The negative ERG: clinical phenotypes and disease mechanisms of inner retinal dysfunction

Intraretinal hemorrhages and detailed retinal phenotype of three patients with Alagille syndrome

PURPOSE

To explore patterns of disease expression in Alagille syndrome (ALGS).

METHODS

Patients underwent ophthalmic examination, optical coherence tomography (OCT) imaging, fundus intravenous fluorescein angiography (IVFA), perimetry and full-field electroretinograms (ffERGs). An adult ALGS patient had multimodal imaging and specialized perimetry.

RESULTS

The proband (P1) had a heterozygous pathogenic variant in JAG1; (p.Gln410Ter) and was incidentally diagnosed at age 7 with a superficial retinal hemorrhage, vascular tortuosity, and midperipheral pigmentary changes. The hemorrhage recurred 15 months later. Her monozygotic twin sister (P2) had a retinal hemorrhage at the same location at age 11. Visual acuities for both patients were 20/30 in each eye. IVFA was normal. OCT showed thinning of the outer nuclear in the peripapillary retina. A ffERG showed normal cone-mediated responses in P1 (rod-mediated ERGs not documented), normal ffERGs in P2. Coagulation and liver function were normal. An unrelated 42-year-old woman with a de-novo pathogenic variant (p. Gly386Arg) in JAG1 showed a similar pigmentary retinopathy and hepatic vascular anomalies; rod and cone function was normal across large expanses of structurally normal retina that sharply transitioned to a blind atrophic peripheral retina.

CONCLUSION

Nearly identical recurrent intraretinal hemorrhages in monozygotic twins with ALGS suggest a shared subclinical microvascular abnormality. We hypothesize that the presence of large areas of functionally and structurally intact retina surrounded by severe chorioretinal degeneration, is against a predominant involvement of JAG1 in the function of the neurosensory retina, and that instead, primary abnormalities of chorioretinal vascular development and/or homeostasis may drive the peculiar phenotypes.

Clinical and genetic studies for a cohort of patients with congenital stationary night blindness

BACKGROUND

Congenital stationary night blindness (CSNB) is an inherited retinal disorder. Most of patients have myopia. This study aims to describe the clinical and genetic characteristics of fifty-nine patients with CSNB and investigate myopic progression under genetic cause.

RESULTS

Sixty-five variants were detected in the 59 CSNB patients, including 32 novel and 33 reported variants. The most frequently involved genes were NYX, CACNA1F, and TRPM1. Myopia (96.61%, 57/59) was the most common clinical finding, followed by nystagmus (62.71%, 37/59), strabismus (52.54%, 31/59), and nyctalopia (49.15%, 29/59). An average SE of -7.73 ± 3.37 D progressed to -9.14 ± 2.09 D in NYX patients with myopia, from - 2.24 ± 1.53 D to -4.42 ± 1.43 D in those with CACNA1F, and from - 5.21 ± 2.89 D to -9.24 ± 3.16 D in those with TRPM1 during the 3-year follow-up; the TRPM1 group showed the most rapid progression.

CONCLUSIONS

High myopia and strabismus are distinct clinical features of CSNB that are helpful for diagnosis. The novel variants identified in this study will further expand the knowledge of variants in CSNB and help explore the molecular mechanisms of CSNB.

Cone-driven strong flash electroretinograms in healthy adults: Prevalence of negative waveforms

PURPOSE

Both rod and cone-driven signals contribute to the electroretinogram (ERG) elicited by a standard strong flash in the dark. Negative ERGs usually reflect inner retinal dysfunction. However, in diseases where rod photoreceptor function is selectively lost, a negative waveform might represent the response of the dark-adapted cone system. To investigate the dark-adapted cone-driven waveform in healthy individuals, we delivered flashes on a dim blue background, designed to saturate the rods, but minimally adapt the cones.

METHODS

ERGs were recorded, using conductive fibre electrodes, in adults from the TwinsUK cohort. Responses to 13 cd m-2 s white xenon flashes (similar to the standard DA 10 flash), delivered on a blue background, were analysed. Photopic and scotopic strengths of the background were 1.3 and 30 cd m-2, respectively; through a dilated pupil, this is expected to largely saturate the rods, but adapt the cones much less than the standard ISCEV background.

RESULTS

Mean (SD) participant age was 62.5 (11.3) years (93% female). ERGs from 203 right and 204 left eyes were included, with mean (SD) b/a ratios of 1.22 (0.28) and 1.18 (0.28), respectively (medians, 1.19 and 1.17). Proportions with negative waveforms were 23 and 26%, respectively. Right and left eye b/a ratios were strongly correlated (correlation coefficient 0.74, p < 0.0001). We found no significant correlation of b/a ratio with age.

CONCLUSIONS

Over 20% of eyes showed b/a ratios less than 1, consistent with the notion that dark-adapted cone-driven responses to standard bright flashes can have negative waveforms. The majority had ratios greater than 1. Thus, whilst selective loss of rod function can yield a negative waveform (with reduced a-wave) in some, our findings also suggest that loss of rod function can occur without necessarily yielding a negative ERG. One potential limitation is possible mild cone system adaptation by the background.

Bilateral macular hole in a patient with CAPN5-related neovascular inflammatory vitreoretinopathy

PURPOSE

To characterize the genotype and phenotype of a patient with CAPN5-related neovascular inflammatory vitreoretinopathy (NIV) who have undergone surgery for macular holes.

METHODS

We observed a patient presenting with retinitis pigmentosa and posterior uveitis who later developed vitreoretinal macular traction and a macular hole. Genetic testing was performed using a targeted gene panel. Fundus photography and spectral-domain optical coherence tomography were also performed.

RESULTS

In a targeted gene panel, a monoallelic pathogenic variant, c.750G > T, p.Lys250Asn, in the CAPN5 gene was identified, and CAPN5-NIV was diagnosed. At the first visit, peripheral retinal degeneration and mild posterior uveitis were observed. At that time, neovascularization, epiretinal or fibrous membranes were not observed. After 5 years, vitreomacular traction developed and progressed to a full-thickness macular hole in both eyes. After pars plana vitrectomy, the macular hole was successfully closed without aggravation of uveitis.

CONCLUSION

In this case, a pathogenic variant of CAPN5 lead to a distinct phenotype of retinitis pigmentosa, posterior uveitis, vitreomacular traction, and macular hole without typical inflammatory neovascularization or tractional membranes. Therefore, the clinical variability of CAPN5-NIV and genetic diagnosis should be considered in cases of atypical retinitis pigmentosa with bilateral macular hole.

The Value of Electroretinography in Identifying Candidate Genes for Inherited Retinal Dystrophies: A Diagnostic Guide

Inherited retinal dystrophies (IRDs) are a group of heterogeneous diseases caused by genetic mutations that specifically affect the function of the rod, cone, or bipolar cells in the retina. Electroretinography (ERG) is a diagnostic tool that measures the electrical activity of the retina in response to light stimuli, and it can help to determine the function of these cells. A normal ERG response consists of two waves, the a-wave and the b-wave, which reflect the activity of the photoreceptor cells and the bipolar and Muller cells, respectively. Despite the growing availability of next-generation sequencing (NGS) technology, identifying the precise genetic mutation causing an IRD can be challenging and costly. However, certain types of IRDs present with unique ERG features that can help guide genetic testing. By combining these ERG findings with other clinical information, such as on family history and retinal imaging, physicians can effectively narrow down the list of candidate genes to be sequenced, thereby reducing the cost of genetic testing. This review article focuses on certain types of IRDs with unique ERG features. We will discuss the pathophysiology and clinical presentation of, and ERG findings on, these disorders, emphasizing the unique role ERG plays in their diagnosis and genetic testing.

Adult-onset leukodystrophy with vanishing white matter: a case series of 19 patients

BACKGROUND

Leukodystrophy with vanishing white matter (LVWM) is an autosomal recessive disease with typical pediatric-onset caused by mutations in one of the five EIF2B genes. Adult-onset (AO) cases are rare.

METHODS

In this observational study, we reviewed clinical and laboratory information of the patients with AO-LVWM assessed at two referral centers in Italy and Portugal from Jan-2007 to Dec-2019.

RESULTS

We identified 18 patients (13 females) with AO-LVWM caused by EIF2B5 or EIF2B3 mutations. Age of neurological onset ranged from 16 to 60 years, with follow-ups occurring from 2 to 37 years. Crucial symptoms were cognitive and motor decline. In three patients, stroke-like events were the first manifestation; in another, bladder dysfunction remained the main complaint across decades. Brain MRI showed white matter (WM) rarefaction in all cases, except two. Diffusion-weighted imaging documented focal hyperintensity in the acute stage of stroke-like events. 1H-spectroscopy primarily showed N-acetyl-aspartate reduction; 18fluorodeoxyglucose-PET revealed predominant frontoparietal hypometabolism; evoked potential studies demonstrated normal-to-reduced amplitudes; neuro-ophthalmological assessment showed neuroretinal thinning, and b-wave reduction on full-field electroretinogram. Interestingly, we found an additional patient with LVWM-compatible phenotype and monoallelic variants in two distinct eIF2B genes, EIF2B1 and EIF2B2.

CONCLUSIONS

AO-LVWM presents varying clinical manifestations at onset, including stroke-like events. WM rarefaction is the most consistent diagnostic clue even in the latest onset cases. Spectroscopy and electrophysiological features are compatible with axon, rather than myelin, damage. Cerebral glucose metabolic abnormalities and retinal alterations can be present. LVWM might also be caused by a digenic inheritance affecting the eIF2B complex.

Electroretinographic Responses in Retinopathy of Prematurity Treated Using Intravitreal Bevacizumab or Laser

PURPOSE

Intravitreal injection of bevacizumab (IVB) offers advantages over laser photoablation for treatment of type 1 retinopathy of prematurity (ROP). However, retinal function has not, to date, been quantitatively compared following these interventions. Therefore, electroretinography (ERG) was used compare retinal function among eyes treated using IVB or laser, and control eyes. In addition, among the IVB-treated eyes, ERG was used to compare function in individuals in whom subsequent laser was and was not required.

DESIGN

Prospective clinical cohort study.

METHODS

ERG was used to record dark- and light-adapted stimulus/response functions in 21 children treated using IVB (12 of whom required subsequent laser in at least 1 eye for persistent avascular retina [PAR]). Sensitivity and amplitude parameters were derived from the a-wave, b-wave, and oscillatory potentials (OPs), representing activity in photoreceptor, postreceptor, and inner retinal cells, respectively. These parameters were then referenced to those of 76 healthy, term-born controls and compared to those of 10 children treated using laser only.

RESULTS

In children with treated ROP, every ERG parameter was significantly below the mean in controls. However, these significant ERG deficits did not differ between IVB- and laser-treated eyes. Among children treated using IVB, no ERG parameter was significantly associated with dose or need for subsequent laser.

CONCLUSION

Retinal function was significantly impaired in treated ROP eyes. Function in IVB-treated eyes did not differ from that in laser-treated eyes. Functional differences also did not distinguish those IVB-treated eyes that would subsequently need laser for PAR.

Visual electrophysiology and "the potential of the potentials"

Visual electrophysiology affords direct, quantitative, objective assessment of visual pathway function at different levels, and thus yields information complementary to, and not necessarily obtainable from, imaging or psychophysical testing. The tests available, and their indications, have evolved, with many advances, both in technology and in our understanding of the neural basis of the waveforms, now facilitating more precise evaluation of physiology and pathophysiology. After summarising the visual pathway and current standard clinical testing methods, this review discusses, non-exhaustively, several developments, focusing particularly on human electroretinogram recordings. These include new devices (portable, non-mydiatric, multimodal), novel testing protocols (including those aiming to separate rod-driven and cone-driven responses, and to monitor retinal adaptation), and developments in methods of analysis, including use of modelling and machine learning. It is likely that several tests will become more accessible and useful in both clinical and research settings. In future, these methods will further aid our understanding of common and rare eye disease, will help in assessing novel therapies, and will potentially yield information relevant to neurological and neuro-psychiatric conditions.

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.

Relation between ocular paraneoplastic syndromes and Immune Checkpoint Inhibitors (ICI): review of literature

PURPOSE

To describe different ocular paraneoplastic syndromes in patients treated with Immune Checkpoint Inhibitors (ICI), its relation with different types of ICI and different types of tumors, and its implications for treatment.

METHODS

A comprehensive review of the literature was performed.

RESULTS

Patients treated with ICI can present with different ocular paraneoplastic syndromes, such as Carcinoma Associated Retinopathy (CAR), Melanoma Associated Retinopathy (MAR) and paraneoplastic Acute Exudative Polymorphous Vitelliform Maculopathy (pAEPVM). In literature, the different types of paraneoplastic retinopathy are mostly related to different types of primary tumors, with MAR and pAEPVM seen in melanoma, and CAR in carcinoma. Visual prognosis is limited in MAR and CAR.

CONCLUSION

Paraneoplastic disorders result from an antitumor immune response against a shared autoantigen between the tumor and ocular tissue. ICI enhance the antitumor immune response, which can lead to increased cross-reaction against ocular structures and unmasking of a predisposed paraneoplastic syndrome. Different types of primary tumors are related to different cross-reactive antibodies. Therefore, the different types of paraneoplastic syndromes are related to different types of primary tumors and are probably unrelated to the type of ICI. ICI-related paraneoplastic syndromes often lead to an ethical dilemma. Continuation of ICI treatment can lead to irreversible visual loss in MAR and CAR. In these cases overall survival must be weighed against quality of life. In pAEPVM however, the vitelliform lesions can disappear with tumor control, which may involve continuation of ICI.

MFRP variant results in nanophthalmos, retinitis pigmentosa, variability in foveal avascular zone

BACKGROUND

Membrane frizzled-related protein (MFRP) plays a critical role in ocular development. MFRP mutations are known to cause nanophthalmos and, in some cases, retinitis pigmentosa, foveoschisis, and/or optic nerve head (ONH) drusen. The broad clinical spectrum of MFRP mutations necessitates further investigation of specific genotype-phenotype relationships.

MATERIALS AND METHODS

We reviewed ophthalmologic and genetic medical records of two affected siblings and one unaffected sibling.

RESULTS

Genetic testing revealed variants MFRP c.855T>A, p.(Cys285*) and MFRP c.1235T>C, p.(Leu412Pro) in trans in the two affected siblings. In both cases, photopic and scotopic responses were markedly reduced on electroretinogram (ERG), with greater decrease in scotopic function. Optical coherence tomography for both siblings revealed non-cystoid thickening. Blunted foveal reflexes were also observed in both siblings. Notably, foveal avascular zone abnormalities were seen on fundus autofluorescence in only one affected sibling.

CONCLUSIONS

MFRP-related ocular disease may be underrecognized due to its presentation with high hyperopia and possibly subtle retinal findings. Presence of variants MFRP c.855T>A, p.(Cys285*) and MFRP c.1235T>C, p.(Leu412Pro) in trans resulted in nanophthalmos and retinitis pigmentosa without associated foveoschisis or ONH drusen in our patients, consistent with the incomplete phenotype previously described in Neri et al. Abnormalities in the foveal avascular zone have been noted in other case studies and were inconsistently associated with the variants described here, representing a potential area for future investigation.

X-linked retinoschisis: mutation spectrum and genotype-phenotype relationship in an Italian pediatric cohort

BACKGROUND

X-linked juvenile retinoschisis (×LRS) is an X-linked vitreoretinal degenerative disease that consists of variable phenotypes ranging from severe early-onset defects to subtle abnormalities diagnosed in elderly patients. XLRS is caused by a loss of function of the protein Retinoschisin (RS1), which is essential to preserve retinal integrity and function of photoreceptor-bipolar synapse. The literature data so far mostly agree on the absence of a clear genotype-phenotype correlation in XLRS. We reviewed clinical and molecular characteristics of a cohort of Italian pediatric XLRS patients to assess the presence of a correlation between genotype and phenotype severity.

MATERIALS AND METHODS

We retrospectively examined clinical and genetic features of a cohort of 27 XLRS patients. In this study we included patients with a diagnosis of XLRS confirmed by fundus photography, spectral domain optical coherence tomography, and molecular analysis and with an onset of less than 10 years of age. We sorted RS1 variants according to their effect of RS1 structure and function in three separate groups.

RESULTS

According to previous studies, we did not observe a conclusive genotype-phenotype correlation in our cohort; nevertheless, we noticed that patients harboring RS1 variants leading to RS1-secreted mutants show a more homogeneous phenotype, with an overall good visual acuity, compared to the other two groups.

CONCLUSIONS

Our data support the hypothesis that secretion profile of RS1 could influence the severity of the phenotype. More extensive and functional studies are needed to acquire notions in view of the opportunity of gene replacement therapy for XLRS patients.

Mice Lacking Gpr179 with Complete Congenital Stationary Night Blindness Are a Good Model for Myopia

Mutations in GPR179 are one of the most common causes of autosomal recessive complete congenital stationary night blindness (cCSNB). This retinal disease is characterized in patients by impaired dim and night vision, associated with other ocular symptoms, including high myopia. cCSNB is caused by a complete loss of signal transmission from photoreceptors to ON-bipolar cells. In this study, we hypothesized that the lack of Gpr179 and the subsequent impaired ON-pathway could lead to myopic features in a mouse model of cCSNB. Using ultra performance liquid chromatography, we show that adult Gpr179^-/- mice have a significant decrease in both retinal dopamine and 3,4-dihydroxyphenylacetic acid, compared to Gpr179^+/+ mice. This alteration of the dopaminergic system is thought to be correlated with an increased susceptibility to lens-induced myopia but does not affect the natural refractive development. Altogether, our data added a novel myopia model, which could be used to identify therapeutic interventions.

Association of Missense Variants in VSX2 With a Peculiar Form of Congenital Stationary Night Blindness Affecting All Bipolar Cells

Importance

Congenital stationary night blindness (CSNB) is an inherited stationary retinal disorder that is clinically and genetically heterogeneous. To date, the genetic association between some cases with CSNB and an unusual complex clinical picture is unclear.

Objective

To describe an unreported CSNB phenotype and the associated gene defect in 3 patients from 2 unrelated families.

Design, Setting, and Participants

This retrospective case series was conducted in 2021 and 2022 at a national referral center for rare ocular diseases. Data for 3 patients from a cohort of 140 genetically unsolved CSNB cases were analyzed clinically and genetically.

Exposures

Complete ocular examination including full-field electroretinography and multimodal fundus imaging (spectral-domain optical coherence tomography, color, infrared reflectance, and short-wavelength autofluorescence photographs) were performed. The gene defect was identified by exome sequencing and confirmed by Sanger sequencing and co-segregation analysis in 1 family. Screening was performed for genetically unsolved CSNB cases for VSX2 variants by direct Sanger sequencing.

Main Outcomes and Measures

Ocular and molecular biology findings.

Results

The series included 3 patients whose clinical investigations occurred at ages in the early 30s, younger than 12 years, and in the mid 40s. They had nystagmus, low stable visual acuity, and myopia from birth and experienced night blindness. Two older patients had bilateral lens luxation and underwent lens extraction. Full-field electroretinography revealed an electronegative Schubert-Bornschein appearance, combining characteristics of incomplete and complete CSNB, affecting the function of rod and cone ON- and OFF-bipolar cells. Exome sequencing and co-segregation analysis in a consanguineous family with 2 affected members identified a homozygous variant in VSX2. Subsequently, screening of the CSNB cohort identified another unrelated patient harboring a distinct VSX2 variant.

Conclusions and Relevance

This case series revealed a peculiar pan-bipolar cell retinopathy with lens luxation associated with variants in VSX2. Clinicians should be aware of this association and VSX2 added to CSNB diagnostic gene panels.

Mathematical analysis of phototransduction reaction parameters in rods and cones

Retinal photoreceptor cells, rods and cones, convert photons of light into chemical and electrical signals as the first step of the visual transduction cascade. Although the chemical processes in the phototransduction system are very similar to each other in these photoreceptors, the light sensitivity and time resolution of the photoresponse in rods are functionally different than those in the photoresponses of cones. To systematically investigate how photoresponses are divergently regulated in rods and cones, we have developed a detailed mathematical model on the basis of the Hamer model. The current model successfully reconstructed light intensity-, ATP- and GTP-dependent changes in concentrations of phosphorylated visual pigments (VPs), activated transducins (Tr*s) and phosphodiesterases (PDEs) in rods and cones. In comparison to rods, the lower light sensitivity of cones was attributed not only to the lower affinity of activated VPs for Trs but also to the faster desensitization of the VPs. The assumption of an intermediate inactive state, MIIⁱ, in the thermal decay of activated VPs was essential for inducing faster inactivation of VPs in rods, and possibly also in cones.

Transient Increase of Flicker Electroretinography Amplitudes after Cataract Surgery: Association with Postoperative Inflammation

Purpose

To determine the characteristics and cause of the increase in the amplitude of flicker electroretinography (ERG) after cataract surgery.

Design

Prospective, observational clinical study.

Participants

Thirty patients who underwent cataract surgery.

Methods

Flicker ERGs were recorded with the RETeval system without mydriasis. The central macular thickness (CMT) was measured by OCT and the aqueous flare value (AFV) by laser flare-cell photometry. These examinations were performed before surgery and 1 day, 1 week, 1 month, 2 months, and 3 months after surgery. Linear regression analysis through the origin was used to compare the correlations between the relative changes in flicker ERG amplitudes and the changes in the CMT and AFV at different times after the surgery.

Main Outcome Measures

The amplitude of flicker ERGs, CMT, and AFV.

Results

The mean amplitude of flicker ERGs increased significantly by 31% at 1 week after surgery (P < 0.001); a significant increase in the amplitudes was not present at 3 months after the surgery. The mean AFV was significantly increased at 1 day after surgery (P < 0.001), and the CMT was significantly increased at 1 to 3 months after surgery (P < 0.001). The changes in flicker ERG amplitudes at 1 week after surgery were significantly associated with the changes in the CMT at 1 to 3 months after surgery (P < 0.05), and they were weakly associated with the changes in AFV at 1 day after surgery (P = 0.05).

Conclusions

These results suggest that the increase in the amplitude of flicker ERGs after cataract surgery is a transient phenomenon that has a peak at 1 week after surgery. The increase of flicker ERG amplitude was associated with measures that are frequently used to evaluate postoperative inflammation.

Financial Disclosures

Proprietary or commercial disclosure may be found after the references.

Use of Visual Electrophysiology to Monitor Retinal and Optic Nerve Toxicity of Medications

It is important for clinicians to consider exposure to toxic substances and nutritional deficiencies when diagnosing and managing cases of vision loss. In these cases, physiologic damage can alter the function of key components of the visual pathway before morphologic changes can be detected by traditional imaging methods. Electrophysiologic tests can aid in the early detection of such functional changes to visual pathway components, including the retina or optic nerve. This review provides an overview of various electrophysiologic techniques, including multifocal electroretinogram (mfERG), full-field ERG (ffERG), electrooculogram (EOG), pattern electroretinogram (PERG), and visual evoked potential (VEP) in monitoring the retinal and optic nerve toxicities of alcohol, amiodarone, cefuroxime, cisplatin, deferoxamine, digoxin, ethambutol, hydroxychloroquine, isotretinoin, ocular siderosis, pentosane, PDE5 inhibitors, phenothiazines (chlorpromazine and thioridazine), quinine, tamoxifen, topiramate, vigabatrin, and vitamin A deficiency.

Electronegative electroretinogram in the modern multimodal imaging era

Background

The electronegative electroretinogram (ERG) reflecting inner retinal dysfunction can assist as a diagnostic tool to determine the anatomical location in eye disease. The aim of this study is to determine the frequency and aetiology of electronegative ERG in a tertiary ophthalmology centre and to develop a clinical algorithm to assist patient management.

Methods

Retrospective review of ERGs performed at the Save Sight Institute from January 2011 to December 2020. ERGs were performed according to ISCEV standard. The b:a ratio was analysed in dark adapted (DA) 3.0 or 12.0 recordings. Patients with ratio of ≤1.0 were included.

Results

A total of 4421 patients had ERGs performed during study period, of which 139 patients (3.1%) had electronegative ERG. The electronegative ERG patients' median age at referral time was 37 (0.7–90.6) years. The causative aetiologies were photoreceptor dystrophy (48, 34.5%), Congenital Stationary Night Blindness (CSNB) (33, 23.7%), retinal ischemia (18, 12.9%), retinoschisis (15, 10.8%), paraneoplastic autoimmune retinopathy (PAIR) and nonPAIR (14, 10.1%), batten disease (4, 2.9%), and inflammatory retinopathy (4, 2.9%). There were three patients with an unclassified diagnosis. Thirty‐two patients (23%) had good vision and a normal fundus appearance. Eleven patients (7.9%) had good vision and normal results in all multimodal imaging.

Conclusions

The frequency of electronegative ERG in our referral centre was 3.1% with photoreceptor dystrophy as the main aetiology. A significant number of the cases had good vision with normal fundus or normal multimodal imaging. This further highlights the value of an ERG in this modern multimodal imaging era.

Cell Type-Selective Loss of Peroxisomal β-Oxidation Impairs Bipolar Cell but Not Photoreceptor Survival in the Retina

Retinal degeneration is a common feature in peroxisomal disorders leading to blindness. Peroxisomes are present in the different cell types of the retina; however, their precise contribution to retinal integrity is still unclear. We previously showed that mice lacking the central peroxisomal β-oxidation enzyme, multifunctional protein 2 (MFP2), develop an early onset retinal decay including photoreceptor cell death. To decipher the function of peroxisomal β-oxidation in photoreceptors, we generated cell type selective Mfp2 knockout mice, using the Crx promotor targeting photoreceptors and bipolar cells. Surprisingly, Crx-Mfp2^−/− mice maintained photoreceptor length and number until the age of 1 year. A negative electroretinogram was indicative of preserved photoreceptor phototransduction, but impaired downstream bipolar cell signaling from the age of 6 months. The photoreceptor ribbon synapse was affected, containing free-floating ribbons and vesicles with altered size and density. The bipolar cell interneurons sprouted into the ONL and died. Whereas docosahexaenoic acid levels were normal in the neural retina, levels of lipids containing very long chain polyunsaturated fatty acids were highly increased. Crx-Pex5^−/− mice, in which all peroxisomal functions are inactivated in photoreceptors and bipolar cells, developed the same phenotype as Crx-Mfp2^−/− mice. In conclusion, the early photoreceptor death in global Mfp2^−/− mice is not driven cell autonomously. However, peroxisomal β-oxidation is essential for the integrity of photoreceptor ribbon synapses and of bipolar cells.

A Novel ARL3 Gene Mutation Associated With Autosomal Dominant Retinal Degeneration

Despite major progress in the discovery of causative genes, many individuals and families with inherited retinal degenerations (IRDs) remain without a molecular diagnosis. We applied whole exome sequencing to identify the genetic cause in a family with an autosomal dominant IRD. Eye examinations were performed and affected patients were studied with electroretinography and kinetic and chromatic static perimetry. Sequence variants were analyzed in genes (n = 271) associated with IRDs listed on the RetNet database. We applied a stepwise filtering process involving the allele frequency in the control population, in silico prediction tools for pathogenicity, and evolutionary conservation to prioritize the potential causal variant(s). Sanger sequencing and segregation analysis were performed on the proband and other family members. The IRD in this family is expressed as a widespread progressive retinal degeneration with maculopathy. A novel heterozygous variant (c.200A > T) was identified in the ARL3 gene, leading to the substitution of aspartic acid to valine at position 67. The Asp67 residue is evolutionary conserved, and the change p.Asp67Val is predicted to be pathogenic. This variant was segregated in affected members of the family and was absent from an unaffected individual. Two previous reports of a de novo missense mutation in the ARL3 gene, each describing a family with two affected generations, are the only examples to date of autosomal dominant IRD associated with this photoreceptor gene. Our results, identifying a novel pathogenic variant in ARL3 in a four-generation family with a dominant IRD, augment the evidence that the ARL3 gene is another cause of non-syndromic retinal degeneration.

Negative electroretinograms: genetic and acquired causes, diagnostic approaches and physiological insights

The dark-adapted human electroretinogram (ERG) response to a standard bright flash includes a negative-going a-wave followed by a positive-going b-wave that crosses the baseline. An electronegative waveform (or negative ERG) results when the b-wave is selectively reduced such that the ERG fails to cross the baseline following the a-wave. In the context of a normally sized a-wave, it indicates a site of retinal dysfunction occurring after phototransduction (commonly at the photoreceptor to bipolar cell synapse). This is an important finding. In genetic disease, the pattern of ERG abnormality can point to variants in a small group of genes (frequently those associated with congenital stationary night blindness and X-linked retinoschisis, but negative ERGs can also be seen in other conditions including syndromic disease). In acquired disease, there are numerous causes, but specific features may point to melanoma-associated retinopathy (MAR). In some cases, the visual symptoms precede the diagnosis of the melanoma and so the ERG findings can initiate investigations facilitating early detection and treatment. Negative ERGs can occur in other paraneoplastic conditions, and in a range of other diseases. This review will outline the physiological basis for the negative ERG, report prevalences in the literature from different cohorts, discuss the range of causes, displaying examples of a number of ERG phenotypes, highlight features of a clinical approach to patients, and briefly discuss further insights relating to current flows shaping the a-wave trough and from single-cell transcriptome analysis.

Prevalence of electronegative electroretinograms in a healthy adult cohort

Objective

An electronegative electroretinogram (ERG) can indicate important ocular or systemic disease. This study explored the prevalence of electronegative responses to dark-adapted stimuli in a largely healthy cohort.

Methods and Analysis

211 participants recruited from the TwinsUK cohort underwent ERG testing incorporating international standard (International Society for Clinical Electrophysiology of Vision (ISCEV)) protocols and additional stimuli. Responses were recorded using conductive fibre electrodes, following pupil dilation and 20 min dark adaptation. Responses analysed were to the ISCEV standard and strong flashes (3.0 and 10 cd/m² s), and to additional white flashes (0.67–67 cd/m² s). A-wave and b-wave amplitudes were extracted; b:a ratios were calculated and proportions of eyes with ratios<1 were noted.

Results

Mean (SD) age was 62.4 (11.4) years (median, 64.3; range 23–86 years). 93% were female. Mean (SD) b:a ratios for right and left eyes, respectively, were 1.86 (0.33) and 1.81 (0.29) for the standard flash, and 1.62 (0.25) and 1.58 (0.23) for the stronger flash; average b:a ratio was lower for the stronger flash (p<0.0001). No waveforms were electronegative. For additional flashes, b:a ratio decreased with increasing flash strength. No electronegative waveforms were seen except in three eyes (0.7%) for the strongest flash; in some cases, drift in the waveform may have artefactually reduced the b:a ratio.

Conclusion

For standard dark-adapted stimuli, no participants had electronegative waveforms. The findings support the notion that electronegative waveforms (in response to standard flash strengths) are unusual, and should prompt further investigation.

PROGRESSION OF SCOTOPIC SINGLE-FLASH ELECTRORETINOGRAPHY IN THE STAGES OF CAPN5 VITREORETINOPATHY

PURPOSE

To characterize the changes found in the electroretinography (ERG) recordings of patients with autosomal dominant neovascular inflammatory vitreoretinopathy and correlate with clinical stages of the disease.

METHODS

Retrospective chart review. Bright- and dim-flash full-field scotopic, photopic, and 30-Hz flicker ERGs were obtained according to international standards. The scotopic ERGs were further processed to analyze the oscillatory potential. The patient described in the case report underwent full ERG testing; five patients composed the archival case series data and included scotopic ERG recordings.

RESULTS

Stage I autosomal dominant neovascular inflammatory vitreoretinopathy is characterized by a decrease in the b-wave amplitude on scotopic flash ERG and the disappearance of late OPs; however, the a-wave amplitude is normal. In Stage II, attenuation of early OPs and the c-wave are observed in scotopic ERG recordings, but both a- and b-wave amplitudes are unchanged. For patients in Stage III, there is a continued decline of both a- and b-wave amplitudes in scotopic ERG recordings. There was a loss of recordable scotopic ERG response in patients with Stage IV disease.

CONCLUSION

Electroretinography may be valuable in determining optimal timing for therapeutic intervention and response before loss of recordable retinal function in CAPN5 vitreoretinopathy.

Stargardt disease: Multimodal imaging: A review

Stargardt disease (STGD1) is an autosomal recessive retinal dystrophy, characterised by bilateral progressive central vision loss and subretinal deposition of lipofuscin-like substances. Recent advances in molecular diagnosis and therapeutic options are complemented by the increasing recognition of new multimodal imaging biomarkers that may predict genotype and disease progression. Unique non-invasive imaging features of STDG1 are useful for gene variant interpretation and may even provide insight into the underlying molecular pathophysiology. In addition, pathognomonic imaging features of STGD1 have been used to train neural networks to improve time efficiency in lesion segmentation and disease progression measurements. This review will discuss the role of key imaging modalities, correlate imaging signs across varied STGD1 presentations and illustrate the use of multimodal imaging as an outcome measure in determining the efficacy of emerging STGD1 specific therapies.

Toxic Optic Neuropathy From Quinine Overdose

A 45-year-old man presented with longstanding poor vision in both eyes. His medical history was significant for a remote overdose of quinine. After the ingestion, he fell into a coma and on awakening was not able to see light out of both eyes. Several days later, his central vision began to gradually recover and continued to improve over the span of several months. Presently, he had 20/20 visual acuity in both eyes with severely constricted peripheral visual fields. There were bilateral iris transillumination defects, and both optic nerves were diffusely pale with attenuated vasculature and inner retinal thinning on ocular coherence tomography. We present a patient with the stereotypical findings and natural history of quinine toxicity, a rare and not widely known cause of toxic optic neuropathy and retinopathy.

Hypoxic-ischemic injury causes functional and structural neurovascular degeneration in the juvenile mouse retina

Ischemic stroke is a major cause of long-term disabilities, including vision loss. Neuronal and blood vessel maturation can affect the susceptibility of and outcome after ischemic stroke. Although we recently reported that exposure of neonatal mice to hypoxia–ischemia (HI) severely compromises the integrity of the retinal neurovasculature, it is not known whether juvenile mice are similarly impacted. Here we examined the effect of HI injury in juvenile mice on retinal structure and function, in particular the susceptibility of retinal neurons and blood vessels to HI damage. Our studies demonstrated that the retina suffered from functional and structural injuries, including reduced b-wave, thinning of the inner retinal layers, macroglial remodeling, and deterioration of the vasculature. The degeneration of the retinal vasculature associated with HI resulted in a significant decrease in the numbers of pericytes and endothelial cells as well as an increase in capillary loss. Taken together, these findings suggest a need for juveniles suffering from ischemic stroke to be monitored for changes in retinal functional and structural integrity. Thus, there is an emergent need for developing therapeutic approaches to prevent and reverse retinal neurovascular dysfunction with exposure to ischemic stroke.

Recognizing differentiating clinical signs of CLN3 disease (Batten disease) at presentation

Purpose

To help differentiate CLN3 (Batten) disease, a devastating childhood metabolic disorder, from the similarly presenting early‐onset Stargardt disease (STGD1). Early clinical identification of children with CLN3 disease is essential for adequate referral, counselling and rehabilitation.

Methods

Medical chart review of 38 children who were referred to a specialized ophthalmological centre because of rapid vision loss. The patients were subsequently diagnosed with either CLN3 disease (18 patients) or early‐onset STGD1 (20 patients).

Results

Both children who were later diagnosed with CLN3 disease, as children who were later diagnosed with early‐onset STGD1, initially presented with visual acuity (VA) loss due to macular dystrophy at 5–10 years of age. VA in CLN3 disease decreased significantly faster than in STGD1 (p = 0.01). Colour vision was often already severely affected in CLN3 disease while unaffected or only mildly affected in STGD1. Optic disc pallor on fundoscopy and an abnormal nerve fibre layer on optical coherence tomography were common in CLN3 disease compared to generally unaffected in STGD1. In CLN3 disease, dark‐adapted (DA) full‐field electroretinogram (ERG) responses were either absent or electronegative. In early‐onset STGD1, DA ERG responses were generally unaffected. None of the STGD1 patients had an electronegative ERG.

Conclusion

Already upon presentation at the ophthalmologist, the retina in CLN3 disease is more extensively and more severely affected compared to the retina in early‐onset STGD1. This results in more rapid VA loss, severe colour vision abnormalities and abnormal DA ERG responses as the main differentiating early clinical features of CLN3 disease.

A New Mouse Model for Complete Congenital Stationary Night Blindness Due to Gpr179 Deficiency

Mutations in GPR179 lead to autosomal recessive complete congenital stationary night blindness (cCSNB). This condition represents a signal transmission defect from the photoreceptors to the ON-bipolar cells. To confirm the phenotype, better understand the pathogenic mechanism in vivo, and provide a model for therapeutic approaches, a Gpr179 knock-out mouse model was genetically and functionally characterized. We confirmed that the insertion of a neo/lac Z cassette in intron 1 of Gpr179 disrupts the same gene. Spectral domain optical coherence tomography reveals no obvious retinal structure abnormalities. Gpr179 knock-out mice exhibit a so-called no-b-wave (nob) phenotype with severely reduced b-wave amplitudes in the electroretinogram. Optomotor tests reveal decreased optomotor responses under scotopic conditions. Consistent with the genetic disruption of Gpr179, GPR179 is absent at the dendritic tips of ON-bipolar cells. While proteins of the same signal transmission cascade (GRM6, LRIT3, and TRPM1) are correctly localized, other proteins (RGS7, RGS11, and GNB5) known to regulate GRM6 are absent at the dendritic tips of ON-bipolar cells. These results add a new model of cCSNB, which is important to better understand the role of GPR179, its implication in patients with cCSNB, and its use for the development of therapies.

DEEP PHENOTYPING AND FURTHER INSIGHTS INTO ITM2B-RELATED RETINAL DYSTROPHY

PURPOSE

To reappraise the presentation and the course of ITM2B-related retinal dystrophy and give further insights into ITM2B expression in the retina.

METHODS

The clinical data of nine subjects with ITM2B-related retinal dystrophy were retrospectively reviewed. The genetic mutation was assessed for its influence on splicing in cultured fibroblasts. The cellular expression of ITM2B within the inner retina was investigated in wild-type mice through mRNA in situ hybridization.

RESULTS

All patients complained of decreased vision and mild photophobia around their twenties-thirties. The peculiar feature was the hyperreflective material on optical coherence tomography within the inner retina and the central outer nuclear layer with thinning of the retinal nerve fiber layer. Although retinal imaging revealed very mild or no changes over the years, the visual acuity slowly decreased with about one Early Treatment Diabetic Retinopathy Study letter per year. Finally, full-field electroretinography showed a mildly progressive inner retinal and cone dysfunction. ITM2B mRNA is expressed in all cellular types of the inner retina. Disease mechanism most likely involves mutant protein misfolding and/or modified protein interaction rather than misplicing.

CONCLUSION

ITM2B-related retinal dystrophy is a peculiar, rare, slowly progressive retinal degeneration. Functional examinations (full-field electroretinography and visual acuity) seem more accurate in monitoring the progression in these patients because imaging tends to be stable over the years.

Congenital stationary night blindness in a patient with mild learning disability due to a compound heterozygous microdeletion of 15q13 and a missense mutation in TRPM1

The complete form of congenital stationary night blindness (cCSNB) represents a non-progressive retinal disorder characterized by night vision problems and often congenital nystagmus, reduced vision, high myopia, strabismus and normal fundus appearance. Clinically this form of CSNB can be diagnosed by full-field electroretinogram. The mode of inheritance can be X-linked and autosomal recessive with mutations in genes coding for proteins mainly present at the dendritic tips of ON-bipolar cells. Mutations in NYX, GRM6, GPR179, LRIT3 and TRPM1 lead to this condition. The latter gene defect represents the major form underlying cCSNBC. It codes for the melastatin-related transient receptor 1 expressed in the inner nuclear layer of the retina, with the protein localized in ON-bipolar cells. To date, various homozygous or compound heterozygous mutations in TRPM1 have been reported. Small chromosomal rearrangements are frequent cause of mental retardation. In rare cases deletions can overlap with a mutation on the remaining chromosome and lead to a recessive disorder. Here, we describe a patient with mild neurological deficiencies and cCSNB caused by a microdeletion on 15q32 overlapping with a TRPM1 variant.

Acute unilateral inner retinal dysfunction with photophobia: importance of electrodiagnosis

PURPOSE

To establish with negative electroretinogram (ERG) the clinical entity of eight patients with unilateral severe photophobia, essentially normal fundus, good visual acuity, and severe cone and rod dysfunction.

STUDY DESIGN

Multicenter retrospective observation case series.

METHODS

Comprehensive ophthalmologic examinations were performed, including best-corrected visual acuity (BCVA), full-field ERGs and multifocal ERGs (mfERGs), fundus photographs, and OCT. Systemic and genetic examinations were performed.

RESULTS

The mean (± SD) age at the onset was 60.0 ± 8.4 years, and the six patients noticed severe photophobia in the affected eye in spite of almost normal fundus appearance and good BCVA. The dark-adapted bright flash ERGs in the affected eye had relatively well-preserved a-waves and depressed b-waves, i.e., a negative ERG. Cone ERGs and both b- and d-waves of the photopic long-duration ERGs were almost undetectable. Rod ERGs were severely reduced; however, only two patients complained of night blindness. In five patients, the mfERGs were extinguished in the periphery but preserved in the central retina, resulting in good BCVA. Electrophysiological findings indicated a severe diffuse dysfunction of the inner retina affecting bipolar cells of both ON- and OFF-pathways, and in five patients there was a reduction in the thickness of the inner nuclear layer. In seven patients the retinal arteries were attenuated. Anti-retinal antibodies were detected in the serum of two patients. No genetic causes were found.

CONCLUSIONS

The common features in the eight patients with unilateral negative ERGs suggest a new disease entity of unilateral acute inner retinal layer dysfunction. In most patients, the only subjective complain was photophobia.

Transgenic Expression of Cacna1f Rescues Vision and Retinal Morphology in a Mouse Model of Congenital Stationary Night Blindness 2A (CSNB2A)

Purpose

Congenital stationary night blindness 2A (CSNB2A) is a genetic retinal disorder characterized by poor visual acuity, nystagmus, strabismus, and other signs of retinal dysfunction resulting from mutations in Cacna1f -the gene coding for the pore-forming subunit of the calcium channel Ca_V1.4. Mouse models of CSNB2A have shown that mutations causing the disease deleteriously affect photoreceptors and their synapses with second-order neurons. This study was undertaken to evaluate whether transgenic expression of Cacna1f could rescue morphology and visual function in a Cacna1f-KO model of CSNB2A.

Methods

Strategic creation, breeding and use of transgenic mouse lines allowed for Cre-driven retina-specific expression of Cacna1f in a CSNB2A model. Transgene expression and retinal morphology were investigated with immunohistochemistry in retinal wholemounts or cross-sections. Visual function was assessed by optokinetic response (OKR) analysis and electroretinography (ERG).

Results

Mosaic, prenatal expression of Cacna1f in the otherwise Cacna1f-KO retina was sufficient to rescue some visual function. Immunohistochemical analyses demonstrated wild-type-like photoreceptor and synaptic morphology in sections with transgenic expression of Cacna1f.

Conclusions

This report describes a novel system for Cre-inducible expression of Cacna1f in a Cacna1f-KO mouse model of CSNB2A and provides preclinical evidence for the potential use of gene therapy in the treatment of CSNB2A.

Translational Relevance

These data have relevance in the treatment of CSNB2A and in understanding how photoreceptor integration might be achieved in retinas in which photoreceptors have been lost, such as retinitis pigmentosa, age-related macular degeneration, and other degenerative conditions.

Correlation of electroretinography components with visual function and prognosis of central retinal artery occlusion

We investigated the full-field electroretinographic (ERG) parameters with visual function and prognosis in central retinal artery occlusion (CRAO), according to its severity. 110 affected eyes of CRAO patients were enrolled and compared with fellow uninvolved eyes (N = 110) and normal control eyes (N = 30). B/A ratio and photopic negative response amplitude (PhNR) resulted in statistically significant differences among the CRAO subgroups according to the severity of retinal ischemia. Amplitudes of PhNR indicating ganglion cell function showed a more marked decline in mild to severe ischemia than those of the B-wave. In terms of visual function and outcome, baseline visual acuity and visual field defects were correlated with B/A ratio only (both, P < .001), whereas improvements in visual acuity and visual field were correlated with B-wave amplitude in dark-adapted 3.0 (P = .004 and .006), B/A ratio (P = .023 and .008), and PhNR amplitude (P < .001 and .004). These three ERG parameters were found to be credible predictive factors of visual prognosis. In conclusion, B-wave amplitude in dark-adapted 3.0, B/A ratio, and PhNR amplitude changes in eyes with CRAO are associated with baseline features related to the severity of retinal ischemia, and these are correlated with visual function and prognosis.

Rod bipolar cell dysfunction in POLG retinopathy

OBJECTIVE

To report the clinical and novel electrophysiological features in a child with POLG-related sensory ataxic neuropathy, dysarthria and ophthalmoparesis (SANDO).

METHODS

The proband, a male child of Indian descent, underwent serial systemic and ophthalmological evaluations from birth until 14 years of age. Eye examinations included visual acuity and extraocular movement assessments, fundus photography, spectral domain optical coherence tomography and full-field electroretinography (ERG). Detailed genetic testing was also performed.

RESULTS

The child carried a homozygous mutation in POLG (c.911T > G/p.Leu304Arg) and manifested systemic features such as seizures, headaches, areflexia, hypotonia, myopathy and vomiting. The child's distance visual acuity was 0.50 and 0.40 LogMAR in the right and left eyes, respectively. Bilateral ophthalmoplegia and ptosis were observed at 5 years of age. The dark-adapted (DA) ERG responses to 2.29 cd s m^-2 and 7.6 cd s m^-2 stimuli showed a markedly reduced b/a ratio; an electronegative configuration was noted to a DA 7.6 ERG.

CONCLUSION

This is the first documented case of an electronegative ERG in a POLG-related disorder consistent with generalized rod ON-bipolar dysfunction. The rest of the proband's systemic and ophthalmological features were consistent with SANDO but some features overlapped with other POLG-related disorders such as Alpers-Huttenlocher syndrome and autosomal dominant progressive external ophthalmoplegia demonstrating the wide phenotypic overlap expected due to POLG mutations.

Electronegative Electroretinograms in the United Arab Emirates

PURPOSE

An electronegative electroretinogram (ERG), defined as having a b:a wave ratio ≤1 in the scotopic flash ERG response, indicates relative inner retinal dysfunction. Causes vary depending upon the study population. In the Arabian Gulf, where inherited retinal disease is relatively prevalent, common diagnoses associated with electronegative ERGs have not been described. In this study, we report the frequency and causes of electronegative ERGs in a cohort of Emirati patients with inherited retinal disease.

METHODS

A retrospective review was performed of all full-field ERGs done for Emirati patients in the Ocular Genetics Service of Cleveland Clinic Abu Dhabi from January 2017 to December 2019. Those who had an electronegative ERG in at least one eye were included in the study.

RESULTS

Out of 137 patients, 9 probands (6.6%) had an electronegative ERG. The mean age at presentation was 24 years (range 5-48 years), and five patients (55.6%) were male. The final clinical diagnoses were congenital stationary night blindness (CSNB) (two TRPM1-related and one Oguchi disease), X-linked retinoschisis (XLRS) (one genetically confirmed and two not genetically tested), cone-rod dystrophy (one CRX-related and one not genetically tested), and enhanced S-cone syndrome (ESCS) (one NRL-related). The one patient who did not have bilateral electronegative ERGs was a male with XLRS whose fellow eye had an unrecordable ERG.

CONCLUSIONS

In this series of Emirati patients, an electronegative ERG was most commonly associated with the inherited retinal diseases recessive CSNB and XLRS. An electronegative ERG was noted in a case of NRL-related ESCS.

Association of CRX genotypes and retinal phenotypes confounded by variable expressivity and electronegative electroretinogram

IMPORTANCE

A framework for understanding the phenotypic features of CRX retinopathy was established.

BACKGROUND

To perform a phenotype-genotype correlation analysis in two groups of patients with heterozygous mutations in distinct locations of the CRX gene, encoding the cone-rod homeobox.

DESIGN

Multicentre retrospective study.

PARTICIPANTS

Twenty-one Japanese patients from 14 families with a heterozygous CRX mutation.

METHODS

Retrospective data analysis.

MAIN OUTCOME MEASURES

Clinical records on CRX mutation, symptoms, best-corrected visual acuity (BCVA), visual field, fundus photography, fundus auto-fluorescence, optical coherence tomography and electroretinograms (ERGs).

RESULTS

Six different CRX heterozygous mutations were identified in the subjects. Twelve patients from 9 families shared the p.R41W mutation and 1 patient had the p.R43C mutation, both of which affect the homeobox domain of CRX. These patients often displayed adult-onset retinal dystrophy with macular degeneration. In contrast, five patients with downstream mutations (p.S204fs, p.S213fs, p.G243X and p.L299F) displayed retinal degeneration or macular degeneration with bone-spicule pigmentation. Three asymptomatic carriers with different mutations (p.R41W, p.S213fs and p.G243X) were present in both groups. Nearly all patients and carriers had an electronegative ERG in response to a bright flash under dark adaptation. There was no cross-sectional association between patients' age and BCVA, despite progressive decline in BCVA.

CONCLUSIONS AND RELEVANCE

Heterozygous mutations within or downstream of the homeobox domain in CRX relate to the difference associated retinal phenotypes, which was confounded by variable expressivity and electronegative ERGs. CRX mutations should be considered in patients with an electronegative ERG with minimal or no macular changes.

Juvenile Batten Disease (CLN3): Detailed Ocular Phenotype, Novel Observations, Delayed Diagnosis, Masquerades, and Prospects for Therapy

Purpose

To characterize the retinal phenotype of juvenile neuronal ceroid lipofuscinosis (JNCL), highlight delayed and mistaken diagnosis, and propose an algorithm for early identification.

Design

Retrospective case series.

Participants

Eight children (5 female) with JNCL.

Methods

Review of clinical notes, retinal imaging including fundus autofluorescence and OCT, electroretinography (ERG), and both microscopy and molecular genetic testing.

Main Outcome Measurements

Demographic data, signs and symptoms, visual acuity (VA), fundus autofluorescence and OCT findings, ERG phenotype, and microscopy/molecular genetics.

Results

Participants presented with rapid bilateral vision loss over 1 to 18 months, with mean VA deteriorating from 0.44 logarithm of the minimum angle of resolution (logMAR) (range, 0.20–1.78 logMAR) at baseline to 1.34 logMAR (0.30 logMAR - light perception) at last follow-up. Age of onset ranged from 3 to 7 years (mean, 5.3 years). The age at diagnosis of JNCL ranged from 7 to 10 years (mean, 8.3 years). Six children displayed eccentric fixation, and 6 children had cognitive or neurologic signs at the time of diagnosis (75%). Seven patients had bilateral bull’s-eye maculopathy at presentation. Coats-like exudative vasculopathy, not previously reported in JNCL, was observed in 1 patient. OCT imaging revealed near complete loss of outer retinal layers and marked atrophy of the nerve fiber and ganglion cell layers at the central macula. An electronegative ERG was present in 4 patients (50%), but with additional a-wave reduction, there was an undetectable ERG in the remaining 4 patients. Blood film microscopy revealed vacuolated lymphocytes, and electron microscopy showed lysosomal (fingerprint) inclusions in all 8 patients.

Conclusions

In a young child with bilateral rapidly progressive vision loss and macular disturbance, blood film microscopy to detect vacuolated lymphocytes is a rapid, readily accessible, and sensitive screening test for JNCL. Early suspicion of JNCL can be aided by detailed directed history and high-resolution retinal imaging, with subsequent targeted microscopy/genetic testing. Early diagnosis is critical to ensure appropriate management, counseling, support, and social care for children and their families. Furthermore, although potential therapies for this group of disorders are in early-phase clinical trial, realistic expectations are that successful intervention will be most effective when initiated at the earliest stage of disease.

Verifying complaints of difficulties in night vision using electroretinography and dark adaptation tests

PURPOSE

To determine the electroretinographical and psychophysical parameters that can help to verify patients' complaints of reduced night vision.

METHODS

We tested 275 consecutive patients with normal appearing fundi, complaining of visual difficulties at night, using flash electroretinography (ERG) and dark adaptation (DA) test. Two ERG parameters were used to assess a scotopic retinal function: the amplitude of the response to dim blue flash (the rod response) and the b-wave ratio (measured/expected). Dark adaptation was measured with green- and red-light stimuli after exposure to a bright, bleaching light. The psychophysical parameter of night vision was defined as the threshold for detection of the blue-green stimulus that was measured after 40-45 min in complete darkness.

RESULTS

Fifty-five patients were excluded from the analysis because of a discrepancy between the two ERG parameters in assessment of scotopic retinal function. The remaining 220 patients were divided into 4 groups: (1) normal ERG and normal DA, (2) subnormal ERG and subnormal DA, (3) normal ERG and subnormal DA and (4) subnormal ERG and normal DA. The ERG and DA tests supported the complaint of visual difficulties at night in 67 patients (group 2), while 34 patients were characterized as having normal scotopic visual function (group 1). The other 119 patients (groups 3 and 4) presented a diagnostic dilemma because one test (ERG or dark adaptation) showed normal scotopic function, while the other indicated subnormal scotopic function.

CONCLUSION

Our findings indicate that ERG is an essential, but not sufficient test for verifying patient's complaint on visual difficulties in the dark. We suggest using both electroretinography and psychophysical dark adaptation to test patients complaining of reduced night vision.

Extracting the ON and OFF contributions to the full-field photopic flash electroretinogram using summed growth curves

Under cone-mediated (photopic) conditions, an "instantaneous" flash of light, including both stimulus onset and offset, will simultaneously activate both "ON" and "OFF" bipolar cells, which either depolarize (ON) or hyperpolarize (OFF) in response and, respectively, produce positive-going and negative-going deflections in the electroretinogram (ERG). The stimulus-response (SR) relationship of the photopic ON response demonstrates logistic growth, like that manifested in the rod-mediated (scotopic) b-wave, which is driven by a single class of depolarizing bipolar cell. However, the photopic b-wave SR function is importantly shaped by OFF responses, leading to a "photopic hill." Furthermore, both on and off stimuli elicit activity in both ON and OFF bipolar cells. This has made it difficult to produce meaningful parameters for ready interpretation of the photopic b-wave SR relationship. Therefore, we evaluated whether the sum of sigmoidal SR functions, as descriptors of the depolarizing and hyperpolarizing components of the photopic flash ERG, could be used to elucidate and quantitate the mechanisms that produce the photopic hill. We used a novel fitting routine to optimize a sum of simple sigmoidal curves to SR data in five groups of subjects: Healthy adult, 10-week-old infant, congenital stationary night blindness (CSNB), X-linked juvenile retinoschisis (XJR), and preterm-born, both without and with a history of retinopathy of prematurity (ROP). Differences in ON and OFF amplitude, sensitivity, and implicit time among the groups were then compared using parameters extracted from these fits. We found that our modeling procedure enabled plausible derivations of ON and OFF pathway contributions to the ERG, and that the parameters produced appeared to have physiological relevance. In adult subjects, the ON and OFF amplitudes were similar in magnitude with respectively longer and shorter implicit times. Infant, CSNB, and XJR subjects showed significant ON pathway deficits. History of preterm-birth, without or with a diagnosis of ROP, did not much affect cone responses.

Oguchi's disease with Mizuo-Nakamura phenomenon in a seven-year-old boy

A seven-year-old boy presented with difficulty in night vision of five years duration. Vision was 20/20 OU. Fundus examination revealed a golden sheen over the posterior pole in both eyes which disappeared after 45 minutes of dark adaptation, suggestive of Mizuo-Nakamura phenomenon. Clinical findings were suggestive of Oguchi's disease. ERG was confirmatory.

PRESUMED PHOTORECEPTOR DYSPLASIAS IN PEREGRINE FALCONS ( FALCO PEREGRINUS) AND PEREGRINE FALCON HYBRIDS

We describe a case series of photoreceptor dysplasia with secondary retinal degeneration in juvenile Peregrine Falcons. Six Peregrine Falcons ( Falco peregrinus) and three Peregrine Falcon × Prairie Falcon ( Falco mexicanus) hybrids had early-life visual deficits. Eight birds had visual defects shortly after hatching, and one bird had visual deficits first noticed at 5 mo of age. Complete ophthalmic examinations were performed in each animal. Eight of the animals had electroretinograms, and nine of the animals had their eyes examined histologically after euthanasia. Ophthalmic examinations did not reveal consistent and potentially blinding abnormalities, including an absence of ophthalmoscopic retinal lesions. Electroretinographic findings included subnormal amplitudes (with rod responses more abnormal than cone responses), with a negative b-wave amplitude occurring in one bird. Histologically, a reduction in the number of photoreceptors was present with numerous degenerative changes to the remaining photoreceptors, including frequent blunting and disorganization of photoreceptor outer segments, decreased numbers of cells in the inner nuclear layer, decreased numbers of ganglion cells, decreased thickness of the nerve fiber layer, and decreased myelinated axons within the optic nerve. Ultrastructurally, only minor cone outer segment changes and occasional phagocytic cells were seen. Results strongly suggested a primary retinopathy, characterized by photoreceptor dysplasia and secondary retinal degeneration with loss of cellular elements throughout the retina. The presence of a similar spectrum of findings in related individuals, the early age of onset, and the relative lack of other environmental, ocular, or systemic abnormalities suggested possible heritability.

Phenotypic characterization of complete CSNB in the inbred research beagle: how common is CSNB in research and companion dogs?

PURPOSE

Although congenital stationary night blindness (CSNB) has been described in a Japanese beagle dog research colony, certain clinical correlates with human CSNB have not yet been described, nor has an estimate of frequency of the condition been made in inbred and outbred beagle populations.

METHODS

A beagle with CSNB obtained from a commercial research dog supplier in the USA and matched control dogs (n = 3) underwent examination, refraction, ocular imaging, assessment of visual navigation ability and detailed electroretinography (ERG). Retrospective review of ERGs in two independent groups of inbred (n = 15 and 537, respectively) and one group of outbred dogs (n = 36) was used to estimate CSNB frequency in these populations.

RESULTS

In the affected dog, there were absent dark-adapted b-waves in response to dim-light flashes, severely reduced dark-adapted b-waves in response to bright-light flashes, and normal light-adapted b-waves with a-waves that had broadened troughs. Long-flash ERGs confirmed a markedly reduced b-wave with a preserved d-wave, consistent with cone ON-bipolar cell dysfunction. There was evidence of normal rod photoreceptor a-wave dark adaptation, and rapid light adaptation. In the wider beagle populations, five inbred beagles had a b/a wave ratio of < 1 in dark-adapted bright-flash ERG, whereas no outbred beagles had ERGs consistent with CSNB.

CONCLUSIONS

The identified dog had clinical findings consistent with complete type CSNB, similar to that described in the Japanese colony. CSNB appears to be a rare disorder in the wider beagle population, although its detection could confound studies that use retinal function as an outcome measure in research dogs, necessitating careful baseline studies to be performed prior to experimentation.

ISCEV extended protocol for the photopic On-Off 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.

Expanded Retinal Disease Spectrum Associated With Autosomal Recessive Mutations in GUCY2D

PURPOSE

GUCY2D has been associated with autosomal recessive Leber congenital amaurosis and autosomal dominant cone-rod dystrophy. This report expands the phenotype of autosomal recessive mutations to congenital night blindness, which may slowly progress to mild retinitis pigmentosa.

DESIGN

Retrospective case series.

METHODS

Multicenter study of 5 patients (3 male, 2 female).

RESULTS

All patients presented with night blindness since childhood. Age at referral was 9-45 years. Length of follow-up was 1-7 years. Best-corrected visual acuity at presentation ranged from 20/15 to 20/30 and at most recent visit averaged 20/25. No patient had nystagmus or high refractive error. ISCEV standard electroretinography revealed nondetectable dark-adapted dim flash responses and reduced amplitude but not electronegative dark-adapted bright flash responses with similar waveforms to the reduced-amplitude light-adapted single flash responses. The 30 Hz flicker responses were relatively preserved. Macular optical coherence tomography revealed normal lamination in 3 patients, with abnormalities in 2. Goldmann visual fields were normal at presentation in children but constricted in 1 adult. One child showed loss of midperipheral fields over time. Fundus appearance was normal in childhood; the adult had sparse bone spicule-like pigmentation. Full-field stimulus testing (FST) revealed markedly decreased retinal sensitivity to light. Dark adaptation demonstrated lack of rod-cone break. Two patients had tritanopia. All 5 had compound heterozygous mutations in GUCY2D. Three of the 5 patients harbor the Arg768Trp mutation reported in GUCY2D-associated Leber congenital amaurosis.

CONCLUSIONS

Autosomal recessive GUCY2D mutations may cause congenital night blindness with normal acuity and refraction, and unique electroretinography. Progression to mild retinitis pigmentosa may occur.

Deferoxamine-induced electronegative ERG responses

PURPOSE

To report a case of deferoxamine-induced retinopathy characterized by electroretinography (ERG), optical coherence tomography angiography (OCT-A), and other multimodal imaging.

METHODS

This is an observational case report of one patient. Full-field ERG was performed. OCT-A, spectral-domain optical coherence tomography (SD-OCT), color fundus photography, and fundus autofluorescence were used to characterize the retinopathy induced by deferoxamine use.

RESULTS

A 64-year-old man with a history of β-thalassemia intermedia presented with worsening visual acuity, nyctalopia, and electronegative ERG. OCT-A revealed atrophy of the choriocapillaris in areas of hypoautofluorescence, corresponding to regions of retinal atrophy. SD-OCT showed disruption of the ellipsoid zone, granular hyperreflective deposits within the retinal pigment epithelium, thinning of the retinal layers, and extensive choroidal sclerosis and atrophy of the retinal pigment epithelium.

CONCLUSION

Deferoxamine-induced retinopathy can manifest with electronegative maximal ERG responses, and OCT-A can be used to detect deferoxamine toxicity.