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Biomedical subjects

R S Anderson

Publications and source records attributed to R S Anderson.

At least 19 recordsLinked to original sources
PubMed2006

In vivo macular pigment measurements: a comparison of resonance Raman spectroscopy and heterochromatic flicker photometry.

AIM: To investigate whether two methods of measuring macular pigment-namely, heterochromatic flicker photometry (HFP) and resonance Raman spectroscopy (RRS)--yield comparable data. METHODS: Macular pigment was measured using HFP and RRS in the right eye of 107 participants aged 20-79 years. Correlations between methods were sought and regression models generated. RRS was recorded as Raman counts and HFP as macular pigment optical density (MPOD). The average of the top three of five Raman counts was compared with MPOD obtained at 0.5 degrees eccentricity, and an integrated measure (spatial profile; MPODsp) computed from four stimulus sizes on HFP. RESULTS: The coefficient of variation was 12.0% for MPODsp and 13.5% for Raman counts. MPODsp exhibited significant correlations with Raman counts (r = 0.260, p = 0.012), whereas MPOD at 0.5 degrees did not correlate significantly (r = 0.163, p = 0.118). MPODsp was not significantly correlated with age (p = 0.062), whereas MPOD at 0.5 degrees was positively correlated (p = 0.011). Raman counts showed a significant decrease with age (p = 0.002) and were significantly lower when pupil size was smaller (p = 0.015). CONCLUSIONS: Despite a statistically significant correlation, the correlations were weak, with those in excess of 90% of the variance between MPODsp and Raman counts remaining unexplained, meriting further research.

Adult↗
PubMed2003

[Invariants of spatial summation for S (short wavelength) cone vision].

Spatial summation in the human visual system was studied as a function of retinal eccentricity upon selective stimulation of the short-wavelength sensitive cones. The area of complete spatial summation (Ricco's area) was found to increase with retinal eccentricity while the threshold of stimuli equal in size with Ricco's area remained constant. Comparisons with known morphology of the small bistratified retinal ganglion cells, the only cells known to be excited by S-one ON stimulation, showed that Ricco's area included 2-4 such cells and is up to 1.5 times larger than the dendritic field of a single cell. These relationships were relatively constant within the eccentricity range tested (5-20 deg along the temporal horizontal meridian) and might be the source of threshold invariance of stimuli matching Ricco's area.

Adult↗
PubMed2002

The contrast sensitivity function for detection and resolution of blue-on-yellow gratings in foveal and peripheral vision.

Previous studies using polychromatic gratings have shown that the peripheral grating contrast sensitivity function is significantly different when the task is resolution rather than detection. Specifically, in the middle frequency range, while resolution acuity drops suddenly to zero, detection performance continues up to much higher frequencies, accompanied by observations of aliasing. We wanted to determine if the same holds true for blue-cone isolating gratings in either foveal or peripheral vision. Contrast sensitivity function (CSFs) were measured at the fovea and 20 degrees eccentricity in the temporal retina under conditions of short-wavelength-sensitive (SWS)-cone pathway isolation using a two-alternative forced choice paradigm. The detection and resolution CSF were identical at the low frequency end but at higher frequencies resolution sensitivity falls abruptly while contrast detection remained possible till higher frequencies [cut-off frequencies: fovea detection 6.0 cycles (degree)(-1), resolution 4.6 cycles (degree)(-1); periphery detection 1.6 cycles (degree)(-1), resolution 1.05 cycles (degree)(-1)]. Aliasing was observable when spatial frequency exceeded the resolution limit. Medium/high contrast blue-cone-mediated resolution acuity is sampling limited in both the fovea and periphery. Previous studies of blue-cone contrast sensitivity which employed a detection task do not reflect the true resolution limit.

Color Perception↗
PubMed2001

Binocular summation for grating detection and resolution in foveal and peripheral vision.

Peripheral monocular grating resolution has been shown to be limited by the sampling density of the underlying retinal ganglion cells. We wanted to determine if peripheral resolution is also sampling limited binocularly; and, if so, how great is any improvement in either detection or resolution when viewing binocularly? We measured detection and resolution acuity for sinusoidal gratings in foveal and peripheral vision both monocularly and binocularly. Detection and resolution acuity were very similar in foveal vision and displayed a binocular improvement of 5% over best monocular acuity. However, in peripheral vision, while detection acuity improved by 6% binocularly, resolution acuity improved by 16%, with a subsequently smaller aliasing zone. This improvement was greater than predicted by probability summation and implies that the two monocular ganglion cell sampling arrays combine at a higher level resulting in a higher binocular sampling density.

Female↗
PubMed2001

Effect of localized defocus on detection thresholds for different sized targets in the fovea and periphery.

PURPOSE: Previous studies of optical blur in perimetry have measured the effect of foveal refractive error on peripheral perimetric detection thresholds. Since peripheral refractive error can be significantly different from that of the fovea we wished to remove the ambiguity of previous results by correcting the actual peripheral refractive error first before adding blur. METHODS: We measured detection thresholds in the fovea and at 30 degrees in the horizontal temporal field in two trained observers. Peripheral refractive error was determined at each location and thresholds measured at the same locations for stimuli ranging in size from 0.2 to 6.4 degrees and refractive errors between +/-4.00 diopters. RESULTS: Foveal thresholds increased immediately with increasing refractive error, particularly for smaller stimulus sizes. At 30 degrees, thresholds for smaller stimuli were less affected by defocus initially and then increased more sharply. Larger stimuli were relatively unaffected by defocus such that when stimulus size reached 1.6 degrees there was little or no increase in threshold for refractive error between +/-4.00 diopters. CONCLUSIONS: Peripheral refractive error, largely forgotten by perimetrists, has a significant effect on performance, particularly for smaller stimuli. Differences in foveal vs peripheral viewing can be explained by differences in ganglion cell receptive field sizes.

Fovea Centralis↗
PubMed2001

Controlled trial of acyclovir for chickenpox evaluating time of initiation and duration of therapy and viral resistance.

BACKGROUND: Chickenpox is prevalent in the US despite the availability of an effective vaccine. Acyclovir treatment is limited by concerns about efficacy if given after the first day of rash and by concerns about induction of viral resistance. OBJECTIVE: Evaluate initiation and duration of acyclovir treatment of chickenpox and its effect on viral resistance. STUDY DESIGN: Randomized, placebo-controlled, double blind trial in immunocompetent patients who were stratified by age at enrollment (children, 2 to 11 years; adolescents, > or = 12 to 18 years; adults, > or = 19 years) and duration of rash (< or = 24 h vs. >24 to 48 h). Lesions were staged, counted and cultured; temperatures and symptoms were recorded daily. INTERVENTION: Subjects presenting within 24 h of rash onset (Group A) were randomly assigned to 5 or 7 days of oral acyclovir treatment, 80 mg/kg/day up to a maximum of 3,200 mg/day in four divided doses. Subjects whose rash was >24 to 48 h old were randomized to receive 5 days of acyclovir treatment beginning on the first (Group B1) or second study day (Group B2). Matching placebos were used to ensure that subjects uniformly received 28 doses of study compound. RESULTS: Of the 177 subjects recruited Group A patients who were treated on the first day of rash had the greatest number of significantly shortened event times with 5 days of therapy being equivalent to 7 days. There also were some shorter times to events for Group B1 patients who began therapy on the second day of rash vs. Group B2 patients who started acyclovir on the third. These included: time to maximum lesion formation (adolescents, P = 0.007; children, P = 0.03); 50% healing in adolescents (P = 0.005); and residual facial lesions in adults (P = 0.047). The probability of viral shedding was significantly reduced for Group A subjects vs. Group B1 subjects (P = 0.006). Viruses shed during therapy remained susceptible to acyclovir and retained normal thymidine kinase function. CONCLUSIONS: Immunocompetent children, adolescents and adults with chickenpox displayed a gradation in their clinical responses to acyclovir that correlated with the time from onset of rash to initiation of therapy. Five days of therapy is sufficient because a 7-day course provided no additional benefit. The susceptibility to acyclovir of viruses shed during treatment did not change; however, the effect of therapy on resistance of latent virus was not assessed.

Acyclovir↗
PubMed2001

A simple method for electron energy constancy measurement.

A device is described for use in confirming the energy constancy of clinical electron beams. A wedge shaped absorber is placed over an ionization chamber leading to an energy dependent response. A measurement under the energy filter is divided by a measurement in air to correct for the inherent energy dependence of the chamber. A nearly linear response is demonstrated.

Electrons↗
PubMed2001

Geometry function of a linear brachytherapy source.

An equation is derived for the TG43 geometry function, G(r,theta), of a linear brachytherapy source in terms of its active length. This equation is validated by comparison to published values. It is then used to calculate values of the geometry function for the Model 200 (103)Pd seed, which is a segmented linear source.

Brachytherapy↗
PubMed2001

Evidence for nonacetylcholinesterase targets of organophosphorus nerve agent: supersensitivity of acetylcholinesterase knockout mouse to VX lethality.

The possibility that organophosphate toxicity is due to inhibition of targets other than acetylcholinesterase (AChE, EC 3.1.1.7) was examined in AChE knockout mice. Mice (34-55 days old) were grouped for this study, after it was determined that AChE, butyrylcholinesterase (BChE), and carboxylesterase activities had reached stable values by this age. Mice with 0, 50, or 100% AChE activity were treated subcutaneously with the nerve agent VX. The LD50 for VX was 10 to 12 microg/kg in AChE-/-, 17 microg/kg in AChE+/-, and 24 microg/kg in AChE+/+ mice. The same cholinergic signs of toxicity were present in AChE-/- mice as in wild-type mice, even though AChE-/- mice have no AChE whose inhibition could lead to cholinergic signs. Wild-type mice, but not AChE-/- mice, were protected by pretreatment with atropine. Tissues were extracted from VX-treated and untreated animals and tested for AChE, BChE, and acylpeptide hydrolase activity. VX treatment inhibited 50% of the AChE activity in brain and muscle of AChE+/+ and +/- mice, 50% of the BChE activity in all three AChE genotypes, but did not significantly inhibit acylpeptide hydrolase activity. It was concluded that the toxicity of VX must be attributed to inhibition of nonacetylcholinesterase targets in the AChE-/- mouse. Organophosphorus ester toxicity in wild-type mice is probably due to inhibition or binding to several proteins, only one of which is AChE.

Acetylcholinesterase↗
PubMed2000

Radioimmunoguided surgery using indium-111 capromab pendetide (PROSTASCINT) to diagnose supraclavicular metastasis from prostate cancer.

A 59-year-old man presented with a Gleason score of 4 + 4 = 8 prostate cancer and with multiple bilateral pelvic nodes involved at open pelvic lymph node dissection. On indium-111 capromab pendetide (ProstaScint) scan, there was increased tracer deposition in the prostate, the mesenteric nodes, the right pulmonary hilum, and the left supraclavicular fossa. The ProstaScint injection was repeated, and the gamma probe was used to localize tissue that accumulated radiotracer. Two nodes were excised, one that exhibited increased uptake and one that did not. The radioactive lymph node contained metastatic prostate cancer. No malignancy was found in the second node.

Adenocarcinoma↗
PubMed2000

The effects of chlorothalonil on oyster hemocyte activation: phagocytosis, reduced pyridine nucleotides, and reactive oxygen species production.

The production of reactive oxygen species (ROS) by a putative NADPH oxidase-like enzyme system is thought to contribute to antimicrobial activity in oyster hemocytes. NADPH oxidase in vertebrate phagocytes generates superoxide anion from molecular oxygen and NADPH, which is then converted to additional ROS, including H2O2 and HOCl. The fungicide chlorothalonil (TCIN) is a thiol-reactive compound that binds to protein sulfhydryl groups, which can result in enzyme inactivation. NADPH oxidase, containing several sulfhydryl groups, is a potential target of TCIN. Previous studies have demonstrated that in vitro exposure of fish (Morone saxatilus) macrophages to TCIN (10-500 microg/L) suppressed immunostimulated ROS and baseline NAD[P]H concentration but did not inhibit phagocytosis; the production of NADPH in stimulated cells was decreased only at the highest concentration. In this study, we evaluated the effects of TCIN (10-500 microg/L) on oyster hemocyte functions. As with striped bass macrophages, in vitro exposure to TCIN suppressed hemocyte ROS production in a dose-dependent manner, but did not affect phagocytosis. In contrast to the striped bass data, baseline NAD[P]H concentration was relatively unaffected and immunostimulated NAD[P]H production was marginally suppressed at the higher exposure concentrations. Despite these minor differences, these results suggest that TCIN may also be inhibiting an NAD[P]H oxidase-like enzyme in oyster hemocytes.

Animals↗
PubMed2000

Aliasing in peripheral vision for flickering gratings under different levels of illumination.

PURPOSE: To assess how far retinal illumination can be reduced for sine-wave gratings phase reversing at different temporal frequencies in peripheral vision, while maintaining sampling limited resolution acuity performance, as evidenced by an aliasing zone between detection and resolution. METHODS: Computer generated sine wave gratings were presented with flicker rates from 0 to 40 Hz under retinal illumination levels of 3.5 to -0.5 log trolands. Resolution and detection thresholds were measured at 30 degrees in the horizontal temporal field using a spatial and temporal 2AFC paradigm respectively. RESULTS: At high illumination levels, detection acuity is higher than resolution acuity between 0 and 40 Hz indicating that resolution is sampling limited. As illumination level decreases the aliasing zone becomes narrower, especially at high temporal frequency until it disappears completely at 0.5 log trolands. CONCLUSIONS: Peripheral resolution acuity ceases to be sampling limited below 1.5 log trolands for low temporal frequency gratings and at higher levels for high temporal frequency gratings. Sampling limited acuity was recorded for high frequency gratings under higher illumination levels which could be mediated by the M cells alone, but this is not the case for the lower levels of illumination.

Humans↗
PubMed2000

Care-seeking behavior for upper respiratory infections.

BACKGROUND: Many recent efforts to reduce unnecessary medical services have targeted care of upper respiratory infections (URIs). We tested whether patients who seek care very early in their illness differ from those who seek care later and whether they might require a different approach to care. METHODS: We surveyed by telephone 257 adult patients and 249 parents of child patients who called or visited one of 3 primary care clinics within 10 days (adults) or 14 days (parents) of the onset of uncomplicated URI symptoms. Those who contacted the clinic within the first 2 days of illness were compared with those who made contact later. RESULTS: Although 28% of adults and 41% of parents contacted their clinic within the first 2 days of symptom onset, we found very few differences in the characteristics of the caller or patient between those who called early and later. The illnesses of those who called early were not more severe, and they did not have different beliefs, histories, approaches to medical care, or needs. The only clinician-relevant difference was that adult patients calling in the first 2 days had a greater desire to rule out complications (84.7% vs 64.1% calling in 3-5 days and 70.6% calling after 5 days of illness, P < or = .05). CONCLUSIONS: Those who seek medical care very early for a URI do not appear to be different in clinically important ways. If we are going to reduce overuse of medical care and antibiotics for URIs, clinical trials of more effective and efficient strategies are needed to encourage home care and self-management.

Adolescent↗
PubMed1999

Pyrophosphorolytic dismutation of oligodeoxy-nucleotides by terminal deoxynucleotidyltransferase.

Terminal transferase (TdT), when incubated with a purified(32)P-5"-end-labeled oligonucleotide of defined length in the presence of Co(2+), Mn(2+)or Mg(2+)and 2-mercaptoethanol in cacodylate or HEPES buffer, pH 7.2, exhibits the ability to remove a 3"-nucleotide from one oligonucleotide and add it to the 3"-end of another. When analyzed by urea-PAGE, this activity is observed as a disproportionation of the starting oligonucleotide into a ladder of shorter and longer oligonucleotides distributed around the starting material. Optimal metal ion concentration is 1-2 mM. All three metal ions support this activity with Co(2+)> Mn(2+) congruent with Mg(2+). Oligonucleotides p(dT) and p(dA) are more efficient substrates than p(dG) and p(dC) because the latter may form secondary structures. The dismutase activity is significant even in the presence of dNTP concentrations comparable to those that exist in the nucleus during the G(1)phase of the cell cycle. Using BetaScope image analysis the rate of pyrophosphorolytic dismutase activity was found to be only moderately slower than the poly-merization activity. These results may help explain the GC-richness of immunoglobulin gene segment joins (N regions) and the loss of bases that occur during gene rearrangements in pre-B and pre-T cells.

Animals↗
PubMed1999

Foveal and peripheral thresholds for detection and resolution of vanishing optotype tumbling E's.

We measured detection and resolution acuity for vanishing optotype tumbling E stimuli in both the fovea and at 30 degrees in the periphery to determine if peripheral resolution is sampling limited for this stimulus. In the fovea, where acuity is optically limited, detection and resolution were the same. At 30 degrees, however, detection was markedly better than resolution indicating that peripheral resolution is sampling limited for this stimulus. Detection acuity was higher when contrast was 90% rather than 40%, but resolution did not change with contrast. The vanishing optotype is a legitimate perimetric stimulus to measure retinal ganglion cell density provided the task is resolution and not detection.

Contrast Sensitivity↗