Biomedical subjects

Fernando Vargas-Martín

Publications and source records attributed to Fernando Vargas-Martín.

5 recordsLinked to original sources

PubMed2006

Eye movements of patients with tunnel vision while walking.

PURPOSE: To determine how severe peripheral field loss (PFL) affects the dispersion of eye movements relative to the head in patients walking in real environments. This information should help to define the visual field and clearance requirements for head-mounted mobility visual aids. METHODS: Eye positions relative to the head were recorded in five patients with retinitis pigmentosa who had less than 15 degrees of visual field and in three normally sighted people, each walking in varied environments for more than 30 minutes. The eye-position recorder was made portable by modifying a head-mounted system (ISCAN, Burlington, MA). Custom data processing was implemented, to reject unreliable data. Sample standard deviations of eye position (dispersion) were compared across subject groups and environments. RESULTS: The patients with PFL exhibited narrower horizontal eye-position dispersions than did the normally sighted subjects (9.4 degrees vs. 14.2 degrees , P < 0.0001), and the vertical dispersions of patients with PFL were smaller when they were walking indoors than when walking outdoors (8.2 degrees vs. 10.3 degrees ; P = 0.048). CONCLUSIONS: When walking, the patients with PFL did not increase their scanning eye movements to compensate for missing peripheral vision information. Their horizontal scanning was actually reduced, possibly because of lack of peripheral stimulation. The results suggest that a field of view as wide as 40 degrees may be needed for closed (immersive) head-mounted mobility aids, whereas a much narrower display, perhaps as narrow as 20 degrees , may be sufficient with an open design.

Adult↗

PubMed2005

Visual fields at the wheel.

PURPOSE: "Looked-but-failed-to-see" errors are a common cause of accidents, but it has never been determined whether obstructive elements within an automobile (e.g., window posts or the interior rearview mirror) have actually been an obstacle to vision. This work describes a technique that can easily be used to determine the available visual field of drivers at the wheel and illustrates its potential in a number of applications. METHOD: The technique involves calibrating a minicamera for use as a device for perimetry and then mounting it on spectacles so that it lies between the eyes of the subject who wears them. With the spectacle-mounted camera worn by a driver, snapshots were taken when the automobile was parked and the driver looked in different directions, and video sequences were recorded during natural driving in an urban area and on a winding mountain road. RESULTS: All of the automobiles studied place obstacles to vision for any given direction of gaze, although the resultant scotomata have different sizes and are placed in different regions of the visual field for each combination of car and driver. These regions encroach into central vision as drivers turn their head and eyes as required by the characteristics of the road or the urban area during natural driving, in some cases resulting in very poor visibility regardless of the good vision of the driver and the certification of the automobile. CONCLUSION: Our technique is useful for determining what parts of a given scene are visible to a given driver on a given automobile and, hence, it is useful not only as a tool for accident investigation and in visual ergonomics, but also as an aid for the design of automobiles and road environments.

Adult↗

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↗