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Biomedical subjects

D Allan

Publications and source records attributed to D Allan.

At least 73 records · Page 4Linked to original sources
PubMed1988

Reflection of laser light from ophthalmic contact lenses.

Reflections of laser radiation from ophthalmological contact lenses are measured and hazard analysis calculations are presented. Measurements were made on the contact lenses using ophthalmic argon and krypton lasers. Reflection coefficients were around 0.2% for lenses with 'anti-laser' coatings and in the region of 4% for uncoated lenses. It can be shown that the nominal ocular hazard distance for a typical ophthalmic argon laser beam reflected from a contact lens with a flat front surface is approximately 30 cm for a coated lens and 1 m for an uncoated lens. The necessity of protective glasses for attending staff in particular circumstances is reviewed.

Contact Lenses↗
PubMed1987

Studies with an automated kinetic assay for plasma angiotensin-converting enzyme activity and its potentiation by zinc ion.

Measurement of plasma angiotensin-converting enzyme (ACE) is of value in sarcoidosis and, when specific inhibitors are prescribed therapeutically, in hypertension and heart failure. In this study a rapid kinetic assay for estimation of plasma ACE is described and assessed. In particular the effects of zinc ion have been studied. In contrast to previous reports, a marked potentiation of ACE activity by micromolar concentrations of zinc was noted. The relationship between plasma zinc concentration and ACE activity in vivo was also investigated and related to albumin concentration. The findings may have implications for interpretation of plasma ACE activity in patients with low plasma zinc levels.

Animals↗
PubMed1987

Changes in unsaturated fatty acids in serum lipids of hamsters infected with schistosomes (S. mansoni).

Measurements have been made of the fatty-acid composition of lipids in normal hamster sera compared with sera of hamsters infected with Schistosoma mansoni. The results show a consistent decrease of linoleic and eicosapentaenoic acids, and an increase in arachidonic acid in the phosphatidylcholine and lysophosphatidylcholine of the infected animals. Arachidonic acid was also increased in cholesterol ester, and docosahexaenoic acid was raised in free fatty acid and in phosphatidylcholine in sera from infected animals.

Animals↗
PubMed1987

A sphingomyelinase-resistant pool of sphingomyelin in the nuclear membrane of hen erythrocytes.

Experiments in which hen erythrocytes were exposed to the action of exogenous sphingomyelinase (Staphylococcus aureus) or to their endogenous plasma membrane sphingomyelinase showed that about 15% of the total sphingomyelin was resistant to breakdown either in intact or lysed cells. This resistant pool of sphingomyelin seems likely to reside in the nuclear membranes of the cells, so that essentially all the plasma membrane sphingomyelin can be broken down by exogenous sphingomyelinase acting on intact cells, suggesting that plasma membrane sphingomyelin is exclusively localised in the outer lipid leaflet. Paradoxically, introduction of Ca2+ into the intact cells using A23187 causes the breakdown of up to 30% of total cell sphingomyelin inside the cells but without apparently affecting the putative nuclear pool of sphingomyelin and this suggests that Ca2+ may alter the original disposition of sphingomyelin in the membrane so that originally outer leaflet sphingomyelin becomes accessible to the endogenous sphingomyelinase inside the cells. No differences were seen in the fatty acid compositions of sphingomyelin degradable by exogenous sphingomyelinase, sphingomyelin degradable in the presence of A23187/Ca2+ or the enzyme-resistant pool of sphingomyelin.

Animals↗
PubMed1987

The phospholipid and fatty acid composition of Schistosoma mansoni and of its purified tegumental membranes.

The lipid compositions of mature male and female Schistosoma mansoni and cercariae were compared to that of the hepato-pancreas of unparasitised Biomphalaria globrata (the intermediate snail host), and of red blood cells and sera of hamsters (the mammalian host). Membranes were isolated from the tegument of mature schistosomes by spontaneous release into phosphate-buffered saline, with or without vortexing, and by removal from the parasite's surface using poly-lysine beads. The phospholipid composition of the membranes prepared by the three methods showed a typical plasma membrane-like profile, with high sphingomyelin content (approximately 20%) and cholesterol to phospholipid molar ratio (0.7-1.1). The fatty acid compositions of the resolved phospholipid classes were analysed. Although the composition was in general unremarkable, a high content of eicosaenoic acid (20:1), rarely found in mammals, was noted in whole schistosomes, cercariae, the hepato-pancreas of unparasitised Biomphalaria, and the isolated tegumental membranes. Eicosaenoic acid was also found in adults of Schistosoma japonicum. Host serum lipids from normal and parasitised hamsters contained extremely low amounts of eicosaenoic acid, indicating that this fatty acid is probably continually synthesised by the parasite, probably from preformed fatty acid precursors provided by the host.

Animals↗
PubMed1987

Haematoporphyrin photosensitisation treatment of experimental choroidal melanoma.

Greene amelanotic melanoma transplanted to pigmented rabbit choroid provided the experimental model for studying photosensitisation treatment of choroidal melanoma. Administration of haematoporphyrin derivative (HPD) and subsequent photoradiation with green laser light destroyed much of the melanoma with minimal side effects to normal uvea. The results of treatment were documented by fundus photography and fluorescein angiography. By 24 hours, the irradiated melanoma and surrounding retina appeared whitened and necrotic, with complete non-perfusion of the area. Over the course of one week, the clinical appearance did not alter. Histopathology at 24 hours and 8 days confirmed massive central tumour necrosis, but in all cases this was subtotal. Viable cells were evident at the periphery and also along the base of the tumour. Experimental evaluation of treatment parameters is required before this technique can be recommended for human choroidal melanoma.

Animals↗
PubMed1987

Aiming criteria for neodymium-YAG laser trabeculotomy. A clinico-pathological study.

Recently reported clinical and experimental studies have shown that pulsed neodymium-YAG laser trabeculotomy may reduce intraocular pressure but not in all cases. We report a clinico-pathological study designed to delineate the aiming criteria required to produce a fistula between the anterior chamber and the canal of Schlemm. In summary, the aiming beam must be centred on the reflecting surface of the gonioscopic contact lens, and aimed at the posterior trabecular meshwork. This study also indicates that the energy levels required to produce a discrete trabeculotomy in vivo are similar to those determined by in vitro studies.

Glaucoma, Open-Angle↗
PubMed1987

Intensity of the flash associated with laser-induced plasma in the eye.

A bright flash of light is emitted by the plasma formed at the focus of an ophthalmic Nd: YAG laser. The purpose of this investigation is to determine whether the plasma flash constitutes a hazard to the operator. The intensity of the flash at the slit lamp eyepiece was measured and the experimentally derived value was verified by independent calculation. For hazard assessment purposes, the concept of a spectrally weighted maximum permissible exposure (MPE) is described in the paper. Based on the MPE and our measurements and calculations our conclusion is that viewing the flash in a patient's eye through the microscope would not be considered hazardous to the operator. In contrast, during technical procedures, targets in air are used to produce a plasma and in this situation eye protection is recommended when viewing the flash through the microscope.

Cornea↗
PubMed1987

Parameters for neodymium-YAG laser trabeculotomy: an in-vitro study.

A Biophysic Médical Nanolas Q-Switched pulsed neodymium-YAG laser has been used to produce lesions in human trabecular meshwork in vitro. Sectors of corneoscleral tissue containing trabecular meshwork were suspended in a waterbath which had had a Trokel gonioscopic contact lens mounted into one side by means of a watertight seal. The laser was used to produce lesions in the trabecular meshwork on either side of each specimen. The energy levels delivered ranged from 0.5 to 7.0 mJ, and convergence angles of 10 degrees and 18 degrees were employed. The energy levels required to produce discrete lesions into the canal of Schlemm without perforating the underlying sclera were 3.0-5.0 mJ at the 10 degrees convergence angle and 4.0-6.0 mJ at the 18 degrees convergence angle setting. It is recommended that such data be determined for each type of laser prior to attempting short-pulsed laser internal trabeculotomy in patients with glaucoma.

Humans↗
PubMed1987

Baton twirling: another cause of eye injury.

Baton twirling is an increasingly popular sport, with an estimated 5000 participants in Scotland alone. The baton, weighing over 200 g, is spun at high speeds and frequently thrown over 40 feet (12 m) into the air. We report a case of a 17-year-old girl who sustained a serious eye injury after being struck by a baton. The occurrence of eye injury has not been reported in this sport, and we discuss the potential for injury.

Adolescent↗
PubMed1987

Effect of age on visual acuity after cataract extraction.

The best Snellen visual acuity in the three months after cataract extraction was found to decline with the age of the patient. The relationship was identical in 111 patients who had extracapsular extraction and a Pearce tripod posterior chamber intraocular lens and in 50 patients who had intracapsular extraction with spectacle correction. Vision after operation varied from a mean value of 6/5 at 50 years to 6/12 at 90 years, a decline of 1 line per 13.4 years. In the intracapsular group, over a mean follow-up period of 14 years, the rate of fall in acuity with increasing age after operation was found to be statistically similar to that of the early postoperative acuity plotted against age for both types of operation. This suggests that the rate of decline with age is unchanged after a prolonged period of aphakia with presumed increased exposure to ultraviolet and blue light. The data were found to be similar to the decline in the neurosensory elements of vision with age measured experimentally in 20 phakic subjects by laser interferometry. This method of assessment of contrast sensitivity threshold effectively bypasses changes in the optical media. The findings indicate that the previously recognised drop in visual acuity with age is not related to changes in the aging crystalline lens and support the view that there is a decline in the neurosensory elements of vision. It is important to recognise this deterioration so that results of surgery or other treatment are adjusted to allow for the age of the patients.

Adult↗
PubMed1987

The role of Ca2+-dependent biochemical changes in the ageing process in normal red cells and in the development of irreversibly sickled cells.

During the ageing process of normal red cells and in the formation of irreversibly sickled cells (ISCs) there is a progressive increase in the intracellular concentration of Ca2+. This is parallelled by the development of a variety of morphological and biochemical changes in older fractions of normal cells and in ISCs which are similar to those seen in normal cells exposed to Ca2+ ionophore. These changes include cell shrinkage, loss of membrane lipid and degradation of cytoskeletal proteins and polyphosphoinositides. In this paper we consider the ways in which the Ca2+-dependent biochemical changes may be related to the morphological alterations which are characteristic of ageing and irreversible sickling.

Anemia, Sickle Cell↗
PubMed1986

Changes in membrane polypeptides, polyphosphoinositides and phosphatidate in dense fractions of sickle cells.

When sickle erythrocytes were fractionated on discontinuous isotonic stractan gradients the denser fractions, which were rich in irreversibly sickled cells contained less polyphosphoinositides and more phosphatidate than either lighter sickle cell fractions or normal cells. These changes could be due to activation of a polyphosphoinositide phosphodiesterase in the denser cells. Membrane polypeptide analysis of the denser fractions also showed a marked depletion of band 4.1 and a protein of molecular mass about 110 kDa but an increased amount of a 180 kDa polypeptide which might be a breakdown product of ankyrin. These biochemical alterations could be consequences of Ca2+ accumulation in the denser sickle cells and may contribute to the structural alterations which give rise to irreversibly sickled cells.

Anemia, Sickle Cell↗
PubMed1985

The effects of phorbol ester, diacylglycerol, phospholipase C and Ca2+ ionophore on protein phosphorylation in human and sheep erythrocytes.

Treatment of human or sheep erythrocytes with PMA (phorbol myristate acetate) enhanced [32P]phosphate labelling of membrane polypeptides of approx. 100, 80 and 46 kDa. The 80 kDa and 46 kDa polypeptides coincided with bands 4.1 and 4.9 respectively on Coomassie-Blue-stained gels. Similar but smaller effects were obtained by treating human cells with 1-oleoyl-2-acetyl-rac-glycerol (OAG), exogenous bacterial phospholipase C or ionophore A23187 + Ca2+, each of which treatments would be expected to raise the concentration of membrane diacylglycerol. In contrast, sheep cells, which do not increase their content of diacylglycerol when treated with phospholipase C or A23187 + Ca2+, only showed enhanced phosphorylation with OAG. Neither human nor sheep cells showed any enhanced [32P]phosphate labelling of phosphoproteins when treated with 1-mono-oleoyl-rac-glycerol. It is concluded that diacylglycerol from a variety of sources can activate erythrocyte protein kinase C, but that the most effective diacylglycerol is that derived from endogenous polyphosphoinositides. In contrast with bacterial phospholipase C and A23187, which stimulate synthesis of phosphatidate by increasing the cell-membrane content of diacylglycerol in human erythrocytes, PMA, OAG or 1-mono-oleoyl-rac-glycerol caused no change in phospholipid metabolism.

Animals↗