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Biomedical subjects

R Navarro

Publications and source records attributed to R Navarro.

At least 91 records · Page 5Linked to original sources
PubMed1994

Monochromatic modulation transfer function of the human eye for different pupil diameters: an analytical expression.

The modulation transfer function (MTF) of human eyes for different pupil sizes was measured in a group of normal young subjects by use of a double-pass method. Measurements were carried out in the fovea, with monochromatic red light, paralyzed accommodation, artificial pupils, and optimum spherical refraction in each subject. For each pupil size both the averaged MTF and the intersubject variability were calculated. MTF's were approximated by the sum of two exponential functions. This three-parameter function provides a better approximation to our ocular MTF's than do most of the previous parametric models (usually one exponential), especially at intermediate and high spatial frequencies. Further curve fitting of the parameters allowed us to obtain a general expression for the mean MTF as a function of both pupil diameter and normalized spatial frequency. This equation summarizes our estimates of the average monochromatic retinal image quality of the human eye for any pupil diameter with good accuracy and in a compact way, which allows one to incorporate the eye's image quality easily in any particular study.

Adult↗
PubMed1994

Double-pass and interferometric measures of the optical quality of the eye.

We compare two methods for measuring the modulation transfer function (MTF) of the human eye: an interferometric method similar to that of Campbell and Green [J. Physiol. (London) 181, 576 (1965)] and a double-pass procedure similar to that of Santamaria et al. [J. Opt. Soc. Am. A 4, 1109 (1987)]. We implemented various improvements in both techniques to reduce error in the estimates of the MTF. We used the same observers, refractive state, pupil size (3 mm), and wavelength (632.8 nm) for both methods. In the double-pass method we found close agreement between the plane of subjective best focus for the observer and the plane of objective best focus, suggesting that much of the reflected light is confined within individual cones throughout its double pass through the receptor layer. The double-pass method produced MTF's that were similar to but slightly lower than those of the interferometric method. This additional loss in modulation transfer is probably attributable to light reflected from the choroid, because green light, which reduces the contribution of the choroid to the fundus reflection, produces somewhat higher MTF's that are consistent with the interferometric results. When either method is used, the MTF's lie well below those obtained with the aberroscope method [Vision Res. 28, 659 (1988)]. On the basis of the interferometric method, we propose a new estimate of the monochromatic MTF of the eye.

Adult↗
PubMed1994

Justifying the cost of pharmacy's clinical services.

Internally, when pharmacy managers have attempted to argue for the positive contribution of pharmacy on hospital and physician costs, they were generally unable to definitively prove the linkage between drug use and outcome. They were, however, able to demonstrate an ability to reduce the overall pharmacy program costs by applying a full array of cost-containment strategies to their internal executives as well as plan sponsor's benefit managers and consultants.

Cost Control↗
PubMed1993

Relative contributions of optical and neural limitations to human contrast sensitivity at different luminance levels.

The relative contributions of optical and neural constraints on human contrast sensitivity as a function of spatial frequency were assessed for a range of luminances. First, the overall two-dimensional contrast sensitivity function (CSF) was obtained for three eyes at three luminances (0.05, 0.5 and 20 cd/m2) using a standard two-alternative forced-choice procedure. Second, the two-dimensional modulation transfer function (MTF) of the optics was measured for the same eyes and pupil sizes using a hybrid optical-digital method. The two-dimensional neural transfer function (NTF) was obtained as the ratio between the CSF and the MTF. Minor factors, such as the effect of cone aperture, were also considered in the computations. Our results show that at all luminances, the fall off in contrast sensitivity at high spatial frequencies is mainly due to optical factors. The losses in contrast sensitivity with decreasing luminance are, however, primarily due to noise limitations.

Contrast Sensitivity↗
PubMed1993

Modulation transfer of the human eye as a function of retinal eccentricity.

We measured the monochromatic image quality of the eye across a wide visual field (120 degrees), with natural pupil (4 mm) and accommodation (3 diopters). The method is based on the acquisition and the posterior processing of double-pass aerial images of a point source imaged on the retina, which was kept at a fixed distance from the eye at all retinal eccentricities. The two-dimensional modulation transfer functions (MTF's) computed from the aerial images show that astigmatism is the dominant monochromatic aberration in both the fovea and the periphery and is also the major cause of variability among individuals. We found a slower decline in optical quality with eccentricity than had been found by previous measurements. Our foveal results are in close agreement with those of Campbell and Gubisch [J. Physiol. (London) 186, 558-578 (1966)], but off-axis optical quality is much better than found previously by Jennings and Charman [Am. J. Optom. Physiol. Opt. 55, 582-590 (1978); Vision Res. 21, 445-454 (1981)]. The optical system of the eye seems to follow a wide-angle lens design: the optical quality in the center (fovea) is not particularly good (it is far from the diffraction limit at this pupil size), but the modulation transfer function remains roughly constant for a wide visual field.

Accommodation, Ocular↗
PubMed1993

Effects of aging in retinal image quality.

The retinal image quality characterized by the modulation-transfer function of the eye was measured for two groups of subjects aged in the late twenties and mid sixties, respectively. In both groups, we obtained modulation transfer functions by using a double-pass method under the same experimental conditions: 4-mm artificial pupil, paralyzed accommodation, and objective control of the refractive state and centering. Results showed lower values of modulation in the retinal image for older subjects compared with the younger subjects. The modulation transfer function ratio is similar to that previously found for contrast-sensitivity measurements with subjects in the same age groups. These results suggest that a significant fraction of the loss in spatial vision with age has an optical origin. Apart from the well-known increase in intraocular scattering, there also appears to be an increment in ocular aberration that causes an additional reduction in the contrast of retinal images.

Adult↗
PubMed1993

DNA analysis of haemophilia A families from southern France. Experience of a hospital laboratory.

A sample of 101 individuals from 19 unrelated families from Southern France affected with haemophilia A was studied in our laboratory from 1990 to 1992. The aim of the analysis was to define the carrier status of women related to a haemophiliac, or to find an informative DNA marker for further prenatal diagnosis in obligate carriers. Three intragenic (BclT/intron 18, XbaI/intron 22, AlwNI/intron x7) and two extragenic polymorphisms (TaqI/St14, BglII/DX13) were used for this study. The tested population exhibited some original characteristics, including a lower rate of heterozygosity for the FVIII BclI polymorphism and a number of specificities for the St14 RFLP. We also compared the different methodologies available for each RFLP in a routine diagnostic service, and determined a strategy for linkage analysis in our population.

Adult↗
PubMed1992

Development of a program of behavior modification directed to the rehabilitation of drug-dependent patients: treatment and follow-up of 223 cases.

The study reports treatment and follow-up of compulsive drug-consuming patients (mainly of coca paste). The program used was based on a behavioral cognitive and instructional model. The traditional functional analysis was modified to include the therapeutical work in seven behavioral areas: (1) drug use; (2) behavior during free time; (3) behavior at work; (4) social behavior; (5) self- and environmental management behaviors; (6) problem solving and decision-making behaviors; (7) recognition, evaluation, and modification of irrational beliefs. For each area objectives, therapeutical procedures, control and evaluation methods, and termination criteria were determined. Patients engaged in a multiple activity program and received individual and group therapy. Out of 223 male patients, 130 were discharged (that is, they fulfilled all the conditions stated by the program) and 93 patients abandoned treatment. For evaluation purposes a test was used to determine the accomplishment of the behavioral objectives. Follow-up interviews after 6 to 72 months showed that although 24 patients relapsed to drug use, 106 (81.48%) of the patients who had finished the program restrained from using drugs and obtained high scores in all seven behavioral areas.

Adolescent↗
PubMed1991

In vitro characterization of rat thymic macrophages.

Thymic macrophages have been isolated from Wistar rats and maintained in long-term culture. Day 1-isolated thymic macrophages expressed MHC class I and II antigens, Thy-1, CR3, CD4, ED1, ED2, as well as acid phosphatase and non-specific esterase activities. Whereas cultured macrophages were positive for the activation antigen recognized by the mAb OX48, which was not expressed after isolation, MHC class II and Thy-1 expression were down-regulated during the culture, but could be induced with human rIL-2 or with Con A-SCM, which are also inducers of IL-2R, a cell-surface marker not expressed on Day 1 or on cultured macrophages.

Animals↗
PubMed1991

Total knee arthroplasty in rheumatoid arthritis. A comparison of the polycentric and total condylar prostheses.

From 1971 to 1985, 393 total knee arthroplasties (TKAs) were performed in patients for rheumatoid arthritis. Of these, 112 used polycentric prostheses and 131 used total condylar prostheses. One hundred seven of the patients with polycentric prostheses and 102 of the patients with total condylar prostheses were followed for a minimum of two years (average, 61 and 55 months, respectively). At the time of the latest examination, nine knees with polycentric prostheses required revision surgery: six for tibial component loosening and instability and three for patellofemoral pain. Five knees with total condylar prostheses required revision: one for chronic instability, one for a late posttraumatic patellar fracture, and three for late hematogenous infections. The total condylar prostheses with patellar resurfacing had better scores for pain (8.5 points) than the polycentric prosthesis without patellofemoral resurfacing (7.0 points). The total condylar prosthesis appeared more durable in terms of fixation, with no evidence of aseptic loosening of femoral or tibial components noted in this series thus far.

Arthritis, Rheumatoid↗
PubMed1991

Rat thymic cultures: morphological and phenotypical characterization.

Rat thymic cultures have been established in order to analyse the morpho-functional characteristics of thymic epithelial and non-epithelial cells in vitro. Stromal cultures, originating from implanted thymic fragments, consist of fibroblasts occupying most of the culture surface, epithelial cells forming discrete colonies, thymocytes and bone marrow-derived cells. Epithelial cells show a low class II MHC antigen expression, which is highly increased in semi-adherent cells, and do not interact with thymocytes. Thymocytes proliferate extensively at the beginning of the culture, but almost disappear at the end of the first week; however, restarting of thymocyte proliferation occurs during the second week of culture. Bone marrow-derived cells include ED- Ia+ CR3- IL-2R- dendritic cells (DC), ED+ Ia+ CR3+ IL-2R+ non-adherent thymic phagocytic cells (PTR) and ED+ Ia- CR3- IL-2R- adherent type 1 and 2 macrophages, derived from PTR. Both PTR and DC establish lympho-stromatic complexes with thymocytes present in the cultures. These results suggest that PTR and DC present in rat thymic cultures belong to different cell lineages, and that they are, respectively, the in vitro equivalents of intrathymic macrophages and interdigitating cells.

Animals↗