P1 Implicit Time Research Articles

Electrophysiological Detection of Delayed Postretinal Neural Conduction in Human Amblyopia

To evaluate macular function and neural conduction along postretinal visual pathways in amblyopic patients. Twenty-five anisometropic amblyopic patients (mean age, 7 ± 1.9 years; visual acuity [VA]: 0.44 ± 0.27 logMAR in amblyopic [AM] eyes and 0.023 ± 0.067 logMAR in sound [SE] eyes) and 25 age-similar control subject ([CE] eyes, VA of 0.0 ± 0.0 logMAR in both eyes) were enrolled. In AM, SE, and CE eyes, simultaneous pattern electroretinograms (PERGs) and visual evoked potentials (VEPs) were recorded in response to checks reversed at the rate of two reversals/second stimulating macular or extramacular areas (the check edge subtended 15 minutes and 60 minutes of visual arc, respectively). Nonsignificant differences (ANOVA, P > 0.005) were observed in PERG, in VEP responses to the 60-minute stimulus, and in retinocortical time with the 60-minute stimulus (RCT; the difference between VEP P100 and PERG P50 implicit times) between AM, SE, and CE eyes. AM eyes showed a significant (P < 0.005) increase in VEP P100 implicit time and in RCT in response to the 15-minute stimulus, compared with the values observed in SE and CE eyes. In AM patients, the interocular difference in VA was significantly (Pearson's test, P < 0.005) related to the interocular difference VEP P100 latencies and RCT with the 15-minute stimulus. Amblyopic eyes showed abnormal visual cortical responses only when the macular area was stimulated (increase in VEP P100 implicit times with the 15-minute stimulus). This functional impairment, in the presence of normal macular function (PERG responses similar to control eyes) may be attributable to a delay in postretinal neural conduction (increase in RCT).

Prediction of postoperative visual outcome after pars plana vitrectomy based on preoperative multifocal electroretinography in eyes with diabetic macular edema

To evaluate the role of preoperative optical coherence tomography (OCT), multifocal electroretinography (mfERG), and fluorescein angiography (FA) as prognostic factors for vision after pars plana vitrectomy (PPV) in diabetic macular edema (DME). Thirty-five eyes of 34 patients who underwent PPV were retrospectively reviewed. Best-corrected visual acuity (VA) was measured at baseline, and at 3, 6, and 9 months after surgery. Patients were categorized into two groups according to the final VA. Group 1 consisted of eyes with 0.2 or more logMAR lines of visual recovery, the rest of the eyes being placed in group 2. Preoperative FA findings, central macular thickness and mfERG responses at the central macula were evaluated to determine their effect on visual outcome. Eighteen eyes showed improved VA after PPV, and were classified into group 1. Seventeen eyes were placed in group 2. The presence of macular ischemia did not affect the postoperative visual outcome between the groups, although a trend was noted toward macular ischemia with delayed implicit time. P1 implicit time at the central seven hexagons (eccentricity of 0-5 degrees ) was the only statistically significant factor predicting unfavorable visual outcome. There was significantly delayed implicit time in group 2 patients compared with those of group 1. MfERG responses at other retinal eccentricities and central macular thickness did not show significant association with visual prognosis. Preoperative mfERG parameters, especially the implicit time, can be useful indicators for predicting functional visual prognosis after PPV in DME.

Multifocal electroretinography amplitudes increase after photocoagulation in areas with increased retinal thickness and hard exudates

This study aimed to evaluate local response on multifocal electroretinography (mfERG) and to assess retinal thickness with optical coherence tomography (OCT) after focal laser treatment in areas with retinal oedema and exudates in patients with diabetic retinopathy. Twelve diabetes patients (aged 60 +/- 14 years, diabetes duration 16 +/- 8 years) treated with focal or grid photocoagulation in areas with retinal oedema and/or exudates underwent mfERG and OCT before and 3 months after treatment. The average thickness (in microm) in any of the nine sectors (defined according to the ETDRS) treated with photocoagulation was measured. Amplitudes and implicit times were analysed in corresponding areas on the mfERG. Mean mfERG amplitudes increased after photocoagulation (21.5 +/- 8.0 nV/deg(2) versus 16.8 +/- 6.1 nV/deg(2); p = 0.012), whereas no difference was seen in implicit times. Mean OCT values in the treated regions were lower at follow-up (272 +/- 23 microm versus 327 +/- 79 microm; p = 0.013). No correlation was seen between changes in mfERG response and changes in OCT values. The decrease in retinal thickness was correlated with the number of laser spots applied (p = 0.002). Focal argon laser treatment is effective in reducing retinal thickness. In addition, treated areas tend to show improved retinal function as demonstrated by increased amplitudes on mfERG.

Impact of regional retinal responses on cortical visually evoked responses: Multifocal ERGs and VEPs in the retinitis pigmentosa model

To determine the impact of the regional retinal responses on cortical visually evoked responses, by evaluating the relationship between multifocal ERG (mfERG) and multifocal VEP (mfVEP), in the retinitis pigmentosa (RP) model. MfERGs and mfVEPs were recorded from 20 typical RP patients. Response amplitude density (RAD, nV/deg(2)) and implicit time (ms) of the mfERG 1st order binary kernel (N1-P1) and mfVEP 2nd order binary kernel (P1) components were measured. Ring analysis, matched for mfERG and mfVEP stimuli, was performed between fovea and mid-periphery (0-2.5, 2.5-5, 5-10, 10-15 and 15-20deg). At central and pericentral retinal regions (four eccentricities between 0 and 15deg), mfERG N1 RADs were positively correlated (r0.68, p<0.01) with corresponding mfVEP P1 RADs. Similarly, mfERG P1 implicit times were positively correlated (r>or=0.65, p<0.01) with corresponding mfVEP N1 implicit times. There are quantitative correlations between mfERG and mfVEP components in RP. The data suggest that regional responses of the photoreceptors and off-bipolar cells, the main generators of mfERG N1, have a major impact on the corresponding cortical activity.

Delayed response of the retina after hyperbaric oxygen exposure

To examine retinal electrophysiological function and retinal thickness in healthy eyes before and after hyperbaric oxygen (HBO) exposure. The healthy eye in each of six subjects who underwent experimental HBO treatment for branch retinal vein occlusion in the fellow eye was examined using multifocal electroretinography (mfERG) and optical coherence tomography (OCT) at baseline and following a course of five consecutive daily sessions of exposure to HBO at 2.4 atmospheres of absolute pressure lasting 90 min each. After HBO, P1 implicit times of the mfERG were significantly shorter than at baseline. The response was delayed, being undetectable on the day treatment concluded, whereas a 2.65% reduction in implicit time was seen 1 week later (p = 0.032). The P1 implicit time remained 2.49% shorter than at baseline 1 month after the end of the HBO sessions (p = 0.020). The bulk of the response to HBO was found in the foveal and parafoveal regions. No detectable change was seen in mfERG amplitudes or in the volume or thickness of the retina. A mfERG component related to bipolar and Müller cell function was accelerated by a short intermittent exposure to HBO. The response developed after the end of the HBO exposure and lasted for at least 3 weeks, suggesting that it was prompted by the withdrawal of HBO rather than the onset and subsequent brief exposure to HBO.

Visual Functions after Laser Photocoagulation in Central Serous Chorioretinopathy

The authors evalute the visual functions of patients with unilateral central serous chorioretinopathy (CSC) and compare them with their non-affected eye and with a control group. Fourteen patients with CSC treated with direct laser-photocoagulation were examined preoperatively and followed-up, up to 2 years postoperatively. Baseline best corrected visual acuity (BCVA) and contrast sensitivity (CS) of both eyes of patients was significantly lower in comparison with the controls. BCVA and CS in affected eyes were significantly lower compared to the fellow eye of patients. The final BCVA and CS of patients did not differ significantly from the controls, except CS of affected eyes in the spatial frequency of 3.69 c/deg. Two years after laser treatment, there were only nonsignificant differences of both photopic full-field electroretinography (phERG) and multifocal electroretinography (mfERG) responses between the treated, the nonaffected eye of the patients and the control group with exception of a significantly longer P1 implicit time in the parafoveolar region in affected eyes. Colour discrimination was normal in 85.8% of affected eyes of the patients. Despite a significant improvement of macular function in CSC eyes, functional examination methods do not prove complete resolution of function 2 years after laser-treatment.

Shift of temporal responsivity curve of pattern reversal visually evoked potentials to lower frequencies in patients after recovery from optic neuritis

To investigate the responsivity of the visual system to pattern reversal stimuli of different reversal rates in optic neuritis patients after a full recovery of visual acuity. Thirty eyes with optic neuritis and 30 eyes of age-matched normal controls were studied. Steady-state pattern reversal visually evoked potentials (P-VEPs) were recorded using reversal rates of 2, 10, 20 and 30 Hz. The relationship between the amplitudes of the P-VEPs and reversal rate was analysed. The temporal responsivity curves of the two groups were compared. The means ± standard deviations (SDs) of the P-VEP amplitudes in the normal controls were 7.08 ± 2.97, 8.60 ± 2.37, 4.69 ± 1.99 and 2.11 ± 1.24 μV at reversal rates of 2, 10, 20 and 30 Hz, respectively. The comparable amplitudes from the recovered optic neuritis patients were 8.01 ± 2.45, 6.57 ± 2.54, 2.73 ± 1.76 and 0.94 ± 1.27 μV. The mean amplitude of the P-VEPs elicited at a reversal rate of 2 Hz was not significantly different from that of normal controls. However, the amplitudes of the P-VEPs at reversal rates of 10, 20 and 30 Hz were significantly smaller in the recovered optic neuritis patients than in the controls. In addition, the average maximum amplitude of the P-VEPs was obtained at 10 Hz in normal subjects and at 2 Hz in the recovered optic neuritis patients. These results indicate that the peak of the temporal tuning curve of the P-VEP shifts to lower frequencies in recovered optic neuritis eyes, and that the reduced amplitudes at higher frequencies seem to be characteristic of the visual system of patients with recovered optic neuritis.

Reproducibility of the mfERG between instruments

Purpose First, to examine both the reproducibility of the multifocal electroretinogram (mfERG) recorded on different versions of the same instrument, and the repeatability of the mfERG recorded on a single instrument using two different amplifiers. Second, to demonstrate a means by which multicenter and longitudinal studies that use more than one recording instrument can compare and combine data effectively. Methods Three different amplifiers and two mfERG setups, one using VERIS™ 4.3 software (mfERG1) and another using VERIS™ Pro 5.2 software (mfERG2), were evaluated. A total of 73 subjects with normal vision were tested in three groups. Group 1 (n = 42) was recorded using two amplifiers in parallel on mfERG1. Group 2 (n = 52) was recorded on mfERG2 using a single amplifier. Group 3 was a subgroup of 21 subjects from groups 1 and 2 that were tested sequentially on both instruments. A fourth group of 26 subjects with diabetes were also recorded using the two parallel amplifiers on mfERG1. P1 implicit times and N1-P1 amplitudes of the 103 local first order mfERGs were measured, and the differences between the instruments and amplifiers were evaluated as raw scores and Z-scores based on normative data. Measurements of individual responses and measurements averaged over the 103 responses were analyzed. Results Simultaneous recordings made on mfERG1 with the two different amplifiers showed differences in implicit times but similar amplitudes. There was a mean implicit time difference of 2.5 ms between the amplifiers but conversion to Z-scores improved their agreement. Recordings made on different days with the two instruments produced similar but more variable results, with amplitudes differing between them more than implicit times. For local response implicit times, the 95% confidence interval of the difference between instruments was approximately ±1 Z-score (±0.9 ms) in either direction. For local response amplitude, it was approximately ±1.6 Z-scores (±0.3 μV). Conclusions Different amplifiers can yield quite different mfERG P1 implicit times, even with identical band-pass settings. However, the reproducibility of mfERG Z-scores across recording instrumentation is relatively high. Comparison of data across systems and laboratories, necessary for multicenter or longitudinal investigations, is facilitated if raw data are converted into Z-scores based on normative data.

Electrophysiological and Morphological Changes After Intravitreal Bevacizumab Injection with Macular Edema or Choroidal Neovascularization

Purpose: To evaluate the functional and anatomical statuses of macula with multifocal electroretinogram (mfERG) and optical coherence tomography (OCT) for the treatment of patients with macular edema after intravitreal bevacizumab injection. Methods: Patients were injected with intravitreal bevacizumab (1.875 mg/0.075 ml) for macular edema with choroidal neovascularization (CNV), diabetic retinopathy and retinal vein occlusion. The mfERG and OCT were performed. The results of mfERG were divided into fovea (Ring 1) and parafovea (Ring 2), and amplitude and implicit time were compared. The central macular thickness of OCT and visual acuity were compared with parameters of mfERG. Results: A total of 120 eyes (96 patients) were diagnosed with diabetic retinopathy, CNV with age-related macular degeneration and retinal vein occlusion. Visual acuity improved from logMAR 0.850.39 to 0.540.38 after intravitreal bevacizumab injection. The implicit time of P1 and N2 in mfERG decreased, and the amplitude of P1 showed a statistically significant increase. Central macular thickness decreased from 374.4 to 249.0. Conclusions: After intravitreal bevacizumab injection, functional and anatomical statuses of mfERG and OCT improved. This study demonstrates a method for utilizing mfERG to assess the effectiveness of treatments such as bevacizumab.

Multifocal electroretinography changes in patients on ethambutol therapy

To evaluate the multifocal electroretinography (mfERG) changes in patients on ethambutol therapy. A cross-sectional observational study of 17 visually asymptomatic patients receiving antituberculosis therapy with ethambutol. Patients underwent complete ophthalmic examination and mfERG recordings. The first-order mfERG N1 and P1 response amplitudes and implicit times of six concentric rings were analysed and compared with 17 normal age-similar controls. Correlation analyses were performed between the patients' mfERG parameters with parameters of ethambutol usage (daily dose of ethambutol per body weight, duration of ethambutol therapy, cumulative dose of ethambutol, and cumulative dose of ethambutol per body weight). The mean duration of ethambutol therapy was 3.6 months (range: 2-9 months) and the mean daily dose per body weight was 13.2 mg/kg/day. Analysis of response amplitude measures showed no significant difference in the mfERG N1 and P1 response amplitudes between the ethambutol and control groups at all ring eccentricities (P>0.05). For implicit times, there were significant delays in the mfERG P1 implicit times of rings 4-6 in the ethambutol group compared with controls (P=0.012 to P=0.041). Correlation analyses showed no significant correlation between the mfERG and ethambutol parameters (P>0.05). The mfERG findings suggested that visually asymptomatic patients receiving ethambutol therapy might have localized mild electrophysiological changes involving the peripheral macula. These changes might be related to localized alteration of metabolism or physiological changes associated with ethambutol therapy.

Electrophysiological assessment of visual function in patients with non‐arteritic ischaemic optic neuropathy

Our study aims to evaluate retinal function and neural conduction in post-retinal visual pathways of patients with non-arteritic ischaemic optic neuropathy (NION). Twenty patients (mean age: 63.7 +/- 5.96 year) with NION and 20 age-similar control subjects were enrolled. Simultaneous recording of pattern electroretinograms (PERGs) and visual evoked potentials (VEPs), and Log of minimum angle resolution (MAR) visual acuity (VA) were assessed in NION patients and controls. Significantly (ANOVA, P < 0.01) abnormal PERG and VEP responses, delayed retinocortical time (RCT, difference between VEP P100 and PERG P50 implicit times), and reduced VA were found in NION patients with respect to control subjects. The delay in RCT was not significantly (Pearson's test, P > 0.01) correlated with the PERG impairment. The reduction in VA was significantly (Pearson's test, P < 0.01) correlated to the increase in VEP P100 implicit time and RCT, whereas no correlations (P > 0.01) were found with PERG abnormalities. Non-arteritic ischaemic optic neuropathy patients with a reduction in VA may present two different, unrelated impairments: a dysfunction of the inner retinal layer (abnormal PERG) and abnormal post-retinal neural conduction (abnormal VEP and RCT). The reduction in VA seems to be related to the post-retinal impairment and seems to be independent from the retinal dysfunction.

Intra-sessional and inter-sessional variability of multifocal electroretinogram

The aim of this study was to investigate the intra-sessional and inter-sessional variability of the multifocal electroretinogram (mfERG). Right eyes of 20 healthy adult subjects with uncorrected visual acuity of 1.0 were studied. mfERG recordings were obtained in two sessions by using jet corneal electrodes. The responses were averaged over five retinal regions, the central hexagon (CH: 0.0-2.3 degrees ) and four concentric rings [ring 1 (R1: 2.3-7.4 degrees ), ring 2 (R2: 7.4-12.0 degrees ), ring 3 (R3: 12.0-19.4 degrees ), and ring 4 (R4: 19.4-30.0 degrees )]. In the first session, recordings were repeated while the electrodes stayed in place (the first and the second recordings). Second sessions (third recordings) were performed 1 week later. Individual coefficient of variation (CV; standard deviation/mean) for P1 and N1 amplitudes and implicit times were calculated for the first to second and first to third recordings to assess intra-sessional and inter-sessional variability, respectively, and were evaluated by Wilcoxon-paired samples test. Regarding implicit time and amplitude of mfERG recordings, there was no significant difference between the first to second and first to third recordings (P > 0.05, Bonferroni-corrected Wilcoxon test). CV values significantly decreased with eccentricity in both intra-sessional and inter-sessional comparisons (P < 0.05, Wilcoxon test). However, partial ring averaging showed no significant difference (P > 0.05) between CV values for single hexagons in each ring. Intra-sessional CV values were significantly lower than corresponding inter-sessional values (P < 0.05, Wilcoxon test). Our results support the importance of electrode replacement on variability. The increased number of hexagons that are averaged is the main factor that explains the lower variability in the more peripheral rings.

Local Neuroretinal Function during Acute Hypoxia in Healthy Older People

To measure the effect of acute, mild, systemic hypoxia on neuroretinal function in two different age groups. The slow-flash paradigm of the multifocal electroretinogram (mfERG) was measured in two different oxygenation levels. Twelve participants of two age groups (28 +/- 4 and 55 +/- 5 years) breathed room air (normoxia) or 12% oxygen (hypoxia). During normoxia (SaO(2) = 98%) there was a significantly different effect between the younger and older participants on the mfERG positive waveform components (N1P1 amplitudes and P1 implicit times; P < 0.001). Hypoxia (SaO(2) = 90%) significantly decreased N1P1 response density amplitudes in the central retinal field in both groups, with a larger effect in the older group (P < 0.001). There was no significant change in function of the cellular generators of oscillatory potentials (OPs). The results extend recent findings by showing a greater effect of hypoxia on ON- and OFF-bipolar cell function in healthy older persons than in younger persons, but no effect on OPs during moderate acute hypoxia in either age group.

Multifocal Electroretinogram in Mild to Moderate Essential Hypertension

Purpose. To investigate the local retinal dysfunctions in mild to moderate essential hypertensive patients by using multifocal electroretinogram (mfERG). Methods. Thirty-one patients with stage 1 or stage 2 hypertension (HT) and 31 age- and sex-matched healthy normotensive (NT) subjects were included. Fourteen of the patients had stage 1 and 17 had stage 2 hypertension. Twenty had grade 1 and 11 had grade 2 hypertensive retinopathy. The local retinal functions from the fovea to the peripheral 30 degrees were evaluated by multifocal electroretinogram by dividing this area to central hexagonal area (CH) and four concentric rings around the central hexagon (Rings 1–4). The amplitude and the implicit times of the positive peak (P1) and the negative peak (N1) of the responses were compared between the control subjects and hypertensive patients. Only the right eyes were included. The differences between the hypertensive patients and control subjects were investigated using independent samples t test, and the differences between grade 1 and grade 2 hypertensive retinopathy and stage 1 and stage 2 hypertension were investigated using Mann-Whitney U test. Results. P1 amplitudes in CH (HT: 129.0 ± 29.5, NT: 149.1 ± 45.5, p = 0.043) and in Ring 3 (HT: 37.0 ± 8.0, NT: 41.7 ± 7.8, p = 0.024) and N1 amplitude in Ring 1 (HT: 26.8 ± 7.4, NT: 30.8 ± 7.8, p = 0.048) in the hypertensive patients was significantly reduced when compared to healthy normotensive subjects. There was no significant difference in terms of P1 and N1 implicit times. There was also no significant difference between the patients with stage 1 or stage 2 hypertension and patients with grade 1 or grade 2 hypertensive retinopathy. Conclusion. Hypertensive subjects have local retinal dysfunctions with respect to healthy controls. This result probably originated from retinal ischemia due to changes in retinal and/or choroidal circulation in systemic arterial hypertension.

Multifocal Electroretinogram before and after Epiretinal Membrane Surgery

Purpose: To assess macular function before and after vitrectomy and membrane removal in epiretinal membranes by means of multifocal electroretinogram (mfERG). Methods: The mfERGs (RETIscanⓇ, Roland, Germany) of 28 consecutive patients (28 eyes) with idiopathic epiretinal membranes were recorded before epiretinal membrane surgery and 3 to 6 months after surgery. The average retinal response density and implicit time of each local response were estimated as anatomic macular areas corresponding roughly to 5 rings. Preoperative and postoperative responses of mfERG were compared. The correlation of the change of retinal response density and postoperative macular configuration on optical coherent tomography (OCT) was statistically analyzed. Results: The postoperative value of P1 amplitude and implicit time were not statistically correlated with the preoperative value (p>0.05). There were no significant correlations between the changes of rings 1 and 2 with regard to the retinal response density of the mfERGs and visual acuity. There was no significant correlation between the change of retinal response density and postoperative macular configuration according to OCT. Conclusions: The use of mfERGs does not seem useful for predicting clinical prognosis after epiretinal membrane surgery. Further studies of influence of internal limiting membrane removal on mfERG response should be conducted.

First and second-order kernel multifocal electroretinography abnormalities in acute central serous chorioretinopathy

To evaluate the first and second-order kernel multifocal electroretinogram (mfERG) response abnormalities in patients with acute central serous chorioretinopathy (CSC). This was a cross-sectional observational study in which 45 eyes of 45 patients with acute CSC underwent mfERG recordings. Peak amplitudes and implicit times of the first and second-order kernel responses were analyzed and compared with 20 age-matched normal controls. Correlation analyses were performed between the patients' visual acuity and the first and second-order amplitudes and implicit times. The first-order N1 and P1 mfERG amplitudes in the central three concentric rings were reduced in eyes with acute CSC compared with controls (P < 0.05). The first-order P1 implicit times of the central four rings were also delayed (P < 0.05). For the second-order mfERG response, there were significant reductions in the second-order P1 and N1 amplitudes in rings 3-5 compared with controls (P < 0.05). No significant difference between the second-order P1 and N1 implicit times was found compared with controls (P > 0.05). Correlation analyses showed significant correlations between visual acuity and the first-order N1 response amplitudes of rings 1 and 2, and for the first-order N1 and P1 implicit times of rings 1-4 (P < 0.05). Both first and second-order mfERG response abnormalities occur in eyes with acute CSC. These results suggest that in acute CSC, while outer retinal dysfunction is mostly localized to the central macula, there might be more widespread impairment in adaptive mechanisms of the inner retina or outer plexiform layer dysfunction in the more peripheral macula.

Assessment of Central Retinal Function in Patients with Advanced Retinitis Pigmentosa

To assess central retinal function in patients with advanced retinitis pigmentosa (RP) using the multifocal (mf)ERG and static perimetry. Patients with RP; a nonrecordable, full-field (ff)ERG; and visual acuity (VA) of </= 1.0 logMAR were included. All patients underwent mfERG testing (103 hexagons, and 2.67 and 5.33 cd . s . m(-2) flash intensities) and static perimetry (103 corresponding areas) in the better eye. First-order kernel mfERGs were analyzed for total noise, signal-to-noise ratio, response amplitude, and implicit time. The number of areas with recordable mfERG responses were counted and compared with visual field (VF) sensitivity. Twenty-nine patients aged 16 to 68 years with a VA of 0.02 to 1.0 logMAR and a kinetic VF of 10 degrees to 60 degrees in diameter were included. mfERGs were successfully performed in 22 of 29 patients. Responses were detected in at least one stimulated area in 22 of 22 patients, with an overall response detection of 9.8% in all stimulated areas and no difference between flash intensities. All responses were diminished severely in response density P1-N1, with normal P1 implicit time in 50% of the recordings. No predictive factors for recordable mfERG responses were identified. VF results were recorded reliably in 27 of 29 patients, with a 40% response detection rate. mfERG responses were recordable in at least one area in all successfully tested patients with advanced RP. Response detection and performance was significantly higher for static perimetry. Static perimetry may be a more sensitive primary outcome measure of central vision function than the mfERG in patients with advanced RP and nonrecordable ffERGs.

Experimental hypoxia in human eyes: Implications for ischaemic disease

Objective This study investigated neuroretinal activity under normoxic and hypoxic conditions with the multifocal electroretinogram (mfERG). Methods We used two mfERG paradigms, the fast flicker and slow flash stimulation modes, to measure neuroretinal activity in five healthy participants who breathed room air and a reduced oxygen mixture (14% oxygen, balance nitrogen). We analysed concentric ring N1P1 and P1N2 response density amplitudes, the P1 implicit times as well as the local scalar product (SP) response densities. Results During hypoxia there was a significant reduction of the scalar product response density for the fast flicker ( p < 0.001) and for the slow flash mfERG ( p < 0.001). The N1P1 and P1N2 response densities were lower especially for the central three rings; although these reductions were not significant between the two oxygen conditions, they indicated an overall distortion of the mfERG waveform. Conclusions It is demonstrated that a postreceptoral, primarily ON and OFF bipolar cell deficit is evident in the central retina of healthy young people during short term hypoxia. Significance Our findings suggest that persons with pre-existing ischaemic eye disease may be at risk when exposed to hypoxic conditions.

Multifocal Electroretinogram in Adults and Children With Myopia

To determine the correlation between multifocal electroretinogram (mfERG) parameters and the severity of myopia in adults and children. Observational study. Multifocal electroretinograms were recorded using the VERIS system from randomly selected eyes of 104 children and 31 adults with various degrees of myopia. Dawson, Trick, and Litzkow fiber electrodes were used and the pupil was dilated with 1% tropicamide. Subjective refraction was performed under cycloplegia and axial length measurement was determined by A-scan ultrasonography. The N1 (first negative trough), P1 (first positive peak), and N2 (second negative trough) components of the first-order kernel response of the mfERG were measured and correlated with the refractive data. First-order kernel mfERG responses. The N1, P1, and N2 amplitudes were significantly correlated with the severity of myopia in adult subjects (N1, r = 0.591, P = .001; P1, r = 0.682, P<.001; N2, r = 0.732, P<.001). The response amplitudes of N1, P1, and N2 decreased as the dioptric power of myopia increased. However, there were no significant correlations found between N1 (r = 0.073, P = .30), P1 (r = 0.071, P = .31), and N2 (r = 0.052, P = .46) amplitudes and the severity of myopia in children. The severity of myopia was also significantly correlated with N1 (r = -0.750, P<.001), P1 (r = -0.769, P<.001), and N2 (r = -0.664, P<.001) implicit times in adults with myopia, however, only the P1 (r = -0.166, P = .02) implicit time was significantly correlated with children with myopia. There is a significant correlation between the refractive error and mfERG amplitude in adults with myopia; however, such a relationship is absent in children with myopia. These findings suggest that the severity of myopia has little influence on the ERG amplitude, at least in children.

Cone-Mediated Multifocal Electroretinogram in Age-Related Macular Degeneration

To evaluate the progression of change in the cone-driven multifocal electroretinogram (mfERG) responses in patients previously identified as having high-risk, soft drusen 63 mum or greater. Seventeen eyes of 14 patients were reevaluated after 28 to 41 months. Fundus changes were graded depending on drusen size and extent. Each of the 103 mfERG responses was analyzed and compared with age-matched normal controls and with the baseline measurement. Stable visual acuity was found in 12 of the 17 eyes. Drusen size or extent was increased, decreased, and unchanged in 6, 3, and 8 eyes, respectively. The mfERG responses demonstrated a significant progression in the response density loss and in N1 and P1 implicit time delay compared with the baseline evaluation regardless of drusen change. The extent of response deterioration occurred over the entire retinal area tested. Eyes having decreased drusen at follow-up were typically associated with higher response delays at baseline and follow-up than eyes with stable or increased drusen. Early age-related macular degeneration is associated with a progressive loss in the cone-driven mfERG response despite stable visual acuity. The response deterioration extended beyond the visible drusen area. Implicit times seem to be an important predictor of drusen regression.