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Biomedical subjects

J W Howe

Publications and source records attributed to J W Howe.

At least 19 recordsLinked to original sources
PubMed1992

Electrophysiologically determined contrast sensitivity in patients with ocular hypertension and chronic glaucoma.

Subjectively assessed contrast sensitivity has been found to be abnormal in many patients with glaucoma. We previously reported the use of onset-offset visual evoked potential measurements to determine contrast threshold objectively. We now studied 216 patients (79 with ocular hypertension and 137 with chronic simple glaucoma) with this technique. In comparison with an age-matched control group (68 subjects), mean contrast threshold was found to be significantly different in both patient groups, the degree of significance being greater in the patients with chronic simple glaucoma. Additionally, the slope of the CI-CII amplitude versus log contrast plot was shown to be depressed in the majority of affected eyes in patients with unilateral chronic simple glaucoma. This measure appears to give an indication of suprathreshold contrast processing and is related to the difference in luminance between pattern elements, rather than the quality of the border or "edge" between them. The data support not only an increase in contrast threshold (reduced sensitivity) in early glaucoma and some patients with ocular hypertension but also a suppression in suprathreshold function that is not readily measurable with standard psychophysical methods. The findings are consistent with recent theories concerning the effect of early chronic simple glaucoma on the function of Y-type units of the M (magnocellular)-type pathways.

Aged↗
PubMed1991

Prognostic significance of the pattern visual evoked potential in ocular hypertension.

This paper reports a prospective study on 49 ocular hypertensive patients to evaluate the prognostic significance of transient abnormalities in the pattern visual evoked potential (VEP) in the development of glaucoma. Seven of 24 patients with VEP abnormalities at diagnosis of ocular hypertension developed glaucomatous field defects in the follow-up period as compared with none of 25 patients with normal VEPs at diagnosis. We conclude that appropriately designed pattern VEP testing is a valuable complement to careful (preferably computerised, static) perimetry. In addition, our findings support the contention that, in glaucomatous disease of the optic nerve, rudimentary pattern processing mechanisms--that is 'Y'-type units of the magnocellular pathways--may be affected earlier than luminance processing mechanisms.

Evoked Potentials, Visual↗
PubMed1989

The visual evoked potential in acute primary angle closure glaucoma.

Visual evoked potentials (VEPs) were elicited from 29 patients who had experienced a previous attack of acute primary angle closure glaucoma. The VEPs were shown to be abnormal in at least one of the measures (latency, amplitude, contrast threshold, or slope) in 72.4% of affected eyes, whereas only 41.4% indicated obvious optic nerve damage. It is notable that 48.1% of fellow eyes with no (known) history of acute pressure rise also showed some form of VEP abnormality. The possible pathophysiological mechanisms operating in both affected and fellow eyes are discussed. It is concluded that, despite the presence of possible artefactual influences, the results probably reflect the presence of primary angle closure glaucoma.

Adult↗
PubMed1988

Pattern visual evoked potentials in hyperthyroidism.

Pattern reversal visual evoked potentials (VEPs) have been elicited in 16 female hyperthyroid patients before and after treatment and compared with those from a similar group of age and sex matched control subjects. No effect on latency was seen, and although larger amplitude values were noted in the thyrotoxic group these too were not significant. We would conclude that hyperthyroidism per se has little effect on the pattern reversal VEP, and any observed effect on these potentials is probably due to other factors.

Adult↗
PubMed1988

Globe luxation in histiocytosis X.

A boy with histiocytosis X, first diagnosed at the age of 9 months, presented at the age of 5 years with left globe luxation. Under general anaesthesia the globe was reduced and a temporary paracentral tarsorrhaphy carried out. He was started on a course of oral steroids. Two years later he had normal visual acuity, full ocular movements, and healthy fundi.

Child, Preschool↗
PubMed1988

A citizens' coalition in mental health advocacy: the Maryland experience.

In July 1983 four statewide Maryland citizens' organizations formed a coalition to advocate for persons with mental illnesses. The groups were the Alliance for the Mentally Ill of Maryland; On Our Own of Maryland, a state-wide consumer group; the Maryland Association of Psychosocial Services, representing consumers and providers of rehabilitative services; and the Mental Health Association of Maryland. The chief focus of their advocacy is on making a place in the community for citizens with long-term mental illness. The coalition's rules are simple: to advocate jointly on issues on which they all agree and to not mention their disagreements in public. With a paid lobbyist, the coalition's advocacy has helped produce significant financial and programmatic gains for Maryland's mentally ill citizens.

Chronic Disease↗
PubMed1987

Visual evoked potentials in the older population: age and gender effects.

Pattern reversal Visual Evoked Potentials (VEPs) were elicited from 68 normal subjects (31 males, 37 females) in the age range 40-80 years. With VEP latency, a significant age effect, increasing values with age, was demonstrated, but none in relation to gender. The converse held true for VEP amplitude however, no age effect being observed, but some gender effect in that lower values were elicited from males as compared to females.

Adult↗
PubMed1986

Visual evoked cortical potential to paracentral retinal stimulation in chronic glaucoma, ocular hypertension, and an age-matched group of normals.

Visual evoked cortical potentials (VECPs) to midperipheral stimulation of the visual field were elicited in age-matched groups of patients with unilateral chronic simple glaucoma or ocular hypertension and normal subjects. With a multimodal stimulus approach comprising transient and steady-state pattern reversal and transient onset-offset VECPs, 82.1% of the glaucoma group and 50.9% of the ocular hypertensives revealed significant abnormalities (p less than 0.01) in one or more of the electrophysiological features measured, i.e., latency, phase, amplitude, and contrast threshold.

Adult↗
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.

Aged↗
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↗
PubMed1985

Inter- and intra-examiner reliability of the upper cervical X-ray marking system.

This paper investigates the reliability of the upper cervical X-ray marking procedure. The measurement chosen to be examined was atlas laterality. Twenty X-rays were marked by three experienced upper cervical practitioners for the inter-examiner reliability testing, and two of the doctors marked 10 of the films twice for intra-examiner testing. The average measurement for the 60 markings was 1.83 degrees. The average difference between the 3 doctors was 1.05 degrees. The range of error is 57 percent of the average measurement. With interval agreements, it is shown that at the point where all 3 doctors agree 80 percent of the time, the range of error is 2 degrees, this being over 100 percent of the average measurement. The range of error percentages for the 2 intra-examiner tests were 41 percent and 71 percent. It is concluded that with ranges of error of this magnitude any measured differences produced using this system will be just as likely to be from marking error as from actual atlas position change. This should be considered by practitioners who consider these measurements to be objective evidence for demonstrating the results of chiropractic adjustments.

Cervical Atlas↗