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K W Mitchell

Publications and source records attributed to K W Mitchell.

29 records · Page 2Linked to original sources
PubMed1986

Visual evoked potential latency and contrast sensitivity in patients with posterior chamber intraocular lens implants.

An electrophysiological investigation of visual evoked potential (VEP) latency and contrast sensitivity was performed in a group of 13 patients who had undergone extracapsular cataract surgery with posterior chamber lens implantation. In spite of good postoperative visual acuity, abnormalities were detected in nine of the group (69%). This study suggests that, even with successfully implanted lenses, there may be a reduction in visual function which could be the result of altered transmission through the plastic lenticulus or fibrosis of the posterior lens capsule, and/or subtle changes in retinal architecture, not observed ophthalmoscopically.

Aged↗
PubMed1986

Visual evoked cortical potentials and pattern electroretinograms in Parkinson's disease and control subjects.

Parkinson's disease patients have been shown to have abnormal visually evoked cortical potentials (VEPs) to pattern stimulation. Whereas dopamine is not an important neurotransmitter in the central visual pathways, the retina is rich in dopamine and, together with previous animal and human studies, this suggests that the abnormal VEPs in Parkinson's disease patients may be due to a biochemical and electrophysiological disorder in the retina. This hypothesis has been examined by studying the VEPs and pattern electroretinogram (PERG) of Parkinson's disease patients and matched control subjects. The amplitudes of the cortical and retinal evoked potentials were significantly reduced in Parkinson's disease patients compared with the control subjects and this could not be attributed to any particular feature of the disease or its treatment. There was a significant relationship between the VEP P100 latency and the PERG amplitude. Moreover for those subjects in whom there was an interocular difference in both cortical and retinal evoked potentials, the abnormality was more commonly found in the potentials from the same eye. These findings suggest that the abnormality of the VEP in Parkinson's disease patients is, at least in part, secondary to an abnormality of the retina itself.

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PubMed1986

Visual evoked potential changes in chronic glaucoma and ocular hypertension.

Visual Evoked Potentials have been recorded in a group of normal patients and the results compared with a group of age matched patients with either unilateral chronic glaucoma or ocular hypertension. Pattern reversal transient and steady state responses were analysed and contrast threshold estimated using an onset-offset stimulus. Electrophysiological abnormalities were detected in 82.1 per cent of the glaucoma group and 50.9 per cent of the ocular hypertensives.

Aged↗
PubMed1984

The objective assessment of contrast sensitivity function by electrophysiological means.

In recent years it has been shown that it is of considerable clinical value to determine the visual contrast sensitivity function of the patient. This can reveal the wider effects of pathology on the visual system where visual acuity may or may not be affected. There is a comprehensive literature on subjective approaches of obtaining this function in the clinical environment but very little on alternative objective methods. This paper describes the latter approach, which exploits electrophysiological techniques using the visual evoked cortical potential (VECP) to checkerboard onset-offset stimulation. Its application in a variety of disorders of the visual system is described. The importance of selecting the most appropriate stimulus parameters is discussed, and the relative advantages and disadvantages as compared with psychophysical methods are appraised.

Adult↗
PubMed1979

Prognostic value of the visual evoked response.

29 patients with visual defects have been followed up by serial recording of the visual evoked response (VER). Those patients in whom the VER was initially normal all made a satisfactory visual recovery. In others an initial attenuated response was followed by an improvement in vision and this was accompanied by normalization of the VER. A third group of patients with an initially subnormal VER have remained blind and the VER has shown no improvement.

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PubMedDate not supplied

Electroretinographic findings in macular dystrophy.

The flash and pattern electroretinogram were investigated in a group of families with rare forms of inherited macular dystrophy, which included Sorsby's fundus dystrophy, X-linked retinoschisis and macular dystrophy of uncertain classification and variable expression. Flash electroretinograms, under both photopic and scotopic conditions, were attenuated in both Sorsby's fundus dystrophy and X-linked retinoschisis--with some effect on implicit time being noted in the latter condition--but in the unknown group the effect was less demonstrable, only 50% having attenuated flash electroretinograms. Pattern electroretinograms were reduced in all three conditions and in almost all cases. The study demonstrates that some so-called macular dystrophies also have widespread abnormalities affecting the peripheral retina. These findings may contribute to a better understanding of the underlying pathophysiologic mechanisms in these rare forms of retinal dysfunction.

Adult↗