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Biomedical subjects

R J Jacobs

Publications and source records attributed to R J Jacobs.

At least 37 records · Page 2Linked to original sources
PubMed1996

A cost-effectiveness analysis of OKT3 induction therapy in cadaveric kidney transplantation.

We evaluated the cost-effectiveness of a standard immunosuppressive regimen versus an OKT3 induction regimen in cadaveric kidney transplant recipients. Cost estimates were based on results from a five-center randomized trial comparing the safety and efficacy of OKT3 induction with a conventional triple-drug regimen and financial data from the National Cooperative Transplantation Study, the Medicare Provider and Analysis Review database, and other sources. Patients received OKT3 (5 mg/day) by intravenous (IV) bolus injection for 10 to 14 consecutive days in conjunction with azathioprine, prednisone, and the delayed addition of cyclosporine (CsA) on day 11 (n = 105) or a conventional immunosuppressive regimen consisting of CsA, azathioprine, and prednisone (n = 102). The following measures were used to evaluate the two regimens: costs incurred between transplantation and graft failure; the effectiveness of the two regimens as defined by length of graft survival; and cost-effectiveness ratios through 5 years of observed follow-up and modeled through the expected duration of graft survival. Results showed that OKT3 induction uniformly adds $8,219 to the cost of the transplant hospitalization. However, most of this cost is offset by a reduction in the cost of treating rejection episodes in the OKT3 group (P = 0.002). A trend toward improved graft survival was detected in the OKT3 group (P = 0.158). Through 5 years of observed follow-up, costs per year of graft survival are $30,474 with OKT3 versus $32,687 with the conventional regimen. Modeled through the expected duration of graft survival, OKT3 induction costs $8,335 for each additional year of graft survival. Results are fairly insensitive to wide variations in baseline assumptions. We conclude that OKT3 induction improves the cost-effectiveness of kidney transplantation.

Anti-Infective Agents↗
PubMed1993

Subjective and objective assessment of soft bifocal contact lens performance.

Subjective and objective techniques were used to assess the on-eye performance of soft bifocal contact lenses. In the subjective technique a young observer whose accommodation had been paralyzed with a cycloplegic agent was fitted with the contact lens type under investigation and aligned with a Maxwellian view Badal optometer using a bite-bar. Visual acuity was measured as a function of both target vergence (0.00 to -4.00 D) and pupil size (1 to 5 mm). Aspheric, concentric, and diffractive soft bifocal contact lens designs were investigated. Diffractive and concentric bifocal designs with +2.00 D near additions showed "twin peaks" of visual acuity with one peak at 0.00 D target vergence (equivalent to distance viewing) and the second at -2.00 D target vergence (equivalent to a target at 50 cm). Some aspheric designs produced a relatively constant visual acuity across this vergence range, whereas others gave poor acuity at near. Visual acuity with the Echelon diffractive lens was relatively unaffected by pupil size, confirming theoretical predictions. Visual acuity with concentric designs was also relatively free of pupil size effects. In the objective technique, the variation in surface power across the lens was assessed using video-keratography. This technique provided an elegant means of visualizing the power profile of the lens. The location of the zones of increased power and the magnitude of power variations allowed an accurate prediction of the visual performance measured subjectively. Temporal displacement of lenses may explain the occasions where visual performance did not vary with pupil size.

Accommodation, Ocular↗
PubMed1993

Pseudocyst of the auricle.

BACKGROUND: Pseudocyst of the auricle is a benign swelling of the ear characterized by collection of fluid within an unlined intracartilaginous cavity. The etiology and pathogenesis of this disorder remain unknown. Various forms of management have been described in several case reports and small series. OBJECTIVE: Description of a surgical procedure for successful management of pseudocyst of the auricle. METHODS: Case report of a patient who declined nonsurgical treatment options following failed management with aspiration. RESULTS: The described procedure resulted in cure of the pseudocyst with good cosmetic outcome. CONCLUSION: Pseudocyst of the auricle can be successfully managed by surgical excision of the anterior wall of the cyst.

Adult↗
PubMed1993

Economic impact of hospitalizations for lower abdominal adhesiolysis in the United States in 1988.

Much has been written about adhesion formation and prevention. Little is known about the number and cost of hospitalizations during which adhesiolysis is performed. This report describes the number of hospitalizations and days of care attributable to adhesiolysis in the United States and estimates the costs associated with these stays. The cost per hospital day and associated surgeons' fees are based on prevailing nationwide charges. During 1988, there were 281,982 hospitalizations during which adhesiolysis was performed, accounting for 948,727 days of inpatient care. These hospitalizations were responsible for an estimated $1,179.9 million in expenditures, of which $925.0 million was associated with hospital costs and $254.9 million with surgeons' fees. This estimate does not include outpatient costs and indirect costs. The results of this study demonstrate substantial costs associated with hospitalizations for adhesiolysis. Further understanding and prevention of adhesions may help to reduce unnecessary morbidity and mortality rates.

Abdomen↗
PubMed1991

Radiation dose in temporomandibular joint zonography.

Temporomandibular joint morphology and function can be evaluated by panoramic zonography. Thermoluminescent dosimetry was applied to evaluate the radiation dose to predetermined sites on a phantom eye, thyroid, pituitary, and parotid, and the dose distribution on the skin of the head and neck when the TMJ program of the Zonarc panoramic x-ray unit was used. Findings are discussed with reference to similar radiographic techniques.

Humans↗
PubMed1989

Effect of defocus on visual acuity as measured by source and observer methods.

The relation between refractive error and visual acuity has been measured by two very different methods. In one called "source methods," emmetropes or corrected ametropes view defocused stimuli presented on projection screens or photographs. In the type called "observer methods," focused stimuli are presented to the observers who are either uncorrected ametropes or emmetropes defocused by lenses placed (usually), in the spectacle plane. The study reported in this paper demonstrates for the first time that these two methods of defocusing retinal images and their effects on visual acuity can be correlated. Results show that the source method of producing defocus could be used interchangeably with the observer method in investigating the rates of change of visual acuity with defocus for young normal observers. The angular diameter of the defocused image of a point, the blur disc diameter in object space, allows the two methods to be compared. Although the results show that the two methods are highly correlated, they show that the source method gives a statistically but not clinically significant lower acuity. The results of both methods are used to derive an equation linking refractive error, visual acuity, and pupil diameter.

Accommodation, Ocular↗
PubMed1989

Effect of defocus on blur thresholds and on thresholds of perceived change in blur: comparison of source and observer methods.

The defocus levels required for normal observers to notice the first perceptible blur of a clear test target (blur threshold) and the least perceptible change in the degree of blurriness of an already blurry target (threshold of perceived change in blur) were measured using both the source and observer methods. In the source method observers viewed defocused stimuli presented on a projection screen, whereas in the observer method focused stimuli were presented to observers who were defocused using lenses placed in the spectacle plane. Blur thresholds were found to be dependent on target size and when the Landolt ring targets were near threshold acuity size blur thresholds were as small as 0.10 D. For larger target sizes (0.6 log min arc or more above threshold acuity size) the blur thresholds remained relatively unchanged and were about 0.18 D. Thresholds of perceived change in blur were found to be independent of the initial defocus level. Measurements of the threshold of perceived change in blur were found to be 0.05 to 0.07 D, which is much smaller than the blur threshold values. Comparison of results from the two methods of producing defocus indicate that the source and observer methods can be used interchangeably. However, for the same angular blur disc diameter, the blur thresholds found with the source method were significantly lower than those found with the observer method.

Adult↗
PubMed1988

An analysis of the fluid phase C1q binding assay. The effect of endogenous C1q on the precipitation and detection of an immune complex model.

We examined the effect of endogenous C1q on the sensitivity of the fluid-phase C1q binding assay (C1qBA) in detecting an immune complex (IC) model, heat-aggregated IgG (HAIgG), at concentrations of 10-10,000 micrograms/ml sample. Results in normal human serum (NHS) or plasma (NHP) were compared with those in heat-inactivated NHS (NHS/56) in which most endogenous C1q was depleted by heat denaturation. Higher HAIgG concentrations were required in NHP and NHS to produce the same 125I-C1q precipitation seen in NHS/56. This decreased sensitivity varied from 70% at low HAIgG concentrations to 0% at high concentrations, as predicted for a large pool of endogenous C1q, in equilibrium with 125I-C1q, but in excess of that which could bind to all but the highest concentrations of IC model. In serum depleted of functional C1q on an immunoadsorbant of HAIgG, the precipitation of radiolabeled HAIgG under C1qBA conditions was concentration dependent and generated a saturation curve, showing that only a fraction of IC are usually precipitated in this assay. HAIgG precipitation was enhanced 1.4-fold in NHS/56 (8 micrograms C1q/ml) and three-fold in NHS (67 micrograms C1q/ml) suggesting that IC size is increased by endogenous C1q. In dual label experiments using 131I-HAIgG, the precipitation of 125I-C1q in NHS/56 was directly proportional to IC model precipitation, but markedly discordant in NHP, showing the measurement of IC in heat-inactivated sera superior to that in native serum. A comparison of the C1q:HAIgG ratio in PEG precipitates with that in samples, indicated that equilibrium was established between C1q and IC model. Thus the precipitation of 125I-C1q in the C1qBA represents (1) the fraction of total C1q bound to IC, and (2) the fraction of IC precipitated by PEG.

Antigen-Antibody Complex↗
PubMed1988

Assessment of contrast sensitivity of patients with macular disease using reduced contrast near visual acuity charts.

A set of near Bailey-Lovie logMAR letter charts that varied in contrast from 0.40 dB (C = 0.95) to 58.0 dB (C = 0.001) were used to measure the middle and high spatial frequency range of the contrast sensitivity function (CSF) of 15 subjects with age-related maculopathy (ARM) and 15 age-matched normal subjects. The letter charts were shown to have good test-retest reliability. Compared with measures made using CRT generated square wave gratings of variable contrast and spatial frequency they were also shown to provide a valid measure of CSF in the mid to high spatial frequency range. The 20.0 dB letter chart alone was shown to be a good screening device for macular disease. The letter charts do not provide a measure of the peak of the CSF and a supplementary test of contrast sensitivity is needed to quantify contrast sensitivity at a low spatial frequency. Three measures are proposed as necessary to document foveal visual capability of patients with macular disease: distance logMAR visual acuity to measure high spatial frequency resolution, visual acuity with letter charts of 20 dB contrast to assess mid spatial frequency resolution; and contrast sensitivity for the detection of an edge to estimate contrast sensitivity for larger objects.

Aged↗
PubMed1987

Reliability and validity of simple photographic plate tests of contrast sensitivity.

Sets of edge and square wave grating photographic plates of varying contrasts were used to measure the mid to low spatial frequency range of the contrast sensitivity function (CSF) of 20 subjects with evident ocular disease and 20 age-matched normal subjects. Both plate tests were shown to have good test-retest reliability and to correlate well with electronic cathode ray tube (CRT) measures of CSF. The edge test, when administered in 2-dB steps of ascending contrast, has optimum sensitivity of 0.70 and specificity of 0.84 for detecting the patient with ocular disease with a fail criterion of less than 38 dB. A measure of edge contrast sensitivity was also shown to be a good predictor of the peak of the CSF, which is shown to be largely independent of the visual acuity of the subject. The 2 c/deg and 4 c/deg plates did not provide more information about the visual difficulties of subjects than the edge test. We advocate the use of an edge test as a simple clinical measure of low spatial frequency contrast sensitivity that provides information about visual dysfunction not provided by a measure of visual acuity.

Adult↗
PubMed1985

Simulating refractive errors: source and observer methods.

There are two principal methods of simulating refractive errors. Either the retinal image can be defocused by an optical system, usually a positive lens, placed in front of an observer's eye (observer method), or the source of the retinal image can be defocused as it is projected onto a screen or photograph (source method). There are significant differences between the two methods, differences that make it difficult to compare results. However, the source method, which is the more artificial, seems to be superior for a number of reasons. The results of these two methods can be compared using a common or interchangeable parameter for specifying the level of defocus. A convenient parameter is the size of the defocused image of a point, measured either in image space (linear or angular diameter on the retina) or in object space (angular diameter of the blur disc projected back into object space), with the angular diameter measured from the respective nodal point of the eye. Methods of measuring the angular blur-disc diameter for both methods are discussed and the validity of the formula omega = D delta L, is investigated, where omega is the angular diameter of the blur disc, D is the observer's pupil diameter, and delta L is the dioptric defocus.

Humans↗
PubMed1985

The technical problems of producing photographic prints for the measurement of human contrast thresholds.

Whilst most optometrists today are aware of the need for a practical method of measuring the contrast sensitivity function (CSF), cost and length of testing have usually precluded this measurement. As the Arden Grating Test is a screening test for normal CSF, and since many patients with low vision cannot see any of its gratings, there is a need for a test with an extended contrast range which is calibrated to allow quantitative measurement of contrast thresholds in the clinic. This paper discusses the problems associated with the use of the photographic process to manufacture such a test. A series of stimuli covering a wide range of contrasts were manufactured photographically and evaluated photometrically and psychophysically to validate the photographic process. The results show that the photographic techniques can be controlled sufficiently to enable the manufacture of stimuli of the required contrasts and that, at low contrasts where calibration is inaccurate or impossible, the contrasts produced are linearly related to exposure. The results also show that the illumination and observation conditions need to be accurately controlled for the plate contrast to be unaffected by veiling glare.

Humans↗
PubMed1984

Mechanisms of visual loss in corneal edema.

Although visual disability from corneal edema is a well-recognized clinical finding, it is not easily confirmed by routine visual assessment. A more reliable assessment of visual changes resulting from corneal edema of varying origins is achieved by measurement of changes in the contrast sensitivity function. The measurements can be sensitized by the presence of a glare source to allow a more accurate determination of the nature of the visual loss. Even in the absence of a measurable loss of visual acuity, corneal edema leads to diminished visual function. The magnitude and type of this loss is dependent on the origin of the edema and the site of the corneal response.

Corneal Diseases↗
PubMed1983

Generation of low m.w., C3-bearing immunoglobulin in human serum.

The generation of low m.w. C3-bearing immunoglobulin (lg) in normal human serum by an immune complex (IC) model was investigated in vitro by using discontinuous sucrose density gradient centrifugation (DGC) and an assay that measures C3-bearing Ig. In this method developed to measure circulating IC, all C3 and C3-bearing material is precipitated from serum by using anti-C3 sera in C3d antibody excess, and immune precipitated, C3-bearing Ig is quantitated by the uptake of 125I-5S-anti-IgG. When plasma from patients with clinically active systemic lupus erythematosus was assayed after DGC, most of the reactive material was low m.w. (7S), rather than greater than or equal to 19S as expected for IC, in agreement with a previous report. Low m.w., C3-bearing Ig was found in normal EDTA plasma after extended storage at -29 degrees C but not after storage at -70 degrees C. Such material was also generated in normal human serum during incubation at 37 degrees C and its generation was stimulated by the addition of an IC model, high m.w., heat-aggregated IgG (HMW-HAIgG). In experiments in which the participation of serum IgG was monitored by the addition of 125I-7S-IgG and 131I-HMW-HAIgG was used as an IC model, low m.w., C3-bearing Ig was generated exclusively from serum IgG and the amount generated was proportional to the concentration of 131I-HMW-HAIgG. No significant decrease in sedimentation of 131I-HMW-HAIgG was observed, but the ability of anti-C3 sera to precipitate 131I-HMW-HAIgG decreased 66% 4 hr after initial C activation. These results indicate that generation of nascent C3b in serum results in its interaction with monomeric serum IgG, producing low m.w., C3-bearing IgG. In addition, the data indicate that circulating IC that activate C have a brief time span during which they can be detected by methods that depend upon the binding of C3.

Animals↗
PubMed1978

Visual detection of commencement of aircraft takeoff runs.

Among other things, airport control towers should be sited so that controllers can readily detect whether an aircraft cleared for takeoff has commenced its takeoff run. The detection of movement is not well enough understood to enable confident prediction that a particular site for a tower will enable commencement of takeoff run to be easily observed. A field study was undertaken to establish detection times for commencement of takeoff run by groups of trained and trainee air traffic controllers and untrained observers. It was found that the mean response of observers occurs when the aircraft is displaced about 5' of arc, a value essentially independent of observer experience, observation distance, aircraft velocity, and the clarity with which the aircraft can be seen. Binoculars reduce the mean response time and response variability, although not as much as might be expected. Domains within which control towers can be located to enable detection of takeoff runs within 2 s and 4 s are defined.

Aerospace Medicine↗