheimer’s disease (AD) and may coincide with early accumulation of amyloid-β (Aβ) protein in the retina. These findings have inspired critical research on in vivo ophthalmic Aβ imaging for disease biomarker detection but have not fully answered mechanistic questions on how retinal pathology affects visual signaling between the eye and brain.

Objective:

The goal of this study was to provide a functional and structural assessment of eye-brain communication between retinal ganglion cells (RGCs) and their primary projection target, the superior colliculus, in female and male 3xTg-AD mice across disease stages.

Methods:

Retinal electrophysiology, axonal transport, and immunofluorescence were used to determine RGC projection integrity, and retinal and collicular Aβ levels were assessed with advanced protein quantitation techniques.

Results:

3xTg mice exhibited nuanced deficits in RGC electrical signaling, axonal transport, and synaptic integrity that exceeded normal age-related decrements in RGC function in age- and sex-matched healthy control mice. These deficits presented in sex-specific patterns among 3xTg mice, differing in the timing and severity of changes.

Conclusion:

These data support the premise that retinal Aβ is not just a benign biomarker in the eye, but may contribute to subtle, nuanced visual processing deficits. Such disruptions might enhance the biomarker potential of ocular amyloid and differentiate patients with incipient AD from patients experiencing normal age-related decrements in visual function.

Age-Related Alterations of Proteins in Albino Wistar Rat Retina

Imbalance of homeostasis causes permanent changes in the body with time. The central nervous system is especially prone to these changes since it possesses limited regenerative capacity. In the retina, neurons are damaged during the aging process, and this eventually leads to deterioration of vision. In our 2-year-long study, we examined genetically closely related rat individuals to disclose the hidden retinal causes of age-associated visual dysfunction. Morphometric analysis showed significant reduction of the retina thickness with aging, particularly that of the inner plexiform layer. To reveal changes between the age groups, we used immunohistochemistry against vesicular glutamate transporter 1 protein for photoreceptor and bipolar cell terminals, Brn3a for ganglion cells, calbindin 28 kDa for horizontal cells, parvalbumin for AII amacrines, protein kinase Cα for rod bipolar cells, tyrosine hydroxylase for dopaminergic cells, glial fibrillary acidic protein for glial cells, and peanut-agglutinin labeling for cones. The most significant decrease was observed in the density of photoreceptor and the ganglion cells in the aging process. By using immunocytochemistry and western blot technique, we observed that calbindin and vesicular glutamate transporter 1 protein staining do not change much with aging; tyrosine hydroxylase, parvalbumin and calretinin showed the highest immunoreactivity during the midlife period. Most interestingly, the level of glial fibrillary acidic protein also changes similarly to the previously named markers. Our results provide further evidence that protein content is modified at least in some cell populations of the rat retina, and the number of retinal cells declined with aging. We conclude that senescence alone may cause structural and functional damage in the retinal tissue.

Comparison of structural and functional tests in primary open angle glaucoma

Purpose:

To comparatively analyze the structural and functional tests used in the diagnosis and follow-up of glaucoma.

Methods:

Eighty eyes of 40 patients with primary open angle glaucoma (POAG) and 46 eyes of 23 healthy individuals were included in the study. Transient pattern electroretinography (PERG), steady-state PERG (ssPERG), computerized visual field (VF) screening, and examination of retinal nerve fiber layer (RNFL) and macular thickness on optical coherence tomography (OCT) were undertaken. The results were compared between the groups.

Results:

80 eyes belonging to 40 patients with a diagnosis of POAG (23 female, 17 male) (18 mild 22 moderate POAG) with a mean of 57.37 (±8.6) years, and 46 eyes of 23 healthy individuals (14 female, 9 male) with a mean age of 55.30 (±8.09) years were included in the study. PERG P50 and N95 and ssPERG latency revealed a significant delay in the POAG group. When the wave amplitudes were examined, they were found to be significantly lower in both PERG and sSPERG tests for the POAG group, but the results were more pronounced in ssPERG. The latency values of PERG and ssPERG tests were not significantly correlated with any of the parameters of the remaining tests. However, the amplitude values of these tests had a positive correlation with the mean deviation value and negative correlation with the pattern standard deviation value of VF. All associated parameters were significant for the amplitude value of the ssPERG test.

Conclusion:

For the proper management of glaucoma, rather than approaching damage simply as the loss of retinal ganglion cells or the neuroretinal rim, it is necessary to focus on the ongoing anatomical and functional relationship and evaluate structural and functional tests together. In addition, ssPERG test, which is not widely adopted in routine practice, provides valuable information and is significantly correlated with OCT parameters.

Test-retest repeatability of the pattern electroretinogram and flicker electroretinogram

PURPOSE

To evaluate the repeatability of the steady-state pattern electroretinogram (PERG) and full-field flicker electroretinogram (Flicker ERG) protocols, delivered by the office-based Neuro Optic Vision Assessment (NOVA)™ testing platform, in healthy subjects.

METHODS

Healthy individuals underwent PERG (16° and 24°) and Flicker ERG [fixed luminance (FL) and multi-luminance (ML)] testing protocols. Test-retest repeatability of protocols was calculated using intra-class correlation coefficients (ICC). Reference values of the parameters of the aforementioned tests were also calculated.

RESULTS

The ICCs for the PERG parameters ranged from 0.793 to 0.911 (p < 0.001). The ICCs for the Flicker ERG parameters ranged from 0.968 to 0.994 (p < 0.001). A linear regression analysis was applied to assess the impact of age on ERG responses. Age had a significant impact on all PERG parameters (16° or 24°). The phase response of the FL Flicker ERG significantly decreased with age (β = - 0.837, p ≤ 0.001). The FL Flicker ERG Magnitude was also impacted with a significant quadratic effect of age (β = - 0.0047, p = 0.0004). Similarly, the Phase Area Under the Curve (Phase AUC) of the ML Flicker ERG significantly declined with age (β = - 0.007, p = 0.009), and the impact on the Magnitude AUC was significant as well, with a negative quadratic age effect.

CONCLUSIONS

The PERG and Flicker ERG protocols, delivered by an office-based testing platform, were shown to have good-to-excellent test-retest repeatability when tests were performed in the same order and in immediate succession.

Decoding PERG: A neuro-ophthalmic retinal ganglion cell function review

Purpose of review

Currently, the clinical evaluation of neuro-ophthalmologic diseases are mainly focused on identifying stages where structural or functional damage occur. Recognition of retinal ganglion cell (RGC) functional patterns as well as monitoring RGC dysfunction can be performed using steady-state pattern electroretinogram (PERG). The analysis of the amplitude and latency shift aid on providing information on early damage or monitoring of the RGC, allowing for prompt clinical intervention and management modification, potentially changing the natural history of the disease. The purpose of this article is to review the latest findings in PERG, in early manifest glaucoma, non arteritic ischemic optic neuropathy, multiple sclerosis with unilateral recovered optic neuritis and its fellow eyes.

Recent Findings

The steady-state PERG responses provide new and early specific information in neuro-ophthalmic diseases affecting the inner retina.

Summary

Steady state PERG presents specific amplitude and latency outcomes based on the neuro-ophthalmic disease affecting the inner retina, allowing early recognition of changes at the level of RGC and the degree of RGC dysfunction. In addition, PERG alterations may be induced in healthy subjects as well as susceptible eyes using different stress tests such as head down tilting or water drinking tests.

An Electrophysiological Comparison of Contrast Response Functions in Younger and Older Adults, and Those With Glaucoma

Purpose

Aging and glaucoma both result in contrast processing deficits. However, it is unclear the extent to which these functional deficits arise from retinal or post-retinal neuronal changes. This study aims to disentangle the effects of healthy human aging and glaucoma on retinal and post-retinal contrast processing using visual electrophysiology.

Methods

Steady-state pattern electroretinograms (PERG) and pattern visual evoked potentials (PVEP) were simultaneously recorded across a range of contrasts (0%, 4%, 9%, 18%, 39%, 73%, 97%; 0.8° diameter checks, 31° diameter checkerboard) in 13 glaucoma patients (67 ± 6 years), 15 older (63 ± 8 years) and 14 younger adults (27 ± 3 years). PERG and PVEP contrast response functions were fit with a linear and saturating hyperbolic model, respectively. PERG and PVEP magnitude, timing (phase), and model fit parameters (slope, semi-saturation constant) were compared between groups.

Results

PERG responses were reduced and delayed in older adults relative to younger adults, and further reduced and delayed in glaucoma patients across all contrasts. PVEP signals were also reduced and delayed in glaucoma patients, relative to age-similar (older) controls. However, despite having reduced PERG magnitudes, older adults did not demonstrate reduced PVEP magnitudes.

Conclusions

Older adults with healthy vision demonstrate reduced magnitude and delayed timing in the PERG that is not reflected in the PVEP. In contrast, glaucoma produces functional deficits in both PERG and PVEP contrast response functions. Our results suggest that glaucomatous effects on contrast processing are not a simple extension of those that arise as part of the aging process.

The aging rat retina: from function to anatomy

In healthy beings, age is the ultimate reason of cellular malfunction and death. In the rat retina, age causes a functional decline and loss of specific neuronal populations. In this regard, controversial conclusions have been reported for the innermost retina. Here, we have studied the albino and pigmented retina for the duration of the rat life-span. Independent of age (21 days-22 months), the electroretinographic recordings and the volume of the retina and its layers are smaller in albinos. Functionally, aging causes in both strains a loss of cone- and rod-mediated responses. Anatomically, cell density decreases with age because the retina grows linearly with time; no cell loss is observed in the ganglion cell layer; and only in the pigmented rat, there is a decrease in cone photoreceptors. In old animals of both strains, there is gliosis in the superior colliculi and a diminution of the area innervated by retinal ganglion cells. In conclusion, this work provides the basis for further studies linking senescence to neurodegenerative retinal diseases.

Comparing DTL microfiber and Neuroline skin electrode in the Mini Ganzfeld ERG

BACKGROUND

In infant ERG recordings skin electrodes frequently result in a better compliance. In order to assess the quality of such recordings, we compared the recording characteristics of DTL microfiber and Neuroline surface electrodes using a modified ISCEV protocol in the Mini Ganzfeld ERG.

METHODS

A prospective cohort study on healthy adult subjects was conducted at the Department of Ophthalmology, University of Basel, Switzerland. Thirty healthy volunteers were tested. The microfiber electrode (DTL Plus Electrode) was placed across the cornea, above the lower eyelid. The Neuroline skin electrode was placed on the surface of the lower lid on the opposite eye. The eye on which each electrode type was placed was randomised. Amplitudes of the rod, standard combined, standard flash cone, light-adapted 3.0 Hz flicker and red cone responses were analysed, as well as their respective implicit times.

RESULTS

Both electrode recordings showed the same waveform characteristics. Responses with the Neuroline electrode were significantly weaker than those from the DTL electrode. Amplitudes of the rod, standard combined, standard flash cone, light-adapted 3.0 Hz flicker and red cone responses were up to four times larger when recorded with the DTL electrode (p < 0.005, ANOVA). Implicit times of the red cone ERGs were slightly faster for the Neuroline skin electrode recordings (p ≤ 0.039).

CONCLUSIONS

Comparison of full-field ERG recordings with microfiber DTL and Neuroline skin electrodes showed that DTL electrodes produce larger ERGs. Hence, we provide evidence that both electrode types allow successful full-field ERG recording, although separate normative data for both electrodes are necessary.

Cone-rod dysfunction is a sign of early-onset high myopia

PURPOSE

High myopia (HM) is one of the leading causes of irreversible blindness because of its associated complications. Early-onset HM (eoHM) that presents before primary school age may be genetically determined, whereas late-onset HM (loHM) is affected by genetic and environmental factors. Identification of signs that differentiate eoHM from loHM may provide valuable clues toward understanding the molecular basis of HM.

METHODS

In this study, 42 subjects with HM were recruited, including 32 eoHM (onset age, ≤5 years) and 10 loHM (onset age, 12.4 ± 2.5 years). Clinical data from these two groups were compared, including best visual acuity, refraction, axial length, and electroretinography.

RESULTS

The mean amplitudes of rod b-wave, maximum a-wave, maximum b-wave, cone a-wave, and cone b-wave of patients with eoHM were 179 ± 72 μv, -158 ± 63 μv, 345 ± 105 μv, -20 ± 11 μv, and 42 ± 21 μv, respectively, whereas those of patients with loHM were 252 ± 77 μv, -235 ± 60 μv, 464 ± 65 μv, -36 ± 9 μv, and 104 ± 26 μv, respectively (p < 0.001). Patients with eoHM had significantly reduced responses of cones and rods, especially cones, as compared with patients with loHM. The cone-rod responses in patients with loHM were within normal range.

CONCLUSIONS

The findings suggest that cone-rod dysfunction may be a sign for eoHM compared with loHM.

Temporal and spatial frequencies interact in the contrast transfer function of the pattern electroretinogram

The contrast transfer function (CTF) of the pattern electroretinogram (PERG) depends on temporal frequency. For transient stimulation it is fully linear; at faster stimulation rates it becomes strongly non-linear with an accelerated shape. In this study we investigated a range of stimulus parameters with the aim of studying the influence of temporal and spatial frequencies, as well as contrast levels, on the CTF; effects were quantified via an "index of linearity" IL. Both reversal rate and check size influenced linearity (p<.001), examples: At a constant check size of 0.8 degrees, 7.7 rps: IL=1.0; 0.8 degrees/24 rps: IL=0.5; at a constant reversal rate of 19 rps, IL was 0.5 for 0.8 degrees, but rose to 0.8 both for 0.2 degrees and 18 degrees. The reason for this complex response surface remains a puzzle, it cannot be explained by varying parvo/magnocellular contributions, and its possible influences on recordings in patients merit further studies.

Pattern electroretinogram in glaucoma

PURPOSE OF REVIEW

Several studies have shown that the pattern electroretinogram, a direct, objective method of measuring retinal ganglion cell function, is altered early in ocular hypertension and glaucoma. Renewed interest in the pattern electroretinogram for early detection of pre-perimetric glaucoma has been sparked by noninvasive and reproducible methods of recording using skin electrodes.

RECENT FINDINGS

With the noninvasive pattern electroretinogram, response abnormalities have been detected in up to 50% of glaucoma suspects with normal standard perimetry. In early glaucoma (with either normal or high intraocular pressure), a reduction of intraocular pressure has sometimes yielded improvement in pattern electroretinogram amplitude. A prolonged steady-state stimulus presentation reduces the pattern electroretinogram amplitude and increases optic nerve blood flow in normal subjects, suggesting that sustained activity of retinal ganglion cells is physiologically associated with autoregulatory changes of the neural-vascular system. It is unknown whether this autoregulation is altered in glaucoma. The multifocal pattern electroretinogram does not seem to have an advantage over the pattern electroretinogram in the early detection of glaucoma. The photopic negative response of the diffuse flash electroretinogram has shown changes in glaucoma, but may not be able to detect retinal dysfunction in normal tension glaucoma.

SUMMARY

The pattern electroretinogram is a noninvasive, direct, objective method that may be useful to clinicians in detecting early retinal ganglion cell dysfunction in glaucoma suspects. The pattern electroretinogram may also optimize treatment strategies based on improvement of retinal ganglion cell function.

Normative data for a user-friendly paradigm for pattern electroretinogram recording

PURPOSE

To provide normative data for a user-friendly paradigm for the pattern electroretinogram (PERG) optimized for glaucoma screening (PERGLA).

DESIGN

Prospective nonrandomized case series.

PARTICIPANTS

Ninety-three normal subjects ranging in age between 22 and 85 years.

METHODS

A circular black-white grating of 25 degrees visual angle, reversing 16.28 times per second, was presented on a television monitor placed inside a Ganzfeld bowl. The PERG was recorded simultaneously from both eyes with undilated pupils by means of skin cup electrodes taped over the lower eyelids. Reference electrodes were taped on the ipsilateral temples. Electrophysiologic signals were conventionally amplified, filtered, and digitized. Six hundred artifact-free repetitions were averaged. The response component at the reversal frequency was isolated automatically by digital Fourier transforms and was expressed as a deviation from the age-corrected average. The procedure took approximately 4 minutes.

MAIN OUTCOME MEASURES

Pattern electroretinogram amplitude ( micro V) and phase (pi rad); response variability (coefficient of variation [CV] = standard deviation [SD] / mean x 100) of amplitude and phase of 2 partial averages that build up the PERG waveform; amplitude ( micro V) of background noise waveform, obtained by multiplying alternate sweeps by +1 and -1; and interocular asymmetry (CV of amplitude and phase of the PERG of the 2 eyes).

RESULTS

On average, the PERG has a signal-to-noise ratio of more than 13:1. The CVs of intrasession and intersession variabilities in amplitude and phase are lower than 10% and 2%, respectively, and do not depend on the operator. The CV of interocular asymmetries in amplitude and phase are 9.8+/-8.8% and 1.5+/-1.4%, respectively. The PERG amplitude and phase decrease with age. Residuals of linear regression lines have normal distribution, with an SD of 0.1 log units for amplitude and 0.019 log units for phase. Age-corrected confidence limits (P<0.05) are defined as +/-2 SD of residuals.

CONCLUSIONS

The PERGLA paradigm yields responses as reliable as the best previously reported using standard protocols. The ease of execution and interpretation of results of PERGLA indicate a potential value for objective screening and follow-up of glaucoma.

Decline of photopic multifocal electroretinogram responses with age is due primarily to preretinal optical factors

Age-related changes in photopic retinal function were evaluated topographically with the multifocal electroretinogram (mfERG). Thirty-two subjects between the ages of 16 and 69 participated. There was a strong dependence on age for all mfERG response measures that was strongest for the group of central retinal responses (i.e., within 5 deg eccentricity) and approximately equal for responses between 5 and 20 deg. After adjustment for crystalline lens optical density and pupil diameter, significant effects of age were limited to central first-order (i.e., within 5 deg) and second-order response kernels. Simulation studies support an optical basis for the observed age-related changes. It is concluded that mfERG changes between the ages of 20 and 70 are due predominantly to preretinal optical factors.

Objective perimetry in glaucoma

PURPOSE

Objective perimetry in glaucoma is described using the multifocal pattern visually evoked potential (VEP). A multichannel recording technique was used to improve signal detection in healthy volunteers and assess its ability to detect glaucoma and early changes in patients with suspected glaucoma.

DESIGN

Prospective, case-control study.

PARTICIPANTS

Thirty healthy volunteers, 30 patients with suspected glaucoma, and 30 patients with glaucomatous visual field defects were tested.

METHOD

The VEP was recorded using cortically scaled, multifocal, pseudorandomly alternated pattern stimuli with the VERIS system (Electro-Diagnostic Imaging, Inc., San Francisco, CA). An array of four bipolar occipital electrodes provided four differently oriented channels for simultaneous recording. Signals were compared for different locations within the field up to 26 degrees of eccentricity. Healthy volunteers, patients with suspected glaucoma, and glaucoma patients with established visual field defects were tested, and results were compared with Humphrey visual fields (Humphrey Systems, Dublin, CA) performed on the same day. For reproducibility, five healthy volunteers were each tested on four separate days. The patients with suspected glaucoma and the established glaucoma patients were analyzed for intereye asymmetry of signals, and these data were compared with the asymmetry values of the healthy volunteers.

RESULTS

Multiple recording channels significantly enhanced the recording of signals from parts of the visual field not reliably sampled with a single channel technique in all healthy volunteers, particularly along the horizontal meridian (P: < 0.001). Signal amplitude did not decline with age in healthy volunteers. Recordings showed good reproducibility within individuals. In all 30 glaucoma patients, the Humphrey visual field defects were well demonstrated by the VEP, and topographic location was strongly correlated (r(s) = 0.79). Despite large interindividual variations in amplitude, scotomas were well demonstrated when compared with normal values. In the patients with suspected glaucoma, smaller changes in signal amplitude could be identified in parts of the field still normal on perimetry using intereye asymmetry analysis.

CONCLUSIONS

The multifocal, multichannel VEP can objectively detect glaucomatous visual field defects. The nasal step region can be more reliably tested using multiple channels. Asymmetry analysis has the potential to detect early defects. This technique represents a significant step toward the clinical application of objective perimetry in glaucoma.

Phasic Pupil Dilation Response to Noxious Stimulation

Abstract The pupil dilation response (PDR) to a painful stimulus is a subtle, event-related increase in pupil diameter that occurs following brief noxious stimulation. It varies in amplitude with increasing stimulus intensity. Two competing hypotheses for the PDR are that (1) it reflects event-related cognitive efforts largely independent of pain, such as the task demand of discriminating intensity and readying a subjective report; and (2) like the pupillary light reflex, it is a simple reflexive response. In this study 21 subjects (11 male, 10 female) experienced painful stimuli matched in subjective intensity at two sites: finger tip and ear lobe, but they produced no subjective reports. If the PDR is a product of discriminating stimulus intensity levels and forming a report, then it should be minimal or nonexistent when subjects have no choices and make no overt judgments. On the other hand, if it is primarily a simple sympathetic reflex, then onset and peak latency should be longer for finger tip than for ear lobe stimulation because the conduction distance is longer. In addition to addressing these issues, we explored sex differences and the influence of age. Clear and similar PDRs appeared in response to stimulation of both sites despite an absence of subjective report requirements. PDR onset, peak amplitude and peak latency did not differ significantly across stimulation sites. Therefore, the PDR is neither an artifact of subjective report nor an uncomplicated sympathetic reflex. It appears to be an emotional arousal response, such as the defense response, the strength of which depends upon the magnitude of the noxious sensory input. Sex differences emerged, with women demonstrating a borderline larger PDR peak amplitude than men (P = .059) and a more rapid half recovery latency (P = .031). Age did not affect the PDR except at onset, with older subjects demonstrating a later onset latency (P = .003). The PDR may reflect preconscious processing associated with attention and perhaps other cognitive aspects of perception.

Aging and dark adaptation

Older adults have serious difficulty seeing under low illumination and at night, even in the absence of ocular disease. Optical changes in the aged eye, such as pupillary miosis and increased lens density, cannot account for the severity of this problem, and little is known about its neural basis. Dark adaptation functions were measured on 94 adults ranging in age from the 20s to the 80s to assess the rate of rod-mediated sensitivity recovery after exposure to a 98% bleach. Fundus photography and a grading scale were used to characterize macular health in subjects over age 49 in order to control for macular disease. Thresholds for each subject were corrected for lens density based on individual estimates, and pupil diameter was controlled. Results indicated that during human aging there is a dramatic slowing in rod-mediated dark adaptation that can be attributed to delayed rhodopsin regeneration. During the second component of the rod-mediated phase of dark adaptation, the rate of sensitivity recovery decreased 0.02 log unit/min per decade, and the time constant of rhodopsin regeneration increased 8.4 s/decade. The amount of time to reach within 0.3 log units of baseline scotopic sensitivity increased 2.76 min/decade. These aging-related changes in rod-mediated dark adaptation may contribute to night vision problems commonly experienced by the elderly.

Invariance of the pattern electroretinogram evoked by psychophysically equivalent stimuli in human ageing

1. The aim of this study was to assess the contribution of retinal ganglion cells to the decline in contrast sensitivity during human ageing. 2. After determination of the appropriate refraction for each subject, younger subjects were arranged to be exposed to a display luminance which was suprathreshold by the same amount as in older subjects wearing a 4.0 mm diameter artificial pupil with a neutral density filter. 3. In fifty-four subjects, aged 20-99 years, contrast sensitivities measured in response to phase-reversed grating patterns of 2, 5 and 8 cycles per degree declined significantly with increasing age at each spatial frequency studied. 4. Subjects were made psychophysically equivalent by setting the display contrast at x5 and x10 contrast threshold for each subject. The pattern electroretinogram (PERG) was recorded with a sterile silver thread (DLT) electrode placed in the lower canthus of one eye, with the indifferent electrode on the temple and the earth on the forehead. 5. For each contrast multiple at each spatial frequency, the PERG implicit time showed no significant change with age, indicating equivalence of the response across the age range. 6. Control experiments with two young and two elderly subjects established that the PERG implicit time decreased appreciably with increasing contrast, over a range of x2 to x20 contrast threshold. 7. Since the psychophysically equivalent stimulus displays had generated equivalent PERGs in terms of implicit time in young and elderly subjects, this was consistent with the equivalence of retinal ganglion cell function under these conditions. 8. Adverse changes within the retina were therefore inferred to play a major role in the decline in contrast sensitivity with age.