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J R Jiménez

Publications and source records attributed to J R Jiménez.

17 recordsLinked to original sources
PubMed2006

Computed tomography in children with cystic fibrosis: a new way to reduce radiation dose.

AIMS: To determine whether the monitoring of respiratory disease progression in children with cystic fibrosis (CF) can be made using six pre-selected computed tomography (CT) cuts in lieu of the conventional full study. METHODS: Forty one lung CT scans from 21 paediatric patients with CF were analysed. The Bhalla and Nathanson scores of the total lung CT and the six pre-selected CT cuts were compared. RESULTS: The Bhalla mean score of the total lung CT evaluated by two radiologists was 5.62. It was 5.36 when just the six pre-selected sections were evaluated. The difference between means was not statistically significant. The Nathanson mean score of the total lung CT evaluated by both radiologists was 66.11; it was 66.51 when just the six pre-selected sections were evaluated. The difference between means was not statistically significant. The mean total radiation dose from a single whole lung CT scan was 716.22 mGy.cm. A dose of 250.66 mGy.cm was estimated if only six sections were used, with a reduction in radiation of about 65%. CONCLUSION: It is possible to obtain the same radiological information from six pre-selected CT cuts as it is from a full pulmonary CT scan, thereby markedly reducing radiation exposure for children who will require repeat investigations in the future.

Adolescent↗
PubMed2003

The effect of pupil size on binocular summation at suprathreshold conditions.

PURPOSE: To determine the influence of retinal illuminance on monocular or binocular visual reaction time (VRT). METHODS: On two normal subjects, uniform circular stimuli were presented with respect to a reference stimulus at the fovea under suprathreshold conditions, and the detection of positive and negative luminance variations was recorded. Binocular and monocular reaction times were measured (by the index finger pressing on a mouse key) for viewing with both natural and artificial pupils. RESULTS: Binocular reaction times were shorter than monocular reaction times; nevertheless, this binocular-summation effect was less marked in trials with the artificial pupil. Analyses of binocular-summation ratios for contrast changes for both pupil types indicated maximum and minimum binocular-saturation values depending on contrast variations in both positive and negative luminance changes. CONCLUSIONS: Binocular summation can be influenced by pupil size under suprathreshold conditions. Results are discussed in terms of retinal illuminance and cortical pupil response mechanisms.

Adult↗
PubMed2002

Impact of induced aniseikonia on stereopsis with random-dot stereogram.

In this work, we evaluate the impact of induced aniseikonia on stereopsis. For this, we determined the disparity range (maximum disparity), a parameter related to the size of the physical region that can be perceived stereoscopically. A significant decline in the disparity range was detected with aniseikonia induced by size lenses of 3% for five of the seven observers tested; 5% was necessary for the other two observers. The data indicate the influence of aniseikonia in stereopsis and the need to minimize such impact. These results may be useful in surgical processes such as the correction of pseudophakic patients and refractive surgery in which aniseikonia can be induced to alter the binocular function of the patient.

Adult↗
PubMed2002

Maximum disparity with acuvue bifocal contact lenses with changes in illumination.

PURPOSE: To assess the visual performance of Acuvue bifocal contact lenses at different illumination levels using a stereoscopic parameter, the maximum disparity. We compare the results with those for progressive spectacle lenses. METHODS: We used a modified Wheatstone stereoscope and random-dot stereograms (RDS) as tests. The maximum disparity was measured for each observer at different luminance levels. RESULTS: Maximum disparities did not show statistically significant differences for a wide range of luminance levels with contact lenses. The maximum disparities found when some contact-lens users wore progressive spectacle lenses were similar. CONCLUSIONS: The results show that the Acuvue bifocal lenses offer good performance for a near visual task, in this case the maximum disparity, for changes in illumination and are similar to that with progressive spectacle lenses.

Adult↗
PubMed2002

Binocular summation of chromatic changes as measured by visual reaction time.

We determined visual reaction times to monocular and binocular changes in the luminance of isochromatic stimuli and to monocular and binocular changes in the color of isoluminant stimuli. Two isoluminant color changes were tested: chromatic variations along the red-green axis of Boynton's (1986) two-stage color vision model and chromatic variations along the yellow-blue axis of the same model. The results indicate a greater degree of binocular summation for luminance change than for color change. This result was largely independent of the motor component of reaction time.

Adult↗
PubMed2000

Human renal mesangial cells are a target for the anti-inflammatory action of 9-cis retinoic acid.

Mesangial cells play an active role in the inflammatory response to glomerular injury. We have studied in cultured human mesangial cells (CHMC) several effects of 9-cis retinoic acid (9-cRA), an activator of both retinoic acid receptors (RARs) and retinoid X receptors (RXRs). 9-cRA inhibited foetal calf serum-induced CHMC proliferation. It also prevented CHMC death induced by the inflammatory mediator H(2)O(2). This preventive effect was not due to any increase in H(2)O(2) catabolism and it persisted even when both catalase and glutathione synthesis were inhibited. Finally, 9-cRA diminished monocyte adhesion to FCS-stimulated CHMC. Interestingly, the retinoid also inhibited in FCS-stimulated cells the protein expression of two mesangial adhesion molecules, fibronectin and osteopontin, but it did not modify the protein expression of intercellular adhesion molecule-1 and vascular adhesion molecule-1. All major RARs and RXRs isotypes were expressed in CHMC regardless of the presence or absence of 9-cRA. Transcripts to RAR-alpha, RAR-beta and RXR-alpha increased after incubation with 9-cRA whereas RXR-gamma was inhibited, suggesting a major role for RARs and RXRs in 9-cRA-anti-inflammatory effects. 9-cRA was toxic only at 50 microM (a concentration 50 - 5000 times higher than required for the effects above). Cell death occurred by apoptosis, whose onset was associated with a pronounced increase in catalase activity and reduced glutathione content, being more effectively induced by all-trans retinoic acid. Modulation of the oxidant/antioxidant balance failed to inhibit apoptosis. We conclude that mesangial cells might be a target for the treatment of inflammatory glomerulopathies with 9-cRA.

Adult↗
PubMed2000

Associated phoria in relation to stereopsis with random-dot stereograms.

In the present work, we use random-dot stereograms to test a possible relationship between associated phoria and stereopsis. We determined, using a modified constant-stimulus method, the disparity range that indicates the maximum range at which stereoscopic correspondence can be achieved. A total of 27 observers took part in the experiment. The value of the disparity range as a function of the associated phoria (measured with a Mallet unit) seems to indicate that greater associated phoria (fixation disparity) correlates with a deterioration in stereoscopic vision, reducing the disparity range and therefore the space region in which stereoscopic vision can be attained.

Adult↗
PubMed2000

Changes in stereoscopic depth perception caused by decentration of spectacle lenses.

The effect that decentered spectacle (ophthalmic) lenses exert on depth perception has been studied, evaluating stereopsis through the disparity range (maximum horizontal disparity) for random-dot stereograms (RDS). The results show that variations in fusional convergence due to increments of decentration can diminish the stereopsis in observers, reducing the region within which stereoscopic correspondence can take place. Decreases in disparity ranges were found for vertical and horizontal prismatic effects, although the prismatic effect necessary for this was less in the vertical case. A decreased disparity range has also been confirmed with figural-stimuli stereograms and using prisms for generating the prismatic effects.

Adaptation, Ocular↗
PubMed1997

Influence of the luminance and opponent chromatic channels on stereopsis with random-dot stereograms.

The present work examines the relationship between random-dot stereograms (via the disparity range parameter) and color-vision mechanisms (via the luminance channel and red-green and tritan directions at isoluminance). The results clearly indicate that the variations in the stereograms along red-green confusion lines contribute to stereopsis. Stereoscopic perception depends on spatial information for stereograms generated with variations along tritan confusion lines. For observers who perceive stereopsis via tritan directions, the results show a gradation in the disparity range, with the disparity range for stereograms generated by luminance variations being greater than for stereograms generated in red-green directions; the latter range is, in turn, greater than for stereograms generated along tritan directions.

Color Perception↗
PubMed1995

Influence of the luminance signal and red-green and yellow-blue opponent chromatic signals in figural-stimuli stereograms.

The influence of color signals on stereopsis has been studied using figural-stimuli stereograms with variations introduced according to the opponent chromatic channels (red-green and yellow-blue), derived from Boynton's color-vision model. We used wallpaper stereograms, which enable the rank-order disparity ranges of the chromatic and luminance signals to be compared with the rank-order disparity range of proximity, a particular spatial configuration of the stereogram in which there are no variations in chromaticity and/or luminance. The results indicate that both chromatic signals contribute to stereopsis as does the luminance signal, contradicting the model of Hubel and Livingstone. The results also show there are no clear dependencies upon the kind of signal processed, as luminance and chromatic variations are processed with the same efficiency.

Color Perception↗
PubMedDate not supplied

[Therapeutic embolization of renal tumors].

We present our casuistry of 17 embolized kidney adenocarcinomas with fibrin sponge and/or metal spirals. In 13, the embolization was preoperative and in 4 palliative. In two out of the latter group a control aortogram revealing no rechanneling of the renal artery, was performed several weeks later. We mention the clinico-biochemical disorders caused by embolization and the advantages of the different kinds of emboles used and we come to the conclusion that the procedure considerably facilitates the surgical removal and is of value as a palliative method in certain circumstances.

Adenocarcinoma↗