Effects of unsteady fixation on multifocal electroretinogram (mfERG)

Effect of eccentric fixation on the steady-state pattern electroretinogram

PURPOSE

The steady-state pattern electroretinogram (ssPERG) is used to assess retinal ganglion cell function in a variety of research contexts and diagnostic applications. In certain groups of patients or study participants, stable central fixation of the stimulus is not guaranteed. The present study aimed at assessing the effects of misfixation on the ssPERG response to checkerboard reversal stimuli.

METHODS

Using two check sizes (0.8° and 15°), we compared ssPERG responses for several amounts of fixation deviation, ranging from 0° to 19° horizontally and from 0° to 14° diagonally. The stimulus area extended to 15° eccentricity, stimulus reversal rate was 15/s.

RESULTS

Up to around 7° eccentricity, there was no sizable effect of fixation deviation under most conditions. Effects were somewhat larger for nasal than for temporal deviation, in particular for small checks. Diagonal deviation was associated with a response to luminance onset/offset at 7.5 Hz (subharmonic of the reversal rate), most prominently when the interior of a large check was fixated.

CONCLUSION

Generally, moderate inaccuracies of fixation do not have a sizable effect on ssPERG amplitude. However, with large checks, the luminance response has to be considered.

Comparison of DTL and gold cup skin electrodes for recordings of the multifocal electroretinogram

OBJECTIVE

To compare mfERG recordings with the Dawson-Trick-Litzkow (DTL) and gold cup skin electrode in healthy young and old adults and to test the sensitivity of both electrodes to age-related changes in the responses.

METHODS

Twenty participants aged 20-27 years ("young") and 20 participants aged 60-75 ("old") with a visual acuity of ≤ 0 logMAR were included. The mfERG responses were recorded simultaneously using DTL and skin electrodes. P1 amplitudes, peak times and signal-to-noise ratios (SNRs) were compared between both electrodes and across age groups, and correlation analyses were performed. The electrode's performance in discriminating between age groups was assessed via area under curve (AUC) of receiver operating characteristics.

RESULTS

Both electrodes reflected the typical waveform of mfERG recordings. For the skin electrode, however, P1 amplitudes were significantly reduced (p < 0.001; reduction by over 70%), P1 peak times were significantly shorter (p < 0.001; by approx. 1.5 ms), and SNRs were reduced [(p < 0.001; logSNR ± SEM DTL young (old) vs gold cup: 0.79 ± 0.13 (0.71 ± 0.15) vs 0.37 ± 0.15 (0.34 ± 0.13)]. All mfERG components showed strong significant correlations (R² ≥ 0.253, p < 0.001) between both electrodes for all eccentricities. Both electrodes allowed for the identification of age-related P1 changes, i.e., P1-amplitude reduction and peak-time delay in the older group. There was a trend to higher AUC for the DTL electrode to delineate these differences between age groups, which, however, failed to reach statistical significance.

CONCLUSIONS

Both electrode types enable successful mfERG recordings. However, in compliant patients, the use of the DTL electrode appears preferable due to the larger amplitudes, higher signal-to-noise ratio and its better reflection of physiological changes, i.e., age effects. Nevertheless, skin electrodes appear a viable alternative for mfERG recordings in patients in whom the use of corneal electrodes is precluded, e.g., children and disabled patients.

Correlation between electroretinography, foveal anatomy and visual acuity in aniridia due to PAX6 mutations

BACKGROUND

Aniridia patients have poor visual acuity and iris malformation. The fovea in these patients is underdeveloped, but the relationship between structure and electrophysiologic function remains incompletely understood. This study correlates electrophysiology, visual acuity and optical coherence tomography (OCT) in patients with aniridia secondary to mutations in the PAX6 gene and compares with age-similar controls.

METHODS

Patients were recruited from clinical practice. The mfERG protocol was a 4-min 103-hexagon protocol covering approximately 40° in diameter of central retina. Diagnosys full-field ERG (ffERG) and VERIS multifocal ERG (mfERG) were obtained using standard International Society for Clinical Electrophysiology of Vision protocols. OCT central thickness was recorded, and an OCT foveal score was calculated. Nonparametric permutation testing was utilized to determine the statistical significance.

RESULTS

A total of 6 aniridia patients and 25 control patients were recruited. On mfERG, aniridia patients had significantly lower amplitudes in rings 1-3 (p = 0.0006, 0.0013, 0.0132), shorter latencies in ring 1 (p = 0.0312) and longer latencies in rings 5 and 6 (p = 0.0026, p = 0.0042) than controls. There was a significantly positive relationship in aniridia patients between logMAR visual acuity and mfERG amplitude in ring 4 (p = 0.0392) and ring 5 (p = 0.0489). On ffERG, there was no difference in amplitudes, though photopic 3.0 a- and b-wave latency, 30 Hz flicker latency and scotopic 0.01 b-wave latency were significantly longer in aniridia patients versus control (p = 0.0018, 0.0.0005, 1.00 x [Formula: see text], 0.0198). Thicker central macula on OCT correlated with lower mfERG amplitudes in rings 4-6 (p = 0.0369, 0.0292, 0.0255). There was no correlation between visual acuity and central macular thickness or foveal hypoplasia score as determined by OCT.

CONCLUSIONS

Higher amplitude on mfERG correlated with poorer visual acuity in rings 4 and 5 in patients with PAX6 mutations. The slope of the change in amplitude from central to peripheral rings on the mfERG is significantly different in aniridia patients compared to controls, with a slower drop-off of amplitude from center to periphery. Additionally, mfERG in aniridia showed lower amplitudes than controls in rings 1-3. These changes along with the lack of correlation between visual acuity and central macular thickness/OCT score suggest that changes in electrical topography may be important to visual deficits in patients with PAX6 gene mutations.

Fundus motion during mfERG testing

PURPOSE

The purpose of this study was to assess eye movements during a multifocal ERG (mfERG) recording. This study evaluated the relationship between bivariate contour ellipse areas (BCEAs), mfERG amplitudes (Amps) and mfERG implicit times (ITs) with repeat testing and experienced subjects.

METHODS

Thirty subjects were selected (15 experienced to ocular procedures and 15 novices). All were confirmed to have healthy retinas and at least 20/25 vision. MfERGs with a stimulus near 100% contrast and 4-min m-sequence were recorded on two different days using our common clinical technique, which did not constrain the head. VERIS with fundus monitoring system was used for recording with a Burian-Allen electrode. An external camera captured the fundus during each mfERG recording. The optic nerve head position was tracked in each video using a custom algorithm in order to determine BCEAs. Each subject performed one mfERG on two different days. MfERGs were analyzed for Amps and ITs for the fovea and whole eye.

RESULTS

There was no correlation between the mfERG metrics and BCEAs with repeat testing. There were also no differences between the experienced and novice subjects for mfERG Amps, ITs or BCEAs. Eye movements between visits were highly correlated (multiple r = 0.67). BCEAs were larger during mfERGs (1.04 ± 0.8 deg²) than those observed in previous literature using brief viewing tasks (< 0.3 deg²). The proportion of time spent fixating within 1.0 and 2.0 degrees of the central hexagon was 68 and 93%, respectively.

CONCLUSIONS

This study is the first to evaluate the stability of the retina while recording a mfERG in healthy subjects and indicates that the center of fixation during a mfERG stays within the central hexagon. Eye stability during an initial recording is the best indicator of stability on the second recording. The amount of movement during these recordings did not seem to affect the mfERG Amps or ITs. These data suggest clinical confidence with mfERGs when recording novice patients.

Multifocal electroretinography in amblyopia

PURPOSE

To identify whether there are functional abnormalities in the retina of amblyopic eyes using multifocal electroretinography (mfERG).

METHODS

This is a prospective study of patients ≥ 7 years of age identified with unilateral amblyopia (strabismic or anisometropic). Multifocal ERG and flash ERG were performed to compare parameters between the amblyopic and non-amblyopic fellow eyes. A complete analysis of the five ring averages was done including the central ring.

RESULTS

Thirty-eight patients were included: mean age was 14.3 ± 7.3 years; 18 patients were strabismic and 20 were anisometropic. Amblyopic eye responses across the rings in multifocal ERG were diminished compared with fellow non-amblyopic eyes with significant differences detected in the central rings (p = 0.001). On the other hand, flash ERG did not show any consistently significant differences. When divided by severity, amplitudes of central rings were significantly lower in severely amblyopic eyes compared with non-amblyopic eyes (p = 0.001), while in mild amblyopia, no significant differences were observed. No significant difference was observed between anisometropic and strabismic amblyopic eyes.

CONCLUSIONS

Using multifocal ERG, significantly decreased amplitudes were observed in amblyopic eyes compared with normal fellow eyes in the central ring. This correlated with the severity of amblyopia. No difference was observed when comparing the two groups of amblyopia (strabismic and anisometropic). Those findings may help clarify the pathophysiology of amblyopia better and open the door for new objective ways to monitor the response to amblyopia treatment but this needs to be further studied.

The Multifocal On- and Off-Responses in the Human Diabetic Retina

The characteristics of the on- and off-responses in the human diabetic retina by a "long-duration" multifocal electroretinogram (mfERG) paradigm were investigated. Changes in the retinal antagonistic interaction were also evaluated in the early stage of diabetes mellitus (DM). Twenty type II diabetic patients with no or mild non-proliferative diabetic retinopathy (NPDR) and twenty-one age-matched healthy controls were recruited for "long-duration" mfERG measurements. A 61-hexagon mfERG stimulus was displayed under two chromatic conditions (white/black and blue/black) at matched luminance. The amplitudes and implicit times of the on-response components (N1, P1 and N2) and off-response (P2) components were analysed. The blue stimulation generally triggered greater mfERG amplitudes in P1, N2 and P2 (p<0.05) than those from white stimulation in both control and diabetic groups. The diabetic group showed significantly greater N2 amplitude than the controls under white stimulation in mid-retinal regions (Rings 2 and 4) (p<0.05). When the stimulus was changed from white to blue, the diabetic group showed a smaller percentage change in N2 amplitude than the controls in peripheral retinal region (Ring 5) (p<0.02). When a stimulus is changed from white (broad-band spectral stimulation) to blue (narrow-band spectral stimulation), a decrease in the involvement of lateral antagonism would be expected. The larger amplitude of the on-response component (N2) in the diabetic patients suggested an imbalance of lateral antagonism, and the lesser percentage change of N2 amplitude in the diabetic group may indicate an impairment of the cross-talk at the middle retinal level in early stages of DM.

Fixation stability and implication for multifocal electroretinography in patients with neovascular age-related macular degeneration after anti-VEGF treatment

PURPOSE

To quantify fixation stability in patients with neovascular age-related macular degeneration (nAMD) at baseline, 3 and 6 months after anti-vascular endothelial growth factor (anti-VEGF) treatment and furthermore asses the implications of an unsteady fixation for multifocal electroretinography (mfERG) measurements.

METHODS

Fifty eyes of 50 nAMD patients receiving intravitreal anti-VEGF treatment with either bevacizumab or ranibizumab and eight eyes of eight control subjects were included. Fixation stability measurements were performed with the Eye-Link eyetracking system and the retinal area in degrees² (deg²) containing the 68 % most frequently used fixation points (RAF68) was calculated. MfERG P1 amplitude and implicit time were analyzed in six concentric rings and as a summed response. Patients were examined at baseline, 3 and 6 months. Four different mfERG recordings were performed for the control subjects to mimic an involuntary unstable fixation: normal central fixation, 2.4°, 4.8°, and 7.1° fixation instability.

RESULTS

For control subjects, a fixation instability of 2.4° (corresponding to the central hexagon) did not reduce mfERG ring amplitudes significantly, whereas 4.8° and 7.1° fixation instability reduced the amplitudes significantly in rings 1 and 2 (p < 0.001) as well as in the peripheral rings in the 7.1° instability condition (p < 0.001). Fixation stability improved non-significantly for patients at 3 and 6 months. The size of the retinal area of fixation was at baseline, 3 and 6 months negatively correlated to visual acuity (VA) (r_baseline = -0.65, r_{3 months} = -0.60, and r_{6 months} = -0.66 respectively, p < 0.001) and mfERG amplitudes of the three innermost rings (r_baseline = -0.29, p = 0.042, r_3 months = -0.43, p = 0.003 and r_6 months = -0.31, p = 0.042). The VA cutoff for a fixation area less than 5 deg² (approximately the central hexagon) was 65, 77, and 68 ETDRS letters (corresponding a maximal Snellen equivalent of 0.31) at baseline, 3 and 6 months, respectively.

CONCLUSIONS

MfERG amplitudes in recordings of nAMD patients are at substantial risk of being reduced due to poor fixation as a large number of patients may use a fixation area of more than 5 deg². Fixation monitoring during recording as well as interpretation of results should be performed with care, especially in patients with poor visual acuity.

Paraneoplastic neuromyelitis optica associated with ANNA-1 antibodies in invasive thymoma

Background

Thymoma is associated with various paraneoplastic autoimmune disorders. Herein, we report paraneoplastic neuromyelitis optica (NMO) associated with both anti-aquaporin-4 (AQP4) immunoglobulin G (IgG) and type 1 antineuronal nuclear antibody (ANNA-1) in an invasive thymoma patient.

Case presentation

A woman presented with a sudden onset of bilateral progressive visual loss associated with recurrence of invasive thymoma, 6 years after thymectomy and immunosuppressive treatment. AQP4-IgG and ANNA-1 were present in the patient’s serum. Visual outcome was poor despite immunosuppressive treatment. Longitudinally extensive transverse myelitis developed 27 months after the onset of visual symptoms.

Conclusions

We have reported a case of paraneoplastic NMO associated with both AQP4-IgG and ANNA-1 autoantibodies in an invasive thymoma patient.

Clinical usefulness of binocular multifocal electroretinography in patients with monocular macular disease

Purpose

To evaluate the clinical usefulness of binocular multifocal electroretinography (mfERG) by comparing results with conventional monocular mfERG in patients with monocular macular disease.

Methods

mfERG testing was conducted on 32 patients with monocular macular disease and 30 normal subjects. An initial mfERG was simultaneously recorded from both eyes with two recording electrodes under binocular stimulation. A second mfERG was subsequently recorded with conventional monocular stimulation. Amplitudes and implicit times of each ring response of the binocular and monocular recordings were compared. Ring ratios of the binocular and monocular recording were also compared.

Results

In the macular disease group, there were no statistical differences in amplitude or implicit time for each of the five concentric rings between the monocular and binocular recordings. However, with binocular simulation, the ring ratios (ring 1 / ring 4, ring 1 / ring 5) were significantly reduced in the affected eye. In the normal control group, there were no statistical differences in any parameters between the monocular and binocular recordings.

Conclusions

Binocular mfERG could be a good alternative to the conventional monocular test. In addition, given that the test needs stable fixation of the affected eye during the binocular test, the reliability of the test results could be improved, especially for patients with monocular macular disease.

Assessment of neuroretinal function in a group of functional amblyopes with documented LGN deficits

PURPOSE

In this study we examine neuroretinal function in five amblyopes, who had been shown in previous functional MRI (fMRI) studies to have compromised function of the lateral geniculate nucleus (LGN), to determine if the fMRI deficit in amblyopia may have its origin at the retinal level.

METHODS

We used slow flash multifocal ERG (mfERG) and compared averaged five ring responses of the amblyopic and fellow eyes across a 35 deg field. Central responses were also assessed over a field which was about 6.3 deg in diameter. We measured central retinal thickness using optical coherence tomography. Central fields were measured using the MP1-Microperimeter which also assesses ocular fixation during perimetry. MfERG data were compared with fMRI results from a previous study.

RESULTS

Amblyopic eyes had reduced response density amplitudes (first major negative to first positive (N1-P1) responses) for the central and paracentral retina (up to 18 deg diameter) but not for the mid-periphery (from 18 to 35 deg). Retinal thickness was within normal limits for all eyes, and not different between amblyopic and fellow eyes. Fixation was maintained within the central 4° more than 80% of the time by four of the five participants; fixation assessed using bivariate contour ellipse areas (BCEA) gave rankings similar to those of the MP-1 system. There was no significant relationship between BCEA and mfERG response for either amblyopic or fellow eye. There was no significant relationship between the central mfERG eye response difference and the selective blood oxygen level dependent (BOLD) LGN eye response difference previously seen in these participants.

CONCLUSIONS

Retinal responses in amblyopes can be reduced within the central field without an obvious anatomical basis. Additionally, this retinal deficit may not be the reason why the LGN BOLD (blood oxygen level dependent) responses are reduced for amblyopic eye stimulation.

The value of two-field pattern electroretinogram in routine clinical electrophysiologic practice

PURPOSE

To investigate the clinical use of the large-field pattern electroretinogram (PERG) as an adjunct test to the International-standard PERG in an unselected sequential cohort of patients referred for routine electrophysiologic assessment.

METHODS

Pattern electroretinograms to both 15° × 11° (International Society for Clinical Electrophysiology of Vision Standard) and 30° × 22° (large field) checkerboard field sizes were recorded in 277 consecutive electrophysiology patients, aged 10-79 years. Most patients had additional tests including full-field electroretinogram, electrooculogram, multifocal electroretinograms, or cortical visual evoked potential. Patient data were compared with data from 27 control subjects.

RESULTS

Satisfactory 2-field PERG data were obtained in 91% (N = 253) of patients; data from 24 patients (9%) were excluded because of poor compliance (n = 17) or nystagmus (n = 7). Standard PERGs were consistent with macular dysfunction in 44% of cases; large-field PERG revealed macular dysfunction in an additional 8% of eyes and helped to distinguish between localized central, predominantly paracentral, and widespread macular dysfunction. The results were consistent with multifocal electroretinogram and/or imaging studies on the same patients. In some patients with optic nerve disease, the large-field PERG provided clearer evidence of normal macular function than the standard PERG.

CONCLUSION

Routine use of the large-field PERG is a valuable complement to standard-field PERG testing in the evaluation and management of patients with different forms of macular or generalized retinal dysfunction and can be useful in patients with optic nerve disease.

Multifocal electroretinography

Multifocal electroretinography (mfERG) provides functional and objective evidence of retinal dysfunction. We have found mfERG to be especially useful in the management of occult outer retinopathy and Stargardt's disease.

Test-retest reliability and inter-ocular symmetry of multi-focal electroretinography in Stargardt disease

PURPOSE

To evaluate test-retest reliability and inter-ocular symmetry of multi-focal electroretinography recordings in Stargardt disease and in patients without retinal pathology.

METHODS

Multi-focal electroretinography were recorded with continuous fundus monitoring using the VERIS multifocal recording system using an array of 103 hexagons spanning 50 degrees of central retina. Recordings were made sequentially from one eye (test-retest) followed by recordings from the fellow eye. A departure score, expressed as a percentage difference from the first recording (or from the fellow eye), was calculated for each comparison and parameter.

RESULTS

Multi-focal electroretinography response topographies were similar within and between eyes for a particular individual and parameter. However, local response variability within and between eyes was significantly higher in Stargardt disease than in patients without retinal pathology for both amplitude and timing parameters. Amplitude variability in Stargardt disease decreased with more peripheral targets and with larger stimuli but never to the levels achieved with normal observers.

CONCLUSIONS

Both test-retest reliability and inter-ocular symmetry of multi-focal electroretinography responses were significantly lower in Stargardt disease compared to normal eyes, a finding attributable primarily to unsteady fixation. The greater variability between eyes in Stargardt disease may also reflect pathological differences in the topography of retinal function. This inherent variability must be taken into consideration if the multi-focal electroretinography is to be sufficiently sensitive to reliably detect small differences in retinal function.