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Biomedical subjects

I J Constable

Publications and source records attributed to I J Constable.

At least 163 records · Page 9Linked to original sources
PubMed1983

The retinal oxygen profile in cats.

This study records for the first time the retinal tissue oxygen partial pressure as a function of location within the retina of the domestic cat. Tissue pO2 was recorded with oxygen sensitive microelectrodes that use the polarographic principle. The mean vitreal pO2 close to the internal limiting membrane was 20.2 +/- 2.3 mmHg. The internal limiting membrane does not act as a diffusion barrier for oxygen. As the electrode was advanced into the inner retina, the tissue pO2 rose gradually to a value of 24.6 +/- 2.3 mmHg and then fell to a minimum of 12.0 +/- 5.5 mmHg before rising again to a value of 29.2 +/- 2.5 mmHg. Further insertion resulted in a sudden steep rise of tissue pO2 values to 72.0 +/- 5.1 mmHg, after which there was no further alteration in measured values. Although the exact location within the retina of the recording electrode was not known, it is probable that the tissue pO2 minimum occurs at about the level of the inner nuclear layer. Therefore, it is probable that the retinal avascular layers receive their oxygen supply primarily from the choroidal circulation in the cat.

Animals↗
PubMed1982

Cholesterol and lipoprotein-cholesterol levels in Western Australian rural diabetics.

Total cholesterol, high-density lipoprotein-cholesterol (HDL-C) and non-HDL-cholesterol (non-HDL-C) were measured in the serum of diabetics from four country regions in Western Australia in order to document the levels and to examine the relationships between treatment mode, degree of diabetic control and lipid concentrations. In most age groups total cholesterol and non-HCL-C did not differ from levels in a large reference population, but HDL-C levels were generally lower. Male NIDDM patients on insulin had greater HDL-C levels than patients on oral hypoglycaemics, but their degree of control as determined by the level of glycosylated haemoglobin was poorer, and amongst female patients on insulin those with higher HDL-C levels had poorer control. These results confirm previous reports of higher HDL-C levels in patients on insulin, but are contrary to reports suggesting that better control is associated with higher HDL-C levels.

Adult↗
PubMed1981

Prevention of corneal burns during high-energy laser iridotomy.

We used a plano hydrophilic bandage contact lens to protect the corneal epithelium and stroma from burns during laser iridotomy. The reduction of energy losses with this method, by the avoidance of corneal epithelial opacities, increases the chance of successful iridotomy when many applications of the laser are needed.

Burns↗
PubMed1981

Glyoxalase phenotypes in patients with diabetes mellitus.

Caucasian diabetic patients in Australian surveys showed a significant difference in the distribution of glyoxalase phenotypes. Insulin dependent diabetic patients with age of onset less than 40 years had a relative excess of glyoxalase homozygote 1-1 and a deficiency of types 2-1 and 2-2. Non-insulin dependent diabetic patients were not significantly different from non-diabetic subjects in the distribution of glyoxalase phenotypes. Insulin dependent diabetic patients without the complications of retinopathy or neuropathy also showed a significant excess of glyoxalase type 1-1 in relation to the control group. Genes controlling glyoxalase polymorphism appear to be associated with the variations of diabetes and its complications.

Australia↗
PubMed1981

Image splitting--a technique for measuring retinal vascular reactivity.

The observation of changes of pial vessel calibre has withstood the test of time in assessing cerebrovascular reactivity. A recent refinement has been the adoption of the image splitting television technique of Baez, which allows accurate and rapid measurements of vessel calibre to be made in situ. This method has been successfully applied to the eye, where the retinal vessels are readily visible through the pupil. Results are presented of preliminary experiments in normal persons, in whom an induced increased in intraocular pressure was associated with retinal vasodilatation.

Arterioles↗
PubMed1981

The Arden grating acuity: effect of age and optical factors in the normal patient, with prediction of the false negative rate in screening for glaucoma.

The Arden contrast sensitivity was investigated in normal persons, cataract eyes, and glaucoma patients with only plates 6 and 7 of the Arden grating set. The mean score of 90 normal eyes on plate 6 was 9.50 +/- 2.29 and on plate 7 it was 9.44 +/- 2.32. The mean scores of patients with early cataract were 14.51 +/- 2.99 on plate 6 and 13.74 +/- 3.26 on plate 7. Several patients with cataract missed the grating on plate 7. Mydriasis and miosis did not affect contrast sensitivity in normal eyes. Mydriasis significantly improved contrast sensitivity in patients with early cataract. In patients with glaucoma enlargement of the pupil from a miotic state to near normal size significantly improved contrast sensitivity. It is predicted that if plate 6 and 7 are used in mass screening for glaucoma in the elderly, there will be a false negative rate of 83% for plate 6 and 52% for plate 7. A false positive rate of 17% is predicted.

Adolescent↗
PubMed1981

Effect of hypoxia on the maintained firing rate of retinal ganglion cells.

The effect of systemic hypoxia on the maintained firing rate (MFR) of single retinal ganglion cells has been measured in the cat at a constant luminance level. Systemic hypoxia was produced by reducing the percentage of oxygen in the respiratory mixture under forced ventilation so that arterial PCO2 and pH were constant. Extracellular recordings were obtained from both X and Y retinal ganglion cells before, during, and after systemic hypoxia, with each cell acting as its own control. The MFR was unaltered by arterial PO2 levels of greater than 45 mm Hg. However, at and below this level of hypoxia the MFR was reversibly increased in 67% of the cells tested. Whether or not this increase occurred was independent of cell type or location. For arterial PO2 values of 24 to 34 mm Hg the initial increase in MFR was followed by a decrease for these cells; for PO2 values of less than 24 mm Hg the MFR showed a large initial increase followed by a complete cessation of firing. The remaining 33% of cells displayed only reduced MFR during hypoxia. The results indicate that ganglion cell function may be drastically affected by hypoxia. This may be relevant to the visual loss of a variety of retinal disorders.

Action Potentials↗
PubMed1981

Regeneration of retinal limiting membranes after chorioretinal biopsy in dogs.

After chorioretinal biopsy in dogs, obtained without vitreous loss, accessory glial cells and fibroblasts filled the defect between cortical vitreous and bare sclera. The proliferating glial cells laid down a new basement membrane which was complete both on the internal and external aspects of the defect. After biopsy complicated by vitreous loss, however, cellular proliferation failed to re-establish complete internal and external limiting membranes, and new formed fibroblastic tissue extended into the vitreous. To our knowledge, this is the first report to describe effective regeneration of the internal limiting membrane of the retina in any species. These findings suggest that when vitreous loss can be avoided, healed chorioretinal biopsies are unlikely to lead to delayed pathological complications.

Animals↗
PubMed1980

Association of retinopathy and glycosylated haemoglobin levels in diabetes mellitus.

One hundred and forty patients with diabetes mellitus were examined in the small mining town of Kalgoorlie, Western Australia. The primary object was to determine the incidence of retinopathy in the diabetic community. One hundred and thirty-eight sets of data were obtained. There were 69 males and 69 females. The diabetes was controlled with orally administered hypoglycaemic agents in 62 patients, in 58 patients with insulin, and in 18 by diet alone. Forty-six of the 138 volunteers (33%), were found to have retinopathy and this included eight of the 14 Aboriginals taking part in the survey. Glycosylated haemoglobin levels ranged from 8.1% to 18.8% (mean 11.7%; SD; 2.28%) of total haemoglobin concentration, and plasma glucose levels from 1.2 mmol/L to 27.3 mmol/L (mean, 9.5 mmol/L, SD, 5.06 mmol/L); there was a positive correlation between levels of glycosylated haemoglobin and plasma glucose (r = 0.63; P less than 0.001). Diabetics with retinopathy had a mean glycosylated haemoglobin level of 12.5% compared with 11.3% in those without this complication. Examination by treatment groups showed that patients with retinopathy whose disease was controlled with insulin had significantly higher levels of glycosylated haemoglobin compared with those without this complication (0.01 greater than P greater than 0.001). Patients whose disease was controlled with orally administered hypoglycaemic agents did not show this difference.

Adolescent↗
PubMed1980

Macular oedema and retinal branch vein occlusion.

The visual prognosis of patients suffering from retinal branch vein occlusion complicated by macular oedema is assessed in relation to the degress of capillary fallout. Extensive retinal capillary fallout associated with macular oedema was found to confer a poor visual prognosis in a series of 89 patients followed for an average time of 14 months. If the degree of capillary fallout associated with marular oedema was minimal, the visual prognosis was considerably improved.

Capillaries↗
PubMed1980

Continual monitoring of fluorescein angiography.

A system has been developed which enables continuous monitoring and recording of circulating fluorescein in the retinal blood vessels. This is achieved with minimal modification of a Zeiss fundus camera. A night vision television camera (lkegami) is used with illumination provided by the standard observation light of the fundus camera. This method offers advantages over standard fluorescein angiography in patient comfort, information obtained and the immediate evaluation of the fluorescein angiograms being available.

Fluorescein Angiography↗