Pattern-reversal Electroretinograms Research Articles

Peripapillary Retinal Nerve Fiber Layer Swelling Predicts Peripapillary Atrophy in a Primate Model of Nonarteritic Anterior Ischemic Optic Neuropathy.

PurposeTo determine the relationship between peripapillary retinal nerve fiber layer (PRNFL) swelling and eventual PRNFL atrophy, and between PRNFL swelling/atrophy and neural function, in a nonhuman primate model of nonarteritic anterior ischemic optic neuropathy (pNAION).MethodspNAION was induced in five normal, adult male rhesus monkeys by laser activation of intravenously injected rose bengal at the optic nerve head. Spectral-domain optical coherence tomography measurements of the PRNFL were performed at baseline; 1 day; 1, 2, and 4 weeks; and several later times over a period of an additional 2 to 3 months. Simultaneous pattern-reversal electroretinograms (PERGs) and visual evoked potentials (VEPs) were recorded and color fundus photographs taken at the same time points.ResultsIn all cases, initial PRNFL swelling was associated with atrophy, and the greater the initial swelling, the greater the degree of eventual atrophy (r = 0.65, P = 0.0002). The change in PRNFL thickness closely correlated with VEP amplitude loss (r = 0.90), although this relationship was only a strong trend (P = 0.083). Furthermore, VEP amplitude loss closely correlated with PERG N95 amplitude loss (r = 0.80, P = 0.00002)ConclusionsIn our model of human NAION, the degree of initial PRNFL swelling correlated with the severity of atrophy. Areas that did not swell developed little to no atrophy. The amount of PRNFL loss was reflected in VEP and PERG N95 amplitude reductions.

Simultaneous retinal and cortical visually evoked electrophysiological responses in between migraine attacks

People with migraine often report aversion to flickering lights and show abnormal results on behavioural tasks that require the processing of temporal visual information. Studies have reported that the cortically evoked electrophysiological response to a flickering visual stimulus is abnormal; however, none have considered whether there is an underlying pre-cortical abnormality. In this cross-sectional study, we consider whether people with migraine have retinal and cortical electrophysiological abnormalities to flickering stimuli. Monocular transient (1 Hz) and steady-state (8.3 Hz) pattern reversal electroretinograms (PERGs) and pattern visual evoked responses (PVERs) were measured simultaneously in 45 people with migraine (26 without aura, 19 with aura) and 30 non-headache controls at a time between migraine attacks. PERG amplitude and timing did not differ significantly between groups. Transient PVER amplitude was significantly reduced (28%) in the migraine with aura group compared to the controls F(2,72) = 3.6, p = 0.03). Both migraine groups showed significant reductions (32%, 39%) in steady-state PVER amplitude relative to controls (F(2,70) = 4.3, p = 0.02). This study finds normal retinal processing of flickering stimuli in the presence of abnormal cortical function between migraine attacks.

Experimentally Reduced Perfusion of One Eye Impairs Retinal Function in Both Eyes

The oscillatory potential index of scotopic white flash electroretinograms is reversibly enhanced in the contralateral eye when the ocular perfusion pressure (OPP) to the test eye is transiently reduced. A transient increase in the intraocular pressure (IOP) and decrease in the OPP in the test eye induced quantifiable vascular changes in the optic nerve head of the contralateral eye. We explored this contralateral phenomenon looking at ganglion cell function in both eyes during elevated IOP and decreased OPP in the test eye only. Our specific objective was to characterize the effects that transient hypoperfusion had on the neural generators of the pattern-reversal electroretinograms (pERGs), the ganglion cells, and preganglion neurons. A transient elevation in the IOP was sustained in 10 healthy subjects by scleral suction to reduce the baseline OPP by 15, 30, 45, and 60% for 2-min intervals. For each level of OPP, pERGs were evoked by a checkerboard with 75 minarc high-contrast black-white checks reversing at 5 Hz and recorded bilaterally using DTL fiber electrodes. The pERGs were also recorded immediately after removal of scleral suction and at 2-min intervals thereafter for an 8-min recovery interval. The unilateral decrease in OPP differentially reduced the pERG in the test and contralateral eyes. The pERG for the test eye returned to baseline amplitude within 2 min of removing the suction cup. In contrast, the pERG in the contralateral eye remained below baseline throughout the entire 8-min recovery interval. The observation of a bilateral decrease in the pERGs while the OPP was decreased in the test eye only suggested that these neuronal changes were modified at more central visual centers for retinal function to be compromised bilaterally. This latter effect may have been mediated by the transiently altered OPP or yet unknown neurohormonal mechanisms.

Visual Retinocortical Function in Dementia of the Alzheimer Type

Background: Some histological investigations have reported anomalies in the primary visual pathways of individuals with dementia of the Alzheimer type (DAT), while others have suggested that these visual structures are spared by the disease process. Objectives: This study was conducted to address this issue of substantial controversy. We determined in vivo whether DAT alters the functioning of the primary visual pathways by evaluating pattern-reversal electroretinograms (ERGs) and cortical visual evoked potentials (VEPs). Methods: Twenty-seven individuals with mild to moderate DAT and 27 age- and sex-matched control subjects were included in the investigation. ERG and VEP recordings were obtained from all participants with the use of a clinical electrodiagnostic system. Stimulus conditions were biased towards a preferential response from the magnocellular and parvocellular subdivisions of the visual system. Results: Amplitude and latency of the ERG were not affected by DAT. The VEP amplitude was not attenuated in DAT individuals, but there was a delay in the latency of the VEPs arising from both magnocellular and parvocellular streams of visual processing. Conclusion: Our results indicate that while the inner retina appears to be spared by the disease process, the visual function is altered upstream in the retinocortical visual pathways of individuals with DAT.

Pattern Electroretinogram Elicited by a Dartboard Pattern

The receptive field size of retinal ganglion cells is closely related to their eccentricity from the fovea. To elicit larger pattern-reversal electroretinograms (P-ERGs), it may be useful to stimulate the retina with patterns having elements that parallel this change in receptive field size. We describe a dartboard pattern consisting of reversal elements that enlarge gradually from the central to the peripheral stimulus field. The utility of the dartboard pattern for eliciting P-ERG was investigated by comparing it with the conventional uniform checkerboard pattern, but with the other stimulus parameters remaining unchanged (96% contrast, 35.9 cd/m² mean luminance, 3.3 rev/s temporal frequency, 15° circular field). The dartboard pattern produced a significantly larger P50 amplitude than did the checkerboard pattern, while no difference in peak latency was found when 54 min of arc was used as a standard check size for the checkerboard pattern. The dartboard pattern for eliciting P-ERG should prove clinically useful.

Simultane Ableitung von VECP und Muster-ERG bei künstlicher Erhöhung des Augeninnendrucks

The visual evoked cortical potentials (VECP) are changed by the artificial increase in intraocular pressure (IOP). The exact location of the damage is still unclear. One possibility is that the increased ocular pressure reduces the blood flow in the optic nerve head. The function of the optic nerve fiber function would be decreased by this effect. Another possibility is that the generation of the signals in the retinal ganglion cells could be influenced by the artificial pressure enhancement. We developed a method of simultaneous recording pattern reversal electroretinograms (PERG) and VECP during artificially raised IOP. The PERG was recorded by cutaneous electrodes (Grass, USA; diameter 5 mm), which were positioned close to the lid margins. The pattern reversal rate was 7.9 reversals/s. In a pilot study, we examined 10 healthy volunteers with artificially increased ocular pressure. In 9 cases, amplitudes showed a more stable behavior in the VECP than in the PERG: the mathematical behavior of the amplitude/pressure curves was more stable in the VECP of 6 volunteers and once in the PERG. Signs of very sufficient autoregulation could be found in the VECP of 7 volunteers and once in the PERG. The critical pressure, at which a further increase in IOP causes a continuous amplitude decrease to the noise level, was 9 times more stable in VECP (median 53 mmHg) than in PERG (median 48 mmHg). The results lead to the conclusion that in healthy persons the artificial pressure rise influences the ganglion cells at an earlier timepoint than the signal transmission in the axons.

The pattern electroretinogram in response to colour contrast in man and monkey

Steady-state pattern-reversal electroretinograms (PERG) were recorded from both monkeys and humans in response to tartan patterns modulated in both space and time in either luminance contrast or chromatic contrast. In both species, all types of patterns cause a strong modulation of the second-harmonic of the PERG. There was no measurable dependency of the PERG on the colour of the stimulus per se: both in humans and monkeys, stimuli with green-black, red-black or yellow-black modulation of the same mean luminance and of the same contrast, produced identical results. However, chromatic stimuli with modulation between equiluminant red and green produced a qualitatively different PERG: the amplitude was lower, particularly at high temporal frequencies, and there was a clear phase lag corresponding to a difference in processing time of about 20 ms.

A novel noninvasive videographic method for quantifying changes in the chromaticity of the optic nerve head with changes in the intraocular pressure, pulsatile choroidal blood flow and visual neural function in humans

Vision loss in glaucoma may be due to the compressive effects of the intraocular pressure (IOP) on the ganglion cell axons, impaired blood flow to the optic nerve, or some combination of these two factors. While reducing the IOP may preserve vision in patients with elevated IOP, not all patients experience longterm benefits from this therapeutic approach. The survival of ganglion cells may be more dependent upon the degree of vascular perfusion of the optic nerve head (ONH). In this report we present some preliminary data on a new noninvasive videographic technique for elaborating the capacity of the ONH vasculature to maintain perfusion constancy in the presence of transient elevations of the IOP and reductions of the ocular perfusion pressure (OPP). Shortterm, stepwise reductions of the OPP in the test eye of visually normal subjects (n = 5) systematically altered both the chromaticity (hue, saturation, brightness) of the ONH and the pulsatile ocular blood flow (POBF) in the choroid. Similar transient reductions in the OPP were seen to impair normal retinal physiology, as indicated by a significant attenuation of the bilateral pattern-reversal electroretinograms (pERGs) in visually normal subjects (n = 7). This technique was also used to reveal spontaneous rhythmical variations in the ONH chromaticity which were linked to the cardiac pulse rate. This so-called “chromatic pulse” of the ONH offers potential as a useful clinical index for evaluating the vascular perfusion of the ONH. The diagnostic and prognostic potential of dynamic digital imaging for the detection of abnormal hemodynamics in the ONH is discussed.

Pattern-reversal Electroretinographic Follow-up of Laser Photocoagulation for Subfoveal Neovascular Lesions in Age-related Macular Degeneration

Pattern-reversal electroretinograms were used as an objective measure of macular integrity in a subset of 42 patients who were randomly assigned at enrollment in the Macular Photocoagulation Study to receive laser photocoagulation or no treatment for a subfoveal neovascular lesion. Pattern-reversal electroretinograms were obtained before randomization, three months and six months after randomization, and at six-month intervals randomization, and at six-month intervals thereafter. Responses were obtained to phase-alternating checkerboards of varying check size. Extrapolation of the best-fit regression line relating log-check size to amplitude was used to determine retinal acuity. At each follow-up period, including three months after laser photocoagulation, treated eyes showed less loss in pattern-reversal electroretinographic acuity than untreated eyes. The decline in pattern-reversal electroretinographic acuity in untreated eyes corresponded to the rapid growth in the area of the subfoveal neovascular lesion. The more gradual decline in treated eyes was consistent with an increase in the area of the treatment scar caused by spreading atrophy.

Effect of Hemifield Stimulation on Simultaneous Steady-State Pattern Reversal Electroretinogram and Visual Evoked Response

Steady-state pattern reversal electroretinograms (PERG) and pattern reversal visual evoked responses (PVER) were recorded simultaneously in 4 normal subjects using hemifield stimulation of the upper/lower and nasal/temporal conditions with 95 and 60% stimulus contrasts. A square-wave checker-board pattern (check size 40 min of arc) was used. The temporal frequency (reversal rate) was 6 Hz (12 reversals/s). With nasal/temporal hemifield stimulation, neither the PERG nor the PVER amplitudes differed significantly with either stimulus contrast. With the upper/lower hemifield stimulation, PERG amplitudes were not significantly different; PVER showed a significantly larger amplitude for lower than for upper hemifield stimulation with both contrasts (ANOVA test: p = 0.0064, 95% contrast; p = 0.0018, 60% contrast). PVER amplitudes recorded with lower hemifield stimulation were 2.05 and 2.63 times larger than those elicited with upper hemifield stimulation, for the 95 and 60% contrasts, respectively. The difference in response to the upper/lower hemifield stimulation, observed only in PVER, suggests that the lower stimulus field dominancy may be processed in a visual pathway proximal to the retinal level.

Evaluation of electrofunctional data following argon-laser trabeculoplasty in primary open-angle glaucoma

To establish whether or not glaucomatous damage is reversible, we obtained pattern-reversal electroretinograms (PERGs) and visual evoked potentials (VEPs) in 25 eyes of 25 patients suffering from bilateral primary open-angle glaucoma (POAG) before and after argon-laser trabeculoplasty. The laser treatment was carried out in only one eye chosen at random, and the fellow eye was used as a control. In the present study we intended to verify the possibility of using electrofunctional techniques to determine the two distinct and, probably, consecutive glaucomatous alterations occurring in ganglion cells: functional (reversible) and anatomical (irreversible). The results obtained indicate that glaucomatous damage is irreversible. We propose that such alterations differ very slightly and that the current electrofunctional techniques may not be sufficiently sophisticated to distinguish between them.

Pattern electroretinogram and chronic ocular hypertension

Pattern-reversal electroretinograms to sinusoidal gratings of variable spatial frequency (0.6–4.8 cycles/degree) have been recorded in 28 normal subjects and 23 patients with ocular hypertension or early glaucoma who were previously treated with timolol maleate during a 12–24 months clinical follow-up. A multivariate analysis of variance showed that pattern electroetinogram amplitude was significantly reduced in patients as compared to control. This reduction was evident only in the low-medium spatial frequency range and was more marked (and progressive) in eyes with abnormal intraocular pressure (22–30 mmHg) as compared to eyes with normal intraocular pressure (14–21 mmHg) during the follow-up period. These results suggest that the pattern electroretinogram may detect the progression of neurosensory deficits associated with ocular hypertension in eyes with inadequate response to medical treatment.

The effects of age on steady-state pattern electroretinograms and visual evoked potentials

Steady-state pattern-reversal electroretinograms and visual evoked potentials were simultaneously recorded in two groups of young and elderly normal volunteers. The young group consisted of 23 subjects (13 women and 10 men) aged 18 to 28 years, and the elderly group consisted of 24 subjects (11 women and 13 men) aged 58 to 77 years. Stimuli were square-wave gratings ranging in spatial frequency from 0.5 to 6 c/deg and phase reversed at a frequency of 4 Hz. Pattern-reversal electroretinograms and visual evoked potentials consisted of a prominent second and a smaller fourth harmonic response. Spatial frequency-amplitude functions of the pattern-reversal electroretinogram second and fourth harmonics were similar for the young and elderly groups. The mean fourth harmonic phase was significantly shifted in elderly subjects compared with young subjects for all spatial frequencies tested. Spatial frequency tuning was observed for amplitude and phase functions of the visual evoked potential second and fourth harmonic responses for both age groups. Age had a significant effect on phase for spatial frequencies above 1.5 c/deg. Amplitude of the fourth harmonic was significantly lower for the elderly group at 1.5-4 c/deg. Phase was significantly different between groups for spatial frequencies below 3 c/deg. Our results suggest that aging influences both retinal and central visual pathways. Aging differentially affected the visual evoked potential second and fourth harmonic responses, suggesting different neuronal origins for these components.

The influence of age on the pattern‐reversal electroretinogram

Pattern reversal electroretinograms (PERGs) in response to 30' checks and 6 degree checks were recorded from 60 eyes of 30 normal healthy individuals aged between 20 and 78 years. Results were assessed to show age changes in the amplitudes and latencies of the PERGs, the ratio of 30' to 6 degree PERG amplitude, the 'N95/P50' ratio and the inter-eye ratio of the 30' PERG. The positive component of the PERG decreases in amplitude and increases in latency with increasing age. In addition, it was found that the 30' PERG/6 degree PERG ratio decreases, the N95/P50 ratio increases and the inter-eye ratio shows a greater difference between the two eyes in the older subjects.

Abnormal pattern electroretinogram in Alzheimer's disease: evidence for retinal ganglion cell degeneration?

We recorded pattern-reversal electroretinograms, flash electroretinograms, pattern-reversal visual evoked potentials, and flash visual evoked potentials in 6 patients with clinically diagnosed Alzheimer's disease and 6 age- and sex-matched control subjects. The mean amplitude of the pattern-reversal electroretinogram in the Alzheimer patients was significantly less than that of the control group (p = 0.004). This anomaly of the pattern-reversal electroretinogram may be a reflection of documented axonal depletion within the optic nerve and the degeneration of retinal ganglion cells seen in Alzheimer's disease. We found Alzheimer patients to have normal pattern-reversal visual evoked potentials and flash electroretinograms, but a delayed second positive component of the flash visual evoked potential. This combination of findings may be of diagnostic import in Alzheimer's disease.

Retinocortical conduction time in diabetics with abnormal pattern reversal electroretinograms and visual evoked potentials

Clinically evident retinal vascular disease in patients with diabetes mellitus may be preceded by an increase in visual evoked potential latency in electrophysiologic testing. This increase may indicate either retinal or optic nerve dysfunction. To determine the origin of the latency increase we initiated a cross-sectional study of simultaneous pattern-reversal electroretinograms and visual evoked potentials. We recorded transient (3.8 reversals/second) pattern electroretinograms and visual evoked potentials using both 15' and 60' high-contrast black-white checks. Fifty-five diabetic patients (34 with no retinopathy and 21 with background retinopathy) and 34 age-matched visual normals (controls) were tested. Group data in diabetics showed significant latency increases in both tests, but not significant differences in retinocortical conduction time were noted. These results suggest that the increases in visual evoked potential latency exhibited by diabetic patients with little or no retinopathy usually reflect altered retinal function rather than optic neuropathy. Two patients with background retinopathy exhibited retinocortical conduction times that exceeded the normal mean by more than two standard deviations, suggesting that optic neuropathy may occasionally occur in diabetic patients with background retinopathy.

Optic nerve involvement in patients with orbital phlebopathy: Pattern-reversal electroretinograms and visual evoked cortical potentials

Pattern-reversal electroretinograms (PERG) and visual evoked cortical potentials (VECP) were recorded from 24 patients with orbital phlebopathy, i.e., characteristic orbital pain and orbital phlebography changes, also occurring in painful ophthalmoplegia (Tolosa-Hunt syndrome). Twelve patients had no visual impairment and 12 had clinical signs of optic nerve involvement.Only two of the patients with optic nerve involvement had the marked VECP latency prolongation, typically seen in multiple sclerosis, on the orbital pain side. The mean amplitudes of the pattern-reversal ERG and VECP from the eyes on the orbital pain side were significantly reduced, when compared to the reference group. The mean VECP latency from these eyes was not significantly increased. These findings indicate that the optic neuropathy in orbital phlebopathy is characterized by axonal dysfunction rather than demyelination like in multiple sclerosis.

Pattern-reversal Electroretinograms and High-pass Resolution Perimetry in Suspected or Early Glaucoma

Twenty-one patients, age 28 to 78 years, with elevated intraocular pressure (IOP) in one or both eyes, were examined with pattern-reversal electroretinograms (PERG), high-pass resolution perimetry (HRP), and conventional computer-assisted perimetry (CAP). Among the 42 eyes, 33 were hypertensive (IOP ≥22 mmHg) and nine were normotensive (IOP ≤20 mmHg). The optic disc was judged abnormal in 14 of the hypertensive and one of the normotensive eyes. Fourteen abnormal PERGs and 19 abnormal HRPs were observed in the 33 hypertensive eyes. Conventional CAP gave abnormal results in three of the hypertensive eyes. Seven of the nine normotensive eyes were normal in all examinations. HRP was abnormal in one of the normotensive eyes and conventional CAP was abnormal in another. Thus, PERG and HRP showed a high incidence of optic nerve dysfunction in suspected or early glaucoma. These new methods should be clinically useful for diagnosis and management of conditions with increased IOP.

Pattern-reversal electroretinograms from normotensive, hypertensive and glaucomatous eyes.

Pattern-reversal electroretinograms (PERG) were recorded from 67 subjects, age 55-77 years, with normotensive (n = 19), hypertensive (n = 37) or glaucomatous (n = 11) eyes. The pathological intraocular pressure (IOP) ranged from 23 to 29 mm Hg in 21 eyes and from 30 to 43 mm Hg in 16 eyes. In 11 eyes (11 patients) manifest glaucoma was present (excavated optic disk, visual field defect). All examined subjects had normal visual acuity and clear optic media. The amplitude of the positive component of the PERG was measured. The mean PERG amplitude was 2.8 +/- 1.2 microV in the eyes with normal IOP (19 +/- 3 mm Hg), 2.2 +/- 1.0 microV in the eyes with moderately elevated IOP (26 +/- 2 mm Hg), 2.0 +/- 0.9 microV in the eyes with IOP above 30 mm Hg (33 +/- 4 mm Hg) and 1.1 +/- 0.6 microV in the glaucomatous eyes. Regression lines of PERG amplitudes versus age were calculated in all groups and showed a decrease in amplitude with increasing age. However, the correlation coefficients were not statistically significant. The decline with age was similar in all groups. The results indicate that the PERG amplitude is reduced in glaucomatous eyes and may be reduced also in ocular hypertension as well as with increasing age.

Pattern-reversal electroretinograms in ocular hypertension.

Pattern-reversal electroretinograms (ERGs) were recorded from seven patients, aged 50 to 69 years, with clinical diagnosis of unilateral ocular hypertension. In four of the seven patients the pattern ERG amplitude from the hypertensive eye was reduced below the normal level of variability, when compared with the amplitude from the opposite normotensive eye (ratio less than 0.8). In three of these four cases excavation of the optic disk in the hypertensive eye was observed 6 to 15 months after the recording of reduced pattern ERG. The finding suggests that pattern ERG may be an useful objective method for early detection of functional damage in eyes with increased intraocular pressure.