The pattern of retinal ganglion cell dysfunction in Leber hereditary optic neuropathy

Electrodiagnostic tests of the visual pathway and applications in neuro-ophthalmology

This article describes the main visual electrodiagnostic tests relevant to neuro-ophthalmology practice, including the visual evoked potential (VEP), and the full-field, pattern and multifocal electroretinograms (ffERG; PERG; mfERG). The principles of electrophysiological interpretation are illustrated with reference to acquired and inherited optic neuropathies, and retinal disorders that may masquerade as optic neuropathy, including ffERG and PERG findings in cone and macular dystrophies, paraneoplastic and vascular retinopathies. Complementary VEP and PERG recordings are illustrated in demyelinating, ischaemic, nutritional (B12), and toxic (mercury, cobalt, and ethambutol-related) optic neuropathies and inherited disorders affecting mitochondrial function such as Leber hereditary optic neuropathy and dominant optic atrophy. The value of comprehensive electrophysiological phenotyping in syndromic diseases is highlighted in cases of SSBP1-related disease and ROSAH (Retinal dystrophy, Optic nerve oedema, Splenomegaly, Anhidrosis and Headache). The review highlights the value of different electrophysiological techniques, for the purposes of differential diagnosis and objective functional phenotyping.

Electroretinographic oscillatory potentials in Leber hereditary optic neuropathy

PURPOSE

Leber hereditary optic neuropathy (LHON) affects retinal ganglion cells causing severe vision loss. Pattern electroretinogram and photopic negative response (PhNR) of the light-adapted (LA) full-field electroretinogram (ERG) are typically affected in LHON. In the present study, we evaluated dark-adapted (DA) and LA oscillatory potentials (OPs) of the flash ERG in genetically characterized LHON patients to dissociate slow from fast components of the response.

METHODS

Seven adult patients (mean age = 28.4 ± 5.6) in whom genetic diagnosis confirmed LHON with mtDNA or nuclear DNAJC30 (arLHON) pathogenic variants were compared to 12 healthy volunteers (mean age = 35.0 ± 12.1). Full-field ERGs were recorded from both eyes. Offline digital filters at 50, 75 and 100 Hz low cutoff frequencies were applied to isolate high-frequency components from the original ERG signals.

RESULTS

ERG a-waves and b-waves were comparable between LHON patients and controls, while PhNR was significantly reduced (p = 0.009) in LHON patients compared to controls, as expected. OPs derived from DA signals (75 Hz low cutoff frequency) showed reduced peak amplitude for OP2 (p = 0.019). LA OP differences between LHON and controls became significant (OP2: p = 0.047, OP3: p = 0.039 and OP4: p = 0.013) when the 100 Hz low-cutoff frequency filter was applied.

CONCLUSIONS

Reduced OPs in LHON patients may represent disturbed neuronal interactions in the inner retina with preserved photoreceptoral (a-wave) to bipolar cell (b-wave) activation. Reduced DA OP2 and high-cutoff LA OP alterations may be further explored as functional measures to characterize LHON status and progression.

Dysregulation of the circRNA_0087207/miR-548c-3p/PLSR1-TGFB2 axis in Leber hereditary optic neuropathy in vitro

BACKGROUND

Leber hereditary optic neuropathy (LHON) is mainly the degeneration of retinal ganglion cells (RGCs) associated with high apoptosis and reactive oxygen species (ROS) levels, which is accepted to be caused by the mutations in the subunits of complex I of the mitochondrial electron transport chain. The treatment is still infant while efforts of correcting genes or using antioxidants do not bring good and consistent results. Unaffected carrier carries LHON mutation but shows normal phenotype, suggesting that the disease's pathogenesis is complex, in which secondary factors exist and cooperate with the primary complex I dysfunction.

METHODS

Using LHON patient-specific induced pluripotent stem cells (iPSCs) as the in vitro disease model, we previously demonstrated that circRNA_0087207 had the most significantly higher expression level in the LHON patient-iPSC-derived RGCs compared with the unaffected carrier-iPSC-derived RGCs. To elaborate the underlying pathologies regulated by circRNA_008720 mechanistically, bioinformatics analysis was conducted and elucidated that circRNA_0087207 could act as a sponge of miR-548c-3p and modulate PLSCR1/TGFB2 levels in ND4 mutation-carrying LHON patient-iPSC-derived RGCs.

RESULTS

Using LHON iPSC-derived RGCs as the disease-based platform, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis on targeted mRNA of miR-548c-3p showed the connection with apoptosis, suggesting downregulation of miR548c-3p contributes to the apoptosis of LHON patient RGCs.

CONCLUSION

We showed that the downregulation of miR548c-3p plays a critical role in modulating cellular dysfunction and the apoptotic program of RGCs in LHON.

A challenging differential diagnosis - Leber's Hereditary Optic Neuropathy

Leber's hereditary optic neuropathy (LHON) is the most common maternally inherited disease linked to mitochondrial DNA (mtDNA). The patients present with subacute asymmetric bilateral vision loss. Approximately 95% of the LHON cases are caused by m.3460G>A (MTND1), m.11778G>A (MTND4), and m.14484T>C (MTND6) mutations. The hallmark of hereditary optic neuropathies determined by mitochondrial dysfunction is the vulnerability and degeneration of retinal ganglion cells (RGC). We present the case of a 28-year-old man who came to our clinic complaining of a subacute decrease in visual acuity of his left eye. From his medical history, we found out that one month before he had the same symptoms in the right eye. From the family history, we noted that an uncle has had vision problems since childhood. We carried out complete blood tests, including specific antibodies for autoimmune and infectious diseases. Laboratory tests and MRI were within normal limits. A blood test of the mtDNA showed the presence of 11778 G>A mutation on the mtND6 gene. The medical history, the fundus appearance, the OCT, and the paraclinical investigations, made us diagnose our patient with Leber's hereditary optic neuropathy. As soon as possible, we began the treatment with systemic idebenone, 900 mg/day. We examined the patient 2, 6, and 10 weeks after initiating the treatment. Abbreviations: LHON = Leber's Hereditary Optic Neuropathy, mtDNA = mitochondrial DNA, VA = visual acuity, RE = right eye, LE = left eye, OCT = Optical coherence tomography, pRNFL = peripapillary retinal nerve fiber layer, GCL = retinal ganglion cells layer, MRI = magnetic resonance imaging, VEP = visual evoked potentials, VEP IT = VEP implicit time, VEP A = VEP amplitude.

The diagnostic accuracy of photopic negative responses evoked by broadband and chromatic stimuli in a clinically heterogeneous population

PURPOSE

To compare the diagnostic accuracy of the photopic negative response (PhNR) elicited by red-blue (RB) and white-white (WW) stimuli, for detection of retinal ganglion cell (RGC) dysfunction in a heterogeneous clinical cohort.

METHODS

Adults referred for electrophysiological investigations were recruited consecutively for this single-centre, prospective, paired diagnostic accuracy study. PhNRs were recorded to red flashes (1.5 cd·s·m-2) on a blue background (10 cd·m-2) and to white flashes on a white background (the latter being the ISCEV standard LA 3 stimulus). PhNR results were compared with a reference test battery assessing RGC/optic nerve structure and function including optical coherence tomography (OCT) retinal nerve fibre layer thickness and mean RGC volume measurements, fundus photography, pattern electroretinography and visual evoked potentials. Primary outcome measures were differences in sensitivity and specificity of the two PhNR methods.

RESULTS

Two hundred and forty-three participants were initially enrolled, with 200 (median age 54; range 18-95; female 65%) meeting inclusion criteria. Sensitivity was 53% (95% confidence intervals [CI] 39% to 68%) and 62% (95% CI 48% to 76%), for WW and RB PhNRs, respectively. Specificity was 80% (95% CI 74% to 86%) and 78% (95% CI 72% to 85%), respectively. There was a statistically significant difference between sensitivities (p = 0.046) but not specificities (p = 0.08) of the two methods. Receiver operator characteristic (ROC) area under the curve (AUC) values were 0.73 for WW and 0.74 for RB PhNRs.

CONCLUSION

PhNRs to red flashes on a blue background may be more sensitive than white-on-white stimuli, but there is no significant difference between specificities. This study highlights the value and potential convenience of using white-on-white stimuli, already used widely for routine ERG assessment.

Red Flags in Primary Mitochondrial Diseases: What Should We Recognize?

Primary mitochondrial diseases (PMDs) are complex group of metabolic disorders caused by genetically determined impairment of the mitochondrial oxidative phosphorylation (OXPHOS). The unique features of mitochondrial genetics and the pivotal role of mitochondria in cell biology explain the phenotypical heterogeneity of primary mitochondrial diseases and the resulting diagnostic challenges that follow. Some peculiar features ("red flags") may indicate a primary mitochondrial disease, helping the physician to orient in this diagnostic maze. In this narrative review, we aimed to outline the features of the most common mitochondrial red flags offering a general overview on the topic that could help physicians to untangle mitochondrial medicine complexity.

Analysis of the slope between P50 and N95 waves of the large field pattern electroretinogram as an additional indicator of ganglion cell dysfunction

AIM

Dysfunction of the retinal ganglion cells (RGC) can be detected by the pattern electroretinogram (PERG) as a reduction of the N95 amplitude, a decrease of the ratio between N95 and P50 amplitude and/or a shortening of P50 peak time. Additionally, the slope from the top of the P50 towards the N95 (P50-N95 slope) is less steep than in control subjects. The aim of the study was to quantitatively evaluate this slope in large field PERGs in controls and patients with RGC dysfunction due to optic neuropathy.

SUBJECTS AND METHODS

Large field (21.6°X27.8°) PERGs and optical coherence tomography (OCT) data from 30 eyes of the 30 patients with different types of clinically confirmed optic neuropathies, and with P50 amplitudes within normal limits and abnormal PERG N95 were retrospectively analysed and compared to 30 healthy eyes of 30 control subjects. The P50-N95 slope was analysed with a linear regression from 50 to 80 ms after the stimulus reversal.

RESULTS

The patients with optic neuropathy exhibited a significant reduction of the N95 amplitude (p < 0.001) and N95/P50 ratio (p < 0.001), the P50 peak time was mildly shorter (p = 0.03). The P50-N95 slope was significantly less steep in eyes with optic neuropathies (- 0.089 ± 0.029 vs. - 0.220 ± 0.041, p < 0.001). Thickness of temporal RNFL and the P50-N95 slope appeared to be the most sensitive and specific parameters for detecting RGC dysfunction (AUC = 1.0).

CONCLUSIONS

The slope between the P50 and N95 waves of a large field PERG is considerably less steep in patients with RGC dysfunction and could thus be an efficient biomarker, particularly in the diagnosis of early or borderline cases.

Leber Hereditary Optic Neuropathy in a Family of Carriers of MT-ND5 m.13042G>T (A236S) Novel Variant

BACKGROUND

A Slovenian three-generation family with 3 individuals with bilateral optic neuropathy and 2 unaffected relatives with a novel homoplasmic missense variant m.13042G > T (A236S) in the ND5 gene is described. A detailed phenotype at initial diagnosis and a follow-up of bilateral optic neuropathy progression is presented for 2 affected individuals.

METHODS

A detailed phenotype analysis with clinical examination in the early and chronic phase with electrophysiology and OCT segmentation is presented. Genotype analysis with full mitochondrial genome sequencing was performed.

RESULTS

Two affected male individuals (maternal cousins) had a profound visual loss at an early age (11 and 20 years) with no recovery. The maternal grandmother exhibited bilateral optic atrophy with a history of visual loss at the age 58 years. The visual loss of both affected male individuals was characterized by centrocecal scotoma, abnormal color vision, abnormal PERG N95, and VEP. Later with disease progression, retinal nerve fiber layer thinning was observed on OCT. We observed no other extraocular clinical features. Mitochondrial sequencing identified a homoplasmic novel variant m.13042G > T (A236S) in the MT-ND5 gene, belonging to a haplogroup K1a.

CONCLUSIONS

Novel homoplasmic variant m.13042G > T (A236S) in the ND5 gene in our family was associated with Leber hereditary optic neuropathy-like phenotype. However, predicting the pathogenicity of a novel ultra-rare missense variant in the mitochondrial ND5 gene is challenging. Genetic counseling should consider genotypic and phenotypic heterogeneity, incomplete penetrance, haplogroup type, and tissue-specific thresholds.

Ocular stress enhances contralateral transfer of lenadogene nolparvovec gene therapy through astrocyte networks

Lenadogene nolparvovec (GS010) was developed to treat a point mutation in mitochondrial ND4 that causes Leber hereditary optic neuropathy. GS010 delivers human cDNA encoding wild-type ND4 packaged into an rAAV2/2 vector that transduces retinal ganglion cells, to induce allotopic expression of hybrid mitochondrial ND4. GS010 clinical trials improved best-corrected visual acuity (BCVA) up to 5 years after treatment. Interestingly, unilateral treatment improved BCVA bilaterally. Subsequent studies revealed GS010 DNA in visual tissues contralateral to the injected eye, suggesting migration. Here we tested whether unilateral intraocular pressure (IOP) elevation could influence the transfer of viral ND4 RNA in contralateral tissues after GS010 delivery to the IOP-elevated eye and probed a potential mechanism mediating translocation in mice. We found IOP elevation enhanced viral ND4 RNA transcripts in contralateral visual tissues, including retinas. Using conditional transgenic mice, we depleted astrocytic gap junction connexin 43 (Cx43), required for distant redistribution of metabolic resources between astrocytes during stress. After unilateral IOP elevation and GS010 injection, Cx43 knockdown eradicated ND4 RNA transcript detection in contralateral retinal tissues, while transcript was still detectable in optic nerves. Overall, our study indicates long-range migration of GS010 product to contralateral visual tissues is enhanced by Cx43-linked astrocyte networks.

PhNR and Peripapillary RNFL Changes in Leber Hereditary Optic Neuropathy With m.G11778A Mutation

PURPOSE

To analyze the functional and structural changes in retinal ganglion cells (RGCs) and their axons that occur during Leber's hereditary optic neuropathy (LHON) using photopic negative response (PhNR) and spectral domain optical coherence tomography (SD-OCT).

METHODS

Individuals diagnosed with LHON and their family members were invited to participate in this cross-sectional study. PhNR and OCT were used. The PhNR amplitude and peripapillary retinal nerve fiber layer (pRNFL) thicknesses were compared among the three groups. In addition, affected individuals were divided into subacute, dynamic and chronic phases based on disease duration in order to evaluate the decay in RGCs function and structure.

RESULTS

73 affected and 30 carriers with a m.11778G>A mutation were included. PhNR amplitude and the thickness of pRNFL significantly decreased in affected individuals and carriers compared to that of the controls (P＜0.001). However, there was no difference between the carriers and the controls (P＞0.05). There was no difference in the PhNR amplitude of different phases (P=0.464). In the subacute phase, only temporal pRNFL thickness decreased significantly (P＜0.001). PRNFL thickness decreased significantly in dynamic phase (P＜0.001). Temporal pRNFL thickness continued to decrease in the chronic phase (P=0.042).

CONCLUSION

In the subacute phase, the function of RGCs was severely impaired. Thickness of pRNFL decreased significantly in four quadrants during disease progression. In the chronic phase, pRNFL thickness decreased slightly. Carriers have shown RGCs dysfunction before pathological changes occur, suggesting subclinical abnormalities.

Visual Evoked Potentials for the Detection of Diabetic Retinal Neuropathy

Visual evoked potentials (VEP) are visually evoked signals that extract electroencephalographic activity in the visual cortex that can detect retinal ganglion cells, optic nerves, chiasmal and retrochiasmal dysfunction, including optic radiations, and the occipital cortex. Because diabetes causes diabetic retinopathy due to microangiopathy and neuropathy due to metabolic abnormalities and intraneural blood flow disorders, assessment of diabetic visual pathway impairment using VEP has been attempted. In this review, evidence on the attempts to assess the visual pathway dysfunction due to abnormal blood glucose levels using VEP is presented. Previous studies have provided significant evidence that VEP can functionally detect antecedent neuropathy before fundus examination. The detailed correlations between VEP waveforms and disease duration, HbA1c, glycemic control, and short-term increases and decreases in blood glucose levels are evaluated. VEP may be useful for predicting postoperative prognosis and evaluating visual function before surgery for diabetic retinopathy. Further controlled studies with larger cohorts are needed to establish a more detailed relationship between diabetes mellitus and VEP.

Case report: Long-term follow-up of two patients with LHON caused by DNAJC30:c.152G>A pathogenic variant-case series

BACKGROUND

We present the disease course and long-term follow-up of two patients who were phenotypically diagnosed with atypical Leber Hereditary Optic Neuropathy (LHON) 14 and 12 years ago, respectively, whereby whole exome sequencing revealed recently described recessive DNAJC30:c.152G>A 152 A>G (p.Tyr51Cys) homozygous pathogenic variant with significant spontaneous visual acuity recovery in one.

CASE PRESENTATION

Two presented unrelated males with atypical LHON with sequential visual acuity (VA) loss were followed for many years. Both patients had negative family history. At the presentation at ages 17 (Case 1) and 18 years (Case 2), both had reduced visual acuity (Snellen): (Case 1) right eye (RE):CF 3m, left eye (LE):0.6, (Case 2) RE:0.2, LE:0.15; and color vision (Ishihara): (Case 1) 1/15 and 13/15; (Case 2) 2/15 and 3/15. Both had hyperemic optic disks (PNO) and central scotoma in their visual fields. Electrophysiology in the acute phase showed reduced and delayed visually evoked potentials (VEP) P100 in both patients, with reduced N95 amplitude in Case 2, and initially normal N95 amplitude in Case 1. Fluorescein angiography showed no early leakage with some late pooling at optic disks. Extensive clinical workout, including brain magnetic resonance imaging (MRI), aquaporin 4 (Aq4), and anti-myelin oligodendrocyte protein (anti-MOG) antibodies, was negative. Intravenous corticosteroids did not improve vision. Both experienced further deterioration several months after the onset accompanied by thinning of the peripapillary retinal nerve fiber layer (RNFL). Genetic testing for typical LHON pathogenic variants and whole mitochondrial DNA (mtDNA) sequencing was negative. 1 year after the onset, modest VA improvement began in Case 2 and continued over the next 3 years. VA improved bilaterally to 0.7, color vision 15/15, and islands of vision appeared within the visual field scotoma. VEP P100 peak time shortened, and amplitude increased, despite further RNFL thinning on optical coherent tomography (OCT). The patient's visual function remained stable during the entire 12-year follow-up period. Case 1 experienced modest VA improvement to 0.1 with some improvement in the visual field seven years after the disease onset, remaining stable during the entire 14-year follow-up period. VEP P100 wave remained undetectable.

CONCLUSIONS

Presented are two autosomal recessive LHON (arLHON, OMIM:619382) cases with the same DNAJC30:c.152G>A pathogenic variant and different degrees of spontaneous visual recovery despite progressive RNFL thinning during a long-term follow-up. This mutation should be screened in every atypical LHON patient.

The Relative Preservation of the Central Retinal Layers in Leber Hereditary Optic Neuropathy

(1) Background: The purpose of this study was to evaluate the thickness of retinal layers in Leber hereditary optic neuropathy (LHON) in the atrophic stage compared with presumably inherited bilateral optic neuropathy of unknown cause with the aim of seeing if any LHON-specific patterns exist. (2) Methods: 14 patients (24 eyes) with genetically confirmed LHON (LHON group) were compared with 13 patients (23 eyes) with negative genetic testing results (mtDNA + WES) and without identified etiology of bilateral optic atrophy (nonLHON group). Segmentation analysis of retinal layers in the macula and peripapillary RNFL (pRNFL) measurements was performed using Heidelberg Engineering Spectralis SD-OCT. (3) Results: In the LHON group, the thickness of ganglion cell complex (GCC) (retinal nerve fiber layer (RNFL)—ganglion cell layer (GCL)—inner plexiform layer (IPL)) in the central ETDRS (Early Treatment Diabetic Retinopathy Study) circle was significantly higher than in the nonLHON group (p < 0.001). In all other ETDRS fields, GCC was thinner in the LHON group. The peripapillary RNFL (pRNFL) was significantly thinner in the LHON group in the temporal superior region (p = 0.001). Longitudinal analysis of our cohort during the follow-up time showed a tendency of thickening of the RNFL, GCL, and IPL in the LHON group in the central circle, as well as a small recovery of the pRNFL in the temporal region, which corresponds to the observed central macular thickening. (4) Conclusions: In LHON, the retinal ganglion cell complex thickness (RNFL-GCL-IPL) appears to be relatively preserved in the central ETDRS circle compared to nonLHON optic neuropathies in the chronic phase. Our findings may represent novel biomarkers as well as a structural basis for possible recovery in some patients with LHON.

WFS1-Associated Optic Neuropathy: Genotype-Phenotype Correlations and Disease Progression

OBJECTIVE

To evaluate the pattern of vision loss and genotype-phenotype correlations in WFS1-associated optic neuropathy (WON).

DESIGN

Multicenter cohort study.

METHODS

The study involved 37 patients with WON carrying pathogenic or candidate pathogenic WFS1 variants. Genetic and clinical data were retrieved from the medical records. Thirteen patients underwent additional comprehensive ophthalmologic assessment. Deep phenotyping involved visual electrophysiology and advanced psychophysical testing with a complementary metabolomic study.

MAIN OUTCOME MEASURES

WFS1 variants, functional and structural optic nerve and retinal parameters, and metabolomic profile.

RESULTS

Twenty-two recessive and 5 dominant WFS1 variants were identified. Four variants were novel. All WFS1 variants caused loss of macular retinal ganglion cells (RGCs) as assessed by optical coherence tomography (OCT) and visual electrophysiology. Advanced psychophysical testing indicated involvement of the major RGC subpopulations. Modeling of vision loss showed an accelerated rate of deterioration with increasing age. Dominant WFS1 variants were associated with abnormal reflectivity of the outer plexiform layer (OPL) on OCT imaging. The dominant variants tended to cause less severe vision loss compared with recessive WFS1 variants, which resulted in more variable phenotypes ranging from isolated WON to severe multisystem disease depending on the WFS1 alleles. The metabolomic profile included markers seen in other neurodegenerative diseases and type 1 diabetes mellitus.

CONCLUSIONS

WFS1 variants result in heterogenous phenotypes influenced by the mode of inheritance and the disease-causing alleles. Biallelic WFS1 variants cause more variable, but generally more severe, vision and RGC loss compared with heterozygous variants. Abnormal cleftlike lamination of the OPL is a distinctive OCT feature that strongly points toward dominant WON.

Comparison between frequency-doubling technology perimetry and standard automated perimetry in early glaucoma

This study aimed to find out the significance of the difference between frequency-doubling technology perimetry (FDT) and standard automated perimetry (SAP) in terms of the detected visual field (VF) damage, and evaluate associated factors to SAP–FDT difference in early glaucoma. Glaucoma patients in early stage (MD better than − 6.0 decibel, 96 eyes) were included in this cross-sectional study. We subtracted mean deviation (MD) and pattern standard deviation (PSD) of FDT from those of SAP, respectively. Additionally, we counted significantly depressed points of P < 5% and P < 1% on the pattern deviation probability plot of both FDT and SAP and defined eyes with significant SAP–FDT difference when the number of abnormal points were greater than 4 points on FDT. We measured lamina cribrosa depth (LCD) and lamina cribrosa curvature index (LCCI) for structural parameters of the optic nerve head from images using enhanced depth imaging of the optical coherence tomography (OCT). Peripapillary vessel density (VD) and presence of microvasculature dropout (MvD), the complete loss of choriocapillaris in localized regions of parapapillary atrophy, was evaluated using deep layer map of OCT angiography (OCT-A) for vascular parameters. Peripheral nasal step (PNS) group had an isolated glaucomatous VF defect within nasal periphery outside 10° of fixation. Parafoveal scotoma (PFS) group had an isolated glaucomatous VF defect within 12 points of a central 10˚ radius. Eyes with significant SAP–FDT difference showed higher detection of MvD on deep layer map of OCT-A, greater LCD, and greater LCCI (all P < 0.05, respectively). In logistic regression analysis, frequent presence of MvD, less presence of disc hemorrhage, and greater LCD were significantly associated with significant SAP–FDT difference. Sub-analysis was performed in eyes with PNS (50 eyes) and PFS (46 eyes). SAP–FDT difference of MD value showed positive association with peripapillary VD on deep layer of OCT-A, which was significant in eyes with PFS compared to eyes with PNS. SAP–FDT difference of PSD value showed negative association with LCCI and LCD, which was significant in eyes with PNS compared to eyes with PFS. Glaucomatous eyes classified by the difference of the detected VF damage on FDT versus SAP showed different clinical features. Greater SAP–FDT difference was significantly associated with structural parameters such as LCD and LCCI. Less SAP–FDT difference was associated with presence of disc hemorrhage and lower deep layer peripepillary VD. There is possibility to use the difference of SAP and FDT to identify associated risk factors in glaucoma patients.

Chromatic discrimination measures in mature observers depend on the response window

Our past anecdotal evidence prompted that a longer response window (RW) in the Trivector test (Cambridge Colour Test) improved mature observers’ estimates of chromatic discrimination. Here, we systematically explored whether RW variation affects chromatic discrimination thresholds measured by the length of Protan, Deutan and Tritan vectors. We employed the Trivector test with three RWs: 3 s, 5 s, and 8 s. Data of 30 healthy normal trichromats were stratified as age groups: ‘young’ (20–29 years), ‘middle-aged’ (31–48 years), and ‘mature’ (57–64 years). We found that for the ‘young’ and ‘middle-aged’, the thresholds were comparable at all tested RWs. However, the RW effect was apparent for the ‘mature’ observers: their Protan and Tritan thresholds decreased at 8-s RW compared to 3-s RW; moreover, their Tritan threshold decreased at 5-s RW compared to 3-s RW. Elevated discrimination thresholds at shorter RWs imply that for accurate performance, older observers require longer stimulus exposure and are indicative of ageing effects manifested by an increase in critical processing duration. Acknowledging low numbers in our ‘middle-aged’ and ‘mature’ samples, we consider our study as pilot. Nonetheless, our findings encourage us to advocate a RW extension in the Trivector protocol for testing mature observers, to ensure veridical measures of their chromatic discrimination by disentangling these from other ageing effects—slowing down of both motor responses and visual processing.

The Relationship Between Stage of Leber's Hereditary Optic Neuropathy and Pattern Electroretinogram Latency

Purpose

The purpose of this study was to compare the baseline steady-state pattern electroretinogram (SS-PERG) of patients with G11778A Leber hereditary optic neuropathy (LHON) with different stages of visual acuity (VA) loss before allotopic gene therapy (GT).

Methods

Patients (n = 28) were enrolled into groups (GT I: chronic bilateral VA ≤35 Early Treatment Diabetic Retinopathy Study [ETDRS]; GT II: acute bilateral VA ≤35 ETDRS; GT III: acute unilateral, VA ≤35 ETDRS, and better eye VA ≥70 ETDRS) and tested with SS-PERG together with 210 age-matched normal controls (NCs). SS-PERG amplitude (nV) and latency (ms) of each eye were averaged for groups GT I, GT II, and NC. Symptomatic eyes (GT III-S) and asymptomatic eyes (GT III-A) of group GT III were included separately and accounted for by using generalized estimating equation (GEE) methods.

Results

Compared to NC, SS-PERG amplitudes were reduced similarly by approximately 50% (P < 0.001) among all GT groups (NC > GT I, GT II, GT III-S, and GT III-A). SS-PERG latencies were shorter by ≥3.5 ms in all LHON groups and differed by disease stage (G III-A < NC, P = 0.002; GT III-S < GT III-A, P = 0.01; GT II < GT III-S, P = 0.03; GT I < NC, P < 0.001, but not different from other GT groups, all P > 0.1).

Conclusions

Although SS-PERG amplitude reduction did not distinguish between disease stages, SS-PERG latency shortening occurred in asymptomatic eyes and symptomatic eyes and distinguished between disease stages.

Translational Relevance

SS-PERG latency shortening is consistent with primary damage of smaller/slower axons and sparing of larger/faster axons and may provide an objective staging of LHON, which may be helpful to determine efficacy in LHON trials.

Neuroimaging in Leber Hereditary Optic Neuropathy: State-of-the-art and future prospects

Leber Hereditary Optic Neuropathy (LHON) is an inherited mitochondrial retinal disease that causes the degeneration of retinal ganglion cells and leads to drastic loss of visual function. In the last decades, there has been a growing interest in using Magnetic Resonance Imaging (MRI) to better understand mechanisms of LHON beyond the retina. This is partially due to the emergence of gene-therapies for retinal diseases, and the accompanying expanded need for reliably quantifying and monitoring visual processing and treatment efficiency in patient populations. This paper aims to draw a current picture of key findings in this field so far, the challenges of using neuroimaging methods in patients with LHON, and important open questions that MRI can help address about LHON disease mechanisms and prognoses, including how downstream visual brain regions are affected by the disease and treatment and why, and how scope for neural plasticity in these pathways may limit or facilitate recovery.

[Electrophysiological and psychophysical studies in assessment of visual functions in patients with hereditary optic neuropathy]

PURPOSE

To study the capabilities of electrophysiological and psychophysical examination methods for assessment of the functional state of ganglion cells, retina and optic nerve in patients with hereditary optic neuropathy (HON).

MATERIAL AND METHODS

The study included 60 patients (118 eyes) with a genetically confirmed diagnosis of HON. All study patients underwent visual field test (VFT), spectral optical coherence tomography (OCT), flash and pattern visual evoked potentials (VEP) (Flash-VEP, FVEP; Pattern-VEP, PVEP), photopic electroretinography with photonegative response (PhNR) registration and the color vision test. In 24 patients (46 eyes), these parameters were assessed before the start of treatment and one year later. The treatment involved the mitochondria-targeted antioxidant SkQ1 - plastoquinonyl-decyl-triphenylphosphonium bromide (PDTP) in the form of eye drops.

RESULTS

The main PVEP components for 1.0° and 0.3° were registered in 20% and in 14% of patient eyes with HON and high visual functions, respectively. After one year of PDTP use, a significant decrease in P100 peak latency was found only in the group with disease duration of ≤1.5 years as of the time of treatment start (p<0.05). Significant differences were observed in the PhNR amplitude (p<0.004) between patients of the main and the control groups, as well as in the PhNR amplitude between patients with visual acuity of ≤0.1 and ≥0.13 (p<0.01). Patients with high visual functions were found to have a correlation between the PhNR amplitude, GCC thickness and the global loss index (GLV).

CONCLUSION

Along with VFT, OCT and color vision tests, electrophysiological studies are one of the main methods of examining patients with HON. After one year of PDTP use, there was a significant decrease in the FVEP P2 peak latency in the group with a disease duration of ≤1.5 years as of the time of treatment start. The PhNR amplitude in patients with high visual functions was found to correlate with structural changes in the ganglion cell layer and the retinal nerve fiber layer.

Clinical electrophysiology of the optic nerve and retinal ganglion cells

Clinical electrophysiological assessment of optic nerve and retinal ganglion cell function can be performed using the Pattern Electroretinogram (PERG), Visual Evoked Potential (VEP) and the Photopic Negative Response (PhNR) amongst other more specialised techniques. In this review, we describe these electrophysiological techniques and their application in diseases affecting the optic nerve and retinal ganglion cells with the exception of glaucoma. The disease groups discussed include hereditary, compressive, toxic/nutritional, traumatic, vascular, inflammatory and intracranial causes for optic nerve or retinal ganglion cell dysfunction. The benefits of objective, electrophysiological measurement of the retinal ganglion cells and optic nerve are discussed, as are their applications in clinical diagnosis of disease, determining prognosis, monitoring progression and response to novel therapies.

Impaired Ganglion Cell Function Objectively Assessed by the Photopic Negative Response in Affected and Asymptomatic Members From Brazilian Families With Leber's Hereditary Optic Neuropathy

Purpose: The photopic negative response (PhNR) is an electrophysiological method that provides retinal ganglion cell function assessment using full-field stimulation that does not require clear optics or refractive correction. The purpose of this study was to assess ganglion cell function by PhNR in affected and asymptomatic carriers from Brazilian families with LHON. Methods: Individuals either under suspicion or previously diagnosed with LHON and their family members were invited to participate in this cross-sectional study. Screening for the most frequent LHON mtDNA mutations was performed. Visual acuity, color discrimination, visual fields, pattern-reversal visual evoked potentials (PRVEP), full-field electroretinography and PhNR were tested. A control group of healthy subjects was included. Full-field ERG PhNR were recorded using red (640 nm) flashes at 1 cd.s/m², on blue (470 nm) rod saturating background. PhNR amplitude (μV) was measured using baseline-to-trough (BT). Optical coherence tomography scans of both the retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC) were measured. PhNR amplitudes among affected, carriers and controls were compared by Kruskal-Wallis test followed by post-hoc Dunn test. The associations between PhNR amplitude and OCT parameters were analyzed by Spearman rank correlation. Results: Participants were 24 LHON affected patients (23 males, mean age=30.5 ± 11.4 yrs) from 19 families with the following genotype: m.11778G>A [N = 15 (62%), 14 males]; m.14484T>C [N = 5 (21%), all males] and m.3460G>A [N = 4 (17%), all males] and 14 carriers [13 females, mean age: 43.2 ± 13.3 yrs; m.11778G>A (N = 11); m.3460G>A (N = 2) and m.14484T>C (N = 1)]. Controls were eight females and seven males (mean age: 32.6 ± 11.5 yrs). PhNR amplitudes were significantly reduced (p = 0.0001) in LHON affected (-5.96 ± 3.37 μV) compared to carriers (-16.53 ± 3.40 μV) and controls (-23.91 ± 4.83; p < 0.0001) and in carriers compared to controls (p = 0.01). A significant negative correlation was found between PhNR amplitude and total macular ganglion cell thickness (r = -0.62, p < 0.05). Severe abnormalities in color discrimination, visual fields and PRVEPs were found in affected and subclinical abnormalities in carriers. Conclusions: In this cohort of Brazilian families with LHON the photopic negative response was severely reduced in affected patients and mildly reduced in asymptomatic carriers suggesting possible subclinical abnormalities in the latter. These findings were similar among pathogenic mutations.

Electrophysiology in neuro-ophthalmology

This chapter reviews common applications of visual electrophysiology relevant to neuro-ophthalmology practice. The use of standard tests and extended protocols are described including the cortical visual evoked potential and pattern and full-field electroretinogram (PERG; ERG) methods, the latter including the photopic negative response. Abnormalities of these recordings are rarely specific but provide valuable diagnostic guidance and an objective measure of visual pathway function, difficult or impossible to infer by other methods. The electrophysiological phenotypes associated with Leber hereditary optic neuropathy, OPA1- and SSBP1-associated dominant optic atrophy, and WFS1-related syndromes are described. Typical changes in retinal and optic nerve function tests associated with acquired disease are highlighted, including those related to demyelination, ischemic, compressive, nutritional and toxic, and nonorganic etiologies. The importance of complementary testing using different electrophysiological techniques is emphasized, for the purposes of differential diagnosis and in disorders that may masquerade as optic nerve pathology.

Retinal Ganglion Cells-Diversity of Cell Types and Clinical Relevance

Retinal ganglion cells (RGCs) are the bridging neurons that connect the retinal input to the visual processing centres within the central nervous system. There is a remarkable diversity of RGCs and the various subtypes have unique morphological features, distinct functions, and characteristic pathways linking the inner retina to the relevant brain areas. A number of psychophysical and electrophysiological tests have been refined to investigate this large and varied population of RGCs. Technological advances, such as high-resolution optical coherence tomography imaging, have provided additional tools to define the pattern of RGC involvement and the chronological sequence of events in both inherited and acquired optic neuropathies. The mechanistic insights gained from these studies, in particular the selective vulnerability and relative resilience of particular RGC subtypes, are of fundamental importance as they are directly relevant to the development of targeted therapies for these invariably progressive blinding diseases. This review provides a comprehensive description of the various types of RGCs, the developments in proposed methods of classification, and the current gaps in our knowledge of how these RGCs are differentially affected depending on the underlying aetiology. The synthesis of the current body of knowledge on the diversity of RGCs and the pathways that are potentially amenable to therapeutic modulation will hopefully lead to much needed effective treatments for patients with optic neuropathies.

Enrichment of retinal ganglion and Müller glia progenitors from retinal organoids derived from human induced pluripotent stem cells - possibilities and current limitations

BACKGROUND

Retinal organoids serve as excellent human-specific disease models for conditions affecting otherwise inaccessible retinal tissue from patients. They permit the isolation of key cell types affected in various eye diseases including retinal ganglion cells (RGCs) and Müller glia.

AIM

To refine human-induced pluripotent stem cells (hiPSCs) differentiated into three-dimensional (3D) retinal organoids to generate sufficient numbers of RGCs and Müller glia progenitors for downstream analyses.

METHODS

In this study we described, evaluated, and refined methods with which to generate Müller glia and RGC progenitors, isolated them via magnetic-activated cell sorting, and assessed their lineage stability after prolonged 2D culture. Putative progenitor populations were characterized via quantitative PCR and immunocytochemistry, and the ultrastructural composition of retinal organoid cells was investigated.

RESULTS

Our study confirms the feasibility of generating marker-characterized Müller glia and RGC progenitors within retinal organoids. Such retinal organoids can be dissociated and the Müller glia and RGC progenitor-like cells isolated via magnetic-activated cell sorting and propagated as monolayers.

CONCLUSION

Enrichment of Müller glia and RGC progenitors from retinal organoids is a feasible method with which to study cell type-specific disease phenotypes and to potentially generate specific retinal populations for cell replacement therapies.

Factors associated with rapid improvement in visual acuity in patients with Leber's hereditary optic neuropathy after gene therapy

PURPOSE

To analyse the factors associated with rapid and significant improvement in visual acuity in patients with Leber's hereditary optic neuropathy (LHON) after gene therapy and explain the theory of this improvement.

METHODS

We recruited 149 patients with LHON, who underwent gene therapy, and divided them into two groups according to the absence or presence of rapid and significant visual acuity improvements within 3 days of treatment. A bivariate logistic regression model was used to analyse relevant factors including age, the period between onset and treatment, baseline values of best corrected visual acuity (BCVA), visual field index (VFI) and pretreatment average retinal nerve fibre-layer thickness (GRNFL). The corresponding parameters for the injected and non-injected eyes were analysed separately.

RESULTS

The period between onset and treatment, and pretreatment baseline BCVA was significantly associated with rapid and significant improvement in visual acuity for both, the injected and non-injected eyes. Moreover, pretreatment baseline VFI and GRNFL were not significantly associated with rapid and significant improvement in visual acuity. Age was significantly associated with rapid and significant improvement in visual acuity of the injected eyes.

CONCLUSION

The period between onset and treatment, and pretreatment baseline BCVA may be important predictors of rapid and significant improvement in visual acuity in patients with LHON after gene therapy.

Electrophysiological and Structural Changes in Chinese Patients with LHON

Objective

To review retrospectively the electrophysiological and structural changes in 13 Chinese patients with Leber hereditary optic neuropathy (LHON).

Methods

26 eyes of 13 patients with a genetically confirmed diagnosis of LHON were categorized into two groups according to the duration of the disease: group 1 (duration less than 3 months) and group 2 (duration between 3 months and 18 years). Clinical history, comprehensive visual electrophysiology, optical coherence tomography (OCT), and color fundus photography were performed.

Results

Fundoscopy showed optic disc hyperemia in group 1 and optic atrophy in group 2. OCT measures of retinal nerve fiber layer (RNFL) thickness around the optic disc and surrounding macula were normal in group 1 but reduced in group 2 (10 of 10 eyes). The thickness of the retinal ganglion cell layer (GCL) plus inner plexiform layer (IPL) surrounding the macula reduced significantly in group 1 and group 2 compared with a healthy control group. Pattern ERG (PERG) P50 amplitude was normal, but the N95/P50 ratio reduced in most of group 1 (4 of 5 eyes) and in all of group 2 (11 eyes). PERG P50 peak time was abnormally short in group 2. Multifocal electroretinography (mfERG) showed subnormal responses associated with ring 1 (the central area) and ring 2 in group 1 and reductions in rings 1, 2, and 3 in group 2.

Conclusion

The study highlights differences in retinal structure and function between the acute and chronic stages of LHON in a group of Chinese patients. There is PERG evidence of retinal ganglion cell dysfunction and OCT evidence of GCL + IPL thinning in both groups, but there is additional peripapillary RNFL loss in the chronic stage, associated with more severe RGC dysfunction. There is multifocal ERG evidence of localized macular dysfunction in both acute and chronic groups. The study highlights the importance of comprehensive electrophysiological and structural assessments of the retina in LHON and is pertinent to studies that aim to monitor disease progression or the effects of future therapeutic interventions.

Glutamate Stimulation Dysregulates AMPA Receptors-Induced Signal Transduction Pathway in Leber's Inherited Optic Neuropathy Patient-Specific hiPSC-Derived Retinal Ganglion Cells

The mitochondrial genetic disorder, Leber’s hereditary optic neuropathy (LHON), is caused by a mutation in MT-ND4 gene, encoding NADH dehydrogenase subunit 4. It leads to the progressive death of retinal ganglion cells (RGCs) and causes visual impairment or even blindness. However, the precise mechanisms of LHON disease penetrance and progression are not completely elucidated. Human-induced pluripotent stem cells (hiPSCs) offer unique opportunities to investigate disease-relevant phenotypes and regulatory mechanisms underlying LHON pathogenesis at the cellular level. In this study, we successfully generated RGCs by differentiation of LHON patient-specific hiPSCs. We modified the protocol of differentiation to obtain a more enriched population of single-cell RGCs for LHON study. Based on assessing morphology, expression of specific markers and electrophysiological activity, we found that LHON-specific hiPSC-derived were more defective in comparison with normal wild-type RGCs. Based on our previous study, whereby by using microarray analysis we identified that the components of glutamatergic synapse signaling pathway were significantly downregulated in LHON-specific RGCs, we focused our study on glutamate-associated α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors. We found that the protein expression levels of the subunits of the AMPA receptor, GluR1 and GluR2, and their associated scaffold proteins were decreased in LHON-RGCs. By performing the co-immunoprecipitation assay, we found several differences in the efficiencies of interaction between AMPA subunits and scaffold proteins between normal and LHON-specific RGCs.

What are the characteristics and progression of visual field defects in patients with Leber hereditary optic neuropathy: a prospective single-centre study in China

OBJECTIVE

To study the characteristics and progression of visual field defects in patients with Leber hereditary optic neuropathy.

DESIGN

Prospective study.

SETTING

3-A-class hospital in China; single-centre study.

PARTICIPANTS

From 100 patients diagnosed with Leber hereditary optic neuropathy, 80 (160 eyes; 68 men and 12 women; youngest patient, 6 years; oldest patient, 35 years) were recruited.

EXPOSURE

All patients were followed up for at least 12 months. Each patient underwent at least three visual field examinations. Patient groups 1-6 were created according to the time of visual field data acquisition. Patient group 7 included patients with a different onset of disease between eyes. Group 8 was composed of patients with a course of disease of 12-24 months when one of the examinations performed. Patients who performed the third examination made up patient group 9.

PRIMARY OUTCOME MEASURES

Prevalence of the different visual field defect types on the basis of severity in groups 1-6. Mean of the difference of visual function between eyes in group 7.

RESULT

In groups 1-6, the prevalences of defects classified using Visual Field Index values were significantly different between groups 1 and 3. In group 7, with the prolongation of the course of the disease, the mean of the difference of visual function between eyes decreased. There was no significant correlation between age and the severity of visual field defect. There was significant correlation between visual acuity and the severity of visual field defect.

CONCLUSION

Visual field defects in patients with Leber hereditary optic neuropathy (G11778A) may continuously progress within 6 months of disease development, and remain stable after 9 months. With the progression of the disease, the differences in visual function between eyes may decrease. The severity of visual field defect seems to be independent of age; however, could be related to visual acuity.

TRIAL REGISTRATION NUMBER

NCT03428178, NCT01267422.

Leber's Hereditary Optic Neuropathy - Case Discussion

Purpose. To report a case of a young patient with a clinical condition suggestive of Leber's hereditary optic neuropathy (LHON) confirmed by genetic testing. Material and methods. We present a case of a 21-year-old Caucasian male with bilateral visual loss. The patient complained of visual loss, initially in the right eye and two weeks thereafter in the left eye. Ophthalmological examination revealed visual acuity of 20/ 400 in both eyes, anterior segment of normal appearance, normal direct and consensual pupillary light reflexes, and absence of a relative afferent pupillary defect. Fundus examination demonstrated bilateral protruding, hyperemic, with blurred margins in the nasal quadrant papilla and reduced excavation, tortuous vessels, peripapillary telangiectasias. The optical coherence tomography (OCT) revealed bilateral increase of the retinal nerve fiber layer (RNFL) thickness and ganglion cell layer - inner plexiform layer complex (GCL-IPL complex) severely thinned. Results. The clinical suspicion of Leber's hereditary optic neuropathy was confirmed by the 3460 mutation, which was identified on blood mitochondrial analysis. Meantime, the visual acuity decreased to CF in both eyes. We initiated treatment with idebenone (300 mg T.I.D.). After three months of follow-up, visual acuity was CF in both eyes, bilateral pupillary light reflexes within normal limits and optic disc pallor was noticed in both eyes. Conclusion. No visual recovery was noticed after one year. We recommended that the idebenone treatment was continued and the patient was followed-up further.

Current and Emerging Treatment Modalities for Leber's Hereditary Optic Neuropathy: A Review of the Literature

Introduction

The purpose of this review is to present the current and emerging treatment alternatives for Leber’s hereditary optic neuropathy (LHON), emphasizing the most recent use of idebenone and stem cells or gene therapy.

Methods

A comprehensive literature review was performed at the PubMed database regarding the various treatment modalities for LHON.

Results

Treatment modalities for LHON include nutritional supplements, activators of mitochondrial biogenesis, brimonidine, and symptomatic and supportive treatment, but nowadays attention is being paid to idebenone and gene therapy or stem cells.

Conclusion

The treatment of LHON remains challenging, given the nature of the disease and its prognosis.

Bilateral vision loss due to Leber's hereditary optic neuropathy after long-term alcohol, nicotine and drug abuse

PURPOSE

Leber's hereditary optic neuropathy is relatively rare, and no clinical pathognomonic signs exist. We present a rare case of bilateral vision loss of a patient with multiple drug abuse in the history.

OBSERVATION

A 31-year-old man presented with a history of progressive, decreased vision in both eyes for 6 month. On examination, his visual acuity was hand motion in both eyes. Funduscopy demonstrated a temporal pallor of the optic disc. Goldmann visual field perimetry showed a crescent visual field in the right eye and a circular decrease to less than 50 ° in the left eye. Electroretinogram showed a scotopic b-wave amplitude reduction. Optical coherence tomographies, Heidelberg Retina tomography, visual evoked potentials, and magnetic resonance imaging with contrast as well as blood tests were normal. The patient reported to consume various kinds of drugs as well as recreational drug use and alcohol consumption since he was 16 years old. We started a hemodilution therapy, believing the patient suffered from a bilateral, toxic optic neuropathy due to his lifestyle. Laboratory results later on showed Leber's hereditary optic neuropathy.

CONCLUSION AND IMPORTANCE

Leber's hereditary optic neuropathy is a rare disease without a typical, pathognomonic presentation. Even though the patient gave good reasons for a toxic optic neuropathy, one should never stop to test for other diseases.