Assessing retinal function with the multifocal technique

Effects of Macuprev® Supplementation in Age-Related Macular Degeneration: A Double-Blind Randomized Morpho-Functional Study Along 6 Months of Follow-Up

Background

To evaluate the effects of Macuprev^® supplementation on macular function and structure in intermediate age-related macular degeneration (AMD) along 6 months of follow-up.

Methods

In this double-blind, monocentric, randomized, and prospective study, 30 patients with intermediate AMD were enrolled and randomly divided into two age-similar groups: 15 patients (AMD-M group; mean age 68.50 ± 8.79 years) received 6-month oral daily supplementation with Macuprev^® (Farmaplus Italia s.r.l., Italy, two tablets/day on an empty stomach, before meals; contained in total lutein 20 mg, zeaxanthin 4 mg, N-acetylcysteine 140 mg, bromelain 2500GDU 80 mg, vitamin D₃ 800 IU, vitamin B₁₂ 18 mg, alpha-lipoic acid 140 mg, rutin 157 mg, vitamin C 160 mg, zinc oxide 16 mg, Vaccinium myrtillus 36% anthocyanosides 90 mg, Ganoderma lucidum 600 mg) and 15 patients (AMD-P group; mean age 70.14 ± 9.87) received two tablets of placebo daily on an empty stomach, before meals. A total of 28 eyes, 14 from each AMD group, completed the study. Multifocal electroretinogram (mfERG) and spectral domain-optical coherence tomography (SD-OCT) were assessed at baseline and after 6 months.

Results

At 6-month follow-up, AMD-M eyes showed a significant increase of mfERG response amplitude density (RAD) recorded from the central macular areas (ring 1, 0–2.5°; ring 2, 2.5–5°), whereas non-significant changes of retinal and choroidal SD-OCT parameters were found when values were compared to baseline. Non-significant correlations between functional and structural changes were found. In AMD-P eyes, non-significant differences for each mfERG and SD-OCT parameters were observed at 6 months.

Conclusions

In intermediate AMD, Macuprev^® supplementation increases the function of the macular pre-ganglionic elements, with no associated retinal and choroidal ultra-structural changes.

Trial Registration

ClinicalTrials.gov identifier, NCT03919019.

Funding

Research for this study was financially supported by the Italian Ministry of Health and Fondazione Roma. Article processing charges were funded by Farmaplus Italia s.r.l., Italy.

Outer Retinal Dysfunction on Multifocal Electroretinography May Help Differentiating Multiple Sclerosis From Neuromyelitis Optica Spectrum Disorder

Purpose: To evaluate the intermediate and outer retina of patients with multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) using OCT and multifocal electroretinography (mf-ERG). Methods: Patients with MS (n = 30), NMOSD (n = 30), and healthy controls (n = 29) underwent visual field (VF), OCT, and mf-ERG testing. The eyes were distributed into 5 groups: MS with or without history of ON (MS+ON, MS-ON), NMOSD with or without ON (NMOSD+ON, NMOSD-ON), and controls. The thickness of the macular retinal nerve fiber layer (mRNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer, outer plexiform layer, outer nuclear layer, and photoreceptor layer was measured. mf-ERG P1 and N1 responses were registered and grouped in 3 sets of rings. The groups were compared using GEE models, and effect size (ES) calculated. Results: Compared to controls, GCL and IPL thickness was significantly smaller in MS+ON (both p < 0.01), MS-ON (p < 0.01 and p = 0.015, respectively), NMOSD+ON (both p < 0.01) and NMOSD-ON (p = 0.03 and p = 0.018, respectively). ES was >0.80. mRNFL was smaller in three of the above groups (p < 0.01, p < 0.001, and p = 0.028; ES > 0.80) but not in MS-ON eyes (p = 0.18). No significant difference was observed for the remaining layers. Compared to controls, P1 and N1 peak times were shorter in MS (p-values in the range 0.049-0.002, ES < 0.50; and 0.049-0.010; ES < 0.50, respectively) but not in NMOSD. These abnormalities were strongly correlated with intermediate and outer retinal layer thickness. Conclusions: mf-ERG data suggest outer retinal abnormalities in MS, but not in NMOSD. Our results may help understand how the two conditions differ regarding retinal damage.

Current perspectives in Bietti crystalline dystrophy

Bietti crystalline dystrophy (BCD) is a rare-inherited disease caused by mutations in the CYP4V2 gene and characterized by the presence of multiple shimmering yellow-white deposits in the posterior pole of the retina in association with atrophy of the retinal pigment epithelium (RPE) and chorioretinal atrophy. The additional presence of glittering dots located at the corneal limbus is also a frequent finding. The CYP4V2 protein belongs to the cytochrome P450 subfamily 4 and is mainly expressed in the retina and the RPE and less expressed in the cornea. The disease has its metabolic origin in the diminished transformation of fatty acid substrates into n-3 polyunsaturated fatty acids due to a dysregulation of the lipid metabolism. In this review, we provide updated insights on clinical and molecular characteristics of BCD including underlying mechanisms of BCD, genetic diagnosis, progress in the identification of causative genetic and epigenetic factors, available techniques of exploration and development of novel therapies. This information will help clinicians to improve accuracy of BCD diagnosis, providing the patient reliable information regarding prognosis and clinical prediction of the disease course.

Multifocal electroretinogram findings in sickle cell maculopathy

BACKGROUND

The aim of the present work was to describe and compare multifocal electroretinogram findings (mfERG) between patients with sickle cell disease (SCD) without clinical sign of maculopathy and controls (HbAA).

METHODS

Both HbSS (homozygous SCD) and HbSC (compound heterozygous SCD) patients, the two most frequent SCD genotypes, were included. All individuals underwent a full ophthalmologic examination (with a fundoscopy), a spectral domain ocular coherence tomography (SD-OCT) and a mfERG.

RESULTS

A total of 86 subjects were included: 54 SCD patients (107 eyes) with 32 HbSS (63 eyes) and 22 HbSC (44 eyes) and 32 controls (64 eyes). None of the eyes showed retinal clinical abnormalities. SD-OCT analysis showed that macular thickness was statistically lower in SCD eyes than in controls. mfERG analysis demonstrated a significant reduction of N1 (initial-negative deflection), and P1 (positive peak) response amplitude densities of HbSS eyes compared to HbAA eyes from the centre (<2°) and to the periphery (>15°). Implicit time response was also reduced in the centre (<2°). N1 and P1 response amplitude densities of HbSC eyes were significantly lower than those of HbAA eyes from the centre (<2°) to the periphery (>15°). N1 implicit time was statistically reduced in HbSS compared to HbSC eyes.

CONCLUSION

Our study is the first one to describe macular electrophysiological dysfunction in SCD patients. Moreover, we confirm that SCD maculopathy is equally frequent in HbSS and HbSC.

The Protective Effects of Blue Light-Blocking Films With Different Shielding Rates: A Rat Model Study

Purpose

To examine light emitting diode (LED)-induced retinal photochemical damage and assess the protective performance of blue light-shielding films with different shielding rates in Sprague-Dawley rats (SD rats).

Methods

SD rats were randomly divided into five groups: blank control (group I), white LED illumination (group II), and white LED illumination combined with shielding of blue light of wavelength 440 nm at 40%, 60%, and 80% (groups III, IV, and V). The illumination was 200 lux. All animals underwent electroretinography (ERG), hematoxylin-eosin (H&E) staining, immunohistochemical (IHC) staining, and transmission electron microscopy (TEM) observation after 14 days of dark-adaptation before illumination, after 14 days of cyclic illumination, and after 14 days of darkness for recovery following illumination.

Results

ERG showed retinal functional loss after LED light exposure. However, retinal cell function was partly recovered after a further 2 weeks of dark adaptation. H&E staining and TEM revealed increases in photoreceptor cell death after illumination. IHC staining demonstrated that oxidative stress was associated with retinal injury. Although retinal light injury was discovered in the LED light-exposure groups, shielding 60% of blue light of wavelength 440 nm (bandwidth 20 nm) protected retinas.

Conclusions

Cyclic illumination of low light intensity (200 lux) for 14 days produced retinal degeneration; shielding 60% of blue light may protect retinas from light damage.

Translational Relevance

This study found the effective shielding rate that could protect retinas from light damage when shielding specific narrow-band harmful blue light; thus providing a more normative method for protecting eyes from blue light hazard.

Five-Year Trends in Multifocal Electroretinogram for Patients With Birdshot Chorioretinopathy

PURPOSE

The aim of this study is to investigate temporal trends in multifocal ERG (mfERG) parameters and analyze their relationships with anatomic and functional markers in patients with birdshot chorioretinopathy (BSCR).

DESIGN

Prospective observational case series.

METHODS

Sixteen BSCR patients were include and underwent 2 standardized follow-up (FU) visits within 5 years following a baseline examination, including mfERG, visual acuity (VA), visual field (VF), Lanthony desaturated panel D-15 test for color vision, quality of life (QoL), fluorescein and indocyanine green angiography, and optical coherence tomography (OCT).

RESULTS

A significant trend toward a decrease in absolute N1 amplitude values was observed over the follow-up period (P < .001) while N1 implicit time remained unchanged. In contrast, P1 amplitude decreased (P < .001) and P1 implicit time increased (P < .001) over the same period. No significant temporal change was found for VA, color vision score, foveal threshold, mean deviation of VF, and QoL. After adjusting for time to FU, increasing N1 and P1 IT were both associated with decreasing values of logMAR, foveal threshold, and QoL and with increasing color vision score and mean deviation of VF. A significant relationship was observed between decreasing P1 amplitude values and increasing mean deviation of VF. Lower absolute values of N1 amplitude were associated with venous vasculitis, whereas lower P1 amplitude values correlated with alteration of the outer retina in OCT.

CONCLUSIONS

Progressive deterioration in mfERG during a 5-year period is detected in BSCR, whereas classical functional test results were unchanged. This study suggests a better sensitivity of mfERG in monitoring the retinal function of BSCR patients.

Changes in fundus reflectivity during myopia development in chickens

Previous studies have shown that changes in functional activity in the retina can be visualized as changes in fundus reflectivity. When the image projected on the retina is low pass filtered or defocused by covering the eye with a frosted diffuser or a negative lens, it starts growing longer and develops myopia. We have tested the hypothesis that the resulting altered retinal activity may show up as changes in fundus reflectivity. Fundus reflectivity was measured in chickens in vivo, both in visible (400-800 nm, white) and near ultraviolet (UV) light (315-380 nm). Two CCD cameras were used; a RGB camera and a camera sensitive in near UV light (peak sensitivity at 360 nm). White and UV LEDs, respectively, placed in the center of the camera lens aperture, served as light sources. Software was written to flash the LEDs and record the average brightness of the pupil that was illuminated by light reflected from the fundus. The average pixel grey level (px) in the pupil was taken as a measure of the amount of reflected light while refractive errors were corrected by trial lenses after pupil brightness was corrected for pupil size. It was found that myopic eyes had brighter pupils in UV light, compared to eyes with normal vision, no matter whether myopia was induced by diffusers or negative lenses (48 ± 9 vs. 28 ± 3, p<0.001 and 47 ± 7 vs. 27 ± 2, respectively). Using SD-OCT in alert chickens it was found that the retinal nerve fiber layer (RNFL) and the retinal ganglion cell layer (RGCL) in the central retina became thinner already at early stages of myopia development, compared to controls (31.2 ± 5.8 µm vs. 43.9 ± 2.6 µm, p<0.001 and 36.9 ± 1.2 µm vs. 44 ± 0.5 µm, respectively). While the decrease in RNFL thickness occurred concomitantly with the increase in UV reflectivity, it remains unclear whether these changes were causally linked. Thinning of the RNFL could be due to reduced neural activity in retinal ganglion cells but also due to metabolic changes in the retina during myopia development.

Classification of disease severity in retinitis pigmentosa

AIM

To develop a simple and easily applicable classification of disease severity in retinitis pigmentosa (RP).

METHODS

This is a retrospective cross-sectional study. Visual acuity (VA), visual field width (VF) and ellipsoid zone width (EZ) were obtained from medical records of patients with RP. A scoring criterion was developed wherein each variable was assigned a score from 0 to 5 depending on its distribution. The cumulative score (from 0 to 15) was used to classify disease severity from grade 0 to 5. The scores were correlated with each other and the final grade. The grades were then correlated with age and disease duration.

RESULTS

The median age (range) of patients (n=93) was 55 (12-87) years, 51% were female, 70% had been diagnosed within 10 years, and 50% had autosomal recessive disease. Most eyes (n=181) at least had a VA of 20/40 (67%), a VF of 20° (75%) and an EZ of 5° (76%). All scores were correlated with each other (r=0.509-0.613; p<0.001 for all) and with the final grade (r=0.790-0.869; p<0.001 for all). Except for grade 0 (5%), all grades were evenly distributed: 21% for grade 1, 23% for grade 2, 22% for grade 3, 17% for grade 4 and 12% for grade 5. Grades were correlated with both age (r=0.252; p<0.001) and disease duration (r=0.383; p<0.001).

CONCLUSIONS

We present a simple, objective and easy to use disease severity classification for RP which can be used to categorise and compare patients.

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

Purpose

To investigate the relationship between perfusion of the choriocapillaris (CC) and macular function in eyes with intermediate age-related macular degeneration.

Methods

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.

Results

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.

Conclusions

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.

Non-syndromic retinitis pigmentosa

Retinitis pigmentosa (RP) encompasses a group of inherited retinal dystrophies characterized by the primary degeneration of rod and cone photoreceptors. RP is a leading cause of visual disability, with a worldwide prevalence of 1:4000. Although the majority of RP cases are non-syndromic, 20-30% of patients with RP also have an associated non-ocular condition. RP typically manifests with night blindness in adolescence, followed by concentric visual field loss, reflecting the principal dysfunction of rod photoreceptors; central vision loss occurs later in life due to cone dysfunction. Photoreceptor function measured with an electroretinogram is markedly reduced or even absent. Optical coherence tomography (OCT) and fundus autofluorescence (FAF) imaging show a progressive loss of outer retinal layers and altered lipofuscin distribution in a characteristic pattern. Over the past three decades, a vast number of disease-causing variants in more than 80 genes have been associated with non-syndromic RP. The wide heterogeneity of RP makes it challenging to describe the clinical findings and pathogenesis. In this review, we provide a comprehensive overview of the clinical characteristics of RP specific to genetically defined patient subsets. We supply a unique atlas with color fundus photographs of most RP subtypes, and we discuss the relevant considerations with respect to differential diagnoses. In addition, we discuss the genes involved in the pathogenesis of RP, as well as the retinal processes that are affected by pathogenic mutations in these genes. Finally, we review management strategies for patients with RP, including counseling, visual rehabilitation, and current and emerging therapeutic options.

ELECTROPHYSIOLOGICAL CHARACTERIZATION OF MACULAR TELANGIECTASIA TYPE 2 AND STRUCTURE-FUNCTION CORRELATION

PURPOSE

To investigate the electrophysiological features of macular telangiectasia Type 2 and their relationship to structure as determined by optical coherence tomography imaging.

METHODS

Forty-two eyes from 21 patients enrolled in the Macular Telangiectasia Natural History Observation Study were reviewed. All patients had full-field and pattern electroretinography (ERG; PERG) with some patients additionally having multifocal electroretinography (mfERG; N = 15) or electrooculography (N = 12). Multiple linear regression modeling assessed the relationship between the ellipsoid zone break size on optical coherence tomography and the central mfERG response.

RESULTS

Full-field ERG and electrooculography were normal in all eyes. Six eyes (14%) from five patients had subnormal PERG P50 amplitudes. Twenty-two of 30 eyes (73%) had reduced central or paracentral stimulus on mfERG. There was a significant correlation between ellipsoid zone break size and both the P1 amplitude (R = 0.37, P = 0.002) and P1:N1 ratio (R = 0.32, P = 0.002) of the central response on mfERG.

CONCLUSION

The electrophysiological findings in macular telangiectasia Type 2 are those of localized central dysfunction and are consistent with the structural data available from imaging and histologic studies. The ellipsoid zone break size correlates with mfERG reduction. The reduced mfERG P1:N1 ratio is consistent with inner retinal dysfunction.

Retinal dysfunction characterizes subtypes of dominant optic atrophy

PURPOSE

To assess preganglionic retinal function using multifocal electroretinogram (mfERG) in patients affected by dominant optic atrophy (DOA) stratified by OPA1 gene mutation.

METHODS

Multifocal electroretinogram (mfERG) was recorded in 18 DOA patients (DOA group, 35 eyes) and 25 age-matched healthy subjects (control group, 25 eyes). Patients were stratified in two groups based on gene mutation: missense mutation (DOA-M group, 11 eyes) and mutation causing haploinsufficiency (DOA-H group, 24 eyes). The mfERG N1-P1 response amplitude density (RAD) has been evaluated in five annular retinal areas with different eccentricity from the fovea (ring 1: 0-5 degrees, R1; ring 2: 5-10 degrees, R2; ring 3: 10-15 degrees, R3; ring 4: 15-20 degrees, R4; and ring 5: 20-25 degrees, R5) and in eight sectors on the basis of the retinal topography: temporal-superior (TS), temporal-inferior (TI), nasal-superior (NS) and nasal-inferior (NI), temporal (T), superior (S), nasal (N) and inferior (I).

RESULTS

Compared to controls, DOA group revealed a significant reduction in N1-P1 RADs values in R1-R4 rings and in TI, NS and N sectors [analysis of variance (ANOVA), p < 0.01). DOA-M group showed a significant reduction in N1-P1 RADs values in R1-R5 rings and in TI, NS, NI, T, N and I sectors (p < 0.01). Dominant optic atrophy-H (DOA-H) group displayed only a significant (p < 0.01) reduction in N1-P1 RADs values, exclusively in R1 and in the NS sector.

CONCLUSION

Preganglionic retinal impairment occurs in DOA with a clear genotype to retinal dysfunction association. Missense mutations are characterized by a far more severe functional impairment.

CLINICAL AND ELECTROPHYSIOLOGICAL EVALUATION AFTER INTRAVITREAL ZIV-AFLIBERCEPT FOR EXUDATIVE AGE-RELATED MACULAR DEGENERATION

Fifteen patients with exudative age-related macular degeneration were treated with intravitreal injections of ziv-aflibercept (1.25 mg). Ziv-aflibercept improved the best-corrected visual acuity, multifocal electroretinography amplitudes, and central retinal thickness from baseline to 26 weeks. No retinal toxicity on full-field electroretinography or adverse events occurred during the follow-up period.

To evaluate the 6-month safety and efficacy of ziv-aflibercept intravitreal injections for treating exudative age-related macular degeneration.

Measuring Retinal Function in the Mouse

Electroretinography is a crucial assay for studying the function and the functional integrity of the retina. The mouse is an important animal model for studying the retinal neurons and circuitries. In addition, it is often used as animal model for human retinal disorders. Therefore, a good understanding of the procedures in animal handling, of the methods for data analysis and of the requirements for stimulators and for the data acquisition equipment is of importance. Here, the currently most common methods and materials for in vivo electroretinography in the mouse are discussed.

Morphological and Functional Inner and Outer Retinal Layer Abnormalities in Eyes with Permanent Temporal Hemianopia from Chiasmal Compression

Purpose

The aims of this study are to compare optical coherence tomography (OCT)-measured macular retinal layers in eyes with permanent temporal hemianopia from chiasmal compression and control eyes; to compare regular and slow-flash multifocal electroretinography (mfERG) in patients and controls; and to assess the correlation between OCT, mfERG, and central visual field (SAP) data.

Methods

Forty-three eyes of 30 patients with permanent temporal hemianopia due to pituitary tumors who were previously submitted to chiasm decompression and 37 healthy eyes of 19 controls were submitted to macular spectral domain OCT, mfERG, and 10-2 SAP testing. After segmentation, the thickness of the macular retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer, and photoreceptor layer (PRL) was measured. Amplitudes and oscillatory potentials (OPs) were measured on regular and slow-flash mfERG, respectively, and expressed as the mean values per quadrant and hemifield.

Results

RNFL, GCL, and IPL thickness measurements were significantly reduced in all quadrants, whereas INL, OPL, and PRL thicknesses were significantly increased in the nasal quadrants in patients compared to those in controls. Significant correlations between OCT and 10-2 SAP measurements were positive for the RNFL, GCL, and IPL and negative for the INL, OPL, and PRL. OPs and mfERG N1 amplitudes were significantly reduced in the nasal hemiretina of patients. Significant correlations were found between OP and mfERG amplitudes for inner and outer nasal hemiretina OCT measurements, respectively.

Conclusion

Patients with permanent temporal hemianopia from previously treated chiasmal compression demonstrated significant thinning of the RNFL, GCL, IPL, and thickening of the INL, OPL, and PRL associated with reduced OP and mfERG N1 amplitudes, suggesting that axonal injury to the inner retina leads to secondary damage to the outer retina in this condition.

A Temporal White Noise Analysis for Extracting the Impulse Response Function of the Human Electroretinogram

PURPOSE

We introduce a method for determining the impulse response function (IRF) of the ERG derived from responses to temporal white noise (TWN) stimuli.

METHODS

This white noise ERG (wnERG) was recorded in participants with normal trichromatic vision to full-field (Ganzfeld) and 39.3° diameter focal stimuli at mesopic and photopic mean luminances and at different TWN contrasts. The IRF was obtained by cross-correlating the TWN stimulus with the wnERG.

RESULTS

We show that wnERG recordings are highly repeatable, with good signal-to-noise ratio, and do not lead to blink artifacts. The wnERG resembles a flash ERG waveform with an initial negativity (N1) followed by a positivity (P1), with amplitudes that are linearly related to stimulus contrast. These N1 and N1-P1 components showed commonalties in implicit times with the a- and b-waves of flash ERGs. There was a clear transition from rod- to cone-driven wnERGs at ∼1 photopic cd.m-2. We infer that oscillatory potentials found with the flash ERG, but not the wnERG, may reflect retinal nonlinearities due to the compression of energy into a short time period during a stimulus flash.

CONCLUSION

The wnERG provides a new approach to study the physiology of the retina using a stimulation method with adaptation and contrast conditions similar to natural scenes to allow for independent variation of stimulus strength and mean luminance, which is not possible with the conventional flash ERG.

TRANSLATIONAL RELEVANCE

The white noise ERG methodology will be of benefit for clinical studies and animal models in the evaluation of hypotheses related to cellular redundancy to understand the effects of disease on specific visual pathways.

Multifocal ERG Responses in Subjects With a History of Preterm Birth

Purpose

The purpose of this study is to assess cone-mediated central retinal function in children with a history of preterm birth, including subjects with and without retinopathy of prematurity (ROP). The multifocal electroretinogram (mfERG) records activity of the postreceptor retinal circuitry.

Methods

mfERG responses were recorded to an array of 103 hexagonal elements that subtended 43° around a central fixation target. The amplitude and latency of the first negative (N1) and first positive (P1) response were evaluated in six concentric rings centered on the fovea. Responses were recorded from 40 subjects with a history of preterm birth (severe ROP, mild ROP, no ROP) and 19 term-born control subjects.

Results

The amplitude of N1 and P1 varied significantly with eccentricity and ROP severity. For all four groups, these amplitudes were largest in the center and decreased with eccentricity. At all eccentricities, N1 amplitude was significantly smaller in severe ROP and did not differ significantly among the other three groups (mild ROP, no ROP, term-born controls). P1 amplitude in all preterm groups was significantly smaller than in controls; P1 amplitude was similar in no ROP and mild ROP and significantly smaller in severe ROP.

Conclusions

These results provide evidence that premature birth alone affects cone-mediated central retinal function and that the magnitude of the effect varies with severity of the antecedent ROP. The lack of difference in mfERG amplitude between the mild and no ROP groups is evidence that the effect of ROP on the neurosensory retina may not depend solely on appearance of abnormal retinal vasculature.

Association between Asymptomatic Unilateral Internal Carotid Artery Stenosis and Electrophysiological Function of the Retina and Optic Nerve

Purpose. This study was designed to assess retinal and optic nerve bioelectrical function in patients with unilateral asymptomatic but hemodynamically significant internal carotid artery stenosis (ICAS). Methods. Forty-two subjects with a diagnosis of unilateral ICAS and 34 controls were analyzed. Full-field electroretinogram (ERG), pattern electroretinogram (PERG), and pattern visual-evoked potentials, as well as optical coherence tomography and ophthalmological examination, were performed. Data analysis included eyes ipsilateral to ICAS (EIS) and eyes contralateral to ICAS (ECS). Results. Intraocular pressure was significantly decreased in EIS and ECS compared to that in the controls. In the macula, both the cube average thickness and cube volume values were significantly reduced both in EIS and ECS compared to those in the controls. Similarly, PERG P50 and N95 wave amplitudes were significantly smaller in EIS and ECS compared to those in the controls. The ERG rod b-wave and rod-cone a-wave amplitudes were decreased, and implicit times were significantly prolonged, whereas the OP wave index was reduced in EIS compared to that in the controls. No differences in IOP, OCT, or ERG and PERG parameters were identified between EIS and ECS. Conclusions. Our study demonstrated that retinal bioelectrical function is negatively affected by ICAS despite the absence of objective clinical signs and symptoms of ocular ischemia.

Time-Dependent Decline in Multifocal Electroretinogram Requires Faster Recording Procedures in Anesthetized Pigs

Purpose

The time-dependent effect of anesthetics on the retinal function is debated. We hypothesize that in anesthetized animals there is a time-dependent decline that requires optimized multifocal electroretinogram (mfERG) recording procedures.

Methods

Conventional and four-frame global-flash mfERG recordings were obtained approximately 15, 60, and 150 minutes after the induction of propofol anesthesia (20 pigs) and isoflurane anesthesia (nine pigs). In six of the propofol-anesthetized pigs, the mfERG recordings were split in 3-minute segments. Two to 4 weeks after initial recordings, an intraocular injection of tetrodotoxin (TTX) was given and the mfERG was rerecorded as described above. Data were analyzed using mixed models in SAS statistical software.

Results

Propofol significantly decreases the conventional and global-flash amplitudes over time. The only significant effect of isoflurane is a decrease in the global-flash amplitudes. At 15 minutes after TTX injection several of the mfERG amplitudes are significantly decreased. There is a linear correlation between the conventional P1 and the global-flash DR mfERG-amplitude (R² = 0.82, slope = 0.72, P < 0.0001). There is no significant difference between the 3-minute and the prolonged mfERG recordings for conventional amplitudes and the global-flash direct response. The global flash–induced component significantly decreases with prolonged mfERG recordings.

Conclusions

A 3-minute mfERG recording and a single stimulation protocol is sufficient in anesthetized pigs. Recordings should be obtained immediately after the induction of anesthesia. The effect of TTX is significant 15 minutes after injection, but is contaminated by the effect of anesthesia 90 minutes after injection. Therefore, the quality of mfERG recordings can be further improved by determining the necessary time-of-delay from intraocular injection of a drug to full effect.

Translational Relevance

General anesthesia is a possible source of error in mfERG recordings. Therefore, it is important to investigate the translational relevance of the results to mfERG recordings in children in general anesthesia.

Testing the clinical value of multifocal electroretinography and microperimetry and the effects of intravitreal therapy with ranibizumab on macular function in the course of wet age-related macular degeneration: a 1-year prospective study

Purpose

To investigate the clinical value of multifocal electroretinography (mfERG) and microperimetry and the effects of intravitreal therapy with ranibizumab (Lucentis^®) on macular function in the course of neovascular age-related macular degeneration (nAMD).

Materials and methods

We conducted a prospective single-arm interventional cohort study with 20 nAMD patients older than 50 years. Examinations were scheduled monthly for 1 year during intravitreal therapy with ranibizumab. The examinations included mfERG, microperimetry, spectral domain optical coherence tomography, and best-corrected visual acuity using ETDRS score.

Results

During the 12-month observation period, a significant positive linear correlation between the logarithm of minimum angle of resolution (logMAR) and scotoma area (r=0.28, 95% confidence interval [CI] 0.21–0.35), between logMAR and fovea thickness in optical coherence tomography (r=0.11, 95% CI 0.04–0.2), and a significant negative correlation between logMAR and mfERG (−0.37, 95% CI −0.43 to −0.31) were observed. A significant ranibizumab effect on logMAR was found (P=0.0065). From a total of 25 relapses, 14 were able to be predicted correctly by mfERG P₁ decrease in the preceding month. However, there was no statistically significant relation between prediction and observed relapses (Fisher’s exact test, P=0.6726).

Conclusion

Our results indicate a possible role of mfERG and microperimetry in the monitoring of macular function and prediction of recurrence during intravitreal pharmacotherapy in wet AMD.

Comparing three different modes of electroretinography in experimental glaucoma: diagnostic performance and correlation to structure

PURPOSE

To compare diagnostic performance and structure-function correlations of multifocal electroretinogram (mfERG), full-field flash ERG (ff-ERG) photopic negative response (PhNR) and transient pattern-reversal ERG (PERG) in a non-human primate (NHP) model of experimental glaucoma (EG).

METHODS

At baseline and after induction of chronic unilateral IOP elevation, 43 NHP had alternating weekly recordings of retinal nerve fiber layer thickness (RNFLT) by spectral domain OCT (Spectralis) and retinal function by mfERG (7F slow-sequence stimulus, VERIS), ff-ERG (red 0.42 log cd-s/m² flashes on blue 30 scotopic cd/m² background, LKC UTAS-E3000), and PERG (0.8° checks, 99% contrast, 100 cd/m² mean, 5 reversals/s, VERIS). All NHP were followed at least until HRT-confirmed optic nerve head posterior deformation, most to later stages. mfERG responses were filtered into low- and high-frequency components (LFC, HFC, >75 Hz). Peak-to-trough amplitudes of LFC features (N1, P1, N2) and HFC RMS amplitudes were measured and ratios calculated for HFC:P1 and N2:P1. ff-ERG parameters included A-wave (at 10 ms), B-wave (trough-to-peak) and PhNR (baseline-to-trough) amplitudes as well as PhNR:B-wave ratio. PERG parameters included P50 and N95 amplitudes as well as N95:P50 ratio and N95 slope. Diagnostic performance of retinal function parameters was compared using the area under the receiver operating characteristic curve (A-ROC) to discriminate between EG and control eyes. Correlations to RNFLT were compared using Steiger's test.

RESULTS

Study duration was 15 ± 8 months. At final follow-up, structural damage in EG eyes measured by RNFLT ranged from 9% above baseline (BL) to 58% below BL; 29/43 EG eyes (67%) and 0/43 of the fellow control eyes exhibited significant (>7%) loss of RNFLT from BL. Using raw parameter values, the largest A-ROC findings for mfERG were: HFC (0.82) and HFC:P1 (0.90); for ff-ERG: PhNR (0.90) and PhNR:B-wave (0.88) and for PERG: P50 (0.64) and N95 (0.61). A-ROC increased when data were expressed as % change from BL, but the pattern of results persisted. At 95% specificity, the diagnostic sensitivity of mfERG HFC:P1 ratio was best, followed by PhNR and PERG. The correlation to RNFLT was stronger for mfERG HFC (R = 0.65) than for PhNR (R = 0.59) or PERG N95 (R = 0.36), (p = 0.20, p = 0.0006, respectively). The PhNR flagged a few EG eyes at the final time point that had not been flagged by mfERG HFC or PERG.

CONCLUSIONS

Diagnostic performance and structure-function correlation were strongest for mfERG HFC as compared with ff-ERG PhNR or PERG in NHP EG.

The neural retina in retinopathy of prematurity

Retinopathy of prematurity (ROP) is a neurovascular disease that affects prematurely born infants and is known to have significant long term effects on vision. We conducted the studies described herein not only to learn more about vision but also about the pathogenesis of ROP. The coincidence of ROP onset and rapid developmental elongation of the rod photoreceptor outer segments motivated us to consider the role of the rods in this disease. We used noninvasive electroretinographic (ERG), psychophysical, and retinal imaging procedures to study the function and structure of the neurosensory retina. Rod photoreceptor and post-receptor responses are significantly altered years after the preterm days during which ROP is an active disease. The alterations include persistent rod dysfunction, and evidence of compensatory remodeling of the post-receptor retina is found in ERG responses to full-field stimuli and in psychophysical thresholds that probe small retinal regions. In the central retina, both Mild and Severe ROP delay maturation of parafoveal scotopic thresholds and are associated with attenuation of cone mediated multifocal ERG responses, significant thickening of post-receptor retinal laminae, and dysmorphic cone photoreceptors. These results have implications for vision and control of eye growth and refractive development and suggest future research directions. These results also lead to a proposal for noninvasive management using light that may add to the currently invasive therapeutic armamentarium against ROP.

[Electrophysiology in ophthalmology]

Electrophysiology is an objective functional test of the visual pathway and allows the location of visual dysfunctions to be detected. The flash electroretinogram (ERG) allows recognition of large area damage to the retina and can distinguish between rod and cone diseases by recording under both dark and light-adapted conditions. Specific stimulation techniques are used for the multifocal ERG (mfERG) which reveals localized retinal dysfunction, e. g. in maculopathies. The pattern ERG (PERG) is an indicator of ganglion cell function and can be used for early detection of glaucoma. The visual evoked potential (VEP) is a cortical response and serves as a functional test of the entire visual pathway from the eye to the visual system of the brain. After presenting each of these methods individually, the article gives assistance in situations where the appropriate electrophysiological method for a given clinical hypothesis is to be selected and explains how the methods can be combined in a reasonable way.

In vivo optical coherence tomography of stimulus-evoked intrinsic optical signals in mouse retinas

Intrinsic optical signal (IOS) imaging promises a noninvasive method for advanced study and diagnosis of eye diseases. Before pursuing clinical applications, it is essential to understand anatomic and physiological sources of retinal IOSs and to establish the relationship between IOS distortions and eye diseases. The purpose of this study was designed to demonstrate the feasibility of <italic<in vivo</italic< IOS imaging of mouse models. A high spatiotemporal resolution spectral domain optical coherence tomography (SD-OCT) was employed for depth-resolved retinal imaging. A custom-designed animal holder equipped with ear bar and bite bar was used to minimize eye movements. Dynamic OCT imaging revealed rapid IOS from the photoreceptor’s outer segment immediately after the stimulation delivery, and slow IOS changes were observed from inner retinal layers. Comparative photoreceptor IOS and electroretinography recordings suggested that the fast photoreceptor IOS may be attributed to the early stage of phototransduction before the hyperpolarization of retinal photoreceptor.

Preserved functional and structural integrity of the papillomacular area correlates with better visual acuity in retinitis pigmentosa

PurposeLinking multifocal electroretinography (mfERG) and optical coherence tomography (OCT) findings with visual acuity in retinitis pigmentosa (RP) patients.DesignProspective, cross-sectional, nonintervention study.SubjectsPatients with typical RP and age-matched controls, who underwent SD-OCT (spectral domain OCT) and mfERG, were included.MethodsMfERG responses were averaged in three zones (zone 1 (0°-3°), zone 2 (3°-8°), and zone 3 (8°-15°)). Baseline-to-trough- (N1) and trough-to-peak amplitudes (N1P1) of the mfERG were compared with corresponding areas of the OCT. The papillomacular area (PMA) was analyzed separately. Correlations between best-corrected visual acuity (BCVA, logMAR) and each parameter were determined.Main outcome measuresComparing structural (OCT) and functional (mfERG) measures with the BCVA.ResultsIn RP patients, the N1 and N1P1 responses showed positive association with the central retinal thickness outside zone 1 (P≤0.002), while the central N1 and the N1P1 responses in zones 1, 2, and 3-with the BCVA (P≤0.007). The integrity of the IS/OS line on OCT showed also a positive association with the BCVA (P<0.001). Isolated analysis of the PMA strengthened further the structure-function association with the BCVA (P≤0.037). Interactions between the BCVA and the OCT, respectively, the mfERG parameters were more pronounced in the RP subgroup without macular edema (P≤0.020).ConclusionIn RP patients, preserved structure-function of PMA, measured by mfERG amplitude and OCT retinal thickness, correlated well with the remaining BCVA. The subgroup analyses revealed stronger links between the examined parameters, in the RP subgroup without appearance of macular edema.

Electroretinography in glaucoma diagnosis

PURPOSE OF REVIEW

Electrophysiological measures of vision function have for decades generated interest among glaucoma researchers and clinicians alike because of their potential to help elucidate pathophysiological processes and sequence of glaucomatous damage, as well as to offer a potential complementary metric of function that might be more sensitive than standard automated perimetry. The purpose of this article is to review the recent literature to provide an update on the role of the electroretinogram (ERG) in glaucoma diagnosis.

RECENT FINDINGS

The pattern reversal ERG (PERG) and the photopic negative response (PhNR) of the cone-driven full-field, focal or multifocal ERG provide objective measures of retinal ganglion cell function and are all sensitive to glaucomatous damage. Recent studies demonstrate that a reduced PERG amplitude is predictive of subsequent visual field conversion (from normal to glaucomatous) and an increased rate of progressive retinal nerve fiber layer thinning in suspect eyes, indicating a potential role for PERG in risk stratification. Converging evidence indicates that some portion of PERG and PhNR abnormality represents a reversible aspect of dysfunction in glaucoma.

SUMMARY

PERG and PhNR responses obtained from the central macula are capable of detecting early-stage, reversible glaucomatous dysfunction.

Therapeutic effect of dexamethasone implant in retinal vein occlusions resistant to anti-VEGF therapy

Purpose

To test the efficacy of the intravitreal dexamethasone (DEX) implant in patients with retinal vein occlusions (RVOs) who have failed multiple anti-vascular endothelial growth factor (anti-VEGF) treatments.

Methods

A randomized exploratory study of ten patients with branch RVO or central RVO who received at least two previous anti-VEGF treatments and had persistent or unresponsive cystoid macular edema. Treatment with the DEX implant was either every 4 months or pro re nata (PRN) depending on their group assignment for 1 year. Multifocal electroretinography and microperimetry were the primary end points, with high-resolution optical coherence tomography and best-corrected visual acuity as the secondary end points.

Results

All patients in both the every 4 month and PRN cohorts who completed the study received the three maximal injections of DEX; therefore, the data from both cohorts were combined and reported as a case series. On average, the multifocal electroretinography amplitude increased significantly from 5.11±0.66 to 24.19±5.30 nV/deg2 at 12 months (P<0.005), mean macular sensitivity increased from 7.67±2.10 to 8.01±1.98 dB at 4 months (P=0.32), best-corrected visual acuity increased significantly from 51.0±5.1 to 55.4±5.1 early treatment of diabetic retinopathy study letters at 2 months (P<0.05), and central retinal thickness decreased from 427.6±39.5 to 367.1±37.8 μm at 4 months (P<0.05). Intraocular pressure increased significantly in one patient, with that patient requiring an additional glaucoma medication for management. Additionally, cataract progression increased significantly (P<0.05) in this patient population and partially limited analysis of other end points.

Conclusion

DEX should be considered as a treatment option in patients with RVOs who have failed anti-VEGF therapy, as the results of this study demonstrated an improvement in retinal morphology and macular function. Cataract progression did occur following multiple consecutive injections; however, steroid-induced glaucoma was not a limiting factor.

Metabolic and functional changes in retinitis pigmentosa: comparing retinal vessel oximetry to full-field electroretinography, electrooculogram and multifocal electroretinography

PURPOSE

To determine a relationship between the retinal vessel saturation alterations and the residual retinal function measured by means of full-field electroretinography (full-field ERG), electrooculogram (EOG) and multifocal electroretinography (mfERG) in patients with retinitis pigmentosa (RP).

METHODS

Retinal vessel oximetry (RO), full-field ERG, EOG and mfERG were performed on 43 eyes of 22 patients suffering from RP and were compared to those of 26 eyes of 13 healthy controls. The oxygen saturation in the first and second branch retinal arterioles (A-SO2 ) and venules (V-SO2 ) was measured, and their difference (A-V SO2 ) was calculated. Full-field ERG amplitudes, EOG parameters and averaged mfERG response amplitudes (within central 3°, between 3° and 8°, 8° and 15°, 15° and 24°) were evaluated in relation to the RO measurements.

RESULTS

V-SO2 correlated negatively with the full-field ERG and EOG values, with increasing functional damage the V-SO2 was higher. The RP group was well distinguished from the controls when the RO measurements were correlated to the averaged N1 (baseline to trough), but also to the N1P1 (trough-to-peak) mfERG response amplitudes. Receiver operating characteristic (ROC) curve of V-SO2 , compared to those of N1 and N1P1 mfERG response averages (15-24°), presented a high differential margin between RP and controls (p < 0.001), shown by an area under the ROC curve of 0.912 (95% CI: 0.840-0.984).

CONCLUSION

Retinal vessel saturation showed a significant relation to full-field ERG, EOG and mfERG. Thus, retinal vessel oximetry could potentially complement electrophysiological tests in monitoring disease progression in patients with RP.

In vivo intrinsic optical signal imaging of mouse retinas

Intrinsic optical signal (IOS) imaging is a promising noninvasive method for advanced study and diagnosis of eye diseases. Before pursuing clinical applications, more IOS studies employing animal models are necessary to establish the relationship between IOS distortions and eye diseases. Ample mouse models are available for investigating the relationship between IOS distortions and eye diseases. However, in vivo IOS imaging of mouse retinas is challenging due to the small ocular lens (compared to frog eyes) and inevitable eye movements. We report here in vivo IOS imaging of mouse retinas using a custom-designed functional OCT. The OCT system provided high resolution (3 μm) and high speed (up to 500 frames/s) imaging of mouse retinas. An animal holder equipped with a custom designed ear bar and bite bar was used to minimize eye movement due to breathing and heartbeats. Residual eye movement in OCT images was further compensated by accurate image registration. Dynamic OCT imaging revealed rapid IOSs from photoreceptor outer segments immediately (<10 ms) after the stimulation delivery, and unambiguous IOS changes were also observed from inner retinal layers with delayed time courses compared to that of photoreceptor IOSs.

The effects of fundus photography on the multifocal electroretinogram

PURPOSE

To determine the effect of flash fundus photography (FFP) on the multifocal electroretinogram (mfERG).

METHODS

Ten subjects underwent mfERG testing on three separate dates. Subjects received either mfERG without FFP, mfERG at 5 and 15 min after FFP, or mfERG at 30 and 45 min after FFP on each date. The FFP groups received 10 fundus photographs followed by mfERG testing, first of the right eye then of the left eye 10 min later. Data were averaged and analyzed in six concentric rings at each time point. Average amplitude and implicit times of the N1, P1, and N2 peaks for each concentric ring at each time point after FFP were compared to baseline.

RESULTS

Flash fundus photography did not lead to a significant change of amplitude or implicit times of N1, P1, or N2 at 5 min after light exposure.

CONCLUSIONS

These findings suggest that it is acceptable to perform mfERG testing without delay after performance of FFP.

Peripapillary retinal vessel diameter correlates with mfERG alterations in retinitis pigmentosa

PURPOSE

To investigate relationship between the peripapillary retinal vessel diameter and the residual retinal function, measured by mfERG, in patients with retinitis pigmentosa (RP).

PATIENTS AND METHODS

A cross-sectional study based on 23 patients with RP (43 eyes) and 20 controls (40 eyes) was performed. Retinal vessel diameters were measured using a computer-based program of the retinal vessel analyser (RVA; IMEDOS Systems UG, Jena, Germany). We evaluated the mean diameter in all four major retinal arterioles (D-A) and venules (D-V) within 1.0-1.5 optic disc diameters from the disc margin. The data were compared with the N1 amplitudes (measured from the baseline to the trough of the first negative wave), with the N1P1 amplitudes (measured from the trough of the first negative wave to the peak of the first positive wave) of the mfERG overall response and with the mfERG responses averaged in zones [zone 1 (0°-3°), zone 2 (3°-8°), zone 3 (8°-15°) and zone 4 (15°-24°)].

RESULTS

Mean (±SD) D-A and D-V were narrower in patients with RP [84.86 μm (±13.37 μm) and 103.35 μm (±13.65 μm), respectively] when compared to controls [92.81 μm (±11.49 μm) and 117.67 μm (±11.93 μm), respectively; the p-values between groups were p = 0.003 for D-A and p < 0.001 for D-V, linear mixed-effects model]. The RP group revealed clear differences compared to the controls: D-A and D-V became narrower with reduced mfERG responses. D-V correlated significantly with the overall mfERG N1 amplitudes (p = 0.013) and with N1P1 amplitudes (p = 0.016). D-V correlated with the mfERG amplitudes averaged in zones: (zone 2, 3 and 4; p ≤ 0.040) and N1P1 mfERG amplitudes (zones 1, 2, 3 and 4; p ≤ 0.013).

CONCLUSIONS

Peripapillary retinal vessel diameter is reduced in RP proportionally to functional alterations.

Multifocal Electroretinogram in Diabetic Macular Edema; Correlation with Visual Acuity and Optical Coherence Tomography

Purpose:

To evaluate multifocal electroretinogram (mfERG) changes in eyes with diabetic macular edema (DME) and investigate any possible correlation with optical coherence tomography (OCT) features and visual acuity (VA).

Methods:

Twenty-nine right eyes of 29 subjects with DME due to non-proliferative diabetic retinopathy and 30 eyes of 30 normal subjects were evaluated. All patients underwent a complete ophthalmic examination. Sixty-one scaled hexagon mfERG responses were recorded. Components of the first order kernel of N1, N2, and P1 in five concentric rings centered on the fovea, were measured in both groups. Correlation and regression analyses were performed among VA, central macular thickness (CMT) based on OCT, mfERG amplitude, and latency of the N1, N2 and P1 waves.

Results:

Significant differences were observed in all mfERG parameters in five-ring regions of the retina between eyes with DME versus controls (P < 0.05). There were significant correlations among VA with N2 (P = 0,001, b = 0.73) and P1 amplitudes (P = 0.001, b = −0.84) in the central macular area, and there was a borderline association between VA and CMT (P = 0.042, b = 0.392).

Conclusion:

Amplitudes of mfERG components (N1, P1, and N2) are significantly reduced and their latencies are delayed in eyes with DME indicating functional impairment in the outer retina. The mfERG total amplitude was significantly correlated with VA even more than CMT, therefore the combined use of OCT and mfERG for macular evaluation may better evaluate visual status in DME patients.

Intrinsic optical signal imaging of retinal physiology: a review

Intrinsic optical signal (IOS) imaging promises to be a noninvasive method for high-resolution examination of retinal physiology, which can advance the study and diagnosis of eye diseases. While specialized optical instruments are desirable for functional IOS imaging of retinal physiology, in depth understanding of multiple IOS sources in the complex retinal neural network is essential for optimizing instrument designs. We provide a brief overview of IOS studies and relationships in rod outer segment suspensions, isolated retinas, and intact eyes. Recent developments of line-scan confocal and functional optical coherence tomography (OCT) instruments have allowed in vivo IOS mapping of photoreceptor physiology. Further improvements of the line-scan confocal and functional OCT systems may provide a feasible solution to pursue functional IOS mapping of human photoreceptors. Some interesting IOSs have already been detected in inner retinal layers, but better development of the IOS instruments and software algorithms is required to achieve optimal physiological assessment of inner retinal neurons.

Evidence for an enduring ischaemic penumbra following central retinal artery occlusion, with implications for fibrinolytic therapy

The rationale behind hyperacute fibrinolytic therapy for cerebral and retinal arterial occlusion is to rescue ischaemic cells from irreversible damage through timely restitution of tissue perfusion. In cerebral stroke, an anoxic tissue compartment (the "infarct core") is surrounded by a hypoxic compartment (the "ischaemic penumbra"). The latter comprises electrically-silent neurons that undergo delayed apoptotic cell death within 1-6 h unless salvaged by arterial recanalisation. Establishment of an equivalent hypoxic compartment within the inner retina following central retinal artery occlusion (CRAO) isn't widely acknowledged. During experimental CRAO, electroretinography reveals 3 oxygenation-based tissue compartments (anoxic, hypoxic and normoxic) that contribute 32%, 27% and 41% respectively to the pre-occlusion b-wave amplitude. Thus, once the anoxia survival time (≈2 h) expires, the contribution from the infarcted posterior retina is irreversibly extinguished, but electrical activity continues in the normoxic periphery. Inbetween these compartments, an annular hypoxic zone (the "penumbra obscura") endures in a structurally-intact but functionally-impaired state until retinal reperfusion allows rapid recovery from electrical silence. Clinically, residual circulation of sufficient volume flow rate generates the heterogeneous fundus picture of "partial" CRAO. Persistent retinal venous hypoxaemia signifies maximal extraction of oxygen by an enduring "polar penumbra" that permeates or largely replaces the infarct core. On retinal reperfusion some days later, the retinal venous oxygen saturation reverts to normal and vision improves. Thus, penumbral inner retina, marginally oxygenated by the choroid or by residual circulation, isn't at risk of delayed apoptotic infarction (unlike hypoxic cerebral cortex). Emergency fibrinolytic intervention is inappropriate, therefore, once the duration of CRAO exceeds 2 h.

Functional optical coherence tomography enables in vivo physiological assessment of retinal rod and cone photoreceptors

Transient intrinsic optical signal (IOS) changes have been observed in retinal photoreceptors, suggesting a unique biomarker for eye disease detection. However, clinical deployment of IOS imaging is challenging due to unclear IOS sources and limited signal-to-noise ratios (SNRs). Here, by developing high spatiotemporal resolution optical coherence tomography (OCT) and applying an adaptive algorithm for IOS processing, we were able to record robust IOSs from single-pass measurements. Transient IOSs, which might reflect an early stage of light phototransduction, are consistently observed in the photoreceptor outer segment almost immediately (<4 ms) after retinal stimulation. Comparative studies of dark- and light-adapted retinas have demonstrated the feasibility of functional OCT mapping of rod and cone photoreceptors, promising a new method for early disease detection and improved treatment of diseases such as age-related macular degeneration (AMD) and other eye diseases that can cause photoreceptor damage.

Prediction of higher visual function in macular degeneration with multifocal electroretinogram and multifocal visual evoked potential

OBJECTIVE

Visual search can be guided by past experience of regularities in our visual environment. This search guidance by contextual memory cues is impaired by foveal vision loss. Here we compared retinal and cortical visually evoked responses in their predictive value for contextual cueing impairment and visual acuity.

METHODS

Multifocal electroretinograms to flash stimulation (mfERGs; 103 locations; 55.8° diameter) and visual evoked potentials to pattern-reversal stimulation (mfVEPs; 60 locations; 48.6° diameter) were recorded monocularly in participants with age-related macular degeneration (n = 14 and 16, respectively). Response magnitudes were calculated as the respective signal-to-noise ratios for each eccentricity. Visual acuities (logMAR, range: 0.0-1.2) and contextual cueing effects on visual search (reaction time gain, range: -0.14-0.15) were correlated with the signal-to-noise ratios. A step-wise regression analysis was applied separately to the mfERG- and mfVEP-dataset to determine the eccentricity range and the processing stage that is critical for these visual functions.

RESULTS

Central mfERGs (1.0-3.2°) were the sole predictor of contextual cueing of visual search (p = 0.006), but they were not significant predictors of visual acuity. In contrast, central mfVEPs (1.3-3.2°) were the sole predictor of visual acuity (p < 0.001), but they were not significant predictors of contextual cueing.

CONCLUSIONS

Contextual cueing is more dependent on parafoveal mfERG magnitude while visual acuity is more dependent on parafoveal mfVEP magnitude. The relation of contextual cueing to parafoveal mfERG magnitudes indicates the predictive value of retinal bipolar cell activity for this advanced level of visual function.

Relation between macular retinal ganglion cell/inner plexiform layer thickness and multifocal electroretinogram measures in experimental glaucoma

PURPOSE

We investigated relations between macular retinal ganglion cell plus inner plexiform layer (RGC+IPL) thickness and macular retinal function revealed by multifocal electroretinonography (mfERG) in a nonhuman primate model of experimental glaucoma.

METHODS

Retinal ganglion cell (RGC) structure and function were followed with spectral-domain optical coherence tomography (SD-OCT) and ERGs in five macaques with unilateral experimental glaucoma. Linear regression was used to study correlations in control (Con) and experimental (Exp) eyes between peripapillary retinal nerve fiber layer (RNFL) thickness, macular RGC+IPL thickness, multifocal photopic negative response (mfPhNR) and high-frequency multifocal oscillatory potentials (mfOP) in slow-sequence mfERG, and low-frequency component (mfLFC) in global-flash mfERG. We used ANOVA and paired t-tests to compare glaucoma-related mfERG changes between superior and inferior hemifields, foveal hexagon, inner three rings, and four quadrants of macula.

RESULTS

Average macular RGC+IPL and temporal RNFL thickness were strongly correlated (r(2) = 0.90, P < 0.001). In hexagon-by-hexagon analysis, all three mfERG measures were correlated (P < 0.001) with RGC+IPL thickness for Con (r(2), 0.33-0.51) and Exp eyes (r(2), 0.17-0.35). The RGC structural and functional metrics decreased as eccentricity increased. The reduction in amplitude of mfERG measures in Exp eyes relative to Con eyes was proportionally greater, in general, than the relative thinning of RGC+IPL at the same location for eyes in which structural loss was not evident, or mild to moderate. Although not statistically significant, percent amplitude reduction of mfERG measures was greatest in the inferior temporal quadrant.

CONCLUSIONS

Macular RGC+IPL thickness and mfERG measures of RGC function can be complementary tools in assessing glaucomatous neuropathy.

The value of clinical electrophysiology in the assessment of the eye and visual system in the era of advanced imaging

Electrophysiological techniques allow clinical investigations to include a 'dissection' of the visual system. Using suitable electrophysiological techniques, the 'dissection' allows function to be ascribed to the different photoreceptors (rod and cone photoreceptors), retinal layers, retinal location or the visual pathway up to the visual cortex. Combined with advances in genetics, retinal biochemistry, visual fields and ocular imaging, it is now possible to obtain a better understanding of diseases affecting the retina and visual pathways. This paper reviews core electrophysiological principles that can complement other examination techniques, including advanced ocular imaging, and help the interpretation of other clinical data and thus, refine and guide clinical diagnosis.

Multifocal electroretinography in diabetic retinopathy and diabetic macular edema

In this review article, we first present a brief overview of the vascular and neural components of diabetic retinopathy. Next, the multifocal electroretinogram (mfERG) technique, which can map neuroretinal function noninvasively, is described. Findings in diabetic retinal disease using the mfERG are reviewed. We then describe the progress that has been made to predict the onset and progression of diabetic retinopathy and edema in specific retinal locations, using quantitative models based on the mfERG. Finally, we consider the implications for the future of these predictive models.

Cone pathway function in relation to asymmetric carotid artery stenosis: correlation to blood pressure

PURPOSE

To examine retinal function in relation to retinal perfusion pressure in patients with carotid artery stenosis.

METHODS

Thirteen patients with carotid artery stenosis without clinical eye disease underwent assessment of ophthalmic artery systolic blood pressure (OSP) by ocular pneumoplethysmography, carotid artery obstructive disease by ultrasonography, intraocular pressure by applanation tonometry, retinal perfusion by fluorescein angiography and retinal function by multifocal electroretinography (mfERG). Data analysis compared the eye on the most stenotic side with the fellow eye in the same patient.

RESULTS

Ophthalmic systolic pressure was 95.8 ± 13.1 mmHg on the side with the highest degree of carotid artery stenosis (mean 94.0%) and 111.7 ± 10.3 mmHg in the fellow eyes on the side with the lesser degree of stenosis (mean 33.9%). Summed mfERG implicit times (N1 and P1) were 3.4% and 2.0% longer (p = 0.013 and 0.021), and N1 and P1 amplitudes were 18.0% and 16.0% (p = 0.0041 and 0.020) lower in eyes on the side with the higher stenosis compared with the contralateral eyes. Shorter implicit times and higher amplitudes were correlated with higher brachial systolic arterial blood pressure (p = 0.0028, 0.011, 0.041 for N1, P1, N2 implicit times, respectively, and p = 0.0086, 0.016, 0.040 for N1, P1, N2 for amplitudes, respectively, corrected for OSP).

CONCLUSION

Cone function deviation was observed in clinically healthy eyes on the side with highest degree of carotid artery stenosis and was found correlated to arterial blood pressure.

Hemi-field and full-field form-deprivation induce timing changes in multifocal ERG responses in chick

PURPOSE

In animal models hemi-field deprivation results in localised, graded vitreous chamber elongation and presumably deprivation induced localised changes in retinal processing. The aim of this research was to determine if there are variations in ERG responses across the retina in normal chick eyes and to examine the effect of hemi-field and full-field deprivation on ERG responses across the retina and at earlier times than have previously been examined electrophysiologically.

METHODS

Chicks were either untreated, wore monocular full-diffusers or half-diffusers (depriving nasal retina) (n = 6-8 each group) from day 8. mfERG responses were measured using the VERIS mfERG system across the central 18.2º× 16.7º (H × V) field. The stimulus consisted of 61 unscaled hexagons with each hexagon modulated between black and white according to a pseudorandom binary m-sequence. The mfERG was measured on day 12 in untreated chicks, following 4 days of hemi-field diffuser wear, and 2, 48 and 96 h after application of full-field diffusers.

RESULTS

The ERG response of untreated chick eyes did not vary across the measured field; there was no effect of retinal location on the N1-P1 amplitude (p = 0.108) or on P1 implicit time (p > 0.05). This finding is consistent with retinal ganglion cell density of the chick varying by only a factor of two across the entire retina. Half-diffusers produced a ramped retina and a graded effect of negative lens correction (p < 0.0001); changes in retinal processing were localized. The untreated retina showed increasing complexity of the ERG waveform with development; form-deprivation prevented the increasing complexity of the response at the 2, 48 and 96 h measurement times and produced alterations in response timing.

CONCLUSIONS

Form-deprivation and its concomitant loss of image contrast and high spatial frequency images prevented development of the ERG responses, consistent with a disruption of development of retinal feedback systems. The characterisation of ERG responses in normal and deprived chick eyes across the retina allows the assessment of concurrent visual and retinal manipulations in this model.

En face optical coherence tomography of transient light response at photoreceptor outer segments in living frog eyecup

This study was designed to test the feasibility of en face mapping of the transient intrinsic optical signal (IOS) response at photoreceptor outer segments and to assess the effect of spatial resolution on functional IOS imaging of retinal photoreceptors. A line-scan optical coherence tomography (LS-OCT) was constructed to achieve depth-resolved functional IOS imaging of living frog eyecups. Rapid en face OCT revealed transient IOS almost immediately (<3 ms) after the onset of visible light flashes at photoreceptor outer segments. Quantitative analysis indicated that the IOS kinetics may reflect dynamics of G-protein binding and releasing in early phases of visual transduction, and high resolution is essential to differentiate positive and negative IOS changes in adjacent locations.

Differential effects of optic media opacities on mfERGs and mfVEPs

OBJECTIVE

To assess different effects of image degradation that could result from optic media opacities on multifocal retinal (mfERG) and cortical responses (mfVEP).

METHODS

Monocular flash-mfERGs and pattern-reversal mfVEPs were recorded. MfERG-P1 amplitudes and implicit times and mfVEP root-mean-square values (RMS) and delays were compared for different filter conditions (none, 8% luminance, 50% luminance, 50% luminance plus blur) in a total of ten participants with normal vision.

RESULTS

Reducing stimulus luminance down to 50% and 8% reduced mfERG amplitudes to 86% and 42%, respectively, with no significant effect on mfVEP amplitude. Implicit times were increased for mfERGs by 0.9 ms and 6.0 ms, respectively, and for mfVEPs by 1.0 ms and 6.3 ms, respectively. For '50% luminance plus blur' mfERG amplitudes were significantly reduced centrally and enhanced peripherally and delayed by 1.3 ms. MfVEPs were reduced close to noise level independent of eccentricity.

CONCLUSIONS

Degradation of the retinal image is a potential source of discrepancies between mfERGs and mfVEPs. Image blur suppresses the mfVEP at all locations and changes mfERG topography, resulting in a selective loss of central responses.

SIGNIFICANCE

Considering optic media opacities is of importance for the correct interpretation of mfERG and mfVEP recordings, particularly in elderly patients.