Biomedical subjects

Fernando Vargas-Martín

Publications and source records attributed to Fernando Vargas-Martín.

3 recordsLinked to original sources

PubMed2002

Measurements of the corneal birefringence with a liquid-crystal imaging polariscope.

An imaging polariscope has been used to analyze the spatially resolved polarization properties of living human corneas. The apparatus is a modified double-pass setup, incorporating a liquid-crystal modulator in the analyzer pathway. Keeping the incident polarization state fixed (first passage), we recorded a series of three images of the pupil's plane corresponding to independent polarization states of the analyzer unit. Azimuth and retardation at each point of the cornea were calculated from those images. Results show that the magnitude of retardation increases along the radius toward the periphery of the cornea. Left-right eye symmetry in retardation was also found. Maps of azimuth indicate that the direction of the corneal slow axis is nasally downward.

Birefringence↗

PubMed2002

Augmented-view for restricted visual field: multiple device implementations.

PURPOSE: An augmented-view device for patients with severely restricted peripheral visual fields (tunnel vision) was proposed, combining a see-through head-mounted display and a simultaneous minified view of a wide field presented as contour information. Here we create and evaluate multiple implementations of the augmented-view concept and report responses from potential users. METHODS: Several prototypes using commercial off-the-shelf devices were implemented. Then they were evaluated in real environments in daylight and at night by two retinitis pigmentosa patients. RESULTS: Effective expansion of the visual field of patients was achieved. Patients indicated their preferences for different properties, devices, and combinations. CONCLUSIONS: Patients found the augmented-view concept of help for their impairment, but wanted much more ergonomic design than the prototypes provided. Benefits, limitations, and possible improvements for the evaluated devices are discussed.

Equipment Design↗

PubMed2002

Effect of the polarization on ocular wave aberration measurements.

Measurement of the eye's wave aberrations has become fairly standard in recent years. However, most studies have not taken into account the possible influence of the polarization state of light on the wave aberration measurements. The birefringence properties of the eye's optical components, in particular corneal birefringence, can be expected to have an effect on the wave aberration estimates obtained under different states of polarization for the measurement light. In the work described, we used a psychophysical aberrometer (the spatially resolved refractometer) to measure the effect of changes in the polarization state of the illumination light on the eye's wave aberration estimates obtained in a single pass. We find, contrary to our initial expectation, that the polarization state of the measurement light has little influence on the measured wave aberration. For each subject, the differences in wave aberrations across polarization states were of the same order as the variability in aberrations across consecutive estimates of the wave front for the same polarization conditions.

Adult↗