Biomedical subjects

P B Kruger

Publications and source records attributed to P B Kruger.

11 recordsLinked to original sources

PubMed1989

Accommodation to size and blur changing in counterphase.

We explored the influence of changing size and blur on accommodation by presenting the two stimuli sinusoidally in counterphase. The frequency response of the accommodative system (0.05 to 1 Hz) was determined using a high-speed infrared optometer while the subject viewed the target in a Badal optometer. Blur was provided by moving the target dioptrically toward and away from the subject, and size of the target was altered by a variable aperture. Both stimuli were varied sinusoidally at the same frequency, but in counterphase. We find that both size and blur can have an influence on accommodation: blur is particularly powerful at low temporal frequencies, whereas size becomes effective at moderate and high temporal frequencies.

Accommodation, Ocular↗

PubMed1988

Changing size (looming) as a stimulus to accommodation and vergence.

Changing size (looming) produces changes in accommodation and vergence. Dynamic responses of vergence and accommodation to sinusoidal looming of a Maltese cross were recorded with an SRI dual-Purkinje-image eyetracker and optometer. The ratio of these two motor responses was compared with the response accommodative convergence/accommodation (AC/A) ratio and convergence accommodation/convergence (CA/A) ratio determined from sinusoidal variations of blur and disparity respectively. The response to changing size was found to be more similar to the AC/A ratio than the CA/C ratio. In addition, when a changing disparity or changing blur stimulus was combined with a changing size stimulus, the response phase lags of accommodation and vergence were decreased. In addition, the CA/C ratio was increased when changing size was added to changing disparity, but the AC/A ratio was unaltered when changing size was added to changing blur. These results indicate that changing size is stimulating accommodation directly and vergence secondarily through an AC/A crosslink.

Accommodation, Ocular↗

PubMed1988

Dynamics of human voluntary accommodation.

Voluntary and reflex accommodation were measured monocularly in five normal subjects using a dynamic infrared optometer. Comparison of the peak velocity/amplitude relation (i.e., "main sequence") showed complete overlapping of the response distributions, suggesting similarity of motoneuronal controller signals for voluntary and reflex accommodation. Voluntary accommodation may represent a preprogrammed maneuver used in a variety of real-life predictable situations to optimize performance. Clinically, it may represent an important component in the training of accommodation dynamics.

Accommodation, Ocular↗

PubMed1987

Dioptric and non-dioptric stimuli for accommodation: target size alone and with blur and chromatic aberration.

The frequency response of the accommodative system (0.05-1 Hz) was determined for various combinations of stimuli: changing target size was presented alone, together with defocus blur, and with both defocus blur and chromatic aberration. A high-speed infrared optometer monitored accommodation while the subject viewed the target in a Badal optometer. Target size was varied sinusoidally and blur was provided by moving the target towards and away from the subject at the same frequency. Chromatic aberration was controlled by using either monochromatic (590 nm) or white (3300 K) light. The target was presented under open-loop conditions when size was the only stimulus. We find that besides the conventional dioptric stimuli, changes in target size that result in changes in apparent distance can have substantial effects on accommodation.

Accommodation, Ocular↗

PubMed1986

Stimuli for accommodation: blur, chromatic aberration and size.

We investigated the frequency response of the accommodative system (0.05-1 Hz) using three stimuli: defocus blur, the effects of the chromatic aberration of the eye, and changing target size. A high-speed infrared optometer monitored accommodation while the subject viewed a target in a Badal optometer. Blur was provided by moving the target sinusoidally towards and away from the subject (1-3 D) and the size of the target was varied at the same frequency. Chromatic aberration was controlled by using either monochromatic (590 nm) or white light (3300 K). Gain and phase plots changed systematically as we varied the number of stimuli presented together. This suggests that besides defocus blur both chromatic aberration and changing size are involved in accommodative control.

Accommodation, Ocular↗

PubMed1985

Changing target size is a stimulus for accommodation.

Accommodation was monitored by using a high-speed infrared optometer while subjects viewed a target that appeared to approach and recede in a sinusoidal manner. The target was presented under open-loop conditions to prevent blurring because of accommodation. The experiments suggest that changing target size can be an effective stimulus on its own. This supports the view that accommodation responds to both dioptric and nondioptric stimuli.

Accommodation, Ocular↗

PubMed1979

Infrared recording retinoscope for monitoring accomodation.

An optometer (infrared recording retinoscope) that provides high resolution measurements of accommodative changes of the eye has been developed. The instrument employs the principle of retinoscopy to monitor changes in the refractive state of the eye. Infrared radiation is scanned across the eye to provide a moving retinal source as in retinoscopy. An electro-optical system replaces the observer in determining the direction and amount of apparent motion in the pupil of the patient. The optometer is sensitive to accommodative changes of 0.12 D over a range of 12 D. The response of the instrument is faster than the most rapid changes of accommodation, and measurements are unaffected by pupil changes or by small eye movements.

Accommodation, Ocular↗

PubMed1978

The effect of accommodative changes on the brightness of the fundus reflex.

This paper demonstrates how accommodation and refractive changes affect the brightness of the reflex observed during retinoscopy. The amount of light entering the peephole of the retinoscope was monitored while accommodation was varied. The light entering the peephole reaches a maximum when the far-point of the eye is co-incident with the retinoscope and drops when the far-point moves behind or in front of the retinoscope. A reduction in the accommodative lag during book retinoscopy would result in brightening of the reflex along with a shift in the "against" direction.

Accommodation, Ocular↗

PubMed1977

Changes in fundus reflex luminance with increased cognitive processing.

A previous study using photoelectric retinoscopy at near showed an increase in fundus reflex luminance when the subject's task was changed from reading simple material to adding numbers. Unfortunately, it was not possible to attribute the luminance change to the change in cognitive task. The present experiment was designed to determine whether an increase in cognitive processing would produce an increase in fundus reflex luminance. When the subjects (N = 19, ages 22 to 27) changed from viewing 2-digit numbers at 40 cm to adding the digits, with no change in the visual stimulus, the increased in 47 of 54 trials--the mean luminance increased approximately 10% (p less than 0.01). This change in fundus reflex luminance is not attributed to change in eye position but rather to a decrease in accommodative lag.

Adult↗

PubMed1977

Brightness changes during book retinoscopy.

Book retinoscopy involves the observation of fundus reflex changes that are said to be related to the reading levels or interpretive levels at which persons are functioning. Recent investigations have shown that increasing the cognitive demand on a person can result in accomodative changes in his eye that increase the luminance of the fundus reflex. Since the ability of observers to distinguish such changes is not known, this experiment was designed to determine the minimum detectable increase in luminance. The experiment involved a 2-alternative forced-choice procedure in which observers were required to indicate during which of 2 designated intervals the reflex from a schematic eye became brighter. The luminance of the reflex had to increase by at least 11% beforeit could be detected. A reduction in the lag of accommodation and dilation of the pupil probably account for the changes observed during book retinoscopy.

Accommodation, Ocular↗

PubMed1975

Luminance changes of the fundus reflex.

A recording retinoscope was developed to measure the luminance of the fundus reflex during problem-solving tasks. 10 students were used as subjects. The luminance of the reflex was recorded while the subjects read 5 passages of graded reading material and performed an addition task. A reversal design was used to determine the effects of pupil changes and accommodation on changes in the luminance of the reflex. Relatively large changes in the luminance of the reflex were recorded. These were due to accommodation. The subjects' comprehension of the reading material did not appear to affect the luminance of the reflex in the manner predicted by previous studies. However, a change in task from simple reading material to an addition task appeared to increase the luminance of the reflex.

Accommodation, Ocular↗