Biomedical subjects

H Owens

Publications and source records attributed to H Owens.

At least 19 recordsLinked to original sources

PubMed2001

Cerebrospinal fluid penetration and pharmacokinetics of levofloxacin in an experimental rabbit meningitis model.

This study was designed to investigate the penetration across the blood-brain barrier of three doses of levofloxacin using a microdialysis probe implanted into the cerebrospinal fluid (CSF) of a rabbit pneumococcal meningitis model. The microdialysis guide cannula was implanted into rabbit subarachnoid space using a stereotaxic frame. After 3 days, 10(4) cfu Streptococcus pneumoniae serotype 3 in 0.3 mL saline was injected via intracisternal puncture and animals were allowed to incubate the organisms for 16-18 h. Groups of animals (n = 5) then received 7, 10.5 or 14 mg/kg iv of the drug over 10 min. Plasma samples were obtained via an ear vein 0, 0.25, 0.5, 0.75, 1, 2, 4, 6 and 8 h after the antibiotic infusion. CSF microdialysis effluent samples were collected every 0.5 h for the entire experiment. Plasma and microdialysis effluent samples were analysed by HPLC. AUC(0-8) in plasma and CSF were computed using the trapezoid rule. The elimination half-life in plasma and CSF was calculated using non-linear regression analysis. The unbound peak plasma concentrations for the three doses studied were 3.9, 6.4 and 10.3 mg/L, respectively. There was a significant increase in the plasma AUC(0-8) [29.7 +/- 6.3, 49.1 +/- 19.1 and 67.6 +/- 8.9 mg x h/L (P < 0.005)]. The unbound peak CSF concentrations were 3.8, 5.7 and 8.6 mg/L and occurred at 0-0.5 h after the administration of the dose. The AUC(CSF(0-8)) was significantly higher as the dose was increased (7 mg/kg, 15.8 +/- 6.6; 10.5 mg/kg, 37.3 +/- 7.8; and 14 mg/kg, 46.4 +/- 20.9 mg x h/L; P < 0.03). The penetration of levofloxacin averaged 53% for the 7 mg/kg dosage group, 76% for the 10.5 mg/kg group and 68% for the 14 mg/kg group. Our results demonstrate that levofloxacin penetration into the CSF averages 66% for the doses that would be used in clinical practice.

Animals↗

PubMed2001

Spreading of the tears after a blink: velocity and stabilization time in healthy eyes.

PURPOSE: To quantify the tear spreading velocity and stabilization time after blinks in healthy patients. METHODS: Video recordings (magnification, x130) were made of the movements of naturally occurring particles in the tear film while patients blinked naturally. After each blink, tear spreading velocity was computed every 40 milliseconds from particle displacements determined from a frame-by-frame analysis of the records. RESULTS: After a blink, tears moved rapidly upward over the cornea. Forty milliseconds after passage of the lid, the velocity was 7.34 +/- 2.73 mm/s (mean +/- standard deviation, n = 20). The time to tear stabilization (i.e., zero velocity) was 1.05 +/- 0.30 seconds. The decay of spreading velocity with time was well described by a logarithmic function for all individual patient data (R2 range, 0.88-0.99; n = 20). We have shown that initial velocity and stabilization time are independent descriptors of tear spreading. Meibomian gland expression markedly reduced initial velocity leaving a normal stabilization time, whereas inhalation of an irritant reduced stabilization time leaving a normal initial velocity. In a patient with Sjögren syndrome, punctal plugs rapidly restored initial velocity and stabilization time from near zero values to normal values. CONCLUSION: We provide normal values for two descriptors of tear spreading, namely initial velocity and time to stabilization. These values can be modified by manipulations that alter tear constituents. Consequently, these descriptors may provide a basis for quantitative, noninvasive tear assessment.

Adolescent↗

PubMed2001

Blur tolerance for luminance and chromatic stimuli.

We investigated the blur tolerance of human observers for stimuli modulated along the isoluminant red-green, the isoluminant yellow-blue, and the luminance (black-white) direction in color space. We report the following results: (i) Blur difference thresholds for red-green and luminance stimuli (of equal cone contrast) are very similar and as low as 0.5 min of visual angle; for yellow-blue the lowest blur thresholds are much higher (1.5 min of visual angle). (ii) The smallest blur thresholds are found for slightly blurred square waves (reference blur of 1 arc min) and not for sharp edges. (iii) Blur thresholds for red-green and black-white follow a Weber law for reference (pedestal) blurs greater than the optimum blur. (iv) Using the model proposed by Watt and Morgan [Vision Res. 24, 1387 (1984)] we estimated the internal blur of the visual system for the black-white and the red-green color directions and arrived at the following estimates: 1.2 arc min for black-white stimuli at 10% contrast and 0.9 arc min for red-green stimuli at 10% cone contrast. Blur tolerance for yellow-blue is independent of external blur and cannot be predicted by the model. (v) The contrast dependence of blur sensitivity is similar for red-green and luminance modulations (slopes of -0.15 and -0.16 in log-log coordinates, respectively) and slightly stronger for yellow-blue (slope = -0.75). Blur discrimination thresholds are not predicted by the contrast sensitivity function of the visual system. Our findings are useful for predicting blur tolerance for complex images and provide a spatial frequency cutoff point when Gaussian low-pass filters are used for noise removal in colored images. They are also useful as a baseline for the study of visual disorders such as amblyopia.

Color↗

PubMed2000

The spatio-chromatic sensitivity of the human visual system.

The response of the human visual system depends on a multitude of image features, such as the wavelength (colour) of the visual stimulus and its spatial frequency content. Hence we need to take into account the spatial and chromatic sensitivity as well as spatio-chromatic interactions to properly characterize visual sensitivity. In this paper we report two experiments that further characterize the spatio-chromatic sensitivity of the human visual system for stationary stimuli, namely the detection of small visual orientation differences and the detection of blur. In both cases we find that the visual system is equally sensitive to red-green and to black-white modulations for a wide range of spatial parameters. Furthermore, the contrast dependence for red green and black white modulations is identical, suggesting that the same mechanism mediates both types of stimulus. Our results are in accordance with the hypothesis that both tasks are mediated by the parvocellular as opposed to the magnocellular pathway.

Color Perception↗

PubMed1999

Prevalence of myopia in Sherpa and Tibetan children in Nepal.

BACKGROUND: Tibetan and Sherpa children living in Nepal share a common ancestry in Tibet and areas to the north of Nepal, but it is evident that these people experience widely contrasting educational and environmental conditions. The purpose of this study was to compare the prevalence of myopia in children with similar genetic backgrounds but who are exposed to contrasting environments. METHODS: Unaided vision and refractive error was measured in 555 Tibetan children in Kathmandu and 270 Sherpa children in the Solu Khumbu region of Nepal. RESULTS: There were marked differences in vision and the prevalence of myopia in the two groups. Ninety-two percent of the Sherpa children had Snellen vision of 20/22 (0.89) or better compared with 70% of the Tibetan children. The range of refractive errors was -6.50 to +7.00 D for the Tibetan children and -1.00 to +3.50 D for the Sherpa children. The Sherpa children had a prevalence of myopia of 2.9% compared with 21.7% for the Tibetan children. CONCLUSIONS: The prevalence of myopia in Sherpa children is low and their rural lifestyle appears to be relatively unstressed. Tibetan children have a higher prevalence of myopia and more rigorous schooling. We did not establish a causal relationship between myopia and the type of schooling, or the environment in general, but we did demonstrate that a simple, rural lifestyle is at least compatible with a virtual absence of myopia.

Adolescent↗

PubMed1998

Evaluation of mild, moderate, and advanced keratoconus using ultrasound pachometry and the EyeSys videokeratoscope.

BACKGROUND: The absolute accuracy of videokeratoscope (VKS) mapping of keratoconus is still in question, with contact lens-induced corneal warpage and chalazion having been shown to resemble this condition closely. Corneal thinning is investigated as a further aid to the diagnosis and description of keratoconus. METHODS: The diagnosis of keratoconus in 41 individuals was verified by measuring the corneal thickness difference (I-S difference) between two disparate corneal locations, one inferior to (I) and one superior to (S) the corneal apex, using a Humphrey model 870 Ultrasound pachometer. Corresponding measures of I-S radii were made using radius values obtained from the EyeSys VKS. RESULTS: A comparison between I-S pachometry and I-S radius demonstrated a marginally increased sensitivity for the latter measurement. Using 95% confidence levels from normative pachometric data, classification of severity of keratoconus is proposed as follows: (1) keratoconus suspect/early keratoconus: I-S pachometry 75 to 100 microns; (2) moderate keratoconus: 100 to 125 microns; and (3) advanced keratoconus: > 125 microns. CONCLUSION: I-S pachometry can be used as a descriptor of keratoconus.

Cornea↗

PubMed1997

The factors associated with effective folic acid prophylaxis in the peri-conceptional period in women attending an ante-natal clinic.

The aim of this study was to examine whether folic acid supplements had been taken and dietary folate intake increased in 662 pregnant women attending the antenatal clinic at St Mary's Hospital, Portsmouth. An assessment was also made of the factors that influenced correct compliance with the recommendations of the Expert Advisory Group on folic acid. Thirty-seven percent (245/662) women had taken folic acid supplements and 26.4% (175/ 662) increased their dietary folate before or during early pregnancy. The majority of women who commenced folic acid supplements after conception did so after the neural tube had closed (220/247). Women were more likely to have adhered to the Expert Advisory Group's recommendations if the pregnancy was planned, the woman was primiparous, there was no past or family history of neural tube defect and the patient had the correct existing knowledge of folic acid prophylaxis. The relevance of these findings to the current Health Education Authority's folic awareness campaign is discussed.

Journal Article↗

PubMed1997

Radius of curvature of the posterior surface of the cornea.

The radius of curvature of the posterior surface of the cornea was measured in the vertical meridian for 120 children aged 6 to 17 years, using a Purkinje image method. The mean radius of curvature (+/-SD) was 6.42 +/- 0.31 mm, with a range from 5.62 to 7.22 mm. The ratio of anterior to posterior corneal radius was 1.210 +/- 0.045 or 0.827 +/- 0.029 when expressed as a reciprocal. There was a significant correlation between the anterior and posterior corneal radius (y = 0.798x + 0.228, r2 = 0.45). The study provides data that may be applied to a four-surface schematic eye.

Adolescent↗

PubMed1996

An evaluation of the keratoconic cornea using computerised corneal mapping and ultrasonic measurements of corneal thickness.

Reports indicate the presence of up to three independent cone shapes in keratoconus (round/oval/global) but the preponderance of one cone over another is unclear. This work evaluates keratoconic corneal topography and corneal thickness using videokeratoscopy and ultrasound pachometry, respectively. An EyeSys videokeratoscope (VKS) (EyeSys Laboratories, Houston, TX, USA) was used to assess the topography of 54 keratoconic eyes (27 subjects) and 27 age-matched normals. In addition, ultrasonic pachometry measurements were made over 14 known areas in normal and keratoconic eyes. Corneal thinning was significant for all keratoconic areas measured except for the far temporal cornea. A correlation between corneal radius and thickness was evident. Analysis of cone shape revealed a potential fourth variety: the asymmetric bow-tie cone. Further topographic evaluation of this cone entity using the VKS revealed its dependence on gaze direction which may account for apparent differences in progression patterns between round and bow-tie cones.

Adult↗

PubMed1995

Obsessional harassment and erotomania in a criminal court population.

The criminal behaviors of harassment and menacing are difficult to control, and of increasing concern to the general public and local law enforcement officials. In 1992, the New York State Legislature modified the Penal Law, responding to public fears and concerns that stalking behavior may become violent. Some persons charged with these types of offenses are suffering from psychiatric disorders. Among these disorders are those classified as Delusional Disorders. According to both DSM-III-R (1987-1993) and DSM-IV (1994), there are five specific types of Delusional Disorder: erotomanic, grandiose, jealous, persecutory and somatic. This type of disorder tends to be chronic. Forty eight cases of persons charged with harassment and menacing in the New York County Criminal and Supreme Court and referred for evaluation to the Forensic Psychiatry Clinic between January 1987 and January 1994 are reviewed. When cases of erotomania and other affectionate/amorous complaints were compared with persecutory/angry forms of harassing behavior, there was a great deal of similarity. When all harassers were compared to the Clinic population as a whole, major differences in ethnicity, age, educational level and sex were noted. Findings are presented regarding incidence, other demographic data, recidivism, violence and clinical diagnosis. The researchers conclude that erotomania does exist, however, there are other psychiatric disorders which can also be diagnosed in individuals accused of harassing and menacing behavior. From the point of view of the victim and the criminal justice system, the similarities in behavior patterns are more important than the different diagnoses.

Adult↗

PubMed1993

Holistic retreats. A New Jersey medical center responds to community needs.

Through Lourdes Wellness Center, sponsored by Lourdes Medical Center, Camden, NJ, religious and laypersons from across the nation can experience holistic spirituality retreats. In holistic spirituality, a person reverences his or her whole self as an expression of and a way to God. Retreats offered through the Wholistic Retreat Program are geared to demonstrate the Christian and Franciscan perspective of the holiness of all creation. Some retreatants say the liturgies are the core of the holistic spirituality retreats, rich in their use of symbol, music, and word. Meals served at the retreats are a celebration of color, texture, and fragrance. Movement and exercise options are always available. Staff from Our Lady of Lourdes Medical Center often come to test retreatants' cholesterol levels, assess their life-styles and health, and provide information on health, fitness, and additional health screenings. Lourdes wellness retreats have a bright future as people increasingly turn to spirituality, preventive care, and alternative ways of healing in our high-stress society.

Catholicism↗

PubMed1992

Pharmacological effects on accommodative adaptation.

We review the research which has attempted to determine whether the characteristics of autonomic innervation of ciliary smooth muscle are relevant to the process of accommodative adaptation. The effect of various topical autonomic drugs on the three phases of adaptation were analyzed: pre-task tonic accommodation (open-loop); within-task accommodative response (closed-loop); and post-task regression of accommodation to pre-task tonic levels. Although it is clear that parasympathetic innervation predominates, there is evidence that some individuals utilize supplementary inhibitory sympathetic innervation. When sympathetic innervation is augmented by substantial levels of concurrent parasympathetic accommodative activity, it may serve to attenuate the magnitude and duration of post-task shifts in tonic accommodation. It is proposed that individuals with a deficit in sympathetic inhibition may therefore be predisposed to anomalies of accommodative adaptation. However, the mechanism by which the oculomotor system responds to such predisposition is at present obscure.

Accommodation, Ocular↗

PubMed1991

Effect of a topical beta-adrenergic receptor antagonist on the dynamics of steady-state accommodation.

The ocular accommodation response to a stationary near target exhibits microfluctuations which are characterized by two dominant components of activity: a low-frequency component (LFC: less than 0.5 Hz) and a high-frequency component (HFC: 1.0-2.2 Hz). We have shown recently that there is a significant correlation between the frequency of arterial pulse (AP) and the peak frequency of the HFC. If the mechanisms by which AP induces the HFC are intraocular they are likely to involve both rhythmic variations in choroidal blood flow and intraocular pressure (IOP) pulse: the former inducing changes in ciliary ring diameter from pulsatile blood volume changes in the ciliary body, the latter producing changes in effective lens power following small shifts in lens position or, with each drop in IOP, reduced resistance to inherent lens substance and capsule elasticity. In addition to its well-known ocular hypotensive effect, topical instillation of the beta-adrenergic receptor antagonist timolol maleate has been shown to reduce significantly the magnitude of the IOP pulse, an effect that has been attributed to the vasoconstrictive action of the drug on the choroidal vasculature. Using a modified Canon IR optometer we report on the effect of 0.5% timolol maleate on the accommodative microfluctuations for a group of 10 emmetropic subjects viewing a target monocularly at a distance of 25 cm. Following a double-blind protocol against a saline control, timolol was shown to reduce the rms for both LFCs and HFCs. An experiment to separate local from systemic effects involved four subjects whose treated and untreated eyes were examined to determine the effects of the consensual reduction in IOP: the results on microfluctuations in the untreated eyes were equivocal but the correlation between arterial pulse frequency and location of the peak frequency of HFC was maintained. The results show that factors relating to IOP and vasculature will affect the magnitude of accommodative microfluctuations.

Accommodation, Ocular↗

PubMed1991

Case payment in Australian hospitals: any skeletons in the cupboard?

This paper examines two major concerns with the proposal to introduce case payment for Australian hospitals. The first relates to the potential negative impact on government budgetary outlays of an open-ended payment system based on output and the second to inherent incentives that may jeopardise quality of care. A number of options for capping payments are presented and the impact of the U.S. Medicare prospective payment system on quality described.

Australia↗

PubMed1990

The frequency characteristics of accommodative microfluctuations for central and peripheral zones of the human crystalline lens.

Temporal variations in the nominally steady-state accommodation response can be characterized approximately by two principal regions of dominant activity: a low frequency region (LFR less than 0.6 Hz) and a high frequency region (HFR greater than 1.0 Hz). The observed changes of activity in the LFR induced by varying stimulus conditions has led to the proposal that this region may be utilized as an error detector in the accommodation feed-back loop. The role of fluctuations in the HFR is, however, equivocal particularly as several reports have shown their magnitude to be positively correlated with pupil size. The implication is that HFRs are a consequence of the mechanical and elastic properties of peripheral rather than central zones of the crystalline lens and hence do not contribute to the accommodation control process. The aim of the study was to compare the incidence and magnitude of microfluctuations in LFRs and HFRs for central and peripheral lens zones when viewing a near target. Accommodation was measured continuously with a modified Canon Autoref R1 infra-red optometer on five young emmetropic subjects. We show that although the total power of the microfluctuations is reduced in the periphery, the form of the power spectra is similar for central and peripheral zones. Thus rather than being spurious effects caused by the periphery of the lens HFRs are present for both central and peripheral lens zones.

Accommodation, Ocular↗

PubMed1990

Arterial pulse modulates steady-state ocular accommodation.

Rapid and continuous fluctuations in ocular focus are known to occur when the eye views a stationary target. The advent of high-speed infra-red optometers has established that these microfluctuations of ocular accommodation have two dominant components: low frequency of less than 0.6 Hz and high frequency between 1.0-2.3Hz. Although the retinal image blur associated with microfluctuations has the potential to guide and maintain optimum accommodation levels, there is no consensus with regard to the respective contribution of each of the dominant frequency components. Using a newly-designed measurement and recording system we show that, when viewing a stationary target located at 25cm, individuals exhibit little variation in the frequency of low frequency components but significant variation in high frequency components. Simultaneous measurements of ocular accommodation and systemic arterial pulse demonstrate that the variation in high frequency component is significantly correlated with arterial pulse frequency. Since control experiments indicate that the microfluctuations are derived from activity of the crystalline lens our observations could provide the basis for a non-invasive method of assessing the effects of arterial pulse on ciliary body/choroidal vasculature, the vitreous/lens interface and intraocular pressure. Further, it is feasible that under certain conditions an abnormal increase in the magnitude of arterial pulse may affect the aggregate nature of accommodative microfluctuations to an extent that disrupts the normal control processes maintaining optimum retinal contrast during sustained near vision.

Accommodation, Ocular↗

PubMed1989

The effect of pupil size on static and dynamic measurements of accommodation using an infra-red optometer.

The study examines to what degree the output of the Canon Auto-ref R1 infra-red (IR) optometer is affected by variations in pupil size for both static measurement of refractive error and for continuous recording of accommodation when switched to its modified mode of operation. In the normal static mode of operation the measurement of refractive state simply depends on the position of the peak photodetector output for each of three meridians: it does not depend on signal amplitude and hence pupil size. However, in continuous mode the actual output of a single photodiode is measured and the measurement is susceptible to changes in pupil size that occur within the area of the exit pupil utilized by the instrument. Using static and dynamic recording on model and human eyes the study shows that a 10% reduction in output signal relative to the maximum output level (for a constant stimulus) occurs for pupil sizes of 3.9 mm. The relatively small exit pupil has important advantages with regard to the use of mydriatic drugs and task-induced changes in pupil diameter.

Accommodation, Ocular↗

PubMed1987

The finance/marketing interface in hospitals.

Almost half of U.S. hospitals now have a marketing function. This new senior level function impacts the roles, responsibilities and routines of other functions. Hospital marketing's impact on planning and public relations have been addressed. This article discusses why the transition to aggressive marketing will affect finance and how the two functions might forge a working partnership.

Feasibility Studies↗