Visual evoked response

Delays in reflex development have been reported in rats during early postnatal life at PbB levels 59 pg/dL (Kishi et al. 1983), and alterations in visual evoked responses and decreased visual acuity in young rats occurred at mean PbB levels of 65 pg/dL (Cooper et al. 1980 Fox et al. 1977, 1982 ... 

Cooper GP, Fox DA, Howell WE, et al. 1980. Visual evoked responses in rats exposed to heavy metals. In MeriganWH, Weiss B, eds. Neurotoxicity of the visual system. New York, NY Raven Press, 203-218. 

Fox DA, Lewkowski JP, Copper GP. 1977. Acute and chronic effects of neonatal lead exposure on development of the visual evoked response in rats. Toxicol Appl Pharmacol 49 449-461. 

M. Firbank, E. Okada, and D. T. Delpy. A theoretical study of the signal contribution of regions of the adult head to near-infrared spectroscopy studies of visual evoked responses. Neuroimage, 8 69-78, 1998. 

At 0.35 ppm, all three subjects exposed for 2 h developed mild headaches, and one of three subjects exposed for 8 h developed a mild headache. Two of three subjects exposed for 8 h developed severe headaches. One subject also developed slight eye irritation, which persisted throughout the 2 h exposure. Four of the nine subjects detected the odor of the compound, which they described as mild at this concentration however, the odor was not detectable after 5 min of exposure. The morphology of the visual evoked response, while variable, was altered, particularly in three subjects exposed for 8 h. The exposure produced an increase in the peak-to-peak amplitude of the 3-4—5 wave complex. The authors interpreted the VER changes as consistent with the VER changes produced by central nervous system depression. 

Uncertainty factors Interspecies 3—The monkey was more susceptible than the rat the lowest concentration in a range was chosen (70 ppm) humans and monkeys showed changes in the visual evoked response at similar concentrations the monkey is a good model for the human. The concentration inducing central nervous system depression does not vary greatly among mammalian species. Intraspecies 3—Individual variation in susceptibility to central nervous system depressants such as anesthetics varies no more than 2-fold. 

Change in visual evoked response 0.35 ppm for 8 h Threshold for impairment of balance 0.5 ppm for 6 h Threshold for abnormal cognitive test 1.5 ppm for 3.2 h End point/Concentration/Rationale A 6-h exposure at 0.5 ppm which resulted in severe headache and was the threshold for loss of equilibrium falls within the AEGL-2 definition of threshold for impaired ability to escape. 

HPPD has been studied with quantitative EEC. Compared to controls, people with HPPD show a faster alpha frequency and shorter visual-evoked-response latency, consistent with LSD-induced cortical disinhibition (Abraham and Duffy 1996). Conversely, the auditory-evoked-response latency is increased. Analyses indicate that these differences are predominant in temporal and left parietal regions. 

Exposure of nonsmokers to 50 ppm for 6-8 hours results in carboxyhemoglobin levels of 8-10%. Several investigators have suggested that the results of behavioral tests such as time discrimination, visual vigilance, choice response tests, visual evoked responses, and visual discrimination threshold may be altered at levels of carboxyhemoglobin below 5%. ... 

Carbon monoxide toxicity has been studied well in humans. If sufficiently prolonged, exposure at concentrations of 200-1,200 ppm can result in a progression of such hypoxic symptoms as headache, decreased night vision, abnormal visual evoked response, nausea, abnormal fine manual dexterity, vomiting,... 

In two experimental models of ischaemia, it has been shown that HU-211 significantly increases cell survival. It was seen that after forebrain ischaemia produced by 20 min of carotid occlusion, the number of viable neurons in the hippocampal CA1 region of HU-211-treated rats was significantly higher than in controls. The same effect was seen in gerbils after 10 min of bilateral carotid occlusion on treatment with HU-211 [197, 198]. A related effect has been noted after rat optic nerve crush injury. Administration of HU-211 improved recovery of the nerve, with the visual evoked response amplitude increasing significantly [199],... 

Hosko, M.J. (1970). The effect of carbon monoxide on the visual evoked response in man. Arch. Environ. Health 21 174-80. 

Visual-evoked potential tests, such as flash electrore-tinography, flash and pattern visual-evoked responses, flicker fusion thresholds, and visual field perimetry, are reported to be the most rehable methods for early detection of ocular abnormahties (8,11,14). The routine use of visual-evoked potentials in the systematic followup of ethambutol-treated patients has been recommended (15). 

Visual evoked responses 20 hours after myelography can be delayed, with a correlation with the severity of headache after myelography the delay in visual-evoked response is less marked with iopamidol than with metrizamide. It has been suggested that this technique may be useful in the assessment of myelographic contrast media toxicity (79). 

Broadbridge AT, Bayliss SG, Firth R, Farrell G. Visual evoked response changes following intrathecal injection of water-soluble contrast media a possible method of assessing neurotoxicity and a comparison of metrizamide and iopamidol. Clin Radiol 1984 35(5) 371-3. 

Patient 20 has been shown to be mosaic for a PEX6 defect (Moser, 1999). Cultured skin fibroblasts and liver biopsy samples have demonstrated a mixture of normal and abnormal cells (Pineda, et al., 1999). The patient is now 16 yr old. Developmental milestones were delayed at 2 yr. Liver biopsy showed micronodular cirrhosis. Neurologic exam at 3.5 yr showed nystagmus, head tremor, and generalized spasticity, and he was unable to walk. At 4 yr of age, he was started on a diet containing medium-chain triglycerides, pure olive oil (20% of daily fat intake), and vitamin A supplementation. This coincided with clinical improvement as evidence by the disappearance of abnormal eye movements and head tremor and reduction of spasticity. This improvement was attributed to a reduction in phytanic acid levels. Visual evoked responses improved between 4 and 6 yr of age. DHA therapy was added to the regimen at age 6.7 yr. Further improvement of the visual evoked responses occurred. At 12 yr, motor and mental improvements have been maintained. He is able to stand with support. His IQ is 60 and he attends a special school. 

Ron E, Modan B, Floro S, et al Mental function following scalp irradiation during childhood. Am J Epidemiol 116 149-160, 1982 Shore RE, Albert RE, Pasternack BS Follow-up study of patients treated by x-ray epilation for tinea capitis. Arch Environ Health 31 17-24, 1976 Yaar I, Ron E, Modan M, et al Long-term cerebral effects of small doses of x-irradiation in childhood as manifested in adult visual evoked responses. Ann Neurol 8 261-268, 1980... 

Hake and Stewart (1977) describe a study in which four male volunteers were exposed to concentrations of 0, 20, 100, and 150 ppm tetrachloroethylene for 7.5 hours/day. Exposure at each concentration lasted for 5 days. Subjective evaluation of electroencephalogiaphic scores suggested cortical depression in subjects exposed to 100 ppm. Coordination, as measured by the Flanagan coordination test, was significantly decreased at some time points during exposure to 100 or 150 ppm. No effects on flash visual-evoked responses, equilibrium tests, math skills, time discrimination, and reaction times were noted. 

It is not clear whether the increase in n-6 DPA due to deficiency in DHA is a mechanism for compensation. In term infants, Jensen etal. l) reported that transient visual evoked responses did not differ significantly despite differences in plasma DHA. On the other hand, Moriguchi et al. (18) reported longer escape latency in the Morris water maze in n-3 EFAD rats. 

The most well known of these evoked potentials are the auditory evoked response (AER), the visual evoked response (VER), and the somatosensory evoked response (SSER). The somatosensory system evoked signal can result from multiple types of stimuli to the body—light touch, pain, pressure, temperature, and proprioception (also called joint and muscle position sense). 

FIGURE 17j45 A visual evoked response wavefomi showing the PIM peak. It is delayed 100 ms from the onset of a visual flash stimulus in healthy people. 

Visual evoked response primary PlNl component Increase in latency Fox et aiy 1977... 

Feeley, D. M., Longo, J. F., Cosden, M. A., Zenick, H. and Padich, R. (1979). Detection of the effects of lead exposure by visual evoked response latency. Physiol. Psychol., 7, 143... 

In a prospective evaluation of various visual parameters for early detection of ethambutol toxicity in 52 patients with tuberculosis attending a Directly Observed Treatment Strategy Centre [67 visual acuity, visual fields, visual-evoked responses, stereoacuity, and retinal nerve fiber layer thickness on optical coherence tomography were assessed after 1 and 2 months of treatment, and 1 month after withdrawal. There was no visual functional defect at baseline. On follow-up, visual acuity, color vision. 

Visual evoked responses (VER) were studied in rats that had been exposed to cadmium or lead during gestation and lactation. Lead caused long-lasting changes in the VER, whereas cadmium appeared to have no definite effects in this respect unless the animals also had a low body weight or low hematocrit. ... 

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