Are visually evoked potentials (VEP) useful for determination of visual acuity?: A clinical trial

Objective demonstration of eyelid spasm relief with smartphone and custom software in hemifacial spasm patients

PURPOSE

To objectively demonstrate eyelid spasms relief in hemifacial spasm (HFS) patients using a smartphone and a custom-made software.

METHODS

Nineteen patients with HFS had standardized videos recorded with a smartphone (iPhone 6S, Apple) camera before and 15 days after receiving onabotulinumtoxinA injections. Nineteen age-matched control subjects were also assessed. The Eye Aspect Ratio (EAR) is an algorithm previously described to determine whether the eye is opened or closed. When the eye is closed, EAR tends to be closer to zero. Analogously, if the eye is wide open, values are greater. A custom-made software using the EAR concept was developed and pre- and post-treatment EARs were analyzed to assess HFS patients.

RESULTS

Botulinum toxin (BoNT) injections led to a significant increase in the average EAR of the affected side: + 10.4% (p = 0.0175) of HFS patients, compared to baseline. Mean EAR before BoNT applications were significantly lower (16.2%) on the affected side (0.25 ± 0.05) of HFS patients when compared to controls (0.30 ± 0.05, p = 0.004). After BoNT injections, no statistically significant difference was observed for the average EAR between the affected side of HFS patients (0.27 ± 0.04) and controls (p = 0.20).

CONCLUSIONS

Use of a smartphone and custom-made software objectively demonstrated eyelid spasm relief in patients with HFS. Additional refinement of this system could permit more accurate assessments of treatment response rates for each patient, making it possible to be used in clinical practice.

Assessment of Human Visual Acuity Using Visual Evoked Potential: A Review

Visual evoked potential (VEP) has been used as an alternative method to assess visual acuity objectively, especially in non-verbal infants and adults with low intellectual abilities or malingering. By sweeping the spatial frequency of visual stimuli and recording the corresponding VEP, VEP acuity can be defined by analyzing electroencephalography (EEG) signals. This paper presents a review on the VEP-based visual acuity assessment technique, including a brief overview of the technique, the effects of the parameters of visual stimuli, and signal acquisition and analysis of the VEP acuity test, and a summary of the current clinical applications of the technique. Finally, we discuss the current problems in this research domain and potential future work, which may enable this technique to be used more widely and quickly, deepening the VEP and even electrophysiology research on the detection and diagnosis of visual function.

VEP estimation of visual acuity: a systematic review

Purpose

Visual evoked potentials (VEPs) can be used to measure visual resolution via a spatial frequency (SF) limit as an objective estimate of visual acuity. The aim of this systematic review is to collate descriptions of the VEP SF limit in humans, healthy and disordered, and to assess how accurately and precisely VEP SF limits reflect visual acuity.

Methods

The protocol methodology followed the PRISMA statement. Multiple databases were searched using “VEP” and “acuity” and associated terms, plus hand search: titles, abstracts or full text were reviewed for eligibility. Data extracted included VEP SF limits, stimulus protocols, VEP recording and analysis techniques and correspondence with behavioural acuity for normally sighted healthy adults, typically developing infants and children, healthy adults with artificially degraded vision and patients with ophthalmic or neurological conditions.

Results

A total of 155 studies are included. Commonly used stimulus, recording and analysis techniques are summarised. Average healthy adult VEP SF limits vary from 15 to 40 cpd, depend on stimulus, recording and analysis techniques and are often, but not always, poorer than behavioural acuity measured either psychophysically with an identical stimulus or with a clinical acuity test. The difference between VEP SF limit and behavioural acuity is variable and strongly dependent on the VEP stimulus and choice of acuity test. VEP SF limits mature rapidly, from 1.5 to 9 cpd by the end of the first month of life to 12–20 cpd by 8–12 months, with slower improvement to 20–40 cpd by 3–5 years. VEP SF limits are much better than behavioural thresholds in the youngest, typically developing infants. This difference lessens with age and reaches equivalence between 1 and 2 years; from around 3–5 years, behavioural acuity is better than the VEP SF limit, as for adults. Healthy, artificially blurred adults had slightly better behavioural acuity than VEP SF limits across a wide range of acuities, while adults with heterogeneous ophthalmic or neurological pathologies causing reduced acuity showed a much wider and less consistent relationship. For refractive error, ocular media opacity or pathology primarily affecting the retina, VEP SF limits and behavioural acuity had a fairly consistent relationship across a wide range of acuity. This relationship was much less consistent or close for primarily macular, optic nerve or neurological conditions such as amblyopia. VEP SF limits were almost always normal in patients with non-organic visual acuity loss.

Conclusions

The VEP SF limit has great utility as an objective acuity estimator, especially in pre-verbal children or patients of any age with motor or learning impairments which prevent reliable measurement of behavioural acuity. Its diagnostic power depends heavily on adequate, age-stratified, reference data, age-stratified empirical calibration with behavioural acuity, and interpretation in the light of other electrophysiological and clinical findings. Future developments could encompass faster, more objective and robust techniques such as real-time, adaptive control.

Registration

International prospective register of systematic reviews PROSPERO (https://www.crd.york.ac.uk/PROSPERO/), registration number CRD42018085666.

Preverbal assessment for amblyopia

PURPOSE

To describe and compare the different methods of preverbal assessment of amblyopia.

RESULTS

Each method of visual assessment has its plusses and minuses.

CONCLUSION

There is no "best" method for assessment for amblyopia. The best method may be a combination of the various described tests.

Does the 'P300' speller depend on eye gaze?

Many people affected by debilitating neuromuscular disorders such as amyotrophic lateral sclerosis, brainstem stroke or spinal cord injury are impaired in their ability to, or are even unable to, communicate. A brain-computer interface (BCI) uses brain signals, rather than muscles, to re-establish communication with the outside world. One particular BCI approach is the so-called 'P300 matrix speller' that was first described by Farwell and Donchin (1988 Electroencephalogr. Clin. Neurophysiol. 70 510-23). It has been widely assumed that this method does not depend on the ability to focus on the desired character, because it was thought that it relies primarily on the P300-evoked potential and minimally, if at all, on other EEG features such as the visual-evoked potential (VEP). This issue is highly relevant for the clinical application of this BCI method, because eye movements may be impaired or lost in the relevant user population. This study investigated the extent to which the performance in a 'P300' speller BCI depends on eye gaze. We evaluated the performance of 17 healthy subjects using a 'P300' matrix speller under two conditions. Under one condition ('letter'), the subjects focused their eye gaze on the intended letter, while under the second condition ('center'), the subjects focused their eye gaze on a fixation cross that was located in the center of the matrix. The results show that the performance of the 'P300' matrix speller in normal subjects depends in considerable measure on gaze direction. They thereby disprove a widespread assumption in BCI research, and suggest that this BCI might function more effectively for people who retain some eye-movement control. The applicability of these findings to people with severe neuromuscular disabilities (particularly in eye-movements) remains to be determined.

Asynchronous blepharospasm, facial and cervical dystonia, and bilateral asynchronous hemifacial spasm

We present a patient with a facial movement disorder that has characteristics of both blepharospasm and bilateral asynchronous hemifacial spasm. Because of the increased incidence of blepharospasm in patients with hemifacial spasm, our patient's clinical presentation is probably not a chance occurrence, but rather a manifestation of some predisposition for these two movement disorders. This unusual constellation of signs and symptoms challenges the current diagnostic criteria and suggests that some of these facial movement disorders may lie on a spectrum, rather than represent distinct entities.

Pattern visual evoked potentials in malingering

OBJECTIVES

We previously developed a new method for estimating objective visual acuity by means of pattern visual evoked potentials (PVEP). In this study, this method was applied to the diagnosis of malingering.

MATERIALS AND METHODS

Six patients ranging in age from 40 to 54 years (mean 47 years) with suspected malingering were evaluated by means of the visual evoked potential test, optokinetic nystagmus (OKN) inhibition test, and the visual field test. In the PVEP study, the stimulus consisted of black and white checkerboards (39', 26', 15', and 9') with a visual angle of 8 degrees, contrast level of 15%, and a frequency of 0.7 Hz. One hundred PVEP responses were averaged per session.

RESULTS

Routine ophthalmic examinations were normal in all patients. Five patients had a tubularly constricted visual field, and the remaining patient had a normal visual field. The objective visual acuities of the six patients estimated from PVEP were better than their subjective visual acuities estimated with Landolt rings.

CONCLUSIONS

Among a variety of psychophysical and electrophysiologic ancillary tests, we consider our PVEP method a useful method for objectively determining visual acuity in a patient with signs of ocular malingering.

Bilateral hemifacial spasm: a report of five cases and a literature review

We describe five patients with bilateral hemifacial spasm evaluated in a Movement Disorders Clinic to illustrate the clinical characteristics and to draw attention to the differential diagnosis of this condition. All patients had unilateral onset followed by bilateral, asymmetric, and asynchronous facial contractions. The mean age of the patients (4 women and 1 man) was 70.6 years (range, 54-81 yrs), and the mean duration of symptoms was 17 years (range, 2-30 yrs). The facial twitching started in the left eyelid in all cases and the opposite side of the face began to twitch on the average 8.4 years (range, 0.2-15 yrs) later. Imaging studies revealed tortuous vertebrobasilar arteries in three patients. Four patients were successfully treated with botulinum toxin injections. Bilateral hemifacial spasm is a rare, peripherally induced disorder that must be differentiated from tics, dystonia including blepharospasm and other cranial dystonia, and other facial dyskinesias. Botulinum toxin injection appears to be the treatment of choice.

Hemifacial spasm: clinical findings and treatment

Hemifacial spasm (HFS) is a peripherally induced movement disorder characterized by involuntary, unilateral, intermittent, irregular, tonic or clonic contractions of muscles innervated by the ipsilateral facial nerve. We reviewed the clinical features and response to different treatments in 158 patients (61% women) with HFS evaluated at our Movement Disorders Clinic. The mean age at onset was 48.5+/-14.1 years (range: 15-87) and the mean duration of symptoms was 11.4+/-8.5 (range: 0.5-53) years. The left side was affected in 56% instances; 5 patients had bilateral HFS. The lower lid was the most common site of the initial involvement followed by cheek and perioral region. Involuntary eye closure which interfered with vision and social embarrassment were the most common complaints. HFS was associated with trigeminal neuralgia in 5.1% of the cases and 5.7% had prior history of Bell's palsy. Although vascular abnormalities, facial nerve injury, and intracranial tumor were responsible for symptoms in some patients, most patients had no apparent etiology. Botulinum toxin type A (BTX-A) injections, used in 110 patients, provided marked to moderate improvement in 95% of patients. Seven of the 25 (28%) patients who had microvascular decompression reported permanent complications and the HFS recurred in 5 (20%). Although occasionally troublesome, HFS is generally a benign disorder that can be treated effectively with either BTX-A or microvascular decompression.

[Familial hemifacial spasm: report of 2 cases]

The authors report the clinical and angiographical findings of two cases of familial hemifacial spasm. This is the fifth description in the literature and presents mother and daughter at the ages of 76 and 51 respectively, in whom the left side was affected. They underwent exams of angioresonance that showed dolichobasilar with left side origin in both patients. The exams also demonstrated postero-inferior cerebellar artery very developed and irregularities in the walls of the vertebral and basilar arteries suggestive of arteriosclerosis in the mother and slightly elongated intracranial vessels in the daughter. Literature review and etiology data of the hemifacial spasm are focused.

Magnetic resonance tomographic angiography in the investigation of hemifacial spasm

Magnetic resonance angiography (MRA), combined with submillimeter magnetic resonance tomographic angiographic sections (MRTA) showed vascular compression of the 7th cranial nerve or its root exit zone (REZ) in the brain stem in 24 of 37 patients (64.86%) with hemifacial spasm. MRA alone was positive for REZ compression in only 19 (51.4%) cases, while conventional MRI was even less revealing, only 10 (27%) cases being positive.