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Biomedical subjects

B R Hammond

Publications and source records attributed to B R Hammond.

30 records · Page 2Linked to original sources
PubMed1996

Cigarette smoking and retinal carotenoids: implications for age-related macular degeneration.

The foveal region of the retina has a yellow pigmentation composed primarily of the carotenoids lutein and zeaxanthin. Past studies have shown that cigarette smoking depresses carotenoid concentrations in the blood. This is the first report on the effects of cigarette smoking on carotenoids in the retina. Macular pigment optical density (MP) was measured psychophysically by comparing foveal and parafoveal sensitivities to light of 460 and 550 nm. General dietary patterns, smoking frequency (cigaretts/day) and personal data were collected by questionnaire. Thirty-four smokers and 34 nonsmokers were compared. Subjects were matched with respect to age, sex, dietary patterns and overall pigmentation (i.e., eye, skin and hair color). The smoking group had a mean MP of 0.16 (SD = 0.12) compared to a mean MP of 0.34 (SD = 0.15) for nonsmokers (P < 0.0001). MP density and smoking frequency were inversely related (r = -0.498 P < 0.001) in a dose-response relationship. A variety of evidence suggests that MP protects the macula from actinic damage both passively (by screening potentially harmful short-wave light) and actively as an antioxidant (e.g., by quenching reactive oxygen species). If smoking causes a reduction in MP density, then smokers may be at risk. Epidemiologic data identifying smoking as a risk factor for the neovascular form of age-related macular degeneration are consistent with this hypothesis.

Adult↗
PubMed1995

Macular pigment density in monozygotic twins.

PURPOSE: Research shows wide variation in macular pigment density between individuals. As are other ocular pigments, this variation may be genetic. To test this hypothesis, the authors measured macular pigment density, serum carotenoid concentrations, and general dietary patterns in 10 pairs of identical twins. METHODS: Macular pigment was measured psychophysically by a 1 degree test stimulus. Foveal and parafoveal sensitivities to 460-nm and 530-nm light were compared. Determining the difference in log sensitivity to the 460-nm light for the fovea (where macular pigment is most dense) and the parafovea (where macular pigment is optically immeasurable), after normalizing with respect to 530 nm, yields a measurement of the optical density of macular pigment. Concentrations of carotenoids within the serum were measured using reverse-phase, high-performance liquid chromatography. Dietary patterns were determined using a food-frequency questionnaire. RESULTS: Statistically significant differences in macular pigment optical density were found for 5 of the 10 twin pairs. For these five pairs, differences in macular pigment density were moderately related to differences in the intake of dietary fat, iron, linoleic and oleic acid, fiber, and total calories (P < 0.10, individually; P < 0.05, for an equally weighted composite of these variables). There was no significant relationship, however, found between macular pigment density and carotenoids in the blood and diet. CONCLUSIONS: Given the putative protective role of macular pigment, variations in macular pigment density may have clinical significance. The conclusion that macular pigment is not completely determined genetically allows the possibility that macular pigment density may be modified for the protective purposes. The current data suggest that dietary fat, iron, and fiber may influence macular pigment levels (perhaps through their influence on carotenoid metabolism). These data suggest that the eventual deposition of macular pigment in the retina is complex and probably is influenced by a number of variables.

Adult↗
PubMed1992

Interocular differences in macular pigment density.

Interocular differences in the optical density of macular pigment were examined. Foveal and parafoveal sensitivities to lights of 460 and 530 nm were measured by heterochromatic flicker photometry for both eyes of ten subjects. These two wavelengths represent the maximum and minimum absorbance for macular pigment. Taking the difference in log sensitivity to the 460 nm light for the fovea and parafovea, after normalizing with respect to 530 nm, yields a measurement of the optical density of the macular pigment. Consistent interocular differences in macular pigment density were found for only two subjects, and these differences were less than 0.1. Other subjects frequently showed significant interocular differences on a given day but showed no consistent differences over the course of many days. In general, the amount of macular pigment measured for one eye was found to be essentially the same as that for the other eye. When measurements were averaged for the two eyes of each subject, significant differences in macular pigment density among subjects were found.

Adult↗
PubMed1985

Ocular responses to superoxide generated by intraocular injection of xanthine oxidase.

Xanthine oxidase (XaO) was injected into the anterior chamber of rabbit eyes by a closed circuit perfusion system. Doses of 1.5 milliunits (mU) or greater produced a maximal leucocyte accumulation after 4 hr, with an initial elevation of ocular pressure in the first 15 min. Similar experiments on rats with intravitreal injections of 0.1-1.5 mU of XaO resulted in a significant accumulation of leucocytes after 5 hr which, at the highest dose of XaO, was partly due to traces of bacterial endotoxin in the XaO. However, in endotoxin-desensitized rats the response to 1.5 milliunits XaO was seven-fold greater than the response to endotoxin alone. Simultaneous administration of xanthine (Xa) substrate with XaO was not required to elicit cell infiltration into the anterior chamber. Dialyzed enzyme was also effective but boiling abolished the response. Addition of XaO to rabbit aqueous humor in vitro decreased the ascorbate content, consistent with the generation of superoxide from an endogenous substrate. The results suggest that enzymatically active XaO, which can cause intraocular generation of superoxide from an XaO substrate present in aqueous humor, initiates the chemotactic response. A chemotactic agent may be generated from superoxide reacting with endogenous precursors in aqueous humor or by selective activation of the lipoxygenase pathway of arachidonic acid metabolism in adjacent tissues.

Animals↗
PubMed1984

Calibration of the Alcon applanation pneumatonograph and Perkins tonometer for use in rabbits and cats.

The Alcon pneumatonograph (PTG) and Perkins tonometer were calibrated for use on rabbits and cats by connecting the eyes of the anaesthetised animal to a pressure manometer and performing tonometry at varying known pressures. The slope of the calibration graph obtained for the PTG was steeper when the stopcock was closed just before tonometry, whereas open and closed stopcock curves were identical using the Perkins tonometer. When using the PTG on rabbits it was found that tonometer readings could exaggerate changes in intraocular pressure unless converted to mmHg using a relevant calibration curve.

Animals↗
PubMed1980

The effects of sensory denervation on the responses of the rabbit eye to prostaglandin E1, bradykinin and substance P.

1 Six to eight days after diathermic destruction of the fifth cranial nerve in the rabbit, the ocular hypertensive and miotic responses to intracameral administration of capsaicin, bradykinin, and prostaglandin E1 were greatly reduced or completely abolished. The response to substance P was not abolished. 2 A response could still be obtained to chemical irritants 36 h after coagulation of the nerve and it is deduced that manifestation of the response is dependent upon functional sensory nerve terminals, and is independent of central connections. 3 It is suggested that prostaglandin E1 and bradykinin act directly upon the sensory nerve endings and that propagation of the response is augmented by axon reflex. 4 In view of the ability of substance P to induce miosis in the denervated eyes, it is presumed that its actions are not mediated via sensory nerves. 5 It is considered possible that the mediator(s) released from sensory nerve endings after chemical irritation or antidromic stimulation may act in the same way as substance P with regard to the miotic effect. 6 Synthetic substance P will only produce ocular hypertension in doses which induce a maximal miotic response. This may either be a question of access or a partial resemblance to the endogenous mediator.

Animals↗
PubMedDate not supplied

A method for the intraocular injection of micro-volumes in small animal species.

A method has been developed for the intraocular administration of small volumes (0.5-1.5 microliters) in small animal species such as guniea pigs and rats. The method was found to yield reproducible injection volumes and resulted in minimal ocular trauma. The aqueous humor of eyes injected with saline contained normal levels of protein and was free of white blood cells. Responses to Prostaglandin E2 and E.Coli endotoxin were dose-dependent and as expected.

Animals↗