Portable Diagnostic System for Age-Related Macular Degeneration Screening Using Visual Evoked Potentials

Psychophysical, electrofunctional, and morphological evaluation in naïve neovascular AMD patients treated with intravitreal anti-VEGF

Objectives

The aim of this study was to investigate the retinal morpho-functional characteristics of patients with neovascular wet age-related macular degeneration (nAMD) treated with intravitreal injection (IV) of aflibercept (AFL).

Methods

The study was conducted on 35 patients previously diagnosed with type 1 nAMD who received a fixed-dosing regimen of aflibercept injections over 12 months. The goal was to assess trends in visual abilities over time by measuring visual acuity (VA), contrast sensitivity (CS), visual evoked potentials (VEPs), and spectral domain-optical coherence tomography (SD-OCT). The same psychophysical, electro-functional, and morphological tests administered at baseline (T0) were repeated 4 to 8 weeks after the last aflibercept injection (Tn), resulting in a total of six examinations.

Results

At Tn, all subjects exhibited improved VA for both far and near distances compared to values detected at T0. Similarly, VEP amplitude and latency values at Tn showed a greater P100 improvement than those observed at T0. Additionally, the CS examination at Tn demonstrated improvement, particularly at high spatial stimulation frequencies. The Tn SD-OCT results highlighted a reduction in macular thickness compared to T0 values.

Conclusions

This exploratory research indicates that intravitreal injections of AFL, following a fixed-dosing regimen, represent a valuable therapeutic approach for enhancing visual performance. This conclusion is supported by comprehensive statistical analysis of psychophysical, electro-functional, and morphological examinations within the same group of patients with nAMD, as demonstrated for the first time.

Portable Multi-focal Visual Evoked Potential Diagnostics for Multiple Sclerosis/Optic Neuritis patients

Purpose

Multiple Sclerosis (MS) is a neuro-inflammatory disease of the Central Nervous System (CNS) in which the body's immune system attacks and destroys myelin sheath that protects nerve fibers and causes disruption in axonal signal transmission. Demyelinating Optic Neuritis (ON) is often a manifestation of MS and involves inflammation of the optic nerve. ON can cause vision loss, pain and discomfort in the eyes, and difficulties in color perception.In this study, we developed NeuroVEP, a portable, wireless diagnostic system that delivers visual stimuli through a smartphone in a headset and measures evoked potentials at the visual cortex from near the O1, Oz, O2, O9 and O10 locations on the scalp (extended 10-20 system) using custom electroencephalography (EEG) electrodes.

Methods

Each test session is constituted by a short 2.5-minute full-field visual evoked potentials (ffVEP) test, followed by a 12.5-minute multifocal VEP (mfVEP) test. The ffVEP test evaluates the integrity of the visual pathway by analyzing the P1 (also known as P100) component of responses from each eye, while the mfVEP test evaluates 36 individual regions of the visual field for abnormalities. Extensive signal processing, feature extraction methods, and machine learning algorithms were explored for analyzing the mfVEP responses. The results of the ffVEP test for patients were evaluated against normative data collected from a group of subjects with normal vision. Custom visual stimuli with simulated defects were used to validate the mfVEP results which yielded 91% accuracy of classification.

Results

20 subjects, 10 controls and 10 with MS and/or ON were tested with the NeuroVEP device and a standard-of-care (SOC) VEP testing device which delivers only ffVEP stimuli. In 91% of the cases, the ffVEP results agreed between NeuroVEP and SOC device. Where available, the NeuroVEP mfVEP results were in good agreement with Humphrey Automated Perimetry visual field analysis. The lesion locations deduced from the mfVEP data were consistent with Magnetic Resonance Imaging (MRI) and Optical Coherence Tomography (OCT) findings.

Conclusion

This pilot study indicates that NeuroVEP has the potential to be a reliable, portable, and objective diagnostic device for electrophysiology and visual field analysis for neuro-visual disorders.

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.

Human retinal dark adaptation tracked in vivo with the electroretinogram: insights into processes underlying recovery of cone- and rod-mediated vision

The substantial time taken for regaining visual sensitivity (dark adaptation) following bleaching exposures has been investigated for over a century. Psychophysical studies yielded the classic biphasic curve representing recovery of cone-driven and rod-driven vision. The electroretinogram (ERG) permits direct assessment of recovery at the level of the retina (photoreceptors, bipolar cells), with the first report over 70 years ago. Over the last two decades, ERG studies of dark adaptation have generated insights into underlying physiological processes. After large bleaches, rod photoreceptor circulating current, estimated from the rod-isolated bright-flash ERG a-wave, takes 30 min to recover, indicating that products of bleaching, thought to be free opsin (unbound to 11-cis-retinal), continue to activate phototransduction, shutting off rod circulating current. In contrast, cone current, assessed with cone-driven bright-flash ERG a-waves, recovers within 100 ms following similar exposures, suggesting that free opsin is less able to shut off cone current. The cone-driven dim-flash a-wave can be used to track recovery of cone photopigment, showing regeneration is 'rate-limited' rather than first order. Recoveries of the dim-flash ERG b-wave are consistent also with rate-limited rod photopigment regeneration (where free opsin, desensitising the visual system as an 'equivalent background', is removed by rate-limited delivery of 11-cis-retinal). These findings agree with psychophysical and retinal densitometry studies, although there are unexplained points of divergence. Post-bleach ERG recovery has been explored in age-related macular degeneration and in trials of visual cycle inhibitors for retinal diseases. ERG tracking of dark adaptation may prove useful in future clinical contexts.