Biomedical subjects

M A Parafita

Publications and source records attributed to M A Parafita.

At least 19 recordsLinked to original sources

PubMed2006

Age differences in central and peripheral intraocular pressure using a rebound tonometer.

AIM: To evaluate the influence of age on the measurements and relationships among central and peripheral intraocular pressure (IOP) readings taken with a rebound tonometer. METHODS: The IOPs were measured using the ICare rebound tonometer on the right eyes of 217 patients (88 men and 129 women) aged 18-85 years (mean 45.9 (SD 19.8) years), at the centre and at 2 mm from the nasal and temporal limbus along the horizontal meridian. Three age groups were established: young (< or =30 years old; n = 75), middle aged (31-60 years old; n = 77) and old patients (>60 years old; n = 65). RESULTS: A high correlation was found between the central and peripheral IOP readings, with the central readings being higher than the peripheral ones. Higher IOP values for the central location were found in the younger patients. Older patients had significantly lower temporal IOP readings than those for the remaining two groups (p<0.001), whereas no significant differences were found among groups when IOP was measured at the central and nasal locations. A significant decrease was observed in the nasal and temporal IOP readings as the age increased (p = 0.011 and 0.006, respectively). CONCLUSION: Older patients had lower IOP values than the middle-aged and younger patients in the temporal peripheral location. A negative correlation was found between age and IOP by rebound tonometry in the corneal periphery but not in its centre.

Adolescent↗

PubMed2006

Non-contact tonometry synchronized with cardiac rhythm and its relationship with blood pressure.

PURPOSE: The main objectives of this study were to determine the differences between non-synchronized intraocular pressure (IOP_N) and intraocular pressure readings synchronized with cardiac pulse and try to determine if these parameters are related to blood pressure values. METHODS: One hundred and sixty-five right eyes from 165 volunteers (107 females, 58 males) aged from 19 to 73 years (mean +/- S.D., 29.93 +/- 11.17) were examined with the Nidek NT-4000, a new non-contact tonometer that allows the measurement of IOP synchronized with the cardiac rhythm. IOP measurements in the four different modes of synchronization were taken in a randomized order. Three measures of each parameter were taken and then averaged. The blood pressure was determined three times with a portable manometer and mean values of systolic and diastolic pressure and the pulse rate were computed. Mean arterial pressure (MAP) was determined as being 1/3 of systolic plus 2/3 of diastolic blood pressure. RESULTS: The mean +/- S.D. values for the standard intraocular pressure (IOP_N: 14.76 +/- 2.86), intraocular pressure in the systolic instant or peak (IOP_P: 14.99 +/- 2.85), intraocular pressure in the middle instant between heartbeats or middle (IOP_M: 14.68 +/- 2.76), and intraocular pressure in the diastolic instant or bottom (IOP_B: 13.86 +/- 2.61) were obtained. The IOP_P was higher than the remaining values. A significant difference in mean IOP existed between IOP_B and the remaining modes of measuring (p < 0.05). Differences were statistically significant for all pair comparisons involving IOP_B. Arterial blood pressure values were systolic 125.5 +/- 14.22, diastolic 77.7 +/- 8.38 and MAP 93.64 +/- 9.44 mmHg. The pulse rate was 77.3 +/- 12.6 beats per minute. Except for the MAP (p = 0.025) there was no significant correlation between different IOP values and systolic or diastolic blood pressure, or pulse rate. CONCLUSIONS: NT-4000 is able to differentiate IOP values when synchronized with the cardiac rhythm and those differences are expected to be within a range of +/-2.5 to +/- 3.0 mmHg. IOP_B seems to be the parameter whose value differs from the non-synchronized and the remaining synchronized parameters in a significant way. Other than a weak association with MAP, no significant correlation between IOP and BP was found. The measurements of IOP readings for the three modes are consistent with timings during the cardiac cycle and IOP pulse cycle.

Adult↗

PubMed2005

The influence of cycloplegia in objective refraction.

The purpose of this study was to compare refractions measured with an autorefractor and by retinoscopy with and without cycloplegia. The objective refractions were performed in 199 right eyes from 199 healthy young adults with a mean age of 21.6 +/- 2.66 years. The measurements were performed first without cycloplegia and repeated 30 min later with cycloplegia. Data were analysed using Fourier decomposition of the power profile. More negative values of component M and J(0) were given by non-cycloplegic autorefraction compared with cycloplegic autorefraction (p < 0.0001). However more positive values for the J(45) vector were given by non-cycloplegic autorefraction, although this difference was not statistically significant (p = 0.233). By retinoscopy, more negative values of component M were obtained with non-cycloplegic retinoscopy (p < 0.0001); for the cylindrical vectors J(0) and J(45) the retinoscopy without cycloplegia yields more negative values (p = 0.234; p = 0.112, respectively). Accepting that differences between cycloplegic and non-cycloplegic retinoscopy are only due to the accommodative response, the present results confirm that when performed by an experienced clinician, retinoscopy is a more reliable method to obtain the objective starting point for refraction under non-cycloplegic conditions.

Accommodation, Ocular↗

PubMed2004

A comparison of the ARK-700A autokeratometer and Medmont E300 corneal topographer when measuring peripheral corneal curvature.

PURPOSE: The purpose of this study was to evaluate if corneal topogometry measurements as taken with the ARK-700A autokeratometer are comparable with those measured by the Medmont E300 videokeratoscope at corresponding locations. METHODS: Central and peripheral radius and eccentricity were measured in 122 right eyes of young normal subjects using autokeratometry and videokeratoscopy, obtained in a random order. RESULTS: Curvature measurements obtained with the ARK700A and Medmont E300 correlated well for the central cornea. Larger differences were observed between peripheral autokeratometry readings and the empirically determined corresponding locations with the videokeratoscope. Correlations between the instruments are inconsistent, resulting in unacceptable confidence intervals. Corneal eccentricity was significantly different between the instruments for the vertical (t = 2.4; p = 0.018) and for the horizontal meridians. In the first case, the difference between the averaged values was not clinically significant, but in the horizontal meridian the AK significantly overestimated eccentricity values (t = -11.5; p < 0.001) with differences which were clinically significant. CONCLUSIONS: Central corneal curvature data obtained by ARK700A and Medmont E300 can be interchanged but the same is not true of peripheral determinations of corneal shape. ARK700A probably measures peripheral corneal shape within an elliptical region between 5 and 7 mm in diameter, with the major axis in the vertical meridian.

Adult↗

PubMed2004

[Changes in axial length/corneal radius ratio (AL/CR) according to refractive state of the eye. Relationship with ocular components].

PURPOSE: Determination of the role of the axial length/corneal radius ratio (AL/CR) in the refractive state and investigation of its relationship with the ocular optical components: AL, CR, anterior chamber depth (ACD), crystalline lens thickness (CT) and vitreous chamber depth (VCD). METHODS: The RE (right eye) of 193 University students 22.27 (SD 3.24) years, with different refractive errors (spherical equivalent range: +3.00 D to -11.00 D), being divided into: emmetropes, hyperopes and myopes (low, moderate and high). The ACE, the CT, the VCD and the AL were measured by ultrasonography (unidimensional echography); and the mean CR by videokeratoscopy. RESULTS: The value of AL/CR obtained was 2.98 (SD 0.69) for emmetropes, 2.89 (SD 0.87) for hyperopes, 3.01 (SD 0.07) in low myopias, 3.10 (SD 0.11) in moderate myopias and 3.23 (SD 0.12) in high myopias. The AL/CR ratio showed a higher correlation with the refractive error. Besides, all the refractive groups were observed to have lower CE values as the AL/CR increased. This tendency is statistically significant in hyperopes, emmetropes and low myopes; and is not in moderate and high myopias. All the study groups could be observed to have a positive and statistically significant correlation between AL/CR and ACD. CONCLUSION: The ratio AL/CR is the most important parameter and the best predictor of the refractive state of the human eye. It provides important information on how best to determine the degree of emmetropization given by the crystalline, decreasing its power and the ACD in concordance with the LA. A value for the ratio AL/CR above 3.00 could be considered as a risk factor for the development of myopia in emmetropic eyes.

Adult↗

PubMed2004

[Corneal asphericity in a young adult population. Clinical implications].

PURPOSE: To determine the relevance of the different ocular optical components in the refractive state of young adults, paying special attention to the corneal topography represented by the asphericity value. SUBJECTS AND METHODS: Corneal topographies and ultrasonic biometries were obtained from 109 university students with different refractive errors (spherical equivalent range: +3.25 D to -11.00 D). A regression study was performed in order to establish the relationships between corneal asphericity and refractive error, as well as other ocular optical components related to the emmetropization mechanism of the eye. RESULTS: The mean asphericity values were -0.23 (SD 0.08, range: -0.42 to -0.03). All the values correspond to the mathematical description of the prolate ellipse, most commonly accepted for the normal human cornea. The statistical correlation between asphericity and equivalent refractive error was not significant, but a significant correlation was found for the asphericity with respect to the radius of curvature, vitreous chamber depth and axial length. CONCLUSIONS: 1) The asphericity values support the generalised morphology of the prolate cornea as the standard. The influence of this configuration on the contact lens fit, refractive surgery or the visual performance of the eye are discussed. 2) Results suggest that, although a relationship between axial length and corneal topography actually exists, it is not likely that the latter has implications for the emmetropization mechanisms which determine the refractive state of the adult eye.

Adult↗

PubMed2003

Clinical performance of non-contact tonometry by Reichert AT550 in glaucomatous patients.

Measuring intraocular pressure (IOP) by non-contact tonometry (NCT) has been demonstrated to be a valid and reliable technique to be used in primary eye care; it is easier to use, it does not transmit infectious diseases, and it is not necessary to use anaesthetic or staining eye drops. Recently, a new NCT device has showed an excellent level of agreement with Goldmann tonometry, but there are no records of its performance in glaucomatous eyes. To rectify this, IOP was measured in twenty-two patients (44 eyes) receiving medical treatment to control elevated IOP, with AT550 and Goldmann tonometry. Mean values of IOP were 18.98 +/- 2.77 and 19.08 +/- 3.02 mmHg using Goldmann and AT550, respectively. Plots of differences against means displayed good agreement (mean difference +/- limits of agreement, -0.09 +/- 3.30); this value was not significantly different from zero (t-test for dependent samples, p = 0.709). In conclusion, IOP values as measured with the AT550 NCT are clinically comparable with those obtained with Goldmann tonometry in glaucomatous patients. This validates this NCT not only for screening of IOP but to follow-up glaucomatous patients with a rapid, non-invasive method.

Exfoliation Syndrome↗

PubMed2003

Changes in corneal structure with continuous wear of high-Dk soft contact lenses: a pilot study.

PURPOSE: Despite numerous studies that have considered the effects of extended wear of high-Dk soft contact lenses on ocular physiology, little attention has been paid to the impact of such lenses on central or peripheral corneal thickness and curvature. The present study aims to report the time course of changes in corneal thickness and curvature that accompanies the 30-night continuous wear of new silicone hydrogel soft contact lenses in a neophyte population in a longitudinal study. METHODS: Six subjects wore high-Dk lotrafilcon (Dk = 140) on a 30-night replacement schedule for 12 months. Only measurements from the right eye were considered for analysis. Topographical measurements of corneal thickness and curvature were taken. The same parameters were monitored for an additional period of 3 months after lens removal. RESULTS: An almost homogenous increase in corneal radius of curvature was detected for all the locations studied, being statistically significant for the 4-mm cord diameter area. This effect was associated with a progressive thinning effect for the central cornea, whereas midperipheral and peripheral areas did not display such a thinning effect during continuous wear. These effects were still evident for the central cornea 3 months after contact lens wear discontinuation. CONCLUSIONS: Continuous wear of high-Dk silicone hydrogel contact lenses is associated with clinically appreciable changes in topographical corneal curvature, whereas only a reduction in corneal thickness is appreciated in the central area. This effect seems to be a result of mechanical pressure induced by these hybrid hyperpermeable materials, characterized by a higher modulus of elasticity. The small sample size compromises the conclusions addressed from this study, and further work will be necessary to confirm the present results.

Adult↗

PubMed2002

Clinical performance of the Reichert AT550: a new non-contact tonometer.

The aim of the present study was to assess the level of accuracy for measurements of intra-ocular pressure (IOP) obtained with a new non-contact tonometer (NCT) the Reichert AT550. Measurements were compared against those obtained with the Reichert Xpert Plus, Goldmann applanation tonometer and Perkins tonometer. Thirty-five university students were assessed with the four tonometers in a randomised order, with non-contact tonometry performed first. Each of the four measurement devices had its own trained clinical observer. Plots of differences of IOP as a function of the mean for each pair of instruments were obtained. No statistically significant differences were found when comparing the AT550 NCT with contact applanation tonometry (AT) (p> 0.05), displaying the closest level of agreement (as represented by the lowest mean difference and the narrowest confidence interval) with the Goldmann tonometer (limits of agreement, 0.12+/-2.17). In conclusion, readings of IOP with the AT550 NCT are clinically comparable with those obtained with Goldmann tonometry in a population with IOP within the normal range.

Adult↗

PubMed2001

Rigid gas permeable contact lens and corneal topography.

We investigated the effect of high Dk daily wear rigid gas permeable contact lenses on corneal topography. Eight young myopic subjects wore hard contact lenses for 21 days. Corneal topography was monitored using the EyeSys system. It was measured every day during the next 21 days after the fitting. We recorded the corneal radius of curvature at 16 peripheral points approximately 1, 2, 3 and 4 mm along the four principal meridians (nasal, superior, inferior and temporal). Our study showed that daily wear RGP Forum 210 does not produce significant alterations of the corneal curvature as a function of time.

Adult↗

PubMed2000

[Topographical pachymetry and pachymetric topography in circumscribed posterior keratoconus].

CASE REPORT: A 29 year-old male patient presenting circumscribed posterior keratoconus in the left eye was studied. After ocular examination, corneal morphometry was studied by a computer-assisted topographic analysis and topographical ultrasonic pachymetry. Corneal thickness profile was represented by a colour-coded map from twenty-five measured points (pachymetric topography). DISCUSSION: Slit lamp biomicroscopy shows a paracentral-localized area of moderate corneal thinning with a nasal-superior concavity on posterior corneal surface. Topographical pachometry and pachometric topography allow to make precise corneal thinning evaluation and offer useful diagnostic data for this rare corneal dystrophy.

Adult↗

PubMed1994

Nifedipine in rat liver cirrhosis.

Rat liver cirrhosis induced by CCl4+ethanol was employed to assess the effectiveness of nifedipine in reducing liver injury. Nifedipine reduced the severity of hepatocellular necrosis, significantly decreased Mallory bodies (p < 0.01), decreased polymorphonuclear inflammatory infiltrate (p < 0.05) and reduced perivenular fibrosis. Plasma lactic acid levels were significantly increased in the CCl4+ethanol group (p < 0.01). Lactacidaemia remained at normal values when the calcium antagonist blocker was employed. Nifedipine did not significantly alter the incidence of cirrhosis in this experimental model.

Animals↗

PubMed1993

Colchicine alters lactate utilization in isolated hepatocytes of rats treated with CCl4 and ethanol.

Lactic acidosis has been described in patients with liver disease. Hyperlactacidaemia results from an imbalance in lactate production versus lactate utilization. It is estimated that the liver utilizes approximately 30 percent of the total lactate produced in the body under basal conditions, primarily by gluconeogenesis. The gluconeogenesis from lactate 10 mM and lactacidaemia were determined in order to investigate the effects of CCl4+ethanol administration in liver injury and, the possible effect of colchicine in our experimental fibrosis model. The tests were determined after 15, 30 or 45 days of treatment. The results indicate that the gluconeogenesis was significantly inhibited in both CCl4+ethanol groups and CCl4+ethanol+colchicine groups. By contrast, the lactacidaemia levels were much higher in the CCl4+ethanol groups than the colchicine groups. Summarising, we have documented that hyperlactacidaemia is due to the inhibition of lactate utilization by the isolated hepatocytes in experimental cirrhosis, and that the improvement in lactacidaemia caused by colchicine is not primarily due to an increase in hepatic lactate utilization.

Alcoholic Intoxication↗

PubMed1993

Effect of colchicine on lactate production by isolated hepatocytes in rats treated with carbon tetrachloride and ethanol.

This study was designed to evaluate the lactate production by isolated hepatocytes in rats with cirrhosis induced by means CCl4 + ethanol and the effect of colchicine in this experimental model of fibrosis. The effect of colchicine on lactate metabolism may be important in explaining the beneficial mechanism of this therapy on liver cirrhosis. Colchicine treatment produced a decrease in perivenular fibrosis and a descense in the degrees of this histological lesion. Colchicine treatment ameliorated the subsequent further development of cirrhosis. Lactate production in colchicine groups were higher than the carbon tetrachloride groups. By contrast, a priori, we observed a decrease in lactacidaemia and a lesser lactate utilization in colchicine groups comparison with CCl4 + ethanol groups. Our results suggest that colchicine improves the fibrosis by a mechanism independent of hepatic lactate metabolism.

Animals↗

PubMed1989

Antigenical alterations of hepatocyte membrane in rats after long-term administration of ethanol and carbon tetrachloride.

The presence of IgG over the hepatocyte's surfaces in ethanol- and/or carbon tetrachloride-pretreated rats was demonstrated as a very thin lineal fluorescent deposition around the membrane. The percentage of parenchymal IgG-positive liver cells ranged between 15 and 100% in all animals of treated groups. This suggests that ethanol may induce hepatic injury mediated by IgG autoantibodies which may be a response to an antigenical determinant present in hepatocytes altered by ethanol and/or carbon tetrachloride treatment.

Alcoholism↗

PubMed1989

[Ultrastructural study of the liver from rats treated with ethanol and/or carbon tetrachloride].

The cellular ultrastructure of isolated hepatocytes and hepatic tissue in ethanol and/or carbon tetrachloride treated rats at different times. The ultrastructural modifications induced by ethanol and carbon tetrachloride, isolated administrations, are similar: Many lipidic vacuoles, several graded-injury mitochondria and R. E. R. degeneration. These effects are also induced by ethanol and carbon tetrachloride association and furthermore nuclei indentations. Some mitochondrial autophagocytosis affecting to the less electrodense hepatocytes are noted.

Animals↗

PubMed1988

Synergism of ethanol and clofibrate in the lauric acid hydroxylation.

The effects of ethanol and clofibrate on lauric acid hydroxylation in isolated rat hepatocytes cultured for 72 h were studied. During culture the lauric acid hydroxylation activity decreases. When the hepatocytes were cultured for 72 h with the addition of 10(-5) M, 10(-4) M and 10(-3) M clofibrate, the lauric acid hydroxylation increased by 42%, 428% and 900%, respectively. The stimulation by ethanol was also significant. The addition of both ethanol and clofibrate to the culture media resulted in a potentiation of this induction.

Animals↗

PubMed1985

Further evidence for effects of ethanol on gonadotrophins and prolactin secretion in female rats.

The effect of different doses of ethanol (0.5, 1.0, 2.0 and 4.0 g/kg) on LH, FSH and prolactin levels has been studied in female rats. Ethanol was administered in preovulatory periods (18 hr of diestrous or 9 hr of proestrous) and hormonal levels were measured at the 18 hr of proestrous. Ethanol administered at the 18 hr of diestrous produces a biphasic effect on serum LH levels. High doses of alcohol significantly decreased LH levels, whereas low doses (0.5 g/kg) increased the hormonal levels. When ethanol-treatment was at the 9 hr of proestrous, it only decreased LH levels with the dose of 4.0 g/kg. Serum FSH levels were unaffected by the preovulatory administration of ethanol. Serum prolactin concentrations were significantly elevated after i.p. administration of ethanol at the 18 hr of diestrous and the 9 hr of proestrous. The hyperprolactinemia is more pronounced in the rats treated at the 9 hr of proestrous. The results of these studies suggest that the ability of ethanol to modify LH and prolactin levels is due to a central depression caused for alcohol. These effects of ethanol could be mediated by the hypothalamic releasing factors and/or could be due to a direct action on the pituitary function. The sum of these effects produces important failures of the reproductive function in the female rat.

Animals↗