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J M Artigas

Publications and source records attributed to J M Artigas.

At least 19 recordsLinked to original sources
PubMed2001

Influence of the luminance level on visual performance with a disposable soft cosmetic tinted contact lens.

The purpose of the present work was to study the effect on visual performance of wearing disposable soft tinted contact lenses for cosmetic purposes. Parameters such as contrast sensitivity (Vistech 6000), colour vision (Farnsworth-Munsell 100-Hue colour test), visual fields (static Goldmann perimetry) and subjective vision (what the wearer feels while wearing the lenses) were studied under different illumination levels in order to check for possible vision losses while wearing these contact lenses at low illumination levels. Sixteen emmetropic subjects were fitted consecutively with seven pairs of different colour lenses (Optima Colors lenses by Bausch & Lomb), and the experimental parameters were measured under four different illumination levels (60, 6, 1, and 0.1 cd/m2; but 15 and 0.3 cd/m2 for the static perimetry) The results obtained showed no statistically significant differences in visual performance between wearing the lenses and not wearing them (p > 0.01), except for the static perimetry, in which statistically significant differences (p < 0.01) occur at eccentricities greater than 30 degrees.

Adolescent↗
PubMed2000

Optic nerve aspergillosis: report of a case diagnosed by fine-needle aspiration biopsy.

The aim of this study was to describe the fine-needle aspiration biopsy (FNAB) procedure in patient with a optic nerve lesion. A case of optic nerve and brain aspergillosis, an infrequent condition that can mimic tumor or tumor-like lesions, is reported. The patient was studied by CT and MRI and definite diagnosis was established by means of an ultrasound-guided FNAB. Specimen preparation revealed the presence of multiple hyphae of Aspergillus fumigatus in the optic nerve lesion. The FNAB procedure is a safe and reliable diagnostic method for suspected intraorbitary tumors and tumor-like conditions especially when other less-invasive modalities have failed to establish the diagnosis and when cytologic confirmation is needed to implement aggressive therapy.

Aged↗
PubMed1998

Characterization of the visual performance with soft daily wear disposable contact lenses.

We investigate the visual performance associated with adaptation to a daily wear soft contact lens on the human eye. For this purpose, we used four parameters, one of which was an objective parameter, while the rest were subjective parameters. The objective parameter was a single quality parameter, a Merit function (Mf) derived from the modulation transfer function (MTF) of the overall [eye + contact lens] system The subjective parameters were the visual acuity (VA), the contrast sensitivity function (CSF) and the standard adaptation criterion of Terry et al. (1993). The normality criterion for the MTF was determined by evaluating the fluctuations of the Mf over a day in five emmetropic observers. Fluctuations with no statistically significant differences in the merit function (p > 0.05) and their standard deviation (8%) defined our standard criterion. The CSF and the VA were similarly measured (for emmetropic observers). The results obtained with emmetropic observers allowed us to establish a standard criterion for the evaluation parameters we propose. When this criterion is applied to daily soft wear disposable contact lenses, their performance proves to be good, since both the objective (MTF) and the subjective parameters (CSF, VA, adaptation criterion) always lie within the range defined by our criterion.

Adaptation, Physiological↗
PubMed1997

Implementations of a novel algorithm for colour constancy.

In agreement with the principles of the relativistic model proposed by Creutzfeldt et al., with the photometric rule (lightness anchoring rule) and with the influence of simultaneous contrast in the appearance of a visual scene, we propose a first-stage mechanism yielding substantial colour constancy. We have defined a set of first-stage colour descriptors, and to test their utility, we have performed a simulation using a Machine Vision System (MVS). The statistical stability of the descriptors for Munsell samples under different illuminants is good.

Algorithms↗
PubMed1997

Influence of the tear film on optical quality of the eye.

The optical quality of the tear film of the eye was tested by measuring the retinal image before and after the break-up time (BUT). An objective method was used based on the evaluation of the retinal image of a point test projected onto the fovea. The loss of an entire tear film would result in a decrease in the optical quality because of corneal irregularities and the formation of an irregular tear lens after the BUT. Our results confirm the expected loss both of non-contact lens wearers and contact lens wearers. Also, the fact that the optical deterioration found after the BUT is greater for contact lens wearers confirms that soft contact lens wear produces a disruption of the tears.

Journal Article↗
PubMed1997

Contact lenses: do they really change the optical performance?

In this investigation the quality of two types of optical correction, hydrogel contact lenses and ophthalmic lenses, was compared by measuring the modulation transfer function (MTF) of the correcting lens plus visual optics system using an objective method. A merit function was defined in order to allow the direct comparison between the optical performance with the two corrections. A study on 10 subjects was undertaken, measuring the MTF of both corrections by using the double pass method. The results show that the optical quality of contact lenses was higher than that with ophthalmic lenses. The contrast sensitivity function (CSF) and visual acuity (VA) were determined as subjective parameters of visual performance.

Journal Article↗
PubMed1997

Human contrast sensitivity in coherent Maxwellian view: effect of coherent noise and comparison with speckle.

Lasers have been used in vision for measuring the neural contrast sensitivity function (CSF) by forming interference fringes on the retina. We distinguish among three kinds of illumination with lasers: incoherent (without noise), Maxwellian or coherent (with coherent noise), and diffuse coherent (with speckle). The three have different characteristics and different CSF's. A coherent imaging system is designed to measure the CSF with fully coherent illumination. This is the CSF of the whole visual system, although it is measured with gratings imaged on the retina. It therefore differs from the neural CSF's measured by other authors with partially coherent illumination. However, the neural CSF's are also obtained in this study with and without noise. The effects of coherent noise and speckle on both the visual system and neural sensitivities are studied and compared. Coherent noise differs from speckle in the following ways: (1) It behaves as a high-pass filter, reducing sensitivity in the low-spatial-frequency range, whereas speckle is a low-pass filter; (2) quantitatively, coherent noise reduces neural sensitivity by a factor k(m) with a maximum value between 4 and 6, whereas speckle reduces neural sensitivity by a factor ks with a maximum value of approximately 25 (1.4 log units) for a 3-mm pupil and up to 35 (1.55 log units) for a 1-mm pupil; (3) the masking effect of the coherent noise is affected by changes in luminance but not by changes in pupil diameter; however, the pupil size is the main parameter affecting the masking effect of the speckle.

Contrast Sensitivity↗
PubMed1997

Cavernous hemangioma of the liver. Diagnostic value of 99mTc-labeled red cell scintigraphy: results in 28 patients.

Cavernous hemangioma is the most common benign tumor of the liver, the organ in which these lesions are most often present. We report on 28 patients who underwent 99mTc-labeled red cell scintigraphy after ultrasound or computerized tomography images suggesting the existence of one or more hepatic angiomas. In 16 patients (57.1%), an accumulation of red blood cells was considered to indicate the existence of hemangiomas. On the basis of subsequent clinical follow-up, ultrasound studies, and in one case laparotomy, all were eventually confirmed to be hemangiomas. The specificity as 100%. In the remaining 12 patients (42.9%), red cell uptake was not observed and the findings were considered negative; in this group, there were 10 true negatives and 2 false negatives in which scintigraphy failed to detect the existing angiomas due to their small size and deep location. The sensitivity was 88.8%. On the basis of the results, it is concluded that labeled red cell scintigraphy is a highly sensitive and specific method for the diagnosis of cavernous hemangioma of the liver. It should be considered the method of choice when this lesion is suspected, thus avoiding the use of more invasive diagnostic procedures such as laparoscopy which, in our study proved to be unnecessary.

Adult↗
PubMed1997

Standard criterion for fluctuations of modulation transfer function in the human eye: application to disposable contact lenses.

It is well known that the modulation transfer function (MTF) characterizes the optical quality of the eye. Recently, some objective techniques have been introduced in order to measure this function in vivo. These techniques could be employed to display the temporal fluctuations of the eye + compensation system and to isolate the effect of the compensation element provided that the standard fluctuations for a normal observer were known. In this work we carry out a study of the MTF of the human eye over a long period of time to quantify the standard fluctuations of the retinal image quality and to establish a standard criterion of normality. We have defined a single quality parameter from each measured MTF to simplify the analysis of the results. We have evaluated this merit function on normal observers three times a day for one month. As expected, random deviations from the mean value of the merit function have been obtained, although fluctuations with no statistical differences of the merit function (P value from ANOVA test P > 0.01) and the standard deviation of these fluctuations (5%) can be chosen as a standard criterion. We have used this result to study the behaviour of a time-varying compensation element: a disposable contact lens. The study of the eye + contact lens system has been carried out with four types of disposable contact lenses for one month. In spite of their generally good behaviour, statistically significant differences from the standard pattern can be observed. This superimposed continuous fluctuation can be due to lens-dependent processes.

Contact Lenses↗
PubMed1997

[Contribution of hepatic scintigraphy with Tc99m blood cells to the imaging diagnosis of cavernous hemangioma. Results in 48 patients].

Cavernous hemangiomas are the most common benign tumours of the liver, being the liver the most frequent organ affected by this lesions. We report 48 patients who underwent 99mTc-red blood cell (RBC) scintigraphy, after ultrasound or tomographic appearance of cavernous hemangioma. Scintigraphy findings in 29 of 48 patients (60.4%) were typical of cavernous hemangioma, hemangioma-positives, after scintigraphy (all true-positives). On clinical, ultrasound and in one case after surgery (exploratory laparotomy) the follow up was positive for hemangioma. Specificity of 100%. In the remaining 19 patients (39.6%) where hemangioma-negative lesions, 17 of 19 where true negatives and the remaining 2 where angiomas false-negatives, both of them were small lesions. The sensitivity for hemangiomas was 89.4%. To conclude with we would like to enhance the high specificity and sensitivity of 99mTc-red blood cell scintigraphy on the diagnosis of cavernous hepatic hemangioma (CHH). We highlight the utility of this specific imaging technique in the final diagnosis of CHH not requiring other invasive diagnosis tests, such as laparoscopy that in our study proved to be unnecessary.

Adult↗
PubMed1997

[Sclerosing hepatocarcinoma not associated with hypercalcemia].

The sclerosing hepatocellular carcinoma is an unusual subtype of hepatocellular carcinoma characterized by an intense fibrous stroma in which the tubular structures are embedded. Histological diagnosis is difficult, and misinterpretation as cholangiocarcinoma or metastatic adenocarcinomas may occur. It usually presents on non-cirrhotic livers. Metastases located outside of the liver are frequent as well as hypercalcemia and low levels of serum phosphate. We report a case of this rare histopathologic subtype of hepatocellular carcinoma in a 35-year-old woman, asymptomatic and with no previous history of chronic liver disease. It was detected by a routine gynaecological ultrasonography. An important increase of serum alpha-fetoprotein was noted. Extension studies showed bilateral lung metastases. Several palliative therapies were tried out, including epirrubicin, with partial response. Twenty months after the diagnosis the patient's situation is nearly terminal.

Adult↗
PubMed1995

Influence of contrast on the recognition of defocused letters: a geometrical model.

We show how contrast (C) affects the recognition of defocused letters. To do this, the maximum distance (threshold distance) at which a subject, with an induced refraction of -5.5 D, can recognize a letter was determined. Our results show that when C = 1, the recognition threshold distance is such that the ratio eta/xi, between the pseudoimage of the letter (eta) and the blur circle (xi), corresponding to any point of the letter at this distance is about eta/xi = 2; the exact value depends on the difficulty of recognition, in agreement with previous experiments. This ratio represents the sharpness of the image in a geometrical treatment of image formation, providing a geometrical criterion for recognition. Reduction in contrast can be compensated by improving the geometrical sharpness; i.e. bringing the object closer to the subject's are point. Our results show that the increment of eta/xi as a function of the contrast is between C = 0.1 and 1.0. We suggest that a similar geometrical criterion for recognition could be used for any contrast (at least down to C = 0.1 and defocus > 1 D), provided that the proper value of eta/xi is used in each case. On this basis we propose a purely geometrical model, which agrees well with the data and predicts the relationships between tolerance to defocus, contrast and visual acuity; including the well-known relation between visual acuity and defocus when contrast is unity.

Contrast Sensitivity↗
PubMed1994

Contrast sensitivity of the visual system in speckle imagery.

The contrast sensitivity function (CSF) of the whole visual system is determined with the use of coherent diffuse illumination. This function provides supplementary data about the effect of speckle on the ability of the visual system to perceive the spatial information contained in an image. The results show that speckle not only prevents perception of the finest details (highest frequencies) but also reduces the visibility of lower frequencies (especially where contrast is low). The difference between the CSF's determined with and without speckle is quantitatively very important. And the ratio between the two CSF's is a measure of the retinal ability to perceive contrast in the presence of speckle noise. The influence of the pupil size and luminance level on the CSF with speckle is studied and compared with the influence of the same parameters on the classical CSF.

Contrast Sensitivity↗
PubMed1993

Influence of the contrast sensitivity function on the reaction time.

The reaction time (RT) vs spatial frequency (SF) curve is determined, using gratings from 1 to 40 c/deg, at seven different contrast levels between 0.95 and 0.02. The form of the RT/SF function: (a) replicated the inverse of the contrast sensitivity function (CSF) at near threshold contrast levels; (b) behaved differently at higher contrasts, exhibiting two branches at contrast close to 1. The interpretation is that there are two factors determining this function: (1) the transition from the operation of fast transient channels at low SF to the operation of slow sustained channels at high SF, the transition taking place within a narrow SF band close to 6 or 8 c/deg (depending on the subject) and (2) the contrast attenuation by the optical and neural transfer function, operating throughout the SF range. At high contrasts, the effect of the first factor can be clearly observed, because the effect of the second factor does not change with spatial frequency except in a region where the RT/SF function changes rapidly. At lower contrasts, however, the second factor becomes increasingly relevant while the first becomes less and less observable.

Contrast Sensitivity↗
PubMed1993

Effect of color on contrast sensitivity with two different accommodative stimuli.

We studied the influence of color and accommodation on the contrast sensitivity function (CSF). At the same time, we measured the effect of axial chromatic aberration (ACA) on the CSF. The CSF's of two observers were determined using red, green, blue, and white light, at 5- and 0.5-m viewing distances. At 5 m the CSF's were measured with natural vision and also with lenses which compensated the ACA. Results show that the effect of ACA on the CSF is to reduce the sensitivity to blue with respect to the red. The difference in sensitivity between these two colors is between 50 and 150% and varies with the frequency and the subject. When the ACA is compensated the influence of the color on the CSF is very small, in our experiment, and this result is discussed in relation to the compensating effects of chromatic adaptation of the color mechanisms. In near vision, the CSF's were measured with natural vision and also with the lenses required to give the same accommodative stimulus for all colors. We discuss the effect of accommodation on the CSF. For both far and near the results are compared with the CSF with white light.

Accommodation, Ocular↗