Electroretinogram Implicit Time Research Articles

INVESTIGATING DIAGNOSTIC BIOMARKERS OF COGNITIVE IMPAIRMENT BY UTILIZING VASCULAR AND NEUROGENIC CHANGES IN THE RETINA

Previous studies have demonstrated that Alzheimer's disease (AD) it is not limited to the brain but also affects the retina. We investigated the correlation between the retinal vascular complexity and neurodegenerative changes in patients with mild cognitive impairment (MCI). Quantification of the retinal structure and function using advanced retinal imaging and full-field electroretinogram (ERG) was performed. Also, visual performance exams were conducted using the Rabin cone contrast test (CCT). Retinal images and ERGs from each subject were obtained. Retinal vascular parameters were calculated using the Singapore Institute Vessel Assessment (SIVA) software which was also used to calculate the fractal dimension (FD) of the retinal vasculature network and retinal vascular caliber, summarized as central retinal artery equivalent (CRAE) and central retinal vein equivalent (CRVE). The Montreal Cognitive Assessment (MoCA) was used to assess cognitive dysfunction. Spearman's linear correlation was performed between variables, the level of significance was set at 5%. For the analysis, Statistics 7.0 software was used (Statsoft Inc., Tulsa, OK). Of the 55 participants, 21 had cognitive impairment (38%), 34 served as healthy controls. We found that the complexity of the branching pattern and caliber of retinal vessels were lower in patients with MCI (FD (mean±SE): 1.310±0.020; CRVE (92.65±1.60; age range [76-86]) in comparison to healthy controls (FD: 1.382±0.002; CRVE: 202.15±0.76; age range [76-86]). Also, drusen and retinal pigment mottling were noted in some elderly MCI subjects. For all full-field ERG measurements, smaller amplitudes and larger peak times were observed in the MCI subjects. The visual performance test with the computerized Rabin CCT revealed functional loss in color vision. Interestingly, FD significantly correlated with CRVE (p=0.0212, r=-0.4628) and with the ERG's implicit time (p=0.0240, r=0.4910) in MCI individuals. To our knowledge, this is the first study to examine the association between FD and full field ERG implicit time in patients with MCI. Our preliminary findings also show that our approach to evaluating visual capacities in elderly individuals may add predictive value of early visual pathway injury associated with MCI and facilitate the introduction of a novel multimodal eye biomarker for the early detection of AD.

Impact of Choriocapillaris Flow on Multifocal Electroretinography in Intermediate Age-Related Macular Degeneration Eyes.

To investigate the relationship between perfusion of the choriocapillaris (CC) and macular function in eyes with intermediate age-related macular degeneration. In this prospective, observational, cross-sectional study, macular optical coherence tomography angiography images and multifocal electroretinograms were obtained in 20 eyes with intermediate age-related macular degeneration from 20 patients. The main outcome measures were (1) the percent nonperfused choriocapillaris area (PNPCA), which represents a measure of the total area of CC vascular dropout, and (2) the average size of the CC signal voids, which represent contiguous regions of CC dropout. Furthermore, amplitude and implicit time of multifocal electroretinograms N1 and P1 waves in the two central rings (R1 and R2) were included in the analysis. Of the 20 patients enrolled, only 17 eyes from 17 patients (13 women) were included in this analysis. Three patients were excluded because of poor scan quality. Mean ± SD age was 75.1 ± 7.9 years (range, 62-89 years). The best corrected visual acuity was 0.17 ± 0.13 logarithm of the minimum angle of resolution. In univariate analysis, both the PNPCA and average signal void size were found to have a significant direct relationship with N1 implicit time in the R2 ring (P = 0.006 and P = 0.035, respectively). Neither PNPCA nor the average signal void size was associated with P1 or N1 implicit times in R1. In intermediate age-related macular degeneration eyes, PNPCA and average signal void size are related to N1 multifocal electroretinogram implicit times, which suggests an association between CC perfusion and photoreceptor function.

Normal clinical electroretinography parameters for poodle, Labrador retriever, Thai ridgeback, and Thai Bangkaew.

The purpose of the present study was to establish normal electroretinogram (ERG) parameters using 56 normal eyes of four dog breeds common in Thailand: poodle, Labrador retriever, Thai ridgeback, and Thai Bangkaew. Standard ERG findings were bilaterally recorded using a handheld multi-species ERG unit with an ERG-jet lens electrode for 28 dogs under preanesthesia with diazepam, anesthesia with propofol, and anesthesia maintenance with isoflurane. There were significant differences in the mean values of ERG amplitudes and implicit times among the four dog breeds (p < 0.05) except for the b-wave implicit time of the photopic 30 Hz flicker response with 3 cd.s/m2 (p = 0.610). Out of the four breeds, Thai Bangkaew had the longest implicit time (p < 0.001) of scotopic low intensity responses, b-wave of scotopic standard intensity responses (3 cd.s/m2), a-wave of the higher intensity response (10 cd.s/m2), and a-wave of the photopic single flash response (3 cd.s/m2). For the b/a ratio, only the ratio of the Cone response was significantly different among the different breeds. In this summary, normal ERG parameters for four dog breeds were reported. Data from the investigation supported the hypothesis that determination of breed-specific limits of normality for ERG responses is necessary for individual clinics and laboratories.

Differences in neuroretinal function between adult males and females.

To determine whether neuroretinal function differs in healthy adult males and females younger and older than 50 years. This study included one eye from each of 50 normal subjects (29 females and 21 males). Neuroretinal function was assessed using first-order P1 implicit times (ITs) and N1-P1 amplitudes (AMPs) obtained from photopic multifocal electroretinograms. To assess local differences, retinal maps of local IT and (separately) AMP averages were constructed for each subject group. To examine global differences, each subject's 103 ITs and (separately) AMPs were also averaged to create whole-eye averages. Subsequently, retinal maps and whole-eye averages of one subject group were compared with those of another. In subjects younger than 50 years, neuroretinal function differed significantly between the males and females: local ITs were significantly shorter at 83 of 103 tested retinal locations, and whole-eye IT averages were shorter (p = 0.015) in the males compared with the females. In contrast, no analysis indicated that the males and females older than 50 years were significantly different. A subanalysis showed that the females who reported a hysterectomy (n = 5) had the longest whole-eye ITs of all subject groups (p ≤ 0.0013). In the females who did not report a hysterectomy, neuroretinal function was worse in the females older than 50 years compared with the females younger than 50 years: local ITs were significantly longer at 62 of 103 retinal locations tested, and whole-eye IT averages tended to be greater (p = 0.04). Conversely, ITs were not statistically different between the younger and older males. N1-P1 amplitudes did not differ between the sexes. Multifocal electroretinogram IT differs between males and females, depending on the age group and hysterectomy status.

Severity of middle cerebral artery occlusion determines retinal deficits in rats

Middle cerebral artery occlusion (MCAO) using the intraluminal suture technique is a common model used to study cerebral ischemia in rodents. Due to the proximity of the ophthalmic artery to the middle cerebral artery, MCAO blocks both arteries, causing both cerebral ischemia and retinal ischemia. While previous studies have shown retinal dysfunction at 48h post-MCAO, we investigated whether these retinal function deficits persist until 9days and whether they correlate with central neurological deficits.Rats received 90min of transient MCAO followed by electroretinography at 2 and 9days to assess retinal function. Retinal damage was assessed with cresyl violet staining, immunohistochemistry for glial fibrillary acidic protein (GFAP) and glutamine synthetase, and TUNEL staining.Rats showed behavioral deficits as assessed with neuroscore that correlated with cerebral infarct size and retinal function at 2days. Two days after surgery, rats with moderate MCAO (neuroscore <5) exhibited delays in electroretinogram implicit time, while rats with severe MCAO (neuroscore ≥5) exhibited reductions in amplitude. Glutamine synthetase was upregulated in Müller cells 3days after MCAO in both severe and moderate animals; however, retinal ganglion cell death was only observed in MCAO retinas from severe animals. By 9days after MCAO, both glutamine synthetase labeling and electroretinograms had returned to normal levels in moderate animals.Early retinal function deficits correlated with behavioral deficits. However, retinal function decreases were transient, and selective retinal cell loss was observed only with severe ischemia, suggesting that the retina is less susceptible to MCAO than the brain. Temporary retinal deficits caused by MCAO are likely due to ischemia-induced increases in extracellular glutamate that impair signal conduction, but resolve by 9days after MCAO.

Ocular and systemic toxicity of intravitreal topotecan in rabbits for potential treatment of retinoblastoma

Treatment of intraocular retinoblastoma with vitreous seeding is a challenge. Different routes of chemotherapy administration have been explored in order to attaining pharmacological concentrations into the posterior chamber. Intravitreal drug injection is a promissing route for maximum bioavailability to the vitreous but it requires a well defined dose for achieving tumor control while limited toxicity to the retina. Topotecan proved to be a promising agent for retinoblastoma treatment due to its pharmacological activity and limited toxicity. High and prolonged concentrations were achieved in the rabbit vitreous after 5 μg of intravitreal topotecan. However, whether a lower dose could achieve potentially therapeutic levels remained to be determined. Thus, we here study the pharmacokinetics of topotecan after 0.5 μg and the toxicity profile of intravitreal topotecan in the rabbit eye as a potential treatment of retinoblastoma. A cohort of rabbits was used to study topotecan disposition in the vitreous after a single dose of 0.5 μg of intravitreal topotecan. In addition, an independent cohort of non-tumor bearing rabbits was employed to evaluate the clinical and retinal toxicity after four weekly injections of two different doses of intravitreal topotecan (Group A, 5 μg/dose; Group B, 0.5 μg/dose) to the right eye of each animal. The same volume (0.1 ml) of normal saline was administered to the left eye as control. A third group of rabbits (Group C) served as double control (both eyes injected with normal saline). Animals were weekly evaluated for clinical and hematologic values and ocular evaluations were performed with an inverse ophthalmoscope to establish potential topotecan toxicity. Weekly controls included topotecan quantitation in plasma of all rabbits. Electroretinograms (ERGs) were recorded before and after topotecan doses. One week after the last injection, topotecan concentrations were measured in vitreous of all eyes and samples for retinal histology were obtained. Our results indicate that topotecan shows non linear pharmacokinetics after a single intravitreal dose in the range of 0.5–5 μg in the rabbit. Vitreous concentration of lactone topotecan was close to the concentration assumed to be therapeutically active after 5 h of 0.5 μg intravitreal administration. Eyes injected with four weekly doses of topotecan (0.5 or 5 μg/dose) showed no significant differences in their ERG wave amplitudes and implicit times in comparison with control (p > 0.05). Animals showed no weight, hair loss or significant changes in hematologic values during the study period. There were no significant histologic damage of the retinas exposed to topotecan treatments. After intravitreal administration no topotecan could be detected in plasma during the follow-up period nor in the vitreous of treated and control animals after 1 week of the last injection. The present data shows that four weekly intravitreal injection of 5 μg of topotecan is safe for the rabbit eye. Despite multiple injections of 0.5 μg of topotecan are also safe to the rabbit eye, lactone topotecan vitreous concentrations were potentially active only after 5 h of the administration. We postulate promising translation to clinics for retinoblastoma treatment.

EARLY NEURAL AND VASCULAR CHANGES IN THE ADOLESCENT TYPE 1 AND TYPE 2 DIABETIC RETINA

This cross-sectional study examines the existence and frequency of functional and structural abnormalities in the adolescent Type 1 diabetic retina. We also compare the results with those of adolescents with Type 2 diabetes. Thirty-two adolescents with Type 1 diabetes (5.7 ± 3.6 years; mean duration ± SD), 15 with Type 2 diabetes (2.1 ± 1.3 years), and 26 age-matched control subjects were examined. Multifocal electroretinogram responses from 103 retinal regions were recorded. Optical coherence tomography was used to measure retinal thickness. Vascular diameter around the optic nerve was also assessed. Nine of the 32 (28%) adolescents with Type 1 diabetes and 6 of the 15 (40%) with Type 2 diabetes had significant multifocal electroretinogram implicit time delays compared with 2 of the 26 controls (8%). Retinal thicknesses in both patient groups were significantly (P ≤ 0.01) thinner than controls. The Type 2 group also showed significant (P ≤ 0.03) retinal venular dilation (235.8 ± 5.9 μm) compared with controls (219.6 ± 4.0 μm). The present study illustrates that subtle but significant functional and structural changes occur very early in Type 1 diabetes. Adolescents with Type 2 diabetes appear to be more affected than those with Type 1 diabetes. Further longitudinal examination of the etiology and progression of these abnormalities is warranted.

Disease Course of Patients with Unilateral Pigmentary Retinopathy

To evaluate the change in ocular function by eye in patients with unilateral pigmentary retinopathy. Longitudinal regression was used to estimate mean exponential rates of change in Goldmann visual field area (V4e white test light) and in full-field electroretinogram (ERG) amplitudes to 0.5- and 30-Hz white flashes in 15 patients with unilateral pigmentary retinopathy. Snellen visual acuity was assessed case by case. Mean annual rates of change for the affected eyes were -4.9% for visual field area, -4.7% for ERG amplitude to 0.5-Hz flashes, and -4.6% for ERG amplitude to 30-Hz flashes. All three rates were faster than the corresponding age-related rates of change for the fellow normal eyes (P = 0.0006, P = 0.003, P = 0.03, respectively). An initial cone ERG implicit time to 30-Hz flashes in affected eyes ≥ 40 ms predicted a faster mean rate of decline of visual field area and of ERG amplitude to 0.5- and 30-Hz flashes (P < 0.0001 for all three measures). The visual acuity of affected eyes was more likely to decrease in patients presenting at >35 years of age than in patients presenting at a younger age (P = 0.0004). The affected eye in unilateral pigmentary retinopathy shows a progressive loss of peripheral retinal function that cannot be attributed to aging alone and that is faster in eyes with a more prolonged initial cone ERG implicit time. Patients presenting at >35 years of age are at greater risk for losing visual acuity.

Light-adapted electroretinograms in optic nerve hypoplasia

The purpose of the study is to characterise retinal function using light-adapted electroretinograms (ERGs) in a series of young children with ONH, congenital dysplasia of retinal ganglion cells. ERGs were recorded with chloral hydrate sedation in 27 children with ONH (18 with bilateral and 9 with unilateral ONH, age 4-35 months) and an adult reference population (n = 12). Stimuli included ISCEV standard flash, oscillatory potentials (OPs) and standard flicker as well as a light-adapted luminance-response series (photopic hill). The disc diameter to disc macula (DD:DM) ratio was measured from fundus photographs. The results are eyes with ONH, classified by DD:DM, were severe (<or=0.15, n = 22), moderate (0.16-0.30, n = 22), mild (0.31-0.35, n = 1), and fellow eyes (>0.35, n = 9), all had prolonged ERG implicit times and smaller i-waves than those of adults. Eyes with moderate or severe ONH also had smaller amplitudes for OPs and flicker ERGs and required stronger flashes to obtain the peak b-wave amplitude. Abnormalities of the photopic hill were a common but inconsistent feature of ONH and were not indicative of ONH severity. Abnormalities of the photopic hill of the ERG suggest that some cases of ONH may have retinal dysfunction with specific deficits in the ON or OFF pathways of the retina. ONH is a complex and heterogeneous condition that may involve dysfunction distal to the retinal ganglion cells.

ERGs in children with pancreatic enzyme insufficient and pancreatic enzyme sufficient cystic fibrosis

We recorded scotopic and photopic flash electroretinograms (ERGs) in pediatric subjects with cystic fibrosis, aged 4 to 18 years, who were either pancreatic insufficient (PI) or pancreatic sufficient (PS). The aim of the study was to determine whether vitamin supplementation in the PI group allowed comparable retinal function in these two groups. ERGs were recorded from a mixed-gender group of 41 children and adolescents (4 to 17 years of age) with cystic fibrosis. The subjects were grouped according to pancreatic function into PI (n = 29) and PS (n = 12). Full-field flash ERGs were recorded from one eye using a DTL fiber. The pupil was dilated prior to recording using two drops of 0.5% tropicamide. ISCEV photopic and scotopic stimuli and recording conditions were used. Serum levels of vitamin A, beta carotene and retinol binding protein (RBP) were measured on the day of ERG recording. There was no significant difference in ERG amplitudes or implicit times between PI and PS groups. Vitamin A, beta carotene, and RBP levels were not significantly different across the two groups and were not correlated with implicit times or amplitudes of any of the ERG types recorded here. Similarity of ERGs across the PI and PS cystic fibrosis patient populations tested here suggests that the supplementation protocol applied to these populations allows similar levels of retinal function (as indicated by flash ERG parameters) in the two groups.

Visual function and dysfunction in early and late age-related maculopathy

Late age-related maculopathy (ARM) is responsible for the majority of blind registrations in the Western world among persons over 50 years of age. It has devastating effects on quality of life and independence and is becoming a major public health concern. Current treatment options are limited and most aim to slow progression rather than restore vision; therefore, early detection to identify those patients most suitable for these interventions is essential. In this work, we review the literature encompassing the investigation of visual function in ARM in order to highlight those visual function parameters which are affected very early in the disease process. We pay particular attention to measures of acuity, contrast sensitivity (CS), cone function, electrophysiology, visual adaptation, central visual field sensitivity and metamorphopsia. We also consider the impact of bilateral late ARM on visual function as well as the relationship between measures of vision function and self-reported visual functioning. Much interest has centred on the identification of functional changes which may predict progression to neovascular disease; therefore, we outline the longitudinal studies, which to date have reported dark-adaptation time, short-wavelength cone sensitivity, colour-match area effect, dark-adapted foveal sensitivity, foveal flicker sensitivity, slow recovery from glare and slower foveal electroretinogram implicit time as functional risk factors for the development of neovascular disease. Despite progress in this area, we emphasise the need for longitudinal studies designed in light of developments in disease classification and retinal imaging, which would ensure the correct classification of cases and controls, and provide increased understanding of the natural course and progression of the disease and further elucidate the structure-function relationships in this devastating disorder.

Variability of full-field electroretinogram responses in subjects without diffuse photoreceptor cell disease

Purpose To evaluate test–retest variability in electroretinogram (ERG) responses in subjects without evidence of diffuse photoreceptor cell disease. Design Cohort study. Participants Forty subjects without diffuse photoreceptor cell disease. Methods Serial ERGs were performed on 40 subjects (mean age at the time of first ERG: 54 years; range: 38–75 years) over a period of 2 to 6 years. These subjects participated in a study by a pharmaceutical company investigating the effects of certain drugs, used for gastrointestinal disorders, on retinal function. None of the subjects showed any evidence of progressive change in retinal function related to the medications. The ERG responses that were evaluated included amplitudes and implicit times for the dark-adapted rod-isolated and rod-dominant responses, light-adapted single flash response, and both light- and dark-adapted 31-Hz flicker responses. Main outcome measures The data were analyzed by using analysis of variance methods, and a threshold criteria for significant change with 95% confidence was calculated for implicit times and an increase or decrease in ERG amplitudes. Results The threshold for significant change varied depending on the ERG stimulus. For the dark-adapted stimuli, a significant decrease in amplitude varied from 35% to 42% as compared with a variation of 53% to 73% for a significant increase. For the light-adapted stimuli, a significant decrease in amplitude varied by 52% as compared with a variation of 109% to 110% for a significant increase. The threshold for significant change for implicit times varied from 3.0 milliseconds to 8.7 milliseconds. Conclusions The measured test–retest variability in ERG amplitudes and implicit times in subjects without diffuse photoreceptor cell disease underscores the importance of conducting similar comprehensive studies of variability in patients with acquired and hereditary retinal diseases. These data are also of value for monitoring disease progression and in future therapeutic trials.

THE EFFECT OF A LOWER BLOOD PRESSURE ON CHOROIDAL FILLING IN AGE-RELATED MACULAR DEGENERATION

To determine whether the occurrence of delayed choroidal filling or a slower foveal electroretinogram (ERG) implicit time is related to systemic blood pressure in patients with age-related macular degeneration. We assessed delayed choroidal filling by fluorescein angiography and foveal ERG implicit time with a hand-held stimulator-ophthalmoscope for the fellow eye of 67 patients with unilateral neovascular age-related macular degeneration. Blood pressure, measured by ascultation, was converted to mean arterial pressure. The relations of delayed choroidal filling and foveal ERG implicit time to the mean arterial pressure were assessed by logistic and linear regression, respectively, controlling for age, gender, and intake of hypertensive medication. The probability of having delayed choroidal filling decreased with increasing mean arterial pressure (P = 0.01). The foveal ERG implicit time was also inversely related to the mean arterial pressure (P = 0.009). Delayed choroidal filling and foveal ERG implicit time are related to blood pressure in patients with age-related macular degeneration.

High-risk characteristics of fellow eyes of patients with unilateral neovascular age-related macular degeneration

Objective This study aimed to determine whether clinical tests of ocular function and macular appearance independently can help to predict which patients with unilateral neovascular age-related macular degeneration (AMD) will have a choroidal neovascular membrane (CNVM) develop in their fellow eye. Design The study design was a prospective cohort study. Participants One hundred twenty-seven patients with unilateral neovascular AMD observed for up to 4.5 years participated. Intervention Functional measurements included visual acuity, macular visual field, glare recovery time, and foveal electroretinogram amplitude and implicit time. Main outcome measure The age-adjusted proportion of patients having a CNVM develop over follow-up assessed by the Cox proportional hazards model with stepwise selection was measured. Results On average, 8.8% of patients had a CNVM develop each year. Independent risk factors for the fellow eye were its glare recovery time in minutes (relative risk = 1.30, confidence interval = 1.10–1.54, P = 0.003) and its extent of visible macular abnormalities on a four-point scale (relative risk = 1.62, confidence interval = 1.06– 2.59, P = 0.03). Of the fellow eyes that converted, the interval to have a CNVM develop was inversely related to the foveal electroretinogram implicit time. Conclusions A slower recovery from glare and more extensive funduscopic changes appear to be independent risk factors for the development of a CNVM in the fellow eyes of patients with unilateral neovascular AMD. A slower foveal electroretinogram implicit time may be a sign of early stage CNVM development, perhaps because of outer retinal ischemia. These results have clinical management implications, particularly for those patients at high risk of having a potentially treatable form of AMD develop.

ERG Abnormalities in Relation to Histopathologic Findings in Vitiligo Mutant Mice

The vitiligo,mivit, mutation has several prenatal and perinatal effects on development of the retinal pigment epithelium, and later, leads to extensive, progressive degeneration of photoreceptor cells in the neural retina of homozygous affected mice. The aim of the present study was to determine by functional criteria how early can abnormalities be detected in the neural retina. Electroretinograms (ERGs) were correlated with histopathological findings in the same animals. Congenic homozygous mutants, heterozygotes, and homozygous wild-type mice were studied at 2, 3, 6, 24 and 56 weeks of age, the same animals being tested serially at the three older time points. The nontested eye of each animal was embedded in Epon and sectioned at 1 μm for light microscopic study. ERG recordings from vitiligo homozygotes differed from heterozygous and wild-type mice, but the latter two groups did not differ from each other. As early as two weeks of age, homozygous mutants showed a significant reduction of rod dominated maximum ERG a-wave and b-wave amplitude. ERG b-wave sensitivity (σ) was significantly reduced, and ERG implicit times were delayed for homozygous mutants at 3 (a-wave) and 6 (b-wave) weeks of age. This is the first study to report reduced and delayed ERG a-waves and b-waves in this animal model, like the early functional abnormalities in human retinitis pigmentosa, and also the first to show short and disoriented rod outer segments, beginning retinal separation from the pigment epithelium, and a few macrophage-like cells already present in the subretinal space at 2 weeks of age (in three of four homozygous mutant eyes examined). Given these early functional and structural abnormalities in the neural retina, it remains to be determined whether themigene targets the retinal pigment epithelial cell, the photoreceptor cell, or both.

Relative effects of aging and age-related macular degeneration on peripheral visual function.

The purpose of this study was to determine the extent of peripheral visual deficits in patients with early age-related macular degeneration (ARMD) using electrophysiological and psychophysical techniques. Dark-adaptation curves, electro-oculograms (EOGs), and electroretinograms (ERGs) were obtained from patients with early ARMD and from normally sighted control subjects. The control subjects' data were used to calculate age-dependent 95% confidence intervals for each measure of visual function. For the control subjects, performance on all our measures of visual function decreased with age. For the patients with early ARMD, the cone system absolute thresholds, EOG ratios, and cone-dominated ERG amplitudes and implicit times were within the range of normal age-related changes. Rod system absolute thresholds, cone-rod break times, and rod-dominated electroretinographic measures were abnormal in some patients. These results suggest that when the effects of aging are taken into account, some patients classified as early ARMD may not show significant changes in peripheral retinal function with standard clinical tests.

Foveal electroretinograms and choroidal perfusion characteristics in fellow eyes of patients with unilateral neovascular age-related macular degeneration.

A prolonged choroidal filling phase on fluorescein angiography has been reported to be a common finding and associated with visual function abnormalities in patients with age-related macular degeneration (AMD). This investigation was carried out to determine whether this perfusion defect was related to the slowing of foveal cone electroretinogram (ERG) implicit time seen in patients with AMD. Fluorescein angiograms and foveal cone ERGs were evaluated in the fellow eyes of 67 patients with unilateral neovascular AMD. Twenty eight (42%) of the eyes had a choroidal perfusion defect. ERG implicit times averaged 1 ms slower (p = 0.0167) and were more likely to be delayed (p = 0.0078) in eyes with abnormal choroidal perfusion than in eyes with normal choroidal filling; significant relations were found also after controlling for age. ERG implicit time was also inversely related to ETDRS visual acuity and positively related to the extent of macular drusen; and the latter showed a borderline significant tendency to be more prevalent in eyes with prolonged choroidal perfusion. However, an association of a delayed ERG implicit time with prolonged choroidal filling remained after controlling for age, acuity, and the extent of drusen. These findings further establish prolonged choroidal perfusion as a common finding in AMD and link it to retinal malfunction.

The electroretinogram during orbital compression following intraorbital regional block for cataract surgery

The electroretinogram (ERG) is a transient biopotential that reflects the electrical response of the distal retina to photostimulation. Disturbances in retinal circulation produce characteristic abnormalities in the ERG wave form. The objective of this study was to investigate the changes in the ERG produced by combined retrobulbar and peribulbar injections of a large volume (8 ml) of local anaesthetic, followed by ocular compression. Electroretinogram recordings were obtained from skin electrodes placed on the infero orbital ridge in response to stroboscopic flash stimulation in 34 adult patients undergoing cataract surgery: (a) prior to regional anaesthesia (baseline condition); (b) within one minute after regional anaesthesia of the orbit (block condition); (c) after ten minutes of orbital compression with a Honan's device at 30 mmHg. (compression condition); (d) and five minutes after removal of orbital compression (recovery condition). The ERG implicit times of both a- and b-wave increased (P < 0.001) after anaesthetic block. The amplitude of the a- and b-waves also decreased (P < 0.001) immediately following anaesthetic block and continued to decrease following application of the compression device (P < 0.01). Following removal of ocular compression the amplitude of the b-wave increased (P < 0.01). Only the a-wave implicit time (P < 0.005) decreased with release of ocular compression. These findings are compatible with the ERG changes of transient retinal ischaemia produced by ocular compression.

Increase in the amplitude of the b-wave of the cone electroretinogram during light adaptation

In experimental and in clinical electrophysiology, cone electroretinograms (ERG) undergo typical changes of the b-wave during the course of light adaptation. B-Waves obtained from twenty healthy subjects, exposed to a rod-desensitizing adapting field for ten minutes show an increase of amplitude. This increase was observed using a short wavelength as well as with a long wavelength stimulus. The cone ERG implicit times decrease slightly during light adaptation. To avoid considerable variation in clinical cone-ERG it is necessary to wait a certain period of time before measuring cone b-waves and comparing them with normative values. Possible mechanisms underlying these adaption-induced ERG changes are discussed.

Temporal aspects of the electroretinogram in sector retinitis pigmentosa.

Temporal aspects of the electroretinogram (ERG) are studied in two patients with bilateral nasal sector retinitis pigmentosa and one patient with bilateral macular degeneration and pericentral retinitis pigmentosa that appeared sectorial in type. In these three patients with sector retinitis pigmentosa, the ERGs in response to full-field light stimuli are reduced in amplitude, but the cone and rod implicit times are normal. In contrast, patients with reduced ERG amplitudes and early stages of widespread recessive retinitis pigmentosa have cone and rod ERG implicit times that are delayed. The results indicate that implicit time and amplitude of ERG responses are independent criteria of retinal function in hereditary retinal degenerations. The temporal aspects of the ERG separate localized retinitis pigmentosa from other types of retinitis pigmentosa where the degeneration is widespread and, therefore, help to define the extent of retinal disease.