Correlations between visual morphological, electrophysiological, and acuity changes in chronic non-arteritic ischemic optic neuropathy

Peripapillary Retinal Nerve Fiber Layer Thickness as a Predictor of Visual Outcomes in Patients with Acute Nonarteritic Anterior Ischemic Optic Neuropathy

Objective

To evaluate the utility of peripapillary retinal nerve fiber layer thickness (pRNFLT) for the prediction of visual outcomes, including visual acuity (VA) and visual field (VF), in subjects with acute nonarteritic anterior ischemic optic neuropathy (NAION).

Materials and Methods

We performed a retrospective study of data relating to 60 eyes of 60 subjects with acute NAION. Of these, reliable VF values were obtained at both the initial and at 6-month follow-up visits for 30 eyes, which were included in the VF analysis. The pRNFLT was measured globally and separately in all four quadrants (superior, inferior, nasal, and temporal) using optical coherence tomography at the initial visit. Multivariate analysis and the area under the curve (AUC) were used to evaluate the utility of pRNFLT for the prediction of visual outcomes, including favorable VA (VA better than or equal to 20/25) and favorable VF (visual field index (VFI) ≥90%), at the 6-month follow-up visit.

Results

The median VA and mean VFI at the initial visit were 0.40 (interquartile range (IQR): 0.40, 0.54; logarithm of the minimum angle of resolution (logMAR)) and 73.07% ± 6.73%, respectively. The median VA and mean VFI at the 6-month follow-up visit were 0.30 (IQR: 0.00, 0.70) logMAR and 69.27% ± 28.94%, respectively. Thinner temporal-quadrant pRNFLT was associated with favorable VA (odds ratio 0.98; p = 0.042) with a cut-off value of 128 µm (AUC 0.839, 95% CI: 0.732-0.947, sensitivity 77.27%, specificity 84.21%). Thinner nasal-quadrant pRNFLT was associated with favorable VF (odds ratio 0.97; p = 0.047) with a cut-off value of 105 µm (AUC 0.780, 95% CI: 0.612-0.948, sensitivity 90.00%, specificity 70.00%).

Conclusions

The pRNFLT is clinically useful for the prediction of visual outcomes in patients with acute NAION. A temporal-quadrant pRNFLT ≤128 µm and a nasal-quadrant pRNFLT ≤105 µm predict favorable VA and VF at the 6-month follow-up visit, respectively.

Forensic Study on Objective Evaluation of Visual Acuity of Ametropia with the Event-related Potential P3

OBJECTIVE

In this study, we aimed to assess the characteristics of the P3 component from an event-related potential (ERP) that was induced by visual acuity (VA) processing. Furthermore, we sought to provide electrophysiological evidence for the objective evaluation of VA.

METHODS

We recruited 32 participants with myopia-related ametropia. They reported no other ocular diseases and had an uncorrected VA of 4.0 in both eyes. We used the block letter "E" at different visual angles and orientations as the graphic stimuli. The oddball paradigm, consisting of 4 modules, was used for ERP analysis. The standard stimuli of each module were identical, with a visual angle of 1°15'. The visual angles of the target stimuli were 1°15', 55', 24', and 15'. The VA test was performed on each eye separately for all participants, and all characteristics of the P3 component were analyzed.

RESULTS

There was no significant difference in the P3 peak letencies between the target stimulation angle 1°15' group and the 55' group, or between the target stimulation angle 24' group and the 15' group. There was a significant difference in the P3 peak letencies between the target stimulation angle 1°15' group and the 24' group as well as the 15' group. There was a significant difference in the P3 peak letencies between the target stimulation angle 55' group and the 24' group as well as the 15' group. No significant differences were observed in the P3 amplitude between modules.

CONCLUSION

In the oddball paradigm, P3 elicitation indicated a cognitive response to the target stimuli. These data showed that the characteristics of P3 can be used as an objective evaluation of VA.

Retinal and Visual Pathways Involvement in Carriers of Friedreich's Ataxia

Friedreich’s ataxia (FRDA) is a rare autosomal recessive neurodegenerative disorder due to the homozygous pathological expansion of guanine-adenine-adenine (GAA) triplet repeats in the first intron of the FXN gene, which encodes for the mitochondrial protein frataxin. In the visual system, the typical manifestations are ocular motility abnormality, optic neuropathy, and retinopathy. Despite the evidence of ophthalmological impairment in FRDA patients, there is a lack of information about the morpho-functional condition of the retina and of the optic pathways in healthy heterozygous carriers of Friedreich’s ataxia (C-FRDA). Ten C-FRDA subjects (providing 20 eyes) and thirty-five Controls (providing 70 eyes) underwent a complete neurological and ophthalmological examination comprehensive of functional (full-field Electroretinogram (ffERG), multifocal Electroretinogram (mfERG), Visual Evoked Potential (VEP), and Pattern Reversal Electroretinogram (PERG)) and morphological assessments (Optical Coherence Tomography, OCT) of the retina, macula, retinal ganglion cells, and visual pathways. The groups’ data were compared using a two-sample t-test. Pearson’s test was used to investigate the morpho-functional correlations. Statistically significant differences (p < 0.01) between C-FRDA and Control eyes for the values of the following parameters were found: ffERG b-wave amplitude, mfERG Response Amplitude Densities, PERG P50 implicit time and P50-N95 amplitude, VEP P100 implicit time, Retinal Nerve Fiber Layer (RNFL) Overall, and Nasal thickness. The values of the OCT macular volume were not statistically different (p > 0.01) between the two Groups. Therefore, our data suggest that, in C-FRDA, a dysfunction of retinal elements without morphological macular impairment may occur. In addition, a morphological impairment of RNFL associated with an abnormal neural conduction along the visual pathways can be also detected.

A Hypothalamic Mechanism Regulates the Duration of a Migraine Attack: Insights from Microstructural and Temporal Complexity of Cortical Functional Networks Analysis

The role of the hypothalamus and the limbic system at the onset of a migraine attack has recently received significant interest. We analyzed diffusion tensor imaging (DTI) parameters of the entire hypothalamus and its subregions in 15 patients during a spontaneous migraine attack and in 20 control subjects. We also estimated the non-linear measure resting-state functional MRI BOLD signal's complexity using Higuchi fractal dimension (FD) and correlated DTI/fMRI findings with patients' clinical characteristics. In comparison with healthy controls, patients had significantly altered diffusivity metrics within the hypothalamus, mainly in posterior ROIs, and higher FD values in the salience network (SN). We observed a positive correlation of the hypothalamic axial diffusivity with migraine severity and FD of SN. DTI metrics of bilateral anterior hypothalamus positively correlated with the mean attack duration. Our results show plastic structural changes in the hypothalamus related to the attacks severity and the functional connectivity of the SN involved in the multidimensional neurocognitive processing of pain. Plastic changes to the hypothalamus may play a role in modulating the duration of the attack.

Functional and Morphological Changes in the Visual Pathway in Patients with Graves’ Orbitopathy

Background: The aim of the study was to perform a functional and structural evaluation of the anterior visual pathway in patients with Graves’ Orbitopathy (GO) using electrophysiological tests and OCT, as well as to identify potential parameters that could be useful in detecting early optic nerve damage. Methods: 47 GO patients were enrolled in the study and divided into three groups, depending on their disease severity: Group 1 with mild GO, Group 2 with moderate-to-severe GO, and Group 3 with dysthyroid optic neuropathy (DON). Pattern visual evoked potential (PVEP), flash visual evoked potential (fVEP), pattern electroretinogram (pERG), and optical coherence tomography (OCT) findings were compared between the groups. Results: In the DON Group (Group 3), N75, P100, and P2 latencies were significantly extended, whereas P100, P50, and N95 amplitudes were significantly reduced as compared to the non-DON group (Groups 1 and 2). Group 3 also had significantly thinner peripapillary retinal nerve fiber layer (RNFL) and macular ganglion cell complex (GCC). In Group 2, as compared to Group 1, P100 amplitudes were significantly reduced for all check sizes, while P100 latency was elongated for the check size of 0.9°. Group 2 also had a significantly thinner average GCC and GCC in the superior quadrant. Conclusions: Electrophysiological examinations may be of use in diagnosis of DON. OCT findings and electrophysiological responses vary in patients with different GO severity. Including regular electrophysiological evaluation and OCT in the examination of patients with GO could be of benefit. However, more research is needed to establish the true significance of pVEP, fVEP, pERG, and OCT in monitoring patients with GO.

Macular Morpho-Functional and Visual Pathways Functional Assessment in Patients with Spinocerebellar Type 1 Ataxia with or without Neurological Signs

Spinocerebellar ataxia type 1 (SCA-ATXN1) is an autosomal dominant, neurodegenerative disease, caused by CAG repeat expansion in the ataxin-1 gene (ATXN1). In isolated reports of patients with neurological signs [symptomatic patients (SP)], macular abnormalities have been described. However, no reports exist about macular anomalies in SCA1 subjects carrying the ATXN1 mutation without neurological signs [not symptomatic carriers (NSC)]. Therefore, the main aim of our work was to evaluate whether the macular functional and morphological abnormalities could be detectable in SP, genetically confirmed and with neurological signs, as well as in SCA-ATXN1-NSC, harboring pathogenic CAG expansion in ATXN1. In addition, we investigated whether the macular involvement could be associated or not to an impairment of RGCs and of their fibers and of the neural conduction along the visual pathways. Herein, nine SCA-ATXN1 subjects (6 SP and 3 NSC) underwent the following examinations: visual acuity and chromatic test assessments, fundus oculi (FO) examination, macular and peripapillary retinal nerve fiber layer thickness (RNFL-T) analysis by Spectral domain-Optical Coherence Tomography (Sd-OCT) acquisition, multifocal electroretinogram (mfERG), pattern reversal electroretinogram (PERG) and visual evoked potentials (VEP) recordings. In four eyes of two SP, visual acuity reduction and chromatic abnormalities were observed; in three of them FO changes associated with macular thinning and outer retinal defects were also detected. In three NSC eyes, slight FO abnormalities were associated with qualitative macular morphological changes. By contrast, abnormal mfERG responses (exclusively from foveal and parafoveal areas) were detected in all SP and NSC (18 eyes). No abnormalities of PERG values, RNFL-T, and VEP responses were found, but in one SP, presenting abnormal papillo-macular bundle neural conduction. Results from our SCA-ATXN1 cohort suggest that a macular dysfunction, detectable by mfERG recordings, may occur in the overt disorder, and unexpectedly in the stage of the disease in which there is still an absence of neurological signs. In NSC, an exclusive dysfunction of preganglionic macular elements can be observed, and this is associated with both normal RGCs function and neural conduction along the visual pathways.

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.

Neural Conduction Along Postretinal Visual Pathways in Glaucoma

Purpose: This study was conducted in order to evaluate retinal ganglion cell (RCG) function and the neural conduction along the postretinal large and small axons and its correlation with retinal nerve fiber layer thickness (RNFL-T) in open-angle glaucoma (OAG) eyes. Methods: Thirty-seven OAG patients (mean age: 51.68 ± 9.83 years) with 24-2 Humphrey mean deviation (MD) between -2.5 and -20 dB and IOP <21 mmHg on pharmacological treatment (OAG group) and 20 age-matched controls (control group) were enrolled. In both groups, simultaneous pattern electroretinograms (PERG) and visual evoked potentials (VEP), in response to checks stimulating macular or extramacular areas (the check edge subtended 15' and 60' of visual arc, respectively), and RNFL-T (measured in superior, inferior, nasal, and temporal quadrants) were assessed. Results: In the OAG group, a significant (ANOVA, p < 0.01) reduction of 60' and 15' PERG P50-N95 and VEP N75-P100 amplitudes and of RNFL-T [overall (average of all quadrants) or temporal] with respect to controls was found; the values of 60' and 15' PERG P50 and VEP P100 implicit times and of retinocortical time (RCT; difference between VEP P100 and PERG P50 implicit times) were significantly (p < 0.01) increased with respect to control ones. The observed increased RCTs were significantly linearly correlated (Pearson's test, p < 0.01) with the reduced PERG amplitude and MD values, whereas no significant linear correlation (p < 0.01) with RNFL-T (overall or temporal) values was detected. Conclusions: In OAG, there is an impaired postretinal neural conduction along both large and small axons (increased 60' and 15' RCTs) that is related to RGC dysfunction, but independent from the RNFL morphology. This implies that, in OAG, the impairment of postretinal neural structures can be electrophysiologically identified and may contribute to the visual field defects, as suggested by the linear correlation between the increase of RCT and MD reduction.

Citicoline in Ophthalmological Neurodegenerative Disease: A Comprehensive Review

Cytidine 5'-diphosphocholine has been widely studied in systemic neurodegenerative diseases, like Alzheimer's disease, Parkinson's disease, and brain ischemia. The rationale for the use of citicoline in ophthalmological neurodegenerative diseases, including glaucoma, anterior ischemic optic neuropathy, and diabetic retinopathy, is founded on its multifactorial mechanism of action and the involvement in several metabolic pathways, including phospholipid homeostasis, mitochondrial dynamics, as well as cholinergic and dopaminergic transmission, all being involved in the complexity of the visual transmission. This narrative review is aimed at reporting both pre-clinical data regarding the involvement of citicoline in such metabolic pathways (including new insights about its role in the intracellular proteostasis through an interaction with the proteasome) and its effects on clinical psychophysical, electrophysiological, and morphological outcomes following its use in ophthalmological neurodegenerative diseases (including the results of the most recent prospective randomized clinical trials).