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

Paediatric norms for photopic electroretinogram testing based on a large cohort of Chinese preschool children

OBJECTIVE

Full-field electroretinogram (ffERG) is an objective test to determine the electroretinal activities in response to light stimulation for investigating retinal physiology and diagnosing retinal diseases. This study aimed to establish a reference data set of photopic electroretinogram (ERG) of Chinese preschool children in Hong Kong to facilitate clinical and research studies.

METHODS AND ANALYSIS

Preschool children aged 3-7 years with normal vision were recruited from local kindergartens. Eye examinations, including cycloplegic spherical equivalent refraction (SER), axial length (AL) and keratometry (K) measurements, were performed. ffERGs of the International Society for Clinical Electrophysiology of Vision (ISCEV) standard photopic flash and 30-Hz flicker protocols were measured using RETeval with Sensor Strip skin electrodes. ERG waveform characteristics were extracted, and relationships between ERG, age, SER, AL and K were evaluated.

RESULTS

A total of 479 children completed the measurements (mean age: 5.0±0.9 years, 45.5% female). Mean, 95% CIs, 5th-95th percentile range of the ERG parameters were reported. Age was positively associated with amplitudes of b-wave and 30-Hz flicker (p<0.01), but negatively associated with implicit times of b-wave and 30-Hz flicker (p<0.01). AL was significantly associated with all amplitudes of a-wave, b-wave and 30-Hz flicker (p≤0.01) and implicit time of both a-wave and 30-Hz flicker (p<0.05). K was positively associated only with 30-Hz flicker amplitude (p=0.01), and no association between all responses and SER.

CONCLUSION

Reference data set of photopic ERG of Chinese preschool children was established. Cross-sectional investigations revealed associations between ERG, age, SER and AL, which were speculated to further implicate the role of retina in refractive error development.

Overcoming the Challenges to Clinical Development of X-Linked Retinitis Pigmentosa Therapies: Proceedings of an Expert Panel

X-linked retinitis pigmentosa (XLRP) is a rare inherited retinal disease manifesting as impaired night vision and peripheral vision loss that progresses to legal blindness. Although several trials of ocular gene therapy for XLRP have been conducted or are in progress, there is currently no approved treatment. In July 2022, the Foundation Fighting Blindness convened an expert panel to examine relevant research and make recommendations for overcoming the challenges and capitalizing on the opportunities in conducting clinical trials of RPGR-targeted therapy for XLRP. Data presented concerned RPGR structure and mutation types known to cause XLRP, RPGR mutation-associated retinal phenotype diversity, patterns in genotype/phenotype relationships, disease onset and progression from natural history studies, and the various functional and structural tests used to monitor disease progression. Panel recommendations include considerations, such as genetic screening and other factors that can impact clinical trial inclusion criteria, the influence of age on defining and stratifying participant cohorts, the importance of conducting natural history studies early in clinical development programs, and the merits and drawbacks of available tests for measuring treatment outcomes. We recognize the need to work with regulators to adopt clinically meaningful end points that would best determine the efficacy of a trial. Given the promise of RPGR-targeted gene therapy for XLRP and the difficulties encountered in phase III clinical trials to date, we hope these recommendations will help speed progress to finding a cure.

Translational Relevance

Examination of relevant data and recommendations for the successful clinical development of gene therapies for RPGR-associated XLRP.

A cross-sectional study to assess the clinical utility of modern visual function assessments in patients with inherited retinal disease: a mixed methods observational study protocol

BACKGROUND

Treatment options for patients with inherited retinal disease are limited, although research into novel therapies is underway. To ensure the success of future clinical trials, appropriate visual function outcome measures that can assess changes resulting from therapeutic interventions are urgently required. Rod-cone degenerations are the most common type of inherited retinal disease. Visual acuity is a standard measure but is typically preserved until late disease stages, frequently making it an unsuitable visual function marker. Alternative measures are required. This study investigates the clinical utility of a range of carefully selected visual function tests and patient reported outcome measures. The aim is to identify suitable outcome measures for future clinical trials that could be considered for regulatory approval.

METHODS

This cross-sectional study involves two participant groups, patients with inherited retinal disease (n = 40) and healthy controls (n = 40). The study has been designed to be flexible and run alongside NHS clinics. The study is split into two parts. Part one includes examining standard visual acuity, low luminance visual acuity, the Moorfields acuity chart visual acuity, mesopic microperimetry and three separate patient reported outcome measures. Part two involves 20 min of dark adaptation followed by two-colour scotopic microperimetry. Repeat testing will be undertaken where possible to enable repeatability analyses. A subset of patients with inherited retinal disease will be invited to participate in a semi-structured interview to gain awareness of participants' thoughts and feelings around the study and different study tests.

DISCUSSION

The study highlights a need for reliable and sensitive validated visual function measures that can be used in future clinical trials. This work will build on work from other studies and be used to inform an outcome measure framework for rod-cone degenerations. The study is in keeping with the United Kingdom Department of Health and Social Care research initiatives and strategies for increasing research opportunities for NHS patients as part of their NHS care.

TRIAL REGISTRATION

ISRCTN registry, ISRCTN24016133, Visual Function in Retinal Degeneration, registered on 18th August 2022.

Zone-wise examination of optical coherence tomography features and their correspondence to multifocal electroretinography in eyes with nonproliferative diabetic retinopathy

PURPOSE

To examine (1) the retinal structure by optical coherence tomography (OCT) and function by means of multifocal electroretinography (mfERG) in eyes with and without nonproliferative diabetic retinopathy (NPDR) (2) for correspondence between local retinal function and OCT zones with retinal lesions.

METHODS

One hundred and thirty-two eligible participants (30 with nonproliferative DR (NPDR) and 102 with diabetes with no DR) underwent comprehensive ophthalmic examination, optical coherence tomography for retinal thickness measures, mfERG, and ultra-wide field fundus photography. OCT Early Treatment Diabetic Retinopathy Study (ETDRS) grid was overlaid on to mfERG plots.

RESULTS

Those with NPDR had significantly thicker full retinal measures in the nine (ETDRS) zones compared to no DR. mfERG P1 latencies in rings 1-6 were significantly delayed, while the response densities in rings 4-6 were lower in the NPDR group. Significant negative correlation was noted between OCT thickness and mfERG P1 response densities in many ETDRS zones. Significant positive correlation was noted between P1 latencies and OCT thickness in a few zones. The combination of cystic spaces, microaneurysms, and hard exudates were present in all zones and were associated with a decrease in P1 response densities compared to no lesions. Reduced P1 response densities were associated with a sporadic delay in the mfERG latencies and vice versa. The number of lesions did not show correspondence to the mfERG measures.

CONCLUSIONS

In eyes with NPDR, retinal function is differentially correlated with the DR lesions on OCT and can be assessed using multimodal imaging modalities.

The Clinical Contribution of Full-Field Electroretinography and 8-Year Experiences of Application in a Tertiary Medical Center

Electroretinography (ERG) is an important and well-established examination for retinal and visual pathway diseases. This study reviewed the medical records of patients who received full-field ERG (ffERG) at a single medical center between 2012 and 2019, which was an 8-year experience in the clinical contribution of ERG. Based on the indication for scheduling ffERG and the final diagnosis, patients could be classified into six groups: ‘retinal dystrophies’, ‘other retinal or macular diseases’, ‘optic neuropathies’, ‘visual complaints’, ‘systemic diseases’, and ‘others’. A total of 1921 full-field electroretinograms (ffERGs) (1655 patients) were included. The average number of ffERGs performed per year was 262 and the number of annual ffERGs was constant. The ‘retinal dystrophies’ group accounted for 36.5% of the studied population, followed by the ‘other retinal or macular diseases’ group (20.2%). The most common systemic disease was central nervous system disease. The rates of abnormal ffERGs in the ‘systemic diseases’, ‘optic neuropathies’, and ‘visual complaints’ groups were 27.3%, 22.6%, and 10.1%, respectively (p < 0.001). Higher rates were found in patients <20 years old in the ‘systemic diseases’ and ‘optic neuropathies’ groups; epilepsy and optic nerve atrophy were the most common diagnoses, respectively. In brief, by quantifying the functional response in the retina, ffERG is indispensable for diagnosis and prognosis in ophthalmologic and multidisciplinary practice.

The potential of marine resources for retinal diseases: a systematic review of the molecular mechanisms

We rely on vision more than on any other sense to obtain information about our environment. Hence, the loss or even impairment of vision profoundly affects our quality of life. Diet or food components have already demonstrated beneficial effects on the development of retinal diseases. Recently, there has been a growing interest in resources from marine animals and plants for the prevention of retinal diseases through nutrition. Especially fish intake and omega-3 fatty acids have already led to promising results, including associations with a reduced incidence of retinal diseases. However, the underlying molecular mechanisms are insufficiently explained. The aim of this review was to summarize the known mechanistic effects of marine resources on the pathophysiological processes in retinal diseases. We performed a systematic literature review following the PRISMA guidelines and identified 107 studies investigating marine resources in the context of retinal diseases. Of these, 46 studies described the underlying mechanisms including anti-inflammatory, antioxidant, antiangiogenic/vasoprotective, cytoprotective, metabolic, and retinal function effects, which we critically summarize. We further discuss perspectives on the use of marine resources for human nutrition to prevent retinal diseases with a particular focus on regulatory aspects, health claims, safety, and bioavailability.

Electro-oculography in bilateral optic neuropathy

Objective

Effect of bilateral, optic neuropathy on the function of retinal pigment epithelium has not been investigated extensively to date. This study aimed to determine the effect of bilateral, optic neuropathy on light peak:dark trough ratio, light peak and dark trough values of electro-oculography. Thirty-seven patients with a clinical diagnosis of bilateral optic neuropathy and 40 control subjects were recruited in this observational, cross-sectional study, carried out at the Neurophysiology unit, Teaching Hospital, Peradeniya, Sri Lanka. Pattern reversal visual evoked potentials, pattern electroretinography and electro-oculography were recorded in all of them.

Results

Twenty-four patients (64.9%) had reduced light peak:dark trough ratio values. The median light peak:dark trough ratio ± inter quartile range of the patient group (1.50 ± 0.4) was significantly lower than that of the controls (1.80 ± 0.2), (p < 0.001). Median dark trough value was significantly higher in patients compared to the control value. These changes may be due to higher conductance of ion channels in the retinal pigment epithelium, sub retinal space creation, changes in choroidal circulation or secondary to photoreceptor abnormalities in the macular region. These results indicate that retinal pigment epithelium might be affected in bilateral optic neuropathy.

Comparative Analysis of Functional and Structural Decline in Retinitis Pigmentosas

Retinitis pigmentosa (RP) is a category of inherited retinal dystrophies that is best prognosticated using electroretinography (ERG). In this retrospective cohort study of 25 patients with RP, we evaluated the correlation between 30 Hz flicker ERG and structural parameters in the retina. Internationally standardized 30 Hz flicker ERG recordings, short-wavelength autofluorescence (SW-AF), and spectral domain–optical coherence tomography (SD-OCT) were acquired at two visits at least one year apart. Vertical and horizontal hyperautofluorescent ring diameter measurements with SW-AF, as well as ellipsoid zone (EZ) line width measurements with SD-OCT, were used as structural parameters of disease progression. The 30 Hz flicker ERG amplitude decreased by 2.2 ± 0.8 µV/year (p = 0.011), while implicit times remained unchanged. For SD-OCT, the EZ line decreased by 204.1 ± 34.7 µm/year (p < 0.001). Horizontal and vertical hyperautofluorescent ring diameters decreased by 161.9 ± 25.6 µm/year and 146.9 ± 34.6 µm/year, respectively (p = 0.001), with SW-AF. A correlation was found between the progression rates of the 30 Hz flicker amplitude recorded with Burian–Allen electrodes and both the horizontal ring diameter (p = 0.020) and EZ line (p = 0.044). SW-AF and SD-OCT, two readily available imaging techniques, may be used to prognosticate disease progression because of the reliability of their measurements and correlation with functional outcome.

Pattern-Reversal Visual Evoked Potential on Smart Glasses

OBJECTIVE

This paper presents an integrated device, based on smart glasses, for the pattern-reversal visual evoked potential (PR-VEP) clinical test.

METHODS

Smart glasses are used to generate the checkerboard changing pattern, with its related red fixation point through an Android application. Electroencephalographic signals, for monitoring the stimulus generated by PR-VEP, were amplified close to the scalp and then transmitted wirelessly to a PC. A MATLAB real-time algorithm processed the incoming signals to extract the final PR-VEP signal.

METHODS

In total, 40 eyes (from 20 subjects, 12 males and 8 females between 24 and 28 years old) were tested and results were compared, with a commercial device for VEP clinical exam, to test the reproducibility and the efficacy of the proposed solution.

RESULTS

PR-VEPs generated by smart glasses showed typical triphasic waveforms: We observed promising results and components in moderate agreement with those obtained using commercial PR-VEP recorder, with potential for improvements after further refinement works.

SIGNIFICANCE

The proposed device leads the way for a portable and low-cost solution.

Intra-Vitreal Administration of Microvesicles Derived from Human Adipose-Derived Multipotent Stromal Cells Improves Retinal Functionality in Dogs with Retinal Degeneration

This study was designed to determine the influence of microvesicles (MVs) derived from multipotent stromal cells isolated from human adipose tissue (hASCs) on retinal functionality in dogs with various types of retinal degeneration. The biological properties of hASC-MVs were first determined using an in vitro model of retinal Muller-like cells (CaMLCs). The in vitro assays included analysis of hASC-MVs influence on cell viability and metabolism. Brain-derived neurotrophic factor (BDNF) expression was also determined. Evaluation of the hASC-MVs was performed under normal and oxidative stress conditions. Preliminary clinical studies were performed on ten dogs with retinal degeneration. The clinical studies included behavioral tests, fundoscopy and electroretinography before and after hASC-MVs intra-vitreal injection. The in vitro study showed that CaMLCs treated with hASC-MVs were characterized by improved viability and mitochondrial potential, both under normal and oxidative stress conditions. Additionally, hASC-MVs under oxidative stress conditions reduced the number of senescence-associated markers, correlating with the increased expression of BDNF. The preliminary clinical study showed that the intra-vitreal administration of hASC-MVs significantly improved the dogs’ general behavior and tracking ability. Furthermore, fundoscopy demonstrated that the retinal blood vessels appeared to be less attenuated, and electroretinography using HMsERG demonstrated an increase in a- and b-wave amplitude after treatment. These results shed promising light on the application of cell-free therapies in veterinary medicine for retinal degenerative disorders treatment.

Optimising the Structure-Function Relationship at the Locus of Deficit in Retinal Disease

Technologies such as optical coherence tomography have facilitated the visualization of anatomical tissues such as that of the retina. The availability of in vivo retinal anatomical data has led to the hypothesis that it may be able to accurately predict visual function from anatomical information. However, accurate determination of the structure-function relationship has remained elusive in part due to contributions of non-retinal sources of variability, thus imposing potential limitations in the fidelity of the relationship. Furthermore, differences in manifestation of functional loss due to different retinal loci of change (inner retina or outer retinal elements) have also been the subject of debate. Here, we assessed the application of a novel, more objective psychophysical paradigm to better characterize the relationship between functional and structural characteristics in the eye. Using ocular diseases with known loci of anatomical change (glaucoma, inner retinal loss; and retinitis pigmentosa, outer retinal loss), we compared conventional more subjective psychophysical techniques that may be contaminated by the presence of non-retinal sources of variability with our more objective approach. We show that stronger correlations between underlying retinal structure and visual function can be achieved across a breadth of anatomical change by using a more objective psychophysical paradigm. This was independent of the locus of structural loss (at the ganglion cells for glaucoma or photoreceptors for retinitis pigmentosa), highlighting the role of downstream retinal elements to serve as anatomical limiting factors for studying the structure-function relationship. By reducing the contribution of non-retinal sources of variability in psychophysical measurements, we herein provide a structure-function model with higher fidelity. This reinforces the need to carefully consider the psychophysical protocol when examining the structure-function relationship in sensory systems.

Visual field mean deviation and relevant factors in 928 Chinese retinitis pigmentosa patients

AIM

To investigate the associations between demographic and clinical factors with the rate of visual field mean derivation (MD) decline in retinitis pigmentosa (RP) patients.

METHODS

Correlations of MDs with the visual acuity and retinal pigmentation were analyzed in 928 RP patients. MD decreasing rate in 10y and potential influences of gender, age, family history and retinal pigmentation on the rate were explored in 201 RP patients.

RESULTS

In the 928 patients, average MD and visual acuity were -14.44±8.61 dB and 0.79±0.35 respectively and when MD was lower than -9.18 dB the visual acuity would be below 1.0 (20/20). The average MD medium between eyes with or without retinal pigmentation was -14.82 dB. In 123 non-pigmented eyes, the average MD were lower than the medium but in 153 pigmented eyes it was higher than that. In the 201 patients, the average decreasing value of MD in 10 years' period was -8.01±3.66 dB and the value were correlated to retinal pigmentation but not to gender, age or RP family history.

CONCLUSION

The rate of MD decline in RP eyes is significantly related to retinal pigmentation. Our study demonstrates the quantitative rate of MD decline in RP patients and the value of MD could well reflect the severity of RP.

Differences in Static and Kinetic Perimetry Results are Eliminated in Retinal Disease when Psychophysical Procedures are Equated

Purpose

We tested the hypothesis that clinical statokinetic dissociation (SKD, defined as the difference in sensitivity to static and kinetic stimuli) at the scotoma border in retinal disease is due to individual criterion bias and that SKD can be eliminated by equating the psychophysical procedures for testing static and kinetic stimulus detection.

Methods

Six subjects with glaucoma and six with retinitis pigmentosa (RP) were tested. Clinical procedures (standard automated perimetry [SAP] and manual kinetic perimetry [MKP]) were used to determine clinical SKD and the region of interest for laboratory-based testing. Two-way Method of Limits (MoL) was used to establish the isocontrast region at the scotoma border in glaucoma and RP subjects. Method of Constant Stimuli (MoCS) and a two-interval forced choice (2IFC) procedure then were used to present static or kinetic (inward or outward) stimuli at different eccentricities within the isocontrast region. The results were fitted with psychometric functions to determine threshold eccentricities.

Results

Clinical SKD was found in glaucoma and RP subjects, with variable magnitude among subjects, but significantly exceeding expected typical measurement variability. The resultant psychometric functions when using MoCS and 2IFC showed equal sensitivity to static and kinetic targets, thus eliminating SKD.

Conclusions

Clinical SKD found using clinical techniques is due to methodologic differences and criterion bias, and is eliminated by using an equated and more objective psychophysical task, similar to normal subjects.

Translational relevance

Eliminating SKD using a psychophysical approach minimizing criterion bias suggests that it is not useful to distinguish between normal and diseased fields.

Reference values of pattern reversal visual evoked potentials in Bulgarian population

AIMS

The aim of this study is to evaluate pattern visual evoked potentials as an objective electrophysiological method and to create reference values for Bulgarian population.

METHODS AND MATERIALS

Standardized four-channel equipment 'Neuro-MEP 4' produced by 'Neurosoft' Company was used. A group of 47 healthy individuals (94 eyes) was studied. The stimulation was monocular, with a contrast-reversing pattern from black to white and vice versa. The investigation was performed with a three-channel recording with equipment adjustments according to the latest published ISCEV standard for pattern visual evoked potentials (2016). Based on a comprehensive overview of the available literature, a protocol of stimulating, amplifying and recording the obtained potentials has been created. The values of pattern visual evoked potential wave components, P50, N75, P100, N145 and P200, were measured.

RESULTS

Based on a created protocol, latency and amplitudes of the individual wave components of pattern visual evoked potentials were obtained. The results were statistically processed to create reference values of all pattern visual evoked potentials components, which are used as reference of the laboratory for the Bulgarian population.

CONCLUSION

Pattern visual evoked potentials are objective electrophysiological method which is used to diagnose and monitor numerous ophthalmological and neurological diseases as well as for objective study of visual acuity and visual field in children and aggravation. The creation of pattern visual evoked potentials reference values for the Bulgarian population and its implementation in clinical practice are of particular importance for studying the visual analyser function.

Behavioral Assessment of Vision in Pigs

Swine (Sus scrofa) are often the 'gold standard' laboratory animal for ophthalmology research due to the anatomic and physiologic similarities between the porcine and human eye and retina. Despite the importance of this model, few tools for behavioral vision assessment in pigs are available. The aim of this study was to identify and validate a feasible and reproducible behavioral test to assess vision in a pig model of photoreceptor degeneration. In addition, a robust behavioral test will reduce stress and enhance enrichment by allowing animals opportunities for environmental exploration and by reducing the number of invasive experimental procedures. Two distinct behavioral approaches were tested: the obstacle-course test and temperament test. In the obstacle-course test, pigs were challenged (after an initial training period) to navigate a 10-object obstacle course; time and the number of collisions with the objects were recorded. In the temperament test, the time needed for pigs to complete 3 different tasks (human-approach, novel-object, and open-door tests) was recorded. The obstacle-course test revealed significant differences in time and number of collisions between swine with vision impairment and control animals, and the training period proved to be pivotal to avoid bias due to individual animal characteristics. In contrast, the temperament test was not altered by vision impairment but was validated to measure stress and behavioral alterations in laboratory pigs undergoing experimental procedures, thus achieving marked refinement of the study.

Diagnosis and Treatment Options for Achromatopsia: A Review of the Literature

Achromatopsia is a complex inherited retinal disease that affects the cone cell function. It is usually an autosomal-recessive disease and is characterized by pendular nystagmus, poor visual acuity, lack of color vision, and marked photophobia. CNGA3, CNGB3, GNAT2, PDE6C, PDE6H, and ATF6 gene mutations have been identified as associated with this disease. New diagnostic and therapeutic tools are being studied. Optical coherence tomography and fundus autofluorescence are important imaging techniques that provide significant information about the progression of the disease. The genetic approach for these patients is a current important issue and gene therapy is an ongoing therapeutic option already being studied in clinical trials. The purpose of this review was to survey the current knowledge on diagnosis and treatment options in achromatopsia. [J Pediatr Ophthalmol Strabismus. 2018;55(2):85-92.].

Retrospective Analysis of Structural Disease Progression in Retinitis Pigmentosa Utilizing Multimodal Imaging

In this report, we assess the natural progression rate of retinitis pigmentosa (RP) over an average of three years using spectral-domain optical coherence tomography (SD-OCT) and short wavelength fundus autofluorescence (SW-AF). Measurement of the ellipsoid zone (EZ) line width and hyperautofluorescent ring diameters was performed in 81 patients with RP in a retrospective, longitudinal fashion. Rate of structural disease progression, symmetry between eyes, and test-retest variability were quantified. We observed on average, EZ-line widths decreased by 140 µm (5.2%, p < 0.001) per year, and average horizontal and vertical hyperautofluorescent ring diameters decreased by 149 µm (3.6%, p < 0.001) and 120 µm (3.9%, p < 0.001) per year, respectively. The 95th percentile of this cohort had differences in progression slopes between eyes that were less than 154 µm, 118 µm, and 132 µm for EZ-line width and horizontal and vertical ring diameters, respectively. For all measures except horizontal ring diameter, progression rates were significantly slower at end-stage disease. From our data, we observed a statistically significant progression rate in EZ line width and SW-AF ring diameters over time, verifying the utility of these measurements for disease monitoring purposes. Additionally, calculated differences in progression slopes between eyes may prove useful for investigators evaluating the efficacy of unilateral treatments for RP in clinical trials.

Using the rd1 mouse to understand functional and anatomical retinal remodelling and treatment implications in retinitis pigmentosa: A review

Retinitis Pigmentosa (RP) reflects a range of inherited retinal disorders which involve photoreceptor degeneration and retinal pigmented epithelium dysfunction. Despite the multitude of genetic mutations being associated with the RP phenotype, the clinical and functional manifestations of the disease remain the same: nyctalopia, visual field constriction (tunnel vision), photopsias and pigment proliferation. In this review, we describe the typical clinical phenotype of human RP and review the anatomical and functional remodelling which occurs in RP determined from studies in the rd/rd (rd1) mouse. We also review studies that report a slowing down or show an acceleration of retinal degeneration and finally we provide insights on the impact retinal remodelling may have in vision restoration strategies.