PubMed Health⌕ Search

Biomedical subjects

R Barbeito

Publications and source records attributed to R Barbeito.

26 records · Page 2Linked to original sources
PubMed1984

The precision of oculocentric direction and its role in the stability of fixation.

We compared stability of fixation midway between two targets (separated horizontally by from 1 to 12 deg) to precision in specifying these targets' oculocentric directions. Unsteadiness of fixation tended to parallel changes in the precision of direction for larger target separations, but was worse than predicted from an addition of estimated oculomoter and sensory variabilities. The data are consistent with the notion that oculocentric direction provides the sensory signals used to maintain fixation, but to account for the magnitude of fixational instability another source of variability, possibly related to attention, must also be considered.

Female↗
PubMed1981

The effect on form perception of change of orientation in the third dimension.

The experiments reported here concern the effect of change of orientation of figures in the third dimension on phenomenal shape. In one experiment, novel two-dimensional wire figures were first shown in one orientation in the sagittal plane, and recognition of them was then tested in an altered orientation in that plane. In another experiment, novel three-dimensional wire figures were first shown in one orientation, and recognition of them was tested following rotation about one of the three major axes of space. The guiding hypotheses were (a) form perception is the end result of a process of figural description; (b) orientation change that alters the perceived location of the top, bottom, and sides of a figure will affect this description; and (c) front-back reversal and rotations about the Y axis will not affect the description because front and back constitute the sides of a figure much as left and right do, and all figural sides are phenomenally equivalent. The findings support these hypotheses except for an unanticipated effect on recognition of 90 degrees rotations about the Y axis. This effect was seen as a hitherto unknown example of egocentrism in perception, since the description is governed by the retinal projection resulting from the particular vantage point of the observer.

Depth Perception↗
PubMedDate not supplied

Seroprevalence of Echinococcus granulosus infection in a Uruguayan rural human population.

Serological tests using hydatid cyst fluid (HCF) are useful as a primary screen for detecting asymptomatic infections due to Echinococcus granulosus in human populations. An enzyme-linked immunosorbent assay (ELISA) performed with whole sheep HCF was used to determine the prevalence of hydatid antibodies in a rural human population in Uruguay. In order to eliminate cross-reactions with sheep proteins in HCF, 1% normal sheep serum was added to each human serum before testing. ELISA seropositives were further tested using the double diffusion test (DD5) and confirmed where possible by ultrasound and X-ray examination. Serum samples were obtained from 420 individuals inhabiting rural areas in the Department of Paysandu (160), Rivera (21) and San José (239). An overall seroprevalence of 1.24% was obtained. Two of 17 seroreactors were subsequently proven to have hydatidosis. These results confirm and extend previous studies indicating an unusually high prevalence of E. granulosus infection in the Uruguayan population.

Adult↗
PubMedDate not supplied

Differences between objective and subjective refractions after radial keratotomy.

BACKGROUND: In patients who are free of pathology, automatic refractions have shown close agreement with the subjective refractions. Clinical experience indicated that the normally strong relationship between objective and subjective refraction is significantly weakened as a result of radial keratotomy. METHODS: Seventy-two patients were refracted before and after surgery, objectively with a Humphrey Model #510 autorefractor and subjectively using a binocular refraction procedure without cycloplegia. All patients were free of ocular disease and had preoperative myopia ranging from -1.00 to -9.00 diopters as determined by the subjective spherical equivalent. RESULTS: The results indicated that the preoperative difference between the mean spherical automatic and subjective refractions was a clinically acceptable 0.25 diopter. However, postoperatively, there was a statistically significant difference of 1.25 D with the automatic refractor determining more myopic refractions. Subsequent analysis revealed that the age of the patient had a direct bearing on this finding with patients less than 40 years of age showing more minus in the automatic refraction than patients 40 years and older. CONCLUSIONS: The postoperative discrepancy between the two refractions may be explained by induced optical aberrations and may contribute towards the visual fluctuations experienced by radial keratotomy patients. It is postulated that the inconsistency in refractive determination is due to optical distortion since the age dependence of this effect may be related to the reduction of pupil size that occurs with aging. In the radial keratotomy patient, the practitioner is faced with a more complex and uncertain refraction that may vary according to refractive procedures used and other factors such as pupil size.

Accommodation, Ocular↗