International Society For Clinical Electrophysiology Of Vision Research Articles

Baseline Detrending for the Photopic Negative Response.

PurposeThe photopic negative response (PhNR) of the light-adapted electroretinogram (ERG) holds promise as an objective marker of retinal ganglion cell function. We compared baseline detrending methods to improve PhNR repeatability without compromising its diagnostic ability in glaucoma.MethodsPhotopic ERGs were recorded in 20 glaucoma and 18 age-matched control participants. A total of 50 brief, red-flashes (1.6 cd.s/m2) on a blue background (10 photopic cd/m2) were delivered using the RETeval device. Detrending methods compared were: (1) increasing the high-pass filter from 1 to 10 Hz and (2) estimating and removing the trend with an increasing polynomial (order from 1–10) applied to the prestimulus interval, prestimulus and postsignal interval, or the whole ERG signal. Coefficient of repeatability (COR%), unpaired Student's t-test, and area under the receiver operating characteristic curve (AUC) were used to compare the detrending methods.ResultsMost detrending methods improved PhNR test–retest repeatability compared to the International Society for Clinical Electrophysiology of Vision (ISCEV) recommended 0.3 to 300 Hz band-pass filter (COR% ± 200%). In particular, detrending with a polynomial (order 3) applied to the whole signal performed the best (COR% ± 44%) while achieving similar diagnostic ability as ISCEV band-pass (AUC 0.74 vs. 0.75, respectively). However, over-correcting with higher orders of processing can cause waveform distortion and reduce diagnostic ability.ConclusionsBaseline detrending can improve the PhNR repeatability without compromising its clinical use in glaucoma. Further studies exploring more complex processing methods are encouraged.Translational RelevanceBaseline detrending can significantly improve the quality of the PhNR.

Electroretinogram abnormalities in nonanterior childhood uveitis.

PurposeA major point of concern in uveitis is the development of irreversible retinal changes after inflammation. In this study, we assess how nonanterior childhood uveitis affects retinal function using full‐field electroretinography (ERG).MethodsCross‐sectional study. ERGs of 63 uveitis eyes (33 children) were measured according to extended International Society for Clinical Electrophysiology of Vision (ISCEV) protocols. ERG abnormalities were investigated in relation to the following clinical parameters: demographics, uveitis characteristics, including severity of inflammation, treatment, best corrected visual acuity (BCVA), cystoid macular oedema (CME) on optical coherence tomography and fluorescein angiography score.ResultsThe ERG showed abnormalities in 34 eyes (54%). The most frequent ERG abnormalities were prolonged implicit times of the cone b‐wave (37%; n = 23/63) and an abnormal 30‐Hz flicker response (implicit time and/or amplitude) (33%; n = 21/63). Factors associated with these ERG abnormalities were CME (p = 0.021) and 3+ vitreous cells (p = 0.021). BCVA in eyes with and without these ERG abnormalities did not statistically differ and was relatively good (median: 0.05 LogMAR, IQR: 0.00–0.15 LogMAR).ConclusionThe ERG is frequently affected in childhood uveitis indicating a global retinal dysfunction. ERG abnormalities seem to be associated with a more severe posterior segment inflammation and a younger age. If an association between ERG abnormalities and long‐term visual outcome can be made in the future, these early ERG findings during the course of childhood uveitis have significance for treatment strategies.

ISCEV extended protocol for the dark-adapted red flash ERG

The International Society for Clinical Electrophysiology of Vision (ISCEV) standard for full-field electroretinography (ERG) describes a minimum procedure, but encourages more extensive testing. This ISCEV extended protocol describes an extension to the ERG standard, namely the dark-adapted (DA) red flash ERG. The DA red flash ERG can be incorporated conveniently within the ISCEV standard ERG protocol after a minimum of 20-min DA and recorded after the DA 0.01 ERG to a flash strength of 0.3 phot cd s m−2, eliciting a waveform with two positive peaks in healthy individuals. The first positive component is the cone-mediated x-wave with a peak at 30–50 ms; the second is a rod-mediated b-wave with a peak time of approximately 100 ms. Shorter DA times may be desirable to shorten the recording time or to alter the prominence of the early cone-mediated x-wave relative to the rod-mediated b-wave. The DA red flash ERG is used to aid the diagnosis of achromatopsia (rod monochromacy), cone dystrophy and other forms of cone system dysfunction, including “Bradyopsia” (RGS9/R9AP-retinopathy), when the DA red flash ERG x-wave is preserved in the absence of ISCEV standard LA ERGs. The DA red flash ERG can also help determine the origin of residual DA ERGs in cases of severe rod dysfunction, for example in disorders such as vitamin A deficiency, fundus albipunctatus (RDH5-retinopathy), Oguchi disease (SAG- or GRK1-retinopathy) and some rod-cone dystrophies. To shorter DA periods, the x-wave may be elicited without the following rod b-wave, shown to be helpful in abbreviated protocols for children.

ISCEV extended protocol for the photopic On\u2013Off ERG

The International Society for Clinical Electrophysiology of Vision (ISCEV) standard for full-field electroretinography (ERG) describes a minimum procedure, but encourages more extensive testing. This ISCEV extended protocol describes an extension to the ERG standard, namely the photopic On–Off ERG, and outlines common clinical applications. A light stimulus duration of 150–200 ms is used in the presence of a rod-suppressing background to elicit cone-driven On- and Off-system ERG components. The On-response occurs after the stimulus onset and has a negative a-wave and positive b-wave. The Off d-wave is a positive component evoked by stimulus offset. Common diagnoses that may benefit from additional photopic On–Off ERG testing include retinal dystrophies and retinal disorders that cause dysfunction at a level that is post-phototransduction or post-receptoral. On–Off ERGs assess the relative involvement of On- and Off-systems and may be of use in the diagnosis of disorders such as complete and incomplete congenital stationary night blindness (complete and incomplete CSNB), melanoma-associated retinopathy, and some forms of autoimmune retinopathy. The photopic On–Off ERGs may also be useful in X-linked retinoschisis, Batten disease, Duchenne muscular dystrophy, spinocerebellar degeneration, quinine toxicity, and other retinal disorders.

ISCEV extended protocol for the photopic negative response (PhNR) of the full-field electroretinogram

The International Society for Clinical Electrophysiology of Vision (ISCEV) Standard for full-field electroretinography (ERG) describes a minimum procedure, but encourages more extensive testing. This ISCEV extended protocol describes an extension to the ERG Standard, namely the photopic negative response (PhNR) of the light-adapted flash ERG, as a well-established technique that is broadly accepted by experts in the field. The PhNR is a slow negative-going wave after the b-wave that provides information about the function of retinal ganglion cells and their axons. The PhNR can be reduced in disorders that affect the innermost retina, including glaucoma and other forms of optic neuropathy. This document, based on existing literature, provides a protocol for recording and analyzing the PhNR in response to a brief flash. The protocol includes full-field stimulation, a frequency bandwidth of the recording in which the lower limit does not exceed 0.3 Hz, and a spectrally narrowband stimulus, specifically, a red flash on a rod saturating blue background. Suggested flash strengths cover a range up to and including the minimum required to elicit a maximum amplitude PhNR. This extended protocol for recording the PhNR provides a simple test of generalized retinal ganglion cell function that could be added to standard ERG testing.

Pattern Onset ERGs and VEPs Produced by Patterns Arising From Light Increment and Decrement.

Our aim was to elaborate how on and off signals contribute to pattern ERGs and pattern visual evoked potentials (VEPs) by using pedestal patterns arising from incremental and decremental onset stimulation. Pattern onset/offset ERGs and VEPs were produced by black and white checks of 60' side length and 88% spatial contrast appearing in a 16° field for 200 ms from white (110 cd/m2), black (7 cd/m2), and gray (48 cd/m2) backgrounds and disappeared for 1000 ms. Twenty healthy subjects participated in the study (median age 19.5, range, 5-31 years), 10 of whom also underwent pattern onset/offset ERG recordings to the same stimuli (median age 25.7, range, 22-31 years). VEPs were recorded from an occipital array referred to Fz. Pattern electroretinograms (PERGs) were recorded from "Dawson-Trick-Litzkow" (DTL) plus corneal electrodes referred to ipsilateral outer canthi. There was high correlation within subjects of the VEP waveform produced by patterns arising from light increment and decrement (group mean correlation coefficient of PVEPs to check appearance from black versus white: 87%). An average of increment and decrement PERGs simulated the onset PERG from a gray background. This waveform is akin to standard International Society for Clinical Electrophysiology of Vision (ISCEV) clinical PERGs to reversing checks. In healthy individuals, the early components of the pattern onset/offset VEP waveforms are comparable to light increment and decrement pedestal stimulation. Pattern onset/offset ERGs to pedestal stimulation may be used to probe simultaneous recording of ERGs with VEPs in order to obtain an assessment of retinal ganglion cell and optic pathway function in patients with less stable fixation.

Ophthalmic features of cone-rod dystrophy caused by pathogenic variants in the ALMS1 gene.

We aim to describe ophthalmic characteristics and systemic findings in a cohort of seven patients with cone-rod retinal dystrophy (CORD) caused by pathogenic variants in the ALMS1 gene. Seven patients with Alström syndrome (ALMS) were included in the study. A comprehensive ophthalmological examination was performed, including best-corrected visual acuity (BCVA), a semiautomated kinetic visual field exam, colour vision testing, full-field electroretinography testing according to International Society for Clinical Electrophysiology of Vision (ISCEV) standards, spectral domain optical coherence tomography (SD-OCT) and fundus autofluorescence (FAF) imaging, and slit lamp and dilated fundus examination. DNA samples were analysed using Sanger sequencing or exome sequencing. In our cohort, the ocular phenotype presented with a wide variability in retinal function and disease severity. However, age of symptom onset (i.e. nystagmus and photophobia) was at 6-9months in all patients. These symptoms mostly mislead to the diagnosis of congenital achromatopsia (ACHM), Leber congenital amaurosis (LCA), isolated CORD or Bardet-Biedl syndrome. The systemic manifestations in our cohort were highly variable. In summary, we can report that most of our ALMS patients primarily presented with nystagmus and severe photophobia since early childhood interestingly without night blindness in the absence of systemic symptoms. Only genetic testing analysing both nonsyndromic retinal disease (RD) genes and syndromic ciliopathy genes by comprehensive panel sequencing can result in the correct diagnosis, genetically and clinically, with important implication for the physical health of the individual.

Effect of axial length on full‐field and multifocal electroretinograms

PurposeThe aim was to investigate the effect of axial length on full‐field electroretinogram (ffERG) and multifocal electroretinogram (mfERG) in young Indian subjects.MethodsOne hundred subjects (44 male) with refractive errors from +0.50 to −18.00 DS and no myopic retinopathy underwent axial length measurement. ffERG was measured, which included scotopic and photopic responses according to International Society for Clinical Electrophysiology of Vision (ISCEV) guidelines. The mfERG was recorded after correcting for refractive error according to ISCEV standards. The dark‐adapted and light‐adapted parameters of ffERG and N1, P1 parameters of six rings in mfERG were analysed with axial length, controlled for refractive error. The subjects were divided into seven groups based on axial length. The b/a ratio of dark‐adapted and light‐adapted 3.0 ffERG and P1/N1 ratio of mfERG amplitudes were analysed for seven groups of axial length.ResultsThe axial length ranged from 21.79 to 30.55-mm. Significant negative correlations were noted for ffERG and mfERG amplitudes, whereas implicit times showed minimal delay with increase in axial length. In ffERG, the scotopic responses were more decreased compared to photopic responses. In mfERG, P1 and N1 amplitudes were significantly decreased in all the rings in all groups and more reduction was noted in the central ring compared to peripheral rings. The P1 amplitudes were more affected as compared to N1 amplitudes. The light‐adapted and dark‐adapted 3.0 ERG b/a ratio and P1/N1 ratio for seven axial length groups did not show statistically significant difference. The ERG parameters were not significant with refractive error.ConclusionThis study quantifies the relationship of axial length with ffERG and mfERG parameters in a young Indian population. Although the amplitudes were reduced significantly, the implicit times were not significantly affected. The ERG parameters were more related to axial length than refractive error. Hence, interpretation of ffERG and mfERG parameters needs careful consideration in subjects with increasing axial length.

7-Hexagon Multifocal Electroretinography for an Objective Functional Assessment of the Macula in 14 Seconds

Purpose: We present the multifocal electroretinogram (mfERG) with a 7-hexagon array as an objective test of macular function that can be recorded in 14 s. We provide normal values and investigate its reproducibility and validity. Methods: Healthy participants underwent mfERG testing according to International Society for Clinical Electrophysiology of Vision (ISCEV) standards using the Espion Profile/D310 multifocal ERG system (Diagnosys, LLC, Lowell, MA, USA). One standard recording of a 61-hexagon array and 2 repeated recordings of a custom 7-hexagon array were obtained. Results: A total of 13 subjects (mean age 46.9 years) were included. The median response densities were 12.5 nV/deg² in the center and 5.2 nV/deg² in the periphery. Intereye correlations were strong in both the center (ρ_Center = 0.821; p < 0.0001) and the periphery (ρ_Periphery = 0.862; p < 0.0001). Intraeye correlations were even stronger: ρ_Center = 0.904 with p < 0.0001 and ρ_Periphery = 0.955 with p < 0.0001. Bland-Altman plots demonstrated an acceptable retest mean difference in both the center and periphery, and narrow limits of agreement. We found strong correlations of the center (ρ_Center = 0.826; p < 0.0001) and periphery (ρ_Periphery = 0.848; p < 0.0001), with recordings obtained by the 61-hexagon method. Conclusions: The 7-hexagon mfERG provides reproducible results in agreement with results obtained according to the ISCEV standard.

Phenotype and Progression of Retinal Degeneration Associated With Nullizigosity of ABCA4.

We describe the phenotypes associated with nullizigosity and nine splicing mutations in the ABCA4 gene. The study included 19 patients with biallelic null mutations (Group A, nullizygous), 27 with splicing mutations in the homozygous state or in trans with a null mutation (Group B), and 20 with p.G1961E in trans with a null mutation (Group C, control). Ages at onset and visual acuities were determined from medical histories. Area of decreased autofluorescence within a 30° × 30° fundus autofluorescence (FAF) image was measured with the Region Finder (N = 58). Full-field electroretinography (ERG) was performed incorporating the International Society for Clinical Electrophysiology of Vision (ISCEV) standard (N = 40). For groups A to C, the median ages of onset were 6, 8, and 17, respectively. Kaplan Meier survival analysis estimated that 50% of patients reached visual acuity below 20/400 at the ages of 29, 48, and 66 years, respectively. The area of reduced FAF was estimated to increase by 1.5, 1.2, and 0.03 mm2 per year, respectively, and cone-rod dystrophy was present in 10/12, 13/15, and 0/13 of cases, respectively. Splicing mutation c.5714+5G>A was associated with a significantly milder phenotype in comparison with nullizygous patients for all parameters. Nullizygosity for ABCA4 is associated with early onset cone-rod dysfunction with rapid progression shown by enlargement of central atrophy on FAF, decline of ERG amplitudes with age, and a high risk of reaching legal blindness by the fourth decade. Most studied splicing mutations were associated with a similarly severe phenotype. Estimated rates of progression may facilitate further genotype-phenotype correlations and inform the design of treatment trials.

Alterations in retinal processing in regular cannabis users

IntroductionCannabis is one of the most prevalent drugs used worldwide. However, the neural consequences of cannabis remain poorly understood. There is a need for a rapid improvement of the scientific knowledge on the cerebral impact of cannabis use. Since the retina is an easy-to-access part of the central nervous system, it can reflect the neurochemistry of the brain.ObjectivesConsidering the anatomical and functional distribution of the cannabinoid system in the retinal ganglion cells, the objective of this study was to assess whether the regular use of cannabis could affect the ganglion cells functioning.AimsAssessment of the ganglion cells function in regular cannabis users compared to healthy controls.MethodsRecordings of pattern electroretinogram (PERG) were performed in regular cannabis users and healthy controls using standard of the International Society for Clinical Electrophysiology of Vision (ISCEV). The amplitude and implicit time of the PERG N95 were assessed.ResultsThe N95 implicit time of PERG was significantly decreased in regular cannabis users compared to healthy controls.ConclusionsWe found alterations in the ganglion cells function in regular cannabis users, as showed by the increase in N95 implicit time. The ganglion cells represent the ultimate retinal relay before the visual information is relayed to the brain and, according to these results, we suppose that the signal elicited by these cells and transferred through the visual pathways is altered in cannabis users. A direct action of exogenous cannabinoids in the retinal glutamatergic transmission is discussed.Disclosure of interestThe authors have not supplied their declaration of competing interest.

The effects of gender and age on the range of the normal human electro-oculogram.

To define the normal ranges for the slow oscillations (SO) and fast oscillations (FO) of the electro-oculogram (EOG) recorded to International Society for Clinical Electrophysiology of Vision (ISCEV) standards. The effects of age and gender on the EOG ranges were examined. ISCEV standard SOs and FOs were recorded from 121 subjects (51 % male) aged from 7 to 72 years. Study variables for the SO were dark trough (DT) and light peak (LP) amplitudes (µV), times to DT and LP (min), and the Arden ratio (LP/DT amplitude). The FO was fit by a sine wave and peak-to-peak amplitude (µV), phase (°), and peak-to-trough (PT) ratios derived. The effects of age, gender and pupil size on EOG parameters were examined by multiple regression analysis. The average Arden ratio was 2.5. Arden ratio decreased with age at a rate of 0.13 per decade of age (R (2) = 0.14, P < 0.0001). The 5th percentile of the Arden ratio decreased from 2.0 to 1.7 between 10 and 60 years of age. Median time to LP was 9 min (interquartile range 8-9 min). Time to LP was age-dependent and increased by 2 min for subjects over 55 years of age compared with those less than 25 years. EOG amplitudes were greater in women than in men (P < 0.005). The average PT ratio was 1.18, which was not affected by age or gender. Time to reach the light trough of the FO was 40 s, which increased with age (1.1 s/decade). No correlation was observed between Arden ratio and PT ratio. The major strength of this study is the definition of the normal range and associated lower limits of ISCEV standard EOGs based on recordings from 121 subjects balanced by gender and spanning the 1st through 8th decades of life. Decreased Arden ratio and increased time to LP are associated with aging, which is likely due to the intricate mechanisms involved in generation of the light rise. Differences between the FO and SO with respect to the effects of aging are consistent with separate generation of these two EOG signals.

53rd Symposium of International Society for Clinical Electrophysiology of Vision (ISCEV), 23-27 June 2015, Ljubljana, Slovenia.

53rd Symposium of International Society for Clinical Electrophysiology of Vision (ISCEV), 23-27 June 2015, Ljubljana, Slovenia.

53rd Symposium of International Society for Clinical Electrophysiology of Vision (ISCEV).

53rd Symposium of International Society for Clinical Electrophysiology of Vision (ISCEV).

Variability of Normal Values of Electroretinogram Parameters Due to Aging in Healthy Individuals.

Aim- To find normal values of implicit time and amplitudes of full-field electroretinogram and to determine their changes with age in healthy Romanian subjects. Material and Methods- The prospective study included 59 healthy subjects aged between 20 and 80 years old; in the end, we had valid ERG recordings for all tests from 54 subjects. All of the participants underwent full-field ERG, recorded with Metrovision MonPack One system. The implicit times and amplitudes were analyzed for a and b waves in dark-adapted 0.01 ERG, dark-adapted 3.0 ERG, dark-adapted oscillatory potentials, light-adapted 3.0 ERG, and 30Hz flicker ERG according to International Society for Clinical Electrophysiology of Vision (ISCEV) protocols. Results- ERG latency values were bigger in subjects above 50 years old than in younger subjects for b wave in dark adapted 0.01, dark adapted 3.0, light adapted 3.0 and dark adapted 3.0 flicker and for a wave in dark adapted 0.01 and dark adapted 3.0 ERG. There was no significant difference in latency values for dark adapted 3.0 oscillatory potentials between young and old subjects. Because of increased variability, we could not prove that observed differences for amplitudes held statistical significance. Conclusions- This study proves there is a major loss in retinal activity due to aging, most of it being caused by the rod cells delayed response. Also, oscillatory potentials do not seem to be affected by age, and could prove a valuable test to investigate for changes in patients with Diabetes mellitus.

ISCEV Standard for full-field clinical electroretinography (2015 update).

This document, from the International Society for Clinical Electrophysiology of Vision (ISCEV), presents an updated and revised ISCEV Standard for full-field clinical electroretinography (ffERG or simply ERG). The parameters for Standard flash stimuli have been revised to accommodate a variety of light sources including gas discharge lamps and light emitting diodes. This ISCEV Standard for clinical ERGs specifies six responses based on the adaptation state of the eye and the flash strength: (1) Dark-adapted 0.01 ERG (rod ERG); (2) Dark-adapted 3 ERG (combined rod-cone standard flash ERG); (3) Dark-adapted 3 oscillatory potentials; (4) Dark-adapted 10 ERG (strong flash ERG); (5) Light-adapted 3 ERG (standard flash "cone" ERG); and (6) Light-adapted 30 Hz flicker ERG. ISCEV encourages the use of additional ERG protocols for testing beyond this minimum standard for clinical ERGs.

Impaired retinal processing in regular cannabis users: Potential benefit of electroretinogram as a biomark

Cannabis is one of the most prevalent drugs used in industrialized countries. Regular cannabis use is associated with impairments in highly integrative cognitive functions such as memory, attention and executive functions. However, the neural impact of cannabis use remains poorly understood. Elucidating the cerebral mechanisms underlying these deficits represents now a crucial step in addictive disorders. The retina is a part of the central nervous system due to its embryonic origin thereby reflecting the neurochemistry of the brain. Furthermore its measure is well standardized allowing good reproducibility. Considering the anatomical and functional distribution of endocannabinoids in the retina [1], we evaluated the retinal function in regular cannabis users and healthy control subjects. Recordings of flash electroretinogram (fERG) were performed in regular cannabis users and healthy controls using guidelines of international society for clinical electrophysiology of vision (ISCEV) [2]. Both amplitude and implicit time of a-wave and b-wave were assessed in scotopic and photopic conditions. Measurements of fERG showed increased implicit time of a-wave and b-wave in both photopic and scotopic conditions in regular cannabis users compared to healthy controls. These findings suggest that retinal processing may be altered at the level of photoreceptor and bipolar cells in regular cannabis users. These results are consistent with previous reports in animal species, which show the involvement of the cannabinoid system in the regulation of the retinal metabolism thus leading to alterations of fERG measurements. Since alterations in the central neurotransmission may affect the ERG measurements, the retina might constitute a possible biomarker of brain disorders in addictive diseases [3].

Standardized full-field electroretinography in the Green Monkey (Chlorocebus sabaeus).

Full-field electroretinography is an objective measure of retinal function, serving as an important diagnostic clinical tool in ophthalmology for evaluating the integrity of the retina. Given the similarity between the anatomy and physiology of the human and Green Monkey eyes, this species has increasingly become a favorable non-human primate model for assessing ocular defects in humans. To test this model, we obtained full-field electroretinographic recordings (ERG) and normal values for standard responses required by the International Society for Clinical Electrophysiology of Vision (ISCEV). Photopic and scotopic ERG recordings were obtained by full-field stimulation over a range of 6 log units of intensity in dark-adapted or light-adapted eyes of adult Green Monkeys (Chlorocebus sabaeus). Intensity, duration, and interval of light stimuli were varied separately. Reproducible values of amplitude and latency were obtained for the a- and b-waves, under well-controlled adaptation and stimulus conditions; the i-wave was also easily identifiable and separated from the a-b-wave complex in the photopic ERG. The recordings obtained in the healthy Green Monkey matched very well with those in humans and other non-human primate species (Macaca mulatta and Macaca fascicularis). These results validate the Green Monkey as an excellent non-human primate model, with potential to serve for testing retinal function following various manipulations such as visual deprivation or drug evaluation.

Electroretinography in dogs using a fiber electrode prototype

We compared two electroretinography (ERG) electrodes in dogs using ERG standards of the International Society for Clinical Electrophysiology of Vision (ISCEV). Ten healthy Yorkshire terrier dogs (mean age, 2.80 ± 1.42 years; 6 females) weighing 5.20 ± 1.56 kg were evaluated using an ERG system for veterinary use. Dark- and light-adapted ERG responses were recorded using an ERG-Jet electrode and a fiber electrode prototype. The examinations were performed during 2 visits, 3 weeks apart. Both electrodes (ERG-Jet or fiber prototype) were used on each animal and the first eye to be recorded (OD × OS) was selected randomly. Three weeks later the examination was repeated on the same animal switching the type of electrode to be used that day and the first eye to be examined. The magnitude and waveform quality obtained with the two electrode types were similar for all ERG responses. ERG amplitudes and implicit times obtained from dogs using the fiber electrode prototype were comparable to those obtained with the ERG-Jet electrode for rod, maximal rod-cone summed, cone, and 30-Hz flicker responses. The fiber electrode prototype is a low-cost device, available as an alternative instrument for clinical veterinary ERG recording for retinal function assessment.

Multifocal electroretinography in type 2 idiopathic macular telangiectasia

To characterize the electroretinographic response of the macula by multifocal electroretinography (mfERG) in patients with type 2 idiopathic macular telangiectasia (MacTel). A prospective study of mfERG in patients with type 2 MacTel was conducted from April 2009 to November 2009. mfERGs were recorded using a visual evoked response imaging system (MonElec2, Metrovision, Perenchies, France). The International Society for Clinical Electrophysiology of Vision (ISCEV) guidelines were followed. Patients with type 2 MacTel confirmed by fundus fluorescein angiography without subretinal neovascularisation were included. For recording purposes, 61 stimulus hexagonal elements were used. The first-order kernel mfERG responses were analyzed. Individual mfERG responses for the hexagons were grouped into concentric rings centered on the fovea for analysis (< 2, 5-10, 10-15 and >15°). Student's t-test and Mann-Whitney U test and linear regression analysis was performed with STATA ver 11.1 (StataCorp, College Station , TX, USA). Twenty eight eyes of 14 patients and 20 eyes of ten normal controls were included in the study. The mean logMAR visual acuity of the patients was 0.51 (Snellen equivalent 20/63). The mean N1 amplitude (nv/deg(2)) of patients were significantly reduced compared to controls and were as follows: 8.91 ± 14.00 vs 43.44 ± 9.55 (p < 0.0001) in less than 2°, 9.24 ± 10.47 vs 22.00 ± 3.87 (p < 0.0001) in 5-10°, 8.57 ± 10.02 vs 15.24 ± 1.89 (p < 0.0001) in 10-15°, and 7.03 ± 6.52 vs 12.47 ± 2.62 in > 15° (p < 0.001). The mean P1 amplitude (nv/deg(2)) was also significantly reduced in patients compared to controls and was as follows: 27.66 ± 37.44 vs 96.20 ± 12.41 (p < 0.0001) in less than 2°, 22.61 ± 19.38 vs 53.78 ± 9.79 (p < 0.0001) in 5-10°, 18.75 ± 20.21 vs 35.22 ± 4.16 (p < 0.001) in 10-15°, and 17.10 ± 12.54 vs 25.71 ± 3.93 (p < 0.001). The implicit time of N1 and P1 were also delayed significantly in all the rings. The mean central foveal thickness assessed by optical coherence tomography (OCT) scan was 84.78 ± 45.12μm. There was poor correlation between mfERG amplitudes or implicit times with either the visual acuity or OCT central thickness. mfERG showed significant reduction in amplitudes and implicit times of the waveforms in patients with type 2 MacTel in all the rings, suggesting a more generalized affection of the macula. The maximum reductions were seen in the <2(o) rings. Although there was poor correlation between the visual acuity and the amplitudes a of the waveforms, mfERG is a useful investigative modality for functional assessment of macula in type 2 MacTel patients.