The Effect of Anticipation on the Transfer Function of the Human Lens System
TL;DR: The transfer function of the human lens system appears to be strongly influenced by the possibility to predict the input signal, and the two aforementioned transfer functions are compared with sinusoidal responses which were strongly influencedby the extent of training and the attention of the subject.
Abstract: The transfer function of the human lens system appears to be strongly influenced by the possibility to predict the input signal. Owing to this the accommodating system can respond very rapidly to a change in target distance when anticipation is used, and it is relatively slow when the subject is unable to anticipate the input signal. An optimal and a minimal transfer function is determined assuming that possibility to anticipate the input signal is relevant. The two aforementioned transfer functions are compared with sinusoidal responses which were strongly influenced by the extent of training and the attention of the subject.
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TL;DR: A review of the available evidence on age‐related change in the lens, capsule, ciliary body and other relevant ocular structures confirms that geometric and viscoelastic lenticular changes play major roles in the progressive loss of accommodation.
Abstract: Current understanding of the anatomy, function and performance of the accommodative system of the young, adult human eye is outlined. Most major current models of the accommodative mechanism are based on Helmholtz's original ideas but, despite of a growing volume of related research, uncertainty continues over the relative contributions made to the overall mechanism by different ocular structures. The changes with age are then discussed. Although the amplitude of accommodation decreases steadily from later childhood, the speed and accuracy of the system within the available amplitude are little impaired until the age of about 40, when the amplitude falls below that needed for normal near work. A review of the available evidence on age-related change in the lens, capsule, ciliary body and other relevant ocular structures confirms that geometric and viscoelastic lenticular changes play major roles in the progressive loss of accommodation. Other factors may also contribute in an, as yet, unquantified way and a full understanding of the origins of presbyopic change remains elusive.
222 citations
TL;DR: The frequency response of the accommodative system is investigated using three stimuli: defocus blur, the effects of the chromatic aberration of the eye, and changing target size, which suggests that besidesdefocus blur both chromatic Aberration and changing size are involved in accommodative control.
140 citations
TL;DR: The ordered arrangement of spectral foci produced by LCA seems to be a fundamental aspect of the stimulus for "reflex" accommodation, and gaining and phase-lag increases when LCA is eliminated, and reversing the aberration severely disrupts accommodation.
123 citations
TL;DR: It is found that accommodation is not driven at all by conventional rendering methods, but that it is driven surprisingly quickly and accurately by the method with defocus and chromatic aberration incorporated.
Abstract: Blur occurs naturally when the eye is focused at one distance and an object is presented at another distance. Computer-graphics engineers and vision scientists often wish to create display images that reproduce such depth-dependent blur, but their methods are incorrect for that purpose. They take into account the scene geometry, pupil size, and focal distances, but do not properly take into account the optical aberrations of the human eye. We developed a method that, by incorporating the viewer's optics, yields displayed images that produce retinal images close to the ones that occur in natural viewing. We concentrated on the effects of defocus, chromatic aberration, astigmatism, and spherical aberration and evaluated their effectiveness by conducting experiments in which we attempted to drive the eye's focusing response (accommodation) through the rendering of these aberrations. We found that accommodation is not driven at all by conventional rendering methods, but that it is driven surprisingly quickly and accurately by our method with defocus and chromatic aberration incorporated. We found some effect of astigmatism but none of spherical aberration. We discuss how the rendering approach can be used in vision science experiments and in the development of ophthalmic/optometric devices and augmented- and virtual-reality displays.
103 citations
TL;DR: The monocular, steady-state response to targets under various colors of illumination is investigated and it is shown that the ocular longitudinal chromatic aberration increases slightly with accommodation.
Abstract: Previous studies of the effects of color on the accommodation response are reviewed. The monocular, steady-state response to targets under various colors of illumination is investigated. It is shown that trained observers change their level of accommodation, when viewing a target at a constant distance, to compensate for the varying ocular longitudinal chromatic aberration as the color of the target is changed. Untrained subjects, however, may initially show inconsistent responses. Results in white and greeen are closely comparable. Dynamic aspects of these effects are illustrated and it is shown that the ocular longitudinal chromatic aberration increases slightly with accommodation. The results are related to current ideas on the accommodative system.
102 citations
References
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TL;DR: Using this optometer, the nature of the accommodation responses when young emmetropic subjects were presented monocularly with a variety of focus-stimulating conditions is investigated.
Abstract: It is not till recently that an optometer has become available (Campbell, 1956; Campbell & Robson, 1959) that enables one to obtain continuous, high-resolution records of changes in the refractive power of the human eye. Using this optometer we have investigated the nature of the accommodation responses when young emmetropic subjects were presented monocularly with a variety of focus-stimulating conditions.
216 citations
TL;DR: An optometer of new design is described which uses infrared energy and therefore possesses the advantage of not acting as a glare source or as a stimulus to accommodation, and is suitable for use in research, but it might readily be modified to suit particular users.
Abstract: The various methods which have been used to detect changes in the refractive power of the eye due to accommodation are reviewed. An optometer of new design is described which uses infrared energy and therefore possesses the advantage of not acting as a glare source or as a stimulus to accommodation. The instrument has a noise equivalent to about 0.05 diopters when it is adjusted to detect fluctuations of accommodation from 0 to 5 cps. Normal fixation movements of the eye do not interfere with the measurements of refractive power. The optometer as described has been constructed from standard optical components which make it suitable for use in research, but it might readily be modified to suit particular users.
101 citations
TL;DR: A servoanalysis of the feedback control system for lens accommodation has been based upon experimental evidence designed to explore the nonlinear properties, and two related models, one with quite unusual aspects, are presented, and independent evidence for these adduced.
Abstract: A servoanalysis of the feedback control system for lens accommodation has been based upon experimental evidence designed to explore the nonlinear properties. Because these nonlinearities are essential to the functioning of the system, a describing function approach was employed. Computation served to obtain open-loop characteristics. The transfer function of the linear part is F( s) = 4 ( 1 + 0.15s) e-0." s ( 1 + 2 [ 0.3( 0.08)] + ( 0.08s) 2) ( 4) and some assignments of portions of this equation to the physical elements of the lens system are suggested. The no-memory nonlinearity has general saturation characteristics; two related models, one with quite unusual aspects, are presented, and independent evidence for these adduced. The combined model accounts for large and small signal responses, stability characteristics, predicts certain noise spectral features of the openand closed-loop lens system. Phase discrepancies, possible sampled data properties, and the even-error-signal operator put forward crucial new experiments.
83 citations
64 citations
TL;DR: An optical monitor is described which records simultaneously and dynamically lens deformation, pupil diameter, and accommodative vergence in human subjects in response to accommodative stimulation.
Abstract: An optical monitor is described which records simultaneously and dynamically lens deformation, pupil diameter, and accommodative vergence in human subjects in response to accommodative stimulation. The stimulus is in the form of an illuminated target moving on the optical axis of one eye. The lens, pupil, and vergence responses are recorded by using infrared-sensitive photodiodes and photomultipliers. The responses are measured and recorded in real time and also are averaged by computer to give ensemble-average responses. The monitor system has a bandwidth to 30 Hz on all channels. System sensitivities are 0.15 diopters, 0.01 mm, and 0.1 deg for lens, pupil diameter, and vergence measurements, respectively. The stimulus dynamic range is 0 to 10 diopters of target position. Computer averages of step responses show marked asymmetrical characteristics of the ocular system.
52 citations