Effect of smoking on visual evoked potential (VEP) and visual reaction time (VRT)

Background: Nicotine in tobacco smoke causes demyelination. Again, hypoxia in long-term smokers is linked to neuropathy. Visual receptors are early sufferer of neuropathy. Visual-Acuity & other ocular tests often fail to detect subtle changes of neuropathy which, however, can be detected by VEP test. Literature review shows that changes in VEP come earlier than PFT changes in smokers. Ironically, smokers claim that smoking improves their reaction time, which can be assessed by VRT. Aims and Objective: To relate smoking status with VEP and VRT. Materials and Methods: Fifty-six subjects (smoker group = 28 & non-smoker group = 28), whose age & sex were matched, were included in the study. Their PFT, pattern VEP of both eyes & VRT were recorded. The data were compared between the two groups using unpaired t-test, considering statistical significance at p<0.05. Results: The FVC (4.35±0.83 vs. 5.32+1.18 l, p=0.022), FEF 25% (7.40+2.38 vs. 8.74+3.90 l/s, p=0.019) & FEF 50% (6.11+1.52 vs. 7.74+2.57, p= 0.010) were significantly lower in smokers compared to nonsmokers. There was no significant difference in P100 wave latency of VEP. But, VRT of smokers were significantly shorter (431.69+60.29 vs. 441.14+123.54 ms, p=0.010). Conclusion: Smokers have shorter visual reaction time and similar visual evoked potential as compared to non-smokers.

Visual Evoked Potentials and Electroretinograms

Electrophysiological testing of vision permits the objective assessment of the function of the retina, visual pathways, and cortices. This chapter covers visual evoked potentials (VEPs) and electroretinography (ERG). Flash ERG is useful in evaluating the outer retinal function and specifically helping in the diagnosis of retinal degeneration, monitoring the progress of retinal diseases, monitoring the retinal toxicity of drugs, and understanding the pathophysiology of retinal disorders. VEPs to various stimuli are useful in evaluating macular disorders, diagnosing optic neuropathies, detecting silent pathologies in the absence of other clinical signs of visual impairment, and evaluating disturbances of visual processing in degenerative diseases of the central nervous system. Simultaneous recording of pattern ERG and pattern VEP permits the differentiation between maculopathies and optic neuropathy.

Assessing Hemianopia Objectively in Stroke Patients Using the VEP Technique: A Pilot Study

The purpose of this pilot study was to assess hemianopic visual field defects objectively in individuals with stroke using the pattern, visual-evoked potential (VEP) technique. Subjects were comprised of 5 adults with documented hemianopic visual field defects. The central field and the intact hemi-field VEP amplitudes were significantly larger than found in the hemianopic field (p < 0.05). However, latency values were similar (p > 0.05). The objective pattern VEP has the potential to be used rapidly and reliably to detect for the presence of hemianopic visual field defects in stroke patients.

Miscoded Visual Processing in Degenerative Retinal Disorder?

Standard electrophysiological procedures for visual testing were applied to record the retinal and cortical electrophysiological responses to contrast stimulation from 35 subjects with unambiguously diagnosed retinitis pigmentosa and severe impairment of visual acuity and field. Stimuli (central 9° of visual field) were sinusoidal bars with spatial frequencies of 0.6–1.2 cycle/degree and 1.3–5.0 cycle/degree for the retinal (pattern-ERG) and cortical (pattern-VEP) responses, respectively; contrast was 80%; reversal at 2.13 Hz. Structured pattern-ERG above noise level was recorded from 29 subjects at 0.6 cycle/degree and from 24 subjects at 1.2 cycle/degree; latencies were increased and amplitude reduced. Pattern-VEP responses above noise level, with increased latencies and reduced amplitude, were observed in 92% of subjects with unilateral and in all subjects with bilateral retinal response. Both responses were phase-locked to stimulus. No correlation with the residual visual acuity or field was detected. The observation is consistent with evidence of the disease sparing the neuroretina and with unconscious visual processing and suggests miscoding of visual information processing.

Statistical Analysis of Spectral Entropy Features for the Detection of Alcoholics Based on Elecroencephalogram (EEG) Signals

EEG happens to be an important tool for brain study providing a non- invasive and cost effective method to detect the effects of alcohol on the human brain. This paper highlights the importance of statistical analysis to determine the usefulness of spectral entropy features for discriminating alcoholics from healthy subjects. The open source EEG database consisting of 10 alcoholic and 10 control subjects recordings under visual stimulus is considered for the study. The EEG signal is preprocessed to remove eye blink artefact using independent component analysis (ICA) and the gamma sub band is extracted by using an elliptic band pass filter to obtain the visually evoked pattern (VEP) signal. The spectral entropy (SEN) coefficients are computed on all the 61 VEP signals of each subject. To obtain a statistical measure of SEN coefficients suitability for classifying the alcoholic EEG, ANOVA tests are performed. Results show that the test exhibits interesting observations in the form of p-value <0.05 (accepted significance level) for most of the channels and p-value >0.05 for the remaining channels. This study may help in identifying those significant channels (p<0.05) which contribute to the classification of both the groups.