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Biomedical subjects

D A Barnes

Publications and source records attributed to D A Barnes.

At least 55 records · Page 3Linked to original sources
PubMed1987

Effect of intrauterine iodine infusion on luteal function and blood PGF2a concentration in cycling goats.

Studies were conducted to determine the effect of iodine infusion on the luteal function of goats, as evident by blood progesterone concentration, and on plasma PGF2a levels. Ten cycling mixed breed goats were synchronized for estrus by PGF2a (5 mg) and given a single intrauterine iodine infusion on day 5 and on day 15 of the estrous cycle. Iodine infusion on day 5 (group II) resulted in shorter estrous length (8.2 days) and a 7-fold increase in plasma PGF2a concentration as compared to control animals (group I) given distilled water infusion. Similar infusion on day 15 (group III), on the other hand, failed to alter the estrous cycle length but induced a moderate increase in PGF2a concentration which lasted only for a brief period. The progesterone levels declined concomitantly as PGF2a levels rose after iodine infusion in group II animals but failed to decline until after 24 hours in group III animals. The studies indicate that the endometrium reacts to the chemical stimuli and releases PGF2a which, in turn, alters the luteal function.

Animals↗
PubMed1987

A method for raytracing through schematic eyes with off-axis components.

A linear algebraic method for tracing skew rays through aspheric surfaces is described. The advantage of this method is that the refracting surfaces can be translated and rotated with respect to each other. The method is used to investigate the optical factors affecting the location of Purkinje images.

Cornea↗
PubMed1987

A schematic eye model for the effects of translation and rotation of ocular components on peripheral astigmatism.

The relative contributions of translation and rotation of the cornea and lens to peripheral astigmatic asymmetry have been investigated using a linear algebraic ray tracing method. It is believed that lenticular rotation is responsible for angle alpha, so bringing about peripheral astigmatic asymmetry, as normally occurs in human eyes over the temporal and nasal retina. Rotation of the cornea may be responsible for the small numbers of eyes which exhibit large amounts of peripheral astigmatic asymmetry. The effects of corneal rotation and translation on the dimensions of the entrance pupil are illustrated.

Astigmatism↗
PubMed1987

A model for retinal shape changes in ametropia.

Modeling ametropic retinal shape changes with an ellipsoid of constant equatorial radius has been found to produce types of peripheral astigmatism which are in good agreement with experimental findings.

Astigmatism↗
PubMed1987

Schematic modelling of peripheral astigmatism in real eyes.

A method is described whereby any schematic eye possessing a two-surfaced, monoindicial lens can be manipulated to yield the same amounts of peripheral astigmatism as found in real eyes. Its optical performance is discussed and it is demonstrated that schematic eyes of this type cannot simultaneously yield the amounts of peripheral astigmatism and spherical aberration that are observed in real eyes.

Astigmatism↗
PubMed1986

Effect of epithelial and stromal edema on the light scattering properties of the cornea.

Transparency of the cornea is dependent on normal metabolism. Any disturbance in function, e.g., corneal edema, results in increased light scattering, reducing contrast sensitivity, and increasing glare susceptibility. A psychophysical method was developed to quantify this visual disability and to separate sources of light scatter within the cornea using three conditions: a no glare condition, a 30 degree angular radius glare condition, and a 3.5 degrees angular radius glare condition. Corneal edema was induced (N = 7) and contrast threshold measurements were recorded for 15 min during edema recovery using a clinically available technique. Retinal contrast attenuation was expressed in terms of light scattering factors (LSFs). Results show that the technique devised separates attenuation of retinal image contrast caused by epithelial and stromal edema and provides quantifiable values for normal light scatter and for that due to epithelial and stromal elements.

Adult↗
PubMed1986

The cortical representation of gradient-adapted multiple-stimulus perimetry.

Some stimuli, if scaled in proportion to the reciprocal of inter ganglion cell receptive field separation (M-scaled) exhibit an isosensitivity profile. Perimetric profiles which are isosensitive across the extent of the normal visual field facilitate multiple stimulus perimetry and provide a convenient method for the detection of abnormality. The purpose of the investigation was to establish whether the stimulus diameters necessary to produce an isosensitive perimetric profile were scaled in proportion to M. Sensitivity profiles for a sample of 15 age-matched observers were obtained with the Friedmann VFA Mk II. The stimulus aperture diameters were then measured under 100 X magnification. The observed elliptical apertures, corrected for obliquity of viewing, plate thickness and distance from the eye were represented as diameters of circles possessing an equivalent area to that of the ellipse. The apparent diameters were then M-scaled relative to stimulus pattern h using the equations of Rovamo and Virsu (1979). An overestimation of the M-scaled diameters relative to the apparent diameters was noted which increased with eccentricity for all four cardinal meridians by a factor of up to 3.5 times. It is suggested that the over compensation indicates that the cortical representation of perimetric spot targets at low photopic adaptation levels depends not only upon retinal ganglion cell density but also upon the variation of ganglion cell characteristics with eccentricity. The implications of this finding for perimetric instrument design are discussed.

Adult↗
PubMed1986

Genetic manipulation of Saccharomyces cerevisiae by use of the LYS2 gene.

The structural gene for alpha-aminoadipate reductase (LYS2) was isolated from a Saccharomyces cerevisiae genomic DNA library by complementation of a lys2 mutant. Both genetic and biochemical criteria confirmed that the DNA obtained corresponds to the LYS2 locus on chromosome II. Subcloning and deletion analysis showed that a functional LYS2 gene is contained within a 4.6-kilobase (kb) EcoRI-HindIII fragment of the original insert, and the slightly larger EcoRI-ClaI segment (4.8 kb) was used to construct a series of cloning vehicles, including integrating, episomal, replicative, and centromeric vectors. The cloned DNA was also used to generate a genomic deletion that lacks all LYS2 coding sequences on chromosome II. The level of the LYS2 transcript (4.2 kb) was 10-fold higher in cells grown on minimal medium than in cells grown on complete medium and was not repressed by the presence of lysine alone. Gene disruption, gene replacement, and promoter analysis of the major alpha-factor structural gene (MF alpha 1) were performed to illustrate the utility of the LYS2 gene for the genetic manipulation of yeasts. Because all fungi synthesize lysine via the alpha-aminoadipate pathway, the techniques developed here for using the S. cerevisiae LYS2 gene should be directly applicable to other fungal systems.

Aldehyde Oxidoreductases↗
PubMed1985

Manipulation of sensitivity in visual field investigation.

Sophistication of computer software and flexibility of stimulus and background luminance parameters in static perimeter design offer the opportunity for increased information in the assessment of the visual field. Relationships between dynamic ranges and resulting sensitivity gradients in a group of 10 normal 21 year old subjects using the Octopus automated perimeter, the Dicon Autoperimeter 2000 and the Friedmann VFA II are assessed. Inadequacies in the use of normative data to assess the visual field are noted. Implications for the use of dynamic range/sensitivity gradient relationships in visual field assessment without reliance on normative data are discussed.

Adult↗
PubMed1984

The qualitative comparative analysis of the visual field using computer assisted, semi-automated and manual instrumentation: I. Scoring system.

Previous methods for the qualitative evaluation of visual field instruments are subject to certain limitations. A system is proposed to overcome these deficiencies. It has been developed from experiences of a clinical study involving 5 different visual field instruments. The method uses 4 levels of analysis and permits separate appraisals of diagnostic potential and detailed inter-instrument comparative evaluation.

Computers↗
PubMed1984

The qualitative comparative analysis of the visual field using computer assisted, semi-automated and manual instrumentation: II. Statistical analysis.

A comparative evaluation of the Octopus automated perimeter (Programmes 21 and 31), the Goldmann Bowl perimeter, the Bjerrum Screen and the Friedmann VFAs MkI and MkII was carried out on a heterogeneous sample of 75 patients. The results for the sample as a whole were analysed statistically in terms of the scoring system developed by Flanagan, Wild, Barnes, Gilmartin, Good and Crews (1984a). Statistically significant differences between the instruments were found at each of the 4 levels of analysis.

Adolescent↗
PubMed1984

The qualitative comparative analysis of the visual field using computer assisted, semi-automated and manual instrumentation: III. Clinical analysis.

A comparative evaluation of the Octopus automated perimeter (Programmes 21 and 31), the Goldmann Bowl perimeter, the Bjerrum Screen and the Friedmann VFAs Mk I and Mk II was carried out on a heterogeneous sample of 75 patients. Field loss was categorized using a modification of the classifications proposed by Greve (1982). The results were analysed using the Level 4 analysis developed by Flanagan, Wild, Barnes, Gilmartin, Good and Crews (1984a). The performance of the various test logics was found to differ between the categories of field defect.

Computers↗
PubMed1984

A review and evaluation of theories of refractive error development.

A review of theories of the development of refractive errors is presented. These are classified into three major groups: the biological-statistical theories, the use-abuse theories and theories of emmetropization. They are commented upon and their merits contrasted. Current research developments which relate to these theories are discussed.

Adolescent↗
PubMed1984

Astigmatic decomposition: an alternative subjective refraction test employing conventional instrumentation.

The Humphrey Vision Analyser introduced the refractive technique of astigmatic decomposition with the aid of Alvarez continuously variable sphere-cylinder lenses. The adaptation of astigmatic decomposition to conventional trial lens systems and a Stokes' lens is described. Refractive errors measured by this technique and by crossed cylinder are compared in 33 optometric patients (one eye each) to assess the relative validity of the method, which compares well with data published on the Humphrey Vision Analyser. Astigmatic decomposition can be considered as an alternative subjective refraction test to more conventional methods.

Astigmatism↗
PubMed1983

Evaluation of transsphenoidal hypophysectomy in the management of patients with advanced malignant melanoma.

Transsphenoidal hypophysectomy was performed in 13 patients with advanced malignant melanoma. Although three minor responses were observed, there were no complete or partial responses. All three patients with bone pain had a decrease in discomfort lasting 1-2 months. All five patients with minor responses or stable disease had postoperative decreases in the excretion of the dihydroxyphenylalanine (DOPA) metabolite 3-O-methyldopamine; all but one patient with clinical progression had postoperative increases in excretion. Average survival of those whose postoperative excretion fell (143 +/- days; range, 60-217+) was significantly longer (P less than 0.004) than that of those whose postsurgical values rose (30 days; range, 15-58).

Adult↗