The multifocal ERG: unmasked by selective cross-correlation

Detection of glaucomatous damage using multifocal ERG

The first-order kernel analysis in multifocal electroretinogram (mfERG) using low contrast stimulation is suggested as a way to detect the inner retinal responses in animal studies. In this case report, this protocol is applied to human patients with glaucoma to demonstrate the possibility of using mfERG as a tool to detect glaucomatous damage. Two patients with glaucoma were recruited and had mfERG measurements with the 103-scaled hexagonal stimulus pattern at low (50 per cent) contrast. Their responses were analysed and compared with those from normal subjects with the mfERG measured under the same condition. In the normal subjects, there were obvious oscillatory components on the ascending and descending limbs of the first-order kernel response to 50 per cent contrast. In the glaucomatous patients, the oscillatory component on the descending limb was obviously diminished. In addition, this component was significantly diminished in the quadrant with a glaucomatous visual field defect. This suggests that the low-contrast stimulation condition in mfERG measurement may provide a good way to detect glaucomatous damage and this may help in clinical diagnosis of glaucoma.

Interocular symmetry of abnormal multifocal electroretinograms in adolescents with diabetes and no retinopathy

PURPOSE

To investigate, in adolescents with type 1 diabetes and no retinopathy, the spatial correspondence between abnormal multifocal electroretinogram (mfERG) responses in the two eyes.

METHODS

mfERG and fundus photographs were measured in both eyes of 68 adolescents with type 1 diabetes and no retinopathy (13 to 19 years old; best corrected visual acuity ≥ 20/20), and 30 age-matched controls. The mfERG stimulus was comprised of 103 hexagons, and subtended 45°. mfERG implicit times (IT) and amplitudes (AMP) were derived. Fifteen patients for IT, and five for AMP with at least one eye defined as abnormal (six or more locations with abnormal Z-scores; P < 0.03) were analyzed.

RESULTS

Nasal retina had significantly more abnormal IT locations compared with temporal retina (P = 0.015), and the opposite was true with regard to abnormal AMP (P < 0.001). The proportion of abnormal responses in the superior retina was not significantly different from that in the inferior retina (P > 0.1 for IT and AMP). Interocular correspondence of locations with abnormal mfERG IT was significant for all 15 patients (P values <0.0001-0.012), and agreement between eyes was 68% to 94% (AC1 agreement coefficient: 0.48-0.94). Overall interocular correspondence was also significant (P < 0.0002), with 86% agreement (AC1 = 0.76). Overall interocular correspondence of locations with abnormal mfERG AMP was also significant (P < 0.0002).

CONCLUSIONS

Interocular spatial correspondence of abnormal mfERG responses exists in adolescents with type 1 diabetes and no retinopathy. This is most apparent for IT abnormalities. This correspondence could be used in clinical trials, and raises the possibility of initiating treatment in both eyes at early disease stages as new topical treatments emerge.

Investigation of the temporal properties of the retina using the m-sequence

The mfERG provides a topographic map of function of the retina and has been used in numerous studies to identify macular, paramacular and peripheral retinal dysfunction. This study investigates the changes in response due to the presentation rate of the stimulus. Twenty subjects gave informed consent to take part in the study, which had local regional ethical committee approval. Only a single hexagon of 8° diameter was presented to reduce ambiguity when identifying the higher-order kernels (HOK). Six rates were tested using a 60-Hz CRT monitor by introducing blank (black ~0 cd/m2) filler frames (FF). The rates tested were 0FF; 1FF; 2FF; 4FF; 7FF; and 14FF. The first-order kernel had largest responses to the slower stimuli (4FF and above). HOK had largest amplitudes at faster rates with the second-order kernel peaking at 1FF. At rates with 4FF and slower, the higher-order kernels were indiscernible above the noise.

Multifocal ERG defects associated with insufficient long-term glycemic control in adolescents with type 1 diabetes

PURPOSE

To investigate the relationship between long-term glycemic control and localized neuroretinal function in adolescents with type 1 diabetes (T1D) without diabetic retinopathy (DR).

METHODS

Standard (103 hexagons) and slow-flash (61 hexagons) multifocal ERGs (standard mfERG and sf mfERG) were recorded in 48 patients and 45 control subjects. Hexagons with delayed responses were identified as abnormal. Negative binomial regression analysis was conducted with the number of abnormal hexagons as the outcome variable. Glycated hemoglobin (HbA(1c)) levels, time since diagnosis of T1D, age at diagnosis of T1D, age at testing, and sex were the covariates. Another model replacing HbA(1c) closest to the date of testing with a 1-year average was also generated.

RESULTS

There were more abnormal hexagons for mfOPs in patients than in control subjects (P = 0.005). There was no significant difference in the mean number of abnormal hexagons for standard mfERG responses between patients and control subjects (P = 0.11). Negative binomial regression analysis for the standard mfERG data demonstrated that a 1-unit increase in HbA(1c) was associated with an 80% increase in the number of abnormal hexagons (P = 0.002), when controlling for age at testing. Analysis using the 1-year HbA(1c) averages did not result in significant findings.

CONCLUSIONS

Poor long-term glycemic control is associated with an increase in areas of localized neuroretinal dysfunction in adolescents with T1D and no clinically visible DR. Stricter glucose control during the early stages of the disease may prevent neuroretinal dysfunction in this cohort.

Cone-mediated multifocal electroretinogram in early age-related maculopathy and its relationships with subjective macular function tests

PURPOSE

To investigate the multifocal electroretinogram (mfERG) and subjective function in early age-related maculopathy (ARM).

METHODS

Seventeen subjects with early ARM with visual acuity (VA) of 6/12 or better and 20 age-matched control subjects were examined. We assessed mfERGs, high and low contrast distance VA, near VA, low luminance VA, contrast sensitivity, saturated and desaturated Panel D-15 and visual fields (mean sensitivity). The mfERG responses were analysed by comparing central-overall (method 1) and superior-inferior (method 2) ratios.

RESULTS

The mfERG did not discriminate between the groups whereas colour vision (tritan deficiency), contrast sensitivity, and high contrast and low contrast VA showed significantly reduced responses for the early ARM group compared with the control group (p < or = 0.01). The mfERG first-order kernel responses correlated significantly with the desaturated D-15 in both methods (r = -0.5, p < or = 0.05). Fundus grading was not correlated with the mfERG measures.

CONCLUSIONS

Although the mfERG correlated significantly with the desaturated D-15 in early ARM, suggesting it operates at a sensitive level, it failed to discriminate between the control and ARM groups. In our sample, the subjective function measures were more sensitive than the mfERG measures.

Emergence of sustained spontaneous hyperactivity and temporary preservation of OFF responses in ganglion cells of the retinal degeneration (rd1) mouse

Complex alterations in the anatomy of outer retinal pathways accompany photoreceptor degeneration in the rd1 mouse model of retinitis pigmentosa, whereas inner retinal neurons appear relatively preserved. However, the progressive loss of photoreceptor input likely alters the neural circuitry of the inner retina. This study investigated resulting changes in the activity of surviving ganglion cells. Multielectrode recording monitored spontaneous and light-evoked extracellular action potentials simultaneously from 30 to 90 retinal ganglion cells of wild-type (wt) or rd1 mice. In rd1 mice, this activity evolves through three phases. First, normal spontaneous "waves" of correlated firing are seen at postnatal day 7 (P7) and last until shortly after eye opening. Second, at P14, full-field light flashes evoke reliable responses in many cells, with preferential preservation of off responses. These diminish as photoreceptor degeneration progresses. Third, once light-evoked responses have disappeared in early adulthood, surviving rd1 ganglion cells fire at a much higher spontaneous frequency than normal, sometimes in rhythmic bursts that are distinct from the developmental "waves." This hyperactivity is sustained well into adulthood, for weeks after photoreceptors have disappeared. Thus striking alterations occur in inner retinal physiology as retinal degeneration progresses in the rd1 mouse. Blindness occurs in the face of sustained hyperactivity among ganglion cells, which remain viable for months despite this activity. On and off responses are differentially affected in early stages of degeneration. While the source of these changes remains to be learned, such features should be considered in designing more effective treatments for these disorders.

Multifocal electroretinogram for assessing sun damage following the solar eclipse of 29 March 2006

AIM

To evaluate the clinical findings and multifocal electroretinography results of cases with solar maculopathy due to eclipse watching.

PATIENTS AND METHOD

Eight eyes of six patients (ages ranged 12-42) who presented to our clinic after the solar eclipse of 29 March 2006 were evaluated in the study. All patients underwent a full ophthalmologic examination and multifocal electroretinography (mfERG).

RESULTS

Visual acuities at the initial examination were between 20/32 and 20/20; and at final examination between 20/25 and 20/20 respectively. Fundoscopic examination disclosed macular pigmentary changes in almost all patients. Fundus Fluorescein Angiography revealed a window defect in six eyes. The initial findings of the mfERG at the first visit showed a decrease in the P1 and N1 amplitudes of the central responses. The following mfERG recordings showed a recovery in central P1 and N1 amplitudes.

CONCLUSION

Decrease in P1 and N1 amplitudes of central macular region can be detected by mfERG in patients with solar maculopathy. Follow-up mfERG test results may recover with the increase of visual acuity.

A multifocal electroretinogram model predicting the development of diabetic retinopathy

The prevalence of diabetes has been accelerating at an alarming rate in the last decade; some describe it as an epidemic. Diabetic eye complications are the leading cause of blindness in adults aged 25-74 in the United States. Early diagnosis and development of effective preventatives and treatments of diabetic retinopathy are essential to save sight. We describe efforts to establish functional indicators of retinal health and predictors of diabetic retinopathy. These indicators and predictors will be needed as markers of the efficacy of new therapies. Clinical trials aimed at either prevention or early treatments will rely heavily on the discovery of sensitive methods to identify patients and retinal locations at risk, as well as to evaluate treatment effects. We report on recent success in revealing local functional changes of the retina with the multifocal electroretinogram (mfERG). This objective measure allows the simultaneous recording of responses from over 100 small retinal patches across the central 45 degrees field. We describe the sensitivity of mfERG implicit time measurement for revealing functional alterations of the retina in diabetes, the local correspondence between functional (mfERG) and structural (vascular) abnormalities in eyes with early nonproliferative retinopathy, and longitudinal studies to formulate models to predict the retinal sites of future retinopathic signs. A multivariate model including mfERG implicit time delays and 'person' risk factors achieved 86% sensitivity and 84% specificity for prediction of new retinopathy development over one year at specific locations in eyes with some retinopathy at baseline. A preliminary test of the model yielded very positive results. This model appears to be the first to predict, quantitatively, the retinal locations of new nonproliferative diabetic retinopathy development over a one-year period. In a separate study, the predictive power of a model was assessed over one- and two-year follow-ups. This permitted successful prediction of new retinopathy development in eyes with and without retinopathy at baseline. Finally, we briefly describe our current research efforts to (a) locally predict future sight-threatening diabetic macular edema, (b) investigate local retinal function change in adolescent patients with diabetes, and (c) better understand the physiological bases of the mfERG delays. The ability to predict the retinal locations of future retinopathy based on mfERG implicit time provides clinicians a powerful tool to screen, follow-up, and even consider early prophylactic treatment of the retinal tissue in diabetic patients. It also aids identification of 'at risk' populations for clinical trials of candidate therapies, which may greatly reduce their cost by decreasing the size of the needed sample and the duration of the trial.

Cone- and rod-mediated multifocal electroretinogram in early age-related maculopathy

PURPOSE

To investigate the cone- and rod-mediated multifocal electroretinograms (mfERG) in early age-related maculopathy (early ARM).

METHODS AND SUBJECTS

We investigated the cone- and rod-mediated mfERG in 17 eyes of 17 subjects with early ARM and 16 eyes of 16 age-matched control subjects with normal fundi. All subjects had a visual acuity of 6/12 or better. We divided the ARM subjects into two groups based on drusen size and retinal pigment epithelium abnormalities-a less advanced (ARM1) and a more advanced (ARM2) group. The mfERG data were compared to templates derived from the control group. We analysed the mfERG results for the central and peripheral fields (CP method) and the superior and inferior fields (SI method).

RESULTS

While the mean cone results showed no statistically significant difference between the groups, the rods showed significantly delayed responses in the ARM1 group for the CP and the SI methods, but not in the ARM2 group, although there was a trend of longer latencies compared to the control group.

CONCLUSION

Our results show a functional impairment of the rods in early ARM subjects. As there is histopathological evidence showing earlier rod than cone impairment in early ARM, following the rod function with the mfERG might be helpful in diagnosis or for monitoring the progression of early ARM.

Transient reduction in retinal function revealed by multifocal electroretinogram after photodynamic therapy

PURPOSE

To evaluate the early changes in retinal function after photodynamic therapy (PDT) by multifocal electroretinogram (mfERG).

DESIGN

Prospective interventional case series.

METHODS

Seventeen eyes from 17 patients scheduled for standard PDT with verteporfin were prospectively recruited. Patients' diagnoses included choroidal neovascularization (CNV) secondary to age-related macular degeneration, idiopathic CNV, myopic CNV, polypoidal choroidal vasculopathy, and central serous chorioretinopathy. Serial mfERG recordings were performed before PDT, and at 4 days, 2 weeks, and 1 month after PDT. The first-order kernel N1 and P1 mfERG response from the central 0 to 7 degrees and peripheral 7 to 25 degrees were grouped and analyzed. The mean response amplitudes and peak latencies of the mfERG recordings were compared longitudinally.

RESULTS

There were statistically significant reductions in the mean N1 response amplitude for the central group at 4 days (P =.007) and 2 weeks after PDT (P =.024), in the mean P1 response amplitude for both the central (P =.006) and peripheral (P =.013) groups at 4 days, and for the central group at 2 weeks after PDT (P =.017). There were also statistically significant increases in the mean P1 response latencies at 4 days (P =.004) and at 2 weeks (P =.018) after PDT for the central group and at 4 days after PDT (P =.026) for the peripheral group. At 1 month after PDT, no significant differences in the N1 and P1 mean response amplitudes and peak latencies were observed compared with pre-PDT mfERG.

CONCLUSIONS

Transient impairments in retinal function for as long as 2 weeks after PDT were noticed by reduction in response amplitudes and a delay in peak latencies of mfERG. These findings may explain the common adverse event of subjective visual disturbance early after PDT with normal findings in visual acuity and ophthalmoscopy.