Reduced contrast sensitivity, pattern electroretinogram ratio, and diminished a-wave amplitude in patients with major depressive disorder.

The electroretinogram (ERG), a non-invasive electrophysiological tool used in ophthalmology, is increasingly applied to investigate neural correlates of depression. The present study aimed to reconsider previous findings in major depressive disorder (MDD) reporting (1) a diminished contrast sensitivity and (2) a reduced patten ERG (PERG) amplitude ratio, and additionally, to assess (3) the photopic negative response (PhNR) from the flash ERG (fERG), with the RETeval® device, a more practical option for clinical routine use. We examined 30 patients with a MDD and 42 healthy controls (HC), assessing individual contrast sensitivity thresholds with an optotype-based contrast test. Moreover, we compared the PERG ratio, an established method for early glaucoma detection, between both groups. The handheld ERG device was used to measure amplitudes and peak times of the fERG components including a-wave, b-wave and PhNR in both MDD patients and HCs. MDD patients exhibited diminished contrast sensitivity together with a reduced PERG ratio, compared to HC. With the handheld ERG device, we found reduced a-wave amplitudes in MDD, whereas no significant differences were observed in the fERG b-wave or PhNR between patients and controls. The reduced contrast sensitivity and PERG ratio in MDD patients supports the hypothesis that depression is associated with altered visual processing. The findings underscore the PERG's potential as a possible objective marker for depression. The reduced a-wave amplitude recorded with the RETeval® system in MDD patients might open new avenues for using handheld ERG devices as simplified approaches for advancing depression research compared to the PERG.

Effect of eccentric fixation on the steady-state pattern electroretinogram.

PURPOSE: The steady-state pattern electroretinogram (ssPERG) is used to assess retinal ganglion cell function in a variety of research contexts and diagnostic applications. In certain groups of patients or study participants, stable central fixation of the stimulus is not guaranteed. The present study aimed at assessing the effects of misfixation on the ssPERG response to checkerboard reversal stimuli. METHODS: Using two check sizes (0.8° and 15°), we compared ssPERG responses for several amounts of fixation deviation, ranging from 0° to 19° horizontally and from 0° to 14° diagonally. The stimulus area extended to 15° eccentricity, stimulus reversal rate was 15/s. RESULTS: Up to around 7° eccentricity, there was no sizable effect of fixation deviation under most conditions. Effects were somewhat larger for nasal than for temporal deviation, in particular for small checks. Diagonal deviation was associated with a response to luminance onset/offset at 7.5 Hz (subharmonic of the reversal rate), most prominently when the interior of a large check was fixated. CONCLUSION: Generally, moderate inaccuracies of fixation do not have a sizable effect on ssPERG amplitude. However, with large checks, the luminance response has to be considered.

ISCEV guidelines for calibration and verification of stimuli and recording instruments (2023 update).

This document developed by the International Society for Clinical Electrophysiology of Vision (ISCEV) provides guidance for calibration and verification of stimulus and recording systems specific to clinical electrophysiology of vision. This guideline provides additional information for those using ISCEV Standards and Extended protocols and supersedes earlier Guidelines. The ISCEV guidelines for calibration and verification of stimuli and recording instruments (2023 update) were approved by the ISCEV Board of Directors 01, March 2023.

Quantification and reduction of cross-vendor variation in multicenter DWI MR imaging: results of the Cancer Core Europe imaging task force.

OBJECTIVES: In the Cancer Core Europe Consortium (CCE), standardized biomarkers are required for therapy monitoring oncologic multicenter clinical trials. Multiparametric functional MRI and particularly diffusion-weighted MRI offer evident advantages for noninvasive characterization of tumor viability compared to CT and RECIST. A quantification of the inter- and intraindividual variation occurring in this setting using different hardware is missing. In this study, the MRI protocol including DWI was standardized and the residual variability of measurement parameters quantified. METHODS: Phantom and volunteer measurements (single-shot T2w and DW-EPI) were performed at the seven CCE sites using the MR hardware produced by three different vendors. Repeated measurements were performed at the sites and across the sites including a traveling volunteer, comparing qualitative and quantitative ROI-based results including an explorative radiomics analysis. RESULTS: For DWI/ADC phantom measurements using a central post-processing algorithm, the maximum deviation could be decreased to 2%. However, there is no significant difference compared to a decentralized ADC value calculation at the respective MRI devices. In volunteers, the measurement variation in 2 repeated scans did not exceed 11% for ADC and is below 20% for single-shot T2w in systematic liver ROIs. The measurement variation between sites amounted to 20% for ADC and < 25% for single-shot T2w. Explorative radiomics classification experiments yield better results for ADC than for single-shot T2w. CONCLUSION: Harmonization of MR acquisition and post-processing parameters results in acceptable standard deviations for MR/DW imaging. MRI could be the tool in oncologic multicenter trials to overcome the limitations of RECIST-based response evaluation. KEY POINTS: • Harmonizing acquisition parameters and post-processing homogenization, standardized protocols result in acceptable standard deviations for multicenter MR-DWI studies. • Total measurement variation does not to exceed 11% for ADC in repeated measurements in repeated MR acquisitions, and below 20% for an identical volunteer travelling between sites. • Radiomic classification experiments were able to identify stable features allowing for reliable discrimination of different physiological tissue samples, even when using heterogeneous imaging data.

[New clinical applications for low-field magnetic resonance imaging : Technical and physical aspects]. / Neue klinische Anwendungsbereiche der Niederfeld-Magnetresonanztomographie : Technische und physikalische Aspekte.

BACKGROUND: Low-field magnetic resonance imaging (MRI) is experiencing a renaissance due to technical innovations. The new-generation devices offer new applications for imaging and a possible solution to increasing cost pressures in the healthcare system. OBJECTIVES: Effects of field strength on technique, physics, image acquisition, and diagnostic quality of examinations are presented. METHODS: Important basic physical parameters for image acquisition and quality are summarized. Initial clinical experience with a new 0.55 T low-field scanner is presented. RESULTS: Field strengths that are lower than the currently used 1.5 T and 3 T field strengths are characterized by an expected lower signal-to-noise ratio in image acquisition. Whether this is a diagnostic limitation needs to be evaluated in studies, as there are several options to offset this perceived drawback, including increasing measurement time or artificial intelligence (AI) postprocessing techniques. In addition, it is necessary to meticulously investigate whether low-field systems allow diagnostically adequate image quality to be achieved in different body regions and different disease entities. Initial studies in our clinic are promising and show, for example, diagnostic quality without relevant loss of time for examinations of the lumbar spine. Advantages of low-field MRI include reduced susceptibility artifacts when imaging the lungs and in patients with metallic implants. CONCLUSION: Low-field scanners offer a variety of new fields of application with field strength-related advantages. In most other clinical examination fields, at least diagnostic quality can be expected.

[Economic aspects of low-field magnetic resonance imaging : Acquisition, installation, and maintenance costs of 0.55 T systems]. / Ökonomische Aspekte der Niederfeld-Magnetresonanztomographie : Anschaffung, Installation und Unterhaltskosten von 0,55 T-Geräten.

BACKGROUND: Low-field magnetic resonance imaging (MRI) scanners offer an opportunity for cost reduction in the healthcare system. This is due to lower manufacturing costs and reduced construction requirements for installation and operation. OBJECTIVES: To discuss potential cost reductions in acquisition, installation, and maintenance by using new low-field MRI systems. METHODS: We provide an overview of key cost drivers and an evaluation of the potential savings of a recent generation 0.55T low-field MRI compared to conventional 1.5T and 3T MRI systems in routine clinical practice. RESULTS: In terms of purchase price, the savings potential of a 0.55T MRI compared to a 1.5T MRI system is about 40-50%. The 25% lower weight of the system reduces the transportation costs incurred, and the smaller size of the unit allows for installation by a remotely controlled mobile robotic system without opening the exterior façade, if the operating site is at ground level. Together with the lack of need to install a quench pipe, this reduces the total cost of installation by up to 70%. The maintenance cost of a 0.55T MRI is approximately 45% less than that of a 1.5T unit with a comparable service contract. Further cost reductions result from the smaller room size and potentially lower energy consumption for examinations and cooling. CONCLUSION: The use of lower field strength MRI systems offers enormous economic and environmental potential for both hospitals and practice operators, as well as for the healthcare system as a whole.

VEP-based acuity estimation: unaffected by translucency of contralateral occlusion.

PURPOSE: Visual evoked potential (VEP) recordings for objective visual acuity estimates are typically obtained monocularly with the contralateral eye occluded. Psychophysical studies suggest that the translucency of the occluder has only a minimal effect on the outcome of an acuity test. However, there is literature evidence for the VEP being susceptible to the type of occlusion. The present study assessed whether this has an impact on VEP-based estimates of visual acuity. METHODS: We obtained VEP-based acuity estimates with opaque, non-translucent occlusion of the contralateral eye, and with translucent occlusion that lets most of the light pass while abolishing the perception of any stimulus structure. The tested eye was measured with normal and artificially degraded vision, resulting in a total of 4 experimental conditions. Two different algorithms, a stepwise heuristic and a machine learning approach, were used to derive acuity from the VEP tuning curve. RESULTS: With normal vision, translucent occlusion resulted in slight, yet statistically significant better acuity estimates when analyzed with the heuristic algorithm (p = 0.014). The effect was small (mean ΔlogMAR = 0.06), not present in some participants, and without practical relevance. It was absent with the machine learning approach. With degraded vision, the difference was tiny and not statistically significant. CONCLUSION: The type of occlusion for the contralateral eye does not substantially affect the outcome of VEP-based acuity estimation.

ISCEV standard for clinical multifocal electroretinography (mfERG) (2021 update).

The multifocal electroretinogram (mfERG) is an electrophysiological test that allows the function of multiple discrete areas of the retina to be tested simultaneously. This document, from the International Society for Clinical Electrophysiology of Vision (ISCEV), presents an updated and revised ISCEV standard for clinical mfERG and defines minimum protocols for basic clinical mfERG recording and reporting so that responses can be recognized and compared from different laboratories worldwide. The major changes compared with the previous mfERG standard relate to the minimum length of m-sequences used for recording, reporting of results and a change in document format, to be more consistent with other ISCEV standards.

VEP estimation of visual acuity: a systematic review.

PURPOSE: Visual evoked potentials (VEPs) can be used to measure visual resolution via a spatial frequency (SF) limit as an objective estimate of visual acuity. The aim of this systematic review is to collate descriptions of the VEP SF limit in humans, healthy and disordered, and to assess how accurately and precisely VEP SF limits reflect visual acuity. METHODS: The protocol methodology followed the PRISMA statement. Multiple databases were searched using "VEP" and "acuity" and associated terms, plus hand search: titles, abstracts or full text were reviewed for eligibility. Data extracted included VEP SF limits, stimulus protocols, VEP recording and analysis techniques and correspondence with behavioural acuity for normally sighted healthy adults, typically developing infants and children, healthy adults with artificially degraded vision and patients with ophthalmic or neurological conditions. RESULTS: A total of 155 studies are included. Commonly used stimulus, recording and analysis techniques are summarised. Average healthy adult VEP SF limits vary from 15 to 40 cpd, depend on stimulus, recording and analysis techniques and are often, but not always, poorer than behavioural acuity measured either psychophysically with an identical stimulus or with a clinical acuity test. The difference between VEP SF limit and behavioural acuity is variable and strongly dependent on the VEP stimulus and choice of acuity test. VEP SF limits mature rapidly, from 1.5 to 9 cpd by the end of the first month of life to 12-20 cpd by 8-12 months, with slower improvement to 20-40 cpd by 3-5 years. VEP SF limits are much better than behavioural thresholds in the youngest, typically developing infants. This difference lessens with age and reaches equivalence between 1 and 2 years; from around 3-5 years, behavioural acuity is better than the VEP SF limit, as for adults. Healthy, artificially blurred adults had slightly better behavioural acuity than VEP SF limits across a wide range of acuities, while adults with heterogeneous ophthalmic or neurological pathologies causing reduced acuity showed a much wider and less consistent relationship. For refractive error, ocular media opacity or pathology primarily affecting the retina, VEP SF limits and behavioural acuity had a fairly consistent relationship across a wide range of acuity. This relationship was much less consistent or close for primarily macular, optic nerve or neurological conditions such as amblyopia. VEP SF limits were almost always normal in patients with non-organic visual acuity loss. CONCLUSIONS: The VEP SF limit has great utility as an objective acuity estimator, especially in pre-verbal children or patients of any age with motor or learning impairments which prevent reliable measurement of behavioural acuity. Its diagnostic power depends heavily on adequate, age-stratified, reference data, age-stratified empirical calibration with behavioural acuity, and interpretation in the light of other electrophysiological and clinical findings. Future developments could encompass faster, more objective and robust techniques such as real-time, adaptive control. REGISTRATION: International prospective register of systematic reviews PROSPERO ( https://www.crd.york.ac.uk/PROSPERO/ ), registration number CRD42018085666.

ISCEV extended protocol for VEP methods of estimation of visual acuity.

The International Society for Clinical Electrophysiology of Vision (ISCEV) standard for visual evoked potentials (VEPs) describes a minimum procedure for clinical VEP testing and encourages more extensive testing. This ISCEV extended protocol is an extension to the VEP standard. It describes procedures for recording multiple VEPs to a range of sizes of pattern stimuli to establish the VEP spatial frequency limit (threshold) and for relating this limit to visual acuity.

Evaluation of the "Freiburg Acuity VEP" on Commercial Equipment.

PURPOSE: To assess the implementation and outcome quality of the Freiburg Acuity VEP methodology (Bach et al. in Br J Ophthalmol 92:396-403, 2008) on the Diagnosys Espion Profile and E3 electrophysiology systems. METHODS: We recorded visual evoked potentials (VEPs) from both eyes of 24 participants, where visual acuity (VA) was either full or reduced with scatter foils to approximately 0.5 and 0.8 LogMAR, resulting in a total of 144 recordings. Behavioral VA was measured in each case under the same conditions using the Freiburg Acuity Test (FrACT); VEP-based acuity was assessed with the "heuristic algorithm," which automatically selects points for regression to zero amplitude. RESULTS: Behavioral VA ranged from - 0.2 to 1.0 LogMAR. The fully automatic heuristic VEP algorithm resulted in 8 of 144 recordings (6%) that were scored as "no result." The other 136 recordings (94%) had an outcome of - 0.20 to 1.3 LogMAR (which corresponds to a range of 20/12.5-20/400, or 6/3.8-6/120, in Snellen ratios; or 1.6-0.1 in decimal acuity). The heuristic VEP algorithm agreed with the behavioral VA to within ± 0.31 LogMAR (95% limits of agreement), which is equivalent to approximately three lines on a VA chart. CONCLUSIONS: The successful implementation of the Freiburg Acuity VEP "heuristic algorithm" on a commercial system makes this capability available to a wider group of users. The limits of agreement of ± 0.31 LogMAR are close to the original implementation at the University of Freiburg and we believe are clinically acceptable for a fully automatic, largely objective assessment of visual acuity.

ERG shrinks by 10% when reducing dark adaptation time to 10 min, but only for weak flashes.

PURPOSE: To compare dark-adapted (DA) ERG between 10, 15 and 20 min of dark adaptation (DA). METHODS: In a counterbalanced random block design, 40 healthy adult subjects were dark-adapted for 10, 15 or 20 min before we recorded ERGs to nine flash strengths from 0.001 to 10.0 cd s/m2 (dilated pupils) with a DTL-like electrode. Before and between sessions, the room was lit. Apart from choosing a wider range of stimulus strengths, and adding shorter DA times, the recordings fully complied with the ISCEV ERG Standard, namely using corneal electrodes, mydriasis and a standard DA sequence. RESULTS: The a-wave amplitude was not affected by any adaptation condition. For the b-wave amplitude, effects of reduced DA time are stronger for weaker flashes: Reducing DA from 20 to 10 min had no measurable effect on the DA 3 ERG, but reduced the DA 0.01 b-wave significantly (p < 0.0001) to 87 ± 2% (mean ± SEM). The DA 0.001 b-wave (not part of the ISCEV ERG Standard) was more affected (down to 72 ± 4%). There was a small, but significant, increase, only for weak flashes, in a- and b-wave peak times for 20 compared to 10-min dark adaptation time. CONCLUSION: Reducing dark adaptation time from 20 to 10 min in normal participants has no effect on the ISCEV DA 3 and DA 10 ERG. The reduction in DA 0.01 ERGs to 87 ± 2% agrees with Hamilton and Graham (Doc Ophthalmol 133:11-19, 2016. https://doi.org/10.1007/s10633-016-9554-x ) who found 90 ± 2% and with Asakawa et al. (Doc Ophthalmol 139:33-44, 2019. https://doi.org/10.1007/s10633-019-09693-8 ) who found 83%. Pending verification in pathophysiological states, the current results suggest that one might be able to correct for the 10% amplitude loss when gaining 10 min through shortened DA.

The "speed" of acuity in scotopic vs. photopic vision.

PURPOSE: The effect of duration of optotype presentation on visual acuity measures has been extensively studied under photopic conditions. However, systematic data on duration dependence of acuity values under mesopic and scotopic conditions is scarce, despite being highly relevant for many visual tasks including night driving, and for clinical diagnostic applications. The present study aims to address this void. METHODS: We measured Landolt C acuity under photopic (90 cd/m2), mesopic (0.7 cd/m2), and scotopic (0.009 cd/m2) conditions for several optotype presentation durations ranging from 0.1 to 10 s using the Freiburg Acuity and Contrast Test. Two age groups were tested (young, 18-29 years, and older, 61-74 years). RESULTS: As expected, under all luminance conditions, better acuity values were found for longer presentation durations. Photopic acuity in young participants decreased by about 0.25 log units from 0.1 to 10 s; mesopic vision mimicked the photopic visual behavior. Scotopic acuities depended more strongly on presentation duration (difference > 0.78 log units) than photopic values. There was no consistent pattern of correlation between luminance conditions across participants. We found a qualitative similarity between younger and older participants, despite higher variability among the latter and differences in absolute acuity: Photopic acuity difference (0.1 vs. 10 s) for the older participants was 0.19 log units, and scotopic difference was > 0.62 log units. CONCLUSION: Scotopic acuity is more susceptible to changes in stimulus duration than photopic vision, with considerable interindividual variability. The latter may reflect differences in aging and sub-clinical pathophysiological processes and might have consequences for visual performance during nocturnal activities such as driving at night. Acuity testing with briefly presented scotopic stimuli might increase the usefulness of acuity assessment for tracking of the health state of the visual system.

Acuity VEP: improved with machine learning.

PURPOSE: Acuity-VEP approaches basically all use the information obtained across a number of check sizes (or spatial frequencies) to derive a measure of acuity. Amplitude is always used, sometimes combined with phase or a noise measure. In our approach, we employ steady-state brief-onset low-contrast checkerboard stimulation and obtain amplitude and significance for six different check sizes, yielding 12 numbers. The rule-based "heuristic algorithm" (Bach et al. in Br J Ophthalmol 92:396-403, 2008. https://doi.org/10.1136/bjo.2007.130245 ) is successful in over 95% with a limit of agreement (LoA) of ± 0.3LogMAR between behavioral and objective acuity for 109 cases. We here aimed to test whether machine learning techniques with this relatively small dataset could achieve a similar LoA. METHODS: Given recent advances in machine learning (ML), we applied a wide class of ML algorithms to this dataset. This was done within the "caret" framework of R using altogether 89 methods, of which rule-based and multiple regression approaches performed best. For cross-validation, using a jackknife (leave-one-out) approach, we predicted each case based on an ML model having been trained on all remaining 108 cases. RESULTS: The ML approach predicted visual acuity well across many different types of ML algorithms. Using amplitude values only (discarding the p values) improved the outcome. Nearly half of the tested ML algorithms achieved an LoA better than the heuristic algorithm; several "Random Forest"- or "multiple regression"-type algorithms achieved an LoA of below ± 0.3. In the cases where the heuristic approach failed, acuity was predicted successfully. We then applied the ML model trained with the Bach et al. [1] dataset to a new dataset from 2018 (78 cases) and found both for the heuristic algorithm and for the ML approach an LoA of ± 0.259, a nearly one-line improvement. CONCLUSIONS: The ML approach appears to be a useful alternative to rule-based analysis of acuity-VEP data. The achieved accuracy is comparable or better (in no case the ML-based acuity differed more than ± 0.29 LogMAR from behavioral acuity), and testability is higher, nearly 100%. Possible pitfalls are examined.

Habitual higher order aberrations affect Landolt but not Vernier acuity.

To assess whether the eye's optical imperfections are relevant for hyperacute vision, we measured ocular wave aberrations, visual hyperacuity, and acuity thresholds in 31 eyes of young adults. Although there was a significant positive correlation between the subjects' performance in Vernier- and Landolt-optotype acuity tasks, we found clear differences in how far both acuity measures correlate with the eyes' optics. Landolt acuity thresholds were significantly better in eyes with low higher order aberrations and high visual Strehl ratios (r2 = 0.22, p = 0.009), and significantly positively correlated with axial length (r2 = 0.15, p = 0.03). A retinal image quality metric, calculated as two-dimensional correlation between perfect and actual retinal image, was also correlated with Landolt acuity thresholds (r2 = 0.27, p = 0.003). No such correlations were found with Vernier acuity performance (r2 < 0.03, p > 0.3). Based on these results, hyperacuity thresholds are, contrary to resolution acuity, not affected by higher order aberrations of the eye.

The Discrepancy between Subjective and Objective Measures of Convergence Insufficiency in Whiplash-Associated Disorder versus Control Participants.

PURPOSE: Motor vehicle accidents (MVAs) are a pandemic associated with human suffering and a burden to national economies. Whiplash-associated disorders (WADs) after MVAs are associated commonly with disability claims, many of which are related to vision. Convergence insufficiency (CI) leads to visual disability associated with symptoms of ocular discomfort. We examined the incidence of symptoms and findings consistent with CI in a cohort of patients after MVA-related WAD compared with age-matched control participants. DESIGN: Prospective cohort study. PARTICIPANTS: Patients with WAD after MVA were recruited from the Orthopedic Emergency Department between July 2014 and March 2017. Control participants were recruited among hospital personnel and relatives of WAD patients. METHODS: The Convergence Insufficiency Symptom Survey (CISS) questionnaire was completed by each participant, followed by a detailed visual examination including measurements of distance and near best-corrected Snellen visual acuity, distance and near cover test, Randot stereopsis, Maddox distance and Maddox-Thorington near heterophoria, near point of convergence, base-out step fusional reserves, and amplitude of accommodation using the push-away method. MAIN OUTCOME MEASURES: The CISS score and binocular measure findings of CI were recorded and analyzed using Student's t test, the chi-square test, and multiple logistic regression adjusted for age and gender. RESULTS: A pathologic CISS score of 16 or more occurred in 26 of 57 WAD patients (45.6%) compared with 6 of 39 control participants (15.4%; P = 0.002). Absolute CISS score was higher in the WAD group compared with the control group (15.3±10.0 vs. 7.7±7.7; P < 0.001). Findings consistent with CI occurred in 7.0% of WAD patients and 7.7% of control participants (P = 0.90). CONCLUSIONS: Visual symptoms suggestive of CI were reported more frequently among WAD patients compared with control participants, yet the incidence of examination findings indicating weakness of convergence was not increased. The discrepancy between subjective and objective measures of CI in WAD patients versus control participants stresses the importance of training healthcare personnel to assess disability using objective, validated standards of examination.

Retinal conduction speed analysis reveals different origins of the P50 and N95 components of the (multifocal) pattern electroretinogram.

The pattern electroretinogram (PERG), an indicator of retinal ganglion cell (RGC) function, comprises a P50 and an N95 component. We addressed the question of whether the N95 originates, like the P50, from the RGC bodies or from the change of axon orientation at the optic nerve head (ONH). Thus, we recorded multifocal PERGs for 36 retinal locations in 21 participants. Second-order kernel responses were analyzed for the dependence of peak time topography on retinal fiber lengths to the ONH separately for the positive and negative excursions. We found that peak times were longer for macular [P1 (P50-like): 50 ms; N2 (N95-like): 76)] than for peripheral responses [P1: 43; N2: 66]. For the N2 another factor was necessary to explain the variability: The time difference (deltaT: N2 minus P1) was found to be proportional to fiber length from ganglion cell body to the ONH. We calculated retinal fiber length using an analytical function by Jansonius et al. (2009, 2012) and found that a linear model with factors eccentricity and fiber length explained 82% of the total N2 time variance (p«0.001). The conduction speeds of the retinal axons were estimated from deltaT to range from 0.5 to 3.0 m/s for parafovea and periphery, respectively. The dependence of deltaT on the distance from ganglion cell body to the ONH suggests that the N2 originates at the ONH rather than at the ganglion cell body. While the multifocal N2 peaks earlier (≈76 ms) than the non-multifocal PERG-N95 (≈95 ms), considerations of high-pass filtering and frequency dependence of the mfPERG-N2 suggest that the source separation (P50 = ganglion cell body vs. N95 = ONH) also holds for the non-multifocal PERG.

Correction to: ISCEV Standard for clinical electro-oculography (2017 update).

The article "ISCEV Standard for clinical electro-oculography (2017 update)", written by Paul A. Constable, Michael Bach, Laura J. Frishman, Brett G. Jeffrey, Anthony G. Robson and for the International Society for Clinical Electrophysiology of Vision, was originally published Online First without open access.

Test-retest reliability of scotopic full-field electroretinograms in rabbits.

PURPOSE: To explore test-retest reliability of standard scotopic full-field ERG measurements in New Zealand White rabbits. The ERG is widely used for testing of retinal integrity after any ocular treatment. We here present detailed stimulus-response dependencies for single healthy and untreated animals, concentrating on test-retest reproducibility. MATERIALS AND METHODS: Five New Zealand White rabbits (aged 8-10 weeks, weight about 2.0-2.5 kg) underwent binocular ERG measurements after intramuscular anesthesia and pharmaceutical pupillary dilatation at a baseline day and 10 days later. Eleven scotopic flash strengths (0.0001-10 cd s/m2) were presented. Variability was quantified via the 95% limits of agreement (LOA). RESULTS: The a-waves displayed the typical monotonic sigmoid amplitude increase with flash strength, and the b-waves peaked at 0.01 cd s/m2, followed by a marked dip at 0.1-0.3 cd s/m2. LOA of both waves went through a maximum in the dip region. LOA divided by mean amplitudes (relative LOA) was fairly flat over flash strength, around 20% beyond the dip. Intraindividual interocular variability was markedly lower, around 10%. CONCLUSIONS: Scotopic ERG responses in rabbits display a region of high variability at 0.1-0.3 cd s/m2; beyond that region the amplitude-LOA is 20%, the interocular LOA being half that value. The use of intraindividual control eyes for testing any toxicity of ocular agents thus appears markedly more sensitive. As a rule of thumb, we found the relative 95% LOA as 33% between individuals, 20% across sessions and 10% between eyes.

VEP-based acuity assessment in low vision.

PURPOSE: Objective assessment of visual acuity (VA) is possible with VEP methodology, but established with sufficient precision only for vision better than about 1.0 logMAR. We here explore whether this can be extended down to 2.0 logMAR, highly desirable for low-vision evaluations. METHODS: Based on the stepwise sweep algorithm (Bach et al. in Br J Ophthalmol 92:396-403, 2008) VEPs to monocular steady-state brief onset pattern stimulation (7.5-Hz checkerboards, 40% contrast, 40 ms on, 93 ms off) were recorded for eight different check sizes, from 0.5° to 9.0°, for two runs with three occipital electrodes in a Laplace-approximating montage. We examined 22 visually normal participants where acuity was reduced to ≈ 2.0 logMAR with frosted transparencies. With the established heuristic algorithm the "VEP acuity" was extracted and compared to psychophysical VA, both obtained at 57 cm distance. RESULTS: In 20 of the 22 participants with artificially reduced acuity the automatic analysis indicated a valid result (1.80 logMAR on average) in at least one of the two runs. 95% test-retest limits of agreement on average were ± 0.09 logMAR for psychophysical, and ± 0.21 logMAR for VEP-derived acuity. For 15 participants we obtained results in both runs and averaged them. In 12 of these 15 the low-acuity results stayed within the 95% confidence interval (± 0.3 logMAR) as established by Bach et al. (2008). CONCLUSIONS: The fully automated analysis yielded good agreement of psychophysical and electrophysiological VAs in 12 of 15 cases (80%) in the low-vision range down to 2.0 logMAR. This encourages us to further pursue this methodology and assess its value in patients.