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Biomedical subjects

J A Medeiros

Publications and source records attributed to J A Medeiros.

6 recordsLinked to original sources
PubMed1979

High resolution microchemical analysis using soft X-ray lithographic techniques.

High resolution x-ray lithographic studies of cells from chick embryo hearts dried by the CO2 critical point method have been made with soft x-ray radiation of different wavelengths. A marked difference in the relief replica in polymethyl methacrylate (PMMA) resulting from the differential absorption by the dried cells of carbon K alpha radiation at 4.48 nm and broad band synchrotron radiation (SR) with lambda is greater than 1.5 nm demonstrates the potential usefulness of the technique in making high resolution (approximately or equal to 10 nm) chemical identification of the constitutents which make up the various parts of the cell.

Animals↗
PubMed1979

Arterial bifurcations in the human retina.

The branching angles and relative diameters of blood vessels in 51 arterial bifurcations in the retina of a normal human eye were measured. In eight other bifurcations, only the total branching angles were measured. The results are compared with theoretical predictions in an attempt to understand the physiological principles governing branching in the cardiovascular system.

Adult↗
PubMed1979

Application of optical transform techniques to laser irradiation of retina.

Novel retinal irradiation techniques for laser damage studies are described; these are straightforward applications of the Fourier transform properties of an optical system. Interposing an appropriate diffracting screen between the laser source and the test eye enables one to simultaneously induce a number of discrete and precisely located retinal exposures with a known gradation of energy. Various kinds of diffracting objects are considered, and it is seen that transparent sinusoidal phase gratings offer the most promise for damage threshold studies. The method provides an objective measure of the ocular focal length at the time of the exposure. The production of arbitrary retinal irradiation patterns for more general research or clinical applications is possible with the extension of the technique by the use of simple holographic methods for forming the appropriate diffracting screens.

Animals↗
PubMed1977

Fusing human rod outer segments from an eye enucleated for choroidal melanoma.

In the retina from an eye enucleated for choroidal melanoma apposed rod outer segments were seen by transmission electron microscopy to be fusing together in groups by the confluence of their plasma membranes and the formation of cytoplasmic bridges between adjacent outer segments. These fusions were seen in areas distant from the melanoma but where the retina was not normal in appearance.

Cell Membrane↗
PubMed1977

Scanning electron microscopy of normal and lased rabbit pigment epithelium.

Scanning electron microscopic (SEM) observations of the rabbit retinal pigment epithelium (RPE) are reported both for normal tissue and for tissue subjected to laser radiation. In normal RPE, cells were observed to be closely packed and to have the characteristic hexagonal shape. The microvilli were abundant and of two types. Suprathreshold lesions were produced with 0.4 musec pulses of high-intensity yellow light (585 nm.) from a dye laser. In the lased RPE, cells were denuded of their microvilli, and a number of cells with single discrete holes were observed. Hypertrophied cells were always present. Within 5 days of irradiation groups of small proliferating RPE cells were found in the lesion area.

Animals↗