Electronegative electroretinogram in the modern multimodal imaging era

[Changes in global ERG in Birdshot chorioretinopathy and correlation with central macular thickness on OCT]

PURPOSE

To describe the characteristics of electroretinograms (ERGs) of a series of patients with Birdshot Chorioretinopathy (BSCR) at various stages and evaluate the correlation between ERG abnormalities and central macular thickness measured on Optical Coherence Tomography (OCT).

MATERIALS AND METHODS

This was a retrospective study of 20 eyes of 10 patients who underwent both a global ERG according to the International society for clinical electrophysiology of vision (ISCEV) protocol and simultaneous macular OCT with measurement of central macular thickness (CMT).

RESULTS

Five eyes had non-discernible ERGs. In the other fifteen eyes, the following abnormalities were found: decreased amplitude of the scotopic (DA 0.01, DA 3.0, and DA 10.0) and photopic (LA 3.0) b-waves, increased implicit time of photopic b-wave (LA 3.0), and changes in oscillatory potentials. After adjusting for age and gender, CMT measured by OCT was correlated with implicit times of the b-wave at LA 3.0 (-0.862; P=0.08) and Flicker 30Hz period (-0.883; P=0.08). No scotopic ERG parameter was correlated with CMT.

CONCLUSION

Retinal electrogenesis is altered in BSCR. There is a correlation between central macular thickness and Flicker 30Hz period and implicit time of b-wave at DA 3.0, as demonstrated by our study. Therefore, OCT can reflect progressive involvement in BSCR and can be a complementary examination to ERG.

Congenital Stationary Night Blindness (CSNB)-Case Reports and Review of Current Knowledge

Purpose: To present the current state of knowledge and our diagnosed patients with congenital stationary night blindness. Material and methods: Data from the PubMed database on CSNB and the presentation of patients with complete and incomplete forms of this condition. Patients underwent routine ophthalmologic examination, optical coherence tomography, and full-field elecroretinogram (ERG-ISCEV), ON-OFF ERG. Results: CSNB is a group of rare, non-progressive retinal diseases characterized by impaired night vision from birth, reduced visual acuity, myopia, nystagmus, and strabismus. Color vision and fundus imaging are most often normal. CSNB is mainly inherited autosomal recessively. Eighteen genes with more than 360 pathogenic variants have been detected in this condition. The effect of gene mutations is to damage the function of rods (Riggs type) and bipolar cells of the retina (Schubert-Bornstein type). The key diagnostic test in CSNB is ERG. In diagnosed cases of complete CSNB the following types have been registered: rod ERG absent, rod-cone response negative (ON bipolar cell defect), and photopic ERG enlarged a-wave. In incomplete CSNB-rod ERG-subnormal, rod-cone response-negative (bipolar cell defect ON, OFF), photopic ERG-subnormal with a double peak in the flicker fusion frequency. Knowledge of the phenotypic changes associated with various gene pathogenic variants is still very limited, hindering the ability to correctly diagnose a patient based on clinical examination and additional ophthalmologic tests. However, some phenotypic features found in our cases were consistent with pathogenic variants previously described in the literature and helped to make a diagnosis that was proven by genetic testing. Conclusions: Congenital stationary night blindness should be considered in the diagnosis of retinal diseases manifesting with impaired night vision. A correct diagnosis is especially important for the patients, as it is nonprogressive, unlike other diseases that should be considered in the differential diagnoses.

A GUCY2D variant associated cone-rod dystrophy with electronegative ERG: A case report and review

Purpose

Cone-rod dystrophies (CORD) are inherited retinal dystrophies characterized by primary cone degeneration with secondary rod involvement. We report two patients from the same family with a dominant variant in the guanylate cyclase 2D (GUCY2D) gene with different phenotypes in the electroretinogram (ERG).

Observations

A 21-year-old lady (Patient 1) was referred due to experiencing blurry vision and color vision impairment. Visual field testing revealed a central scotoma. Spectral-domain optical coherence tomography (SD-OCT) and fundus autofluorescence (FAF) documented macula dysfunction. Reduced amplitude was observed in the photopic responses of ERG. Her 54-year-old father (Patient 2) had similar issues with blurry vision. A dilated fundus examination displayed bilateral macular atrophy. Loss of the ellipsoid zone line and collapse of the outer nuclear segment were noted on the SD-OCT. Photopic ERG responses were extinguished, and an electronegative ERG was observed in the dark-adapted 3.0 ERG. The gene report revealed a c.2512C > T (p.Arg838Cys) variant in GUCY2D for both patients. They were respectively diagnosed as cone dystrophy (COD) and cone-rod dystrophy (CORD).

Conclusions

We report two different clinical phenotypes in GUCY2D-associated COD despite sharing the same variant. A dysfunction in the synaptic junction between the photoreceptor and the secondary neuron was proposed to explain the electronegative ERG. This explanation might extend to other gene-related cases of CORD with electronegative ERG.

The Use of the RETeval Portable Electroretinography Device for Low-Cost Screening: A Mini-Review

Electroretinography (ERG) provides crucial insights into retinal function and the integrity of the visual pathways. However, ERG assessments classically require a complicated technical background with costly equipment. In addition, the placement of corneal or conjunctival electrodes is not always tolerated by the patients, which restricts the measurement for pediatric evaluations. In this short review, we give an overview of the use of the RETeval portable ERG device (LKC Technologies, Inc., Gaithersburg, MD, USA), a modern portable ERG device that can facilitate screening for diseases involving the retina and the optic nerve. We also review its potential to provide ocular biomarkers in systemic pathologies, such as Alzheimer's disease and central nervous system alterations, within the framework of oculomics.

Group comparisons of the individual electroretinogram time trajectories for the ascending limb of the b-wave using a raw and registered time series

OBJECTIVES

The electroretinogram is a clinical test commonly used in the diagnosis of retinal disorders with the peak time and amplitude of the a- and b-waves used as the main indicators of retinal function. However, subtle changes that affect the shape of the electroretinogram waveform may occur in the early stages of disease or in conditions that have a neurodevelopmental or neurodegenerative origin. In such cases, we introduce a statistical approach to mathematically model the shape of the electroretinogram waveform that may aid clinicians and researchers using the electroretinogram or other biological signal recordings to identify morphological features in the waveforms that may not be captured by the time or time-frequency domains of the waveforms. We present a statistical graphics-based analysis of the ascending limb of the b-wave (AL-b) of the electroretinogram in children with and without a diagnosis of autism spectrum disorder (ASD) with a narrative explanation of the statistical approach to illustrate how different features of the waveform based on location and scale derived from raw and registered time series can reveal subtle differences between the groups.

RESULTS

Analysis of the raw time trajectories confirmed findings of previous studies with a reduced and delayed b-wave amplitude in ASD. However, when the individual time trajectories were registered then group differences were visible in the mean amplitude at registered time ~ 0.6 suggesting a novel method to differentiate groups using registration of the ERG waveform.

Reduced Electroretinogram Responses in Morphologically Normal Retina in Patients with Primary Hyperoxaluria Type 1

Purpose

To describe ocular findings in individuals with primary hyperoxaluria type 1 (PH1), focusing on the correlations between retinal anatomy and retinal function. To characterize the retinal alterations that occur at different disease stages by evaluating individuals with diverse degrees of renal impairment associated with PH1.

Design

A cross-sectional study.

Participants

Patients diagnosed with PH1 based on clinical criteria and genetic testing, treated in the Pediatric Nephrology Unit of the Ruth Children's Hospital, Rambam Health Care Campus, Haifa, Israel between 2013 and 2021.

Methods

The ophthalmological assessment included a slit-lamp biomicroscopy of the anterior and posterior segment or indirect ophthalmoscopy. Electroretinography was employed for assessment of the retinal function, and retinal imaging included spectral-domain OCT and fundus autofluorescence. A systematic evaluation of the disease stage was based on clinical criteria including physical examination, purposeful imaging (X-ray, echocardiography, and US abdomen), and laboratory tests as needed.

Main Outcome Measures

Anatomical and functional assessment of the retina in patients with PH1, and the relationship between retinal dysfunction and kidney impairment.

Results

A total of 16 eyes were examined in the study of 8 children ranging in age from 4 to 19 years. Four eyes (25%) showed normal structural and functional retinal findings, 8 eyes (50%) presented functional impairment in the absence of pathological structural findings, and 4 eyes (25%) had advanced retinal damage that manifested as significant morphological and functional impairment. There was no direct relationship between the severity of the renal disease and the severity of the retinal phenotype.

Conclusions

Subjects with PH1 present varying severity levels of the retinal phenotype, with possible discrepancy between the clinical retinal morphology and the retinal function noted on electroretinography. These findings raise questions about the molecular basis of the retinal manifestations in PH1. The presence of functional impairment in the absence of evident crystal deposition in the retina suggests that, in addition to oxalate crystal accumulation, other biomolecular processes may play a role in the development of retinopathy.

Early recognition of CLN3 disease facilitated by visual electrophysiology and multimodal imaging

BACKGROUND

Neuronal ceroid lipofuscinosis is a group of neurodegenerative disorders with varying visual dysfunction. CLN3 is a subtype which commonly presents with visual decline. Visual symptomatology can be indistinct making early diagnosis difficult. This study reports ocular biomarkers of CLN3 patients to assist clinicians in early diagnosis, disease monitoring, and future therapy.

METHODS

Retrospective review of 5 confirmed CLN3 patients in our eye clinic. Best corrected visual acuity (BCVA), electroretinogram (ERG), ultra-widefield (UWF) fundus photography and fundus autofluorescence (FAF), and optical coherence tomography (OCT) studies were undertaken.

RESULTS

Five unrelated children, 4 females and 1 male, with median age of 6.2 years (4.6-11.7) at first assessment were investigated at the clinic from 2016 to 2021. Four homozygous and one heterozygous pathogenic CLN3 variants were found. Best corrected visual acuities (BCVAs) ranged from 0.18 to 0.88 logMAR at first presentation. Electronegative ERGs were identified in all patients. Bull's eye maculopathies found in all patients. Hyper-autofluorescence ring surrounding hypo-autofluorescence fovea on FAF was found. Foveal ellipsoid zone (EZ) disruptions were found in all patients with additional inner and outer retinal microcystic changes in one patient. Neurological problems noted included autism, anxiety, motor dyspraxia, behavioural issue, and psychomotor regression.

CONCLUSIONS

CLN3 patients presented at median age 6.2 years with visual decline. Early onset maculopathy with an electronegative ERG and variable cognitive and motor decline should prompt further investigations including neuropaediatric evaluation and genetic assessment for CLN3 disease. The structural parameters such as EZ and FAF will facilitate ocular monitoring.

Electrophysiological Evaluation of Macular Dystrophies

Macular dystrophies are a heterogeneous group of genetic disorders that often severely threatens the bilateral central vision of the affected patient. While advances in molecular genetics have been instrumental in the understanding and diagnosis of these disorders, there remains significant phenotypical variation among patients within any particular subset of macular dystrophies. Electrophysiological testing remains a vital tool not only to characterize vision loss for differential diagnosis but also to understand the pathophysiology of these disorders and to monitor the treatment effect, potentially leading to therapeutic advances. This review summarizes the application of electrophysiological testing in macular dystrophies, including Stargardt disease, bestrophinopathies, X-linked retinoschisis, Sorsby fundus dystrophy, Doyne honeycomb retina dystrophy, autosomal dominant drusen, occult macular dystrophy, North Carolina macular dystrophy, pattern dystrophy, and central areolar choroidal dystrophy.