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[Diabetes mellitus and the state of ocular accommodation in schoolchildren].

The author presents characteristics of refraction in 67 children and adolescents suffering from diabetes mellitus. The state of accomodative function of the eyes was studied in 39 schoolchildren with spherical refraction. Accomodation was found to be reduced in diabetic schoolchildren, this being connected with a prolonged course of the main disease.

Accommodation, Ocular↗
PubMed1975

Vestibular-ocular accommodation reflex in man.

Stimulation of the vestibular system by angular acceleration produces widespread sensory and motor effects. The present study was designed to study a motor effect which has not been reported in the literature, i.e., the influence of rotary acceleration of the body on ocular accommodation. The accommodation of 10 young men was recorded before and after a high-level deceleration to zero velocity following 30 s of rotation. Accommodation was recorded continuously on an infrared optometer for 110 s under two conditions; while the subjects observed a target set at the far point, and while they viewed the same target through a 0.3-mm pinhole. Stimulation by high-level rotary deceleration produced positive accommodation or a pseudomyopia under both conditions, but the positive accommodation was substantially greater and lasted much longer during fixation through the pinhole. It is hypothesized that this increase in accommodation is a result of a vestibular-ocular accommodation reflex.

Accommodation, Ocular↗
PubMed1983

Ocular accommodation in human infants.

The present longitudinal investigation evaluated the proficiency of the human ocular accommodation system during the 20-week period after birth. Fourteen human infants were tested at specific intervals during the age of 2 through 20 weeks. At each age the refractive state of the eyes during fixation of a vertical-striped, high-contrast stimulus pattern presented at viewing distances ranging from 10 to 50 cm was measured by dynamic retinoscopy. The accommodative performance of the infants demonstrated the following: (1) the newborn accommodation system executes reasonably appropriate responses to weak dioptric stimuli; (2) accommodative accuracy generally decreases from 2 through 8 weeks of age; and (3) accommodative accuracy increases beyond 8 weeks of age until adult-like levels of proficiency are attained between 16 and 20 weeks. Factors which could affect individual accommodative responses and explanations for the observed developmental pattern of accommodative performance are discussed.

Accommodation, Ocular↗
PubMed1995

Red-green opponent channel mediation of control of human ocular accommodation.

1. It has been hypothesized, but not verified empirically, that the control of human ocular accommodation is mediated by either the red-green or yellow-blue colour channels. Our goal was to determine experimentally whether the red-green channel by itself could influence the accommodative response. 2. To find out, we isolated the red-green channel through chromatic bandpass filtering and measured accommodation under dynamic and static conditions. The effect of this filtering was to modulate the red-green channel without disturbing either the yellow-blue or luminance channels. 3. Accommodative gain (ratio of response to stimulus amplitude) declined monotonically with decreasing bandwidth under dynamic conditions. Because the outputs of both the luminance and yellow-blue colour channels did not vary with bandwidth, the only explanation is that the red-green opponent process was responsible for the effect. 4. Under static conditions, however, accommodation was independent of bandwidth. This may be attributable to the decreased sensitivity to chromatic contrast that occurs at low temporal frequencies.

Accommodation, Ocular↗
PubMed1995

Single-unit activity in the primate nucleus reticularis tegmenti pontis related to vergence and ocular accommodation.

1. In the present study we used single-unit recording techniques in alert rhesus monkeys to investigate a precerebellar nucleus, the nucleus reticularis tegmenti pontis (NRTP), for neurons related to vergence and ocular accommodation. 2. In the medial NRTP, we identified 32 cells with activity that linearly increased with increases in the amplitude of the near response and 33 cells with activity that linearly increased with increases in the amplitude of the far response. These near and far response neurons were often encountered close to neurons displaying saccade-related activity, but their activity was related neither to saccadic nor to smooth pursuit eye movements. Micro-stimulation at the site of near or far response neurons often produced changes in vergence angle and accommodation. 3. The NRTP is known to receive cortical afferents and to have reciprocal connections with the cerebellum; therefore it is likely that the near and far response neurons in the medial NRTP form part of a cerebropontocerebellar pathway modulating or controlling vergence and ocular accommodation.

Accommodation, Ocular↗
PubMed1985

The effects of task performance on ocular accommodation and perceived size.

Two studies were conducted to test the hypothesis that performance of cognitive tasks tends to induce outward shifts in ocular accommodation that, in turn, result in changes in perceived size. In the first study, 12 subjects participated in each of 4 conditions; rest or performance of a running-memory task each with either visual or auditory stimuli. In each condition, subjects made four size judgments and their mean accommodation was measured using an infrared optometer. Dark focus of accommodation was measured before and after the experiment. There were no reliable differences among the four conditions, nor between the pre- and postexperiment dark-focus measures. A second study was conducted in which the accommodative state of 10 subjects was recorded during 4 min of rest and 4 min of performing a backward-counting task. The difference between the mean accommodative state during the last minute of rest and task performance approaches statistical reliability. It was concluded that outward shifts in accommodation may be associated with performance of tasks that involve distant targets (e.g., other aircraft in the surrounding airspace) and/or require complex mental transformations (e.g., predicting future position of an intruder aircraft relative to your own aircraft).

Accommodation, Ocular↗
PubMed1985

Modification of pattern reversal VERs by ocular accommodation.

The amplitudes and implicit times of the P-1 component of monocular transient pattern VERs elicited by reversing checkerboard targets were measured in 6 conditions: (1) Ocular accommodation (Ao) elicited by minus power ophthalmic lenses; (2) Ao stimulated by minus lenses with the natural pupil of the test eye dilated and replaced by an artificial pupil; (3) accommodative demand and pupil size fixed with retinal image size (Ir) changed by afocal minifying lenses, (4) accommodative demand and Ir fixed but pupil size changed; (5) Ao elicited by minus lenses for three sizes of reversing checkerboards, and (6) Ao elicited by minus lenses for a constant checkerboard size with three check sizes. The observed decrease in VER amplitude with Ao could not be attributed entirely to the effects of pupil size or Ir. The rate at which the amplitude of P-1 decreased with Ao was not affected by checkerboard check size, but was closely correlated with checkerboard field size. The implicit time of P-1 first decreased slightly below baseline values at low and moderate levels of Ao and then tended to increase significantly at higher levels. The increase in implicit time at high levels of Ao could be explained adequately by the effects of pupil size alone on the VER. However, where Ao occurred without pupillary miosis, the increase in implicit time could only be explained by focusing error.

Accommodation, Ocular↗
PubMed1995

Evolution of control system models of ocular accommodation, vergence and their interaction.

This paper reviews the evolution of inferential models describing ocular accommodation and vergence, which have been developed using the techniques of control engineering. The models are developed by inferring that the observed behaviour of the ocular systems could be produced by particular types of feedback control systems. The models are subsequently tested and improved by modifications resulting from the comparison of model predictions with physiological experimentation. Current models of accommodation and vergence have had considerable success in describing both the steady-state and dynamic behaviours of the individual systems. However, controversy currently exists among researchers, particularly with respect to the composition of models that describe the interaction of the two systems.

Accommodation, Ocular↗
PubMed1994

Behavior of identified Edinger-Westphal neurons during ocular accommodation.

1. The present study used single-unit recording and antidromic activation techniques in alert rhesus monkeys to examine the static and dynamic behavior of 21 parasympathetic, preganglionic neurons of the Edinger-Westphal nucleus (EW) during ocular accommodation. 2. All identified EW neurons were active when viewing at optical infinity with an average firing rate of 11.6 spikes/s. During near viewing, there was a linear relationship between firing rate and accommodation with an overall gain for the population of preganglionic EW neurons of 3.3 (spikes/s)/diopter. 3. The activity of eight identified EW neurons was studied during viewing of targets with conflicting vergence and accommodative demands to dissociate their vergence and accommodation responses. With normal viewing these responses are so closely matched that it cannot be determined if the activity of a cell is related to vergence or to accommodation, but with dissociated viewing these relationships can be determined. Under this viewing condition, six preganglionic EW neurons showed the same relationship to accommodation as they did during normal viewing. However, the activity of two cells could not be explained solely by accommodation, and they showed some activity related to vergence. 4. Microstimulation at the sites of identified EW neurons produced accommodation in the ipsilateral eye. Repeated measures of the effect of microstimulation yielded a value of 75 ms for the latency of the response. This latency was essentially the same in both animals tested. 5. The activity of identified EW neurons is related to the velocity of accommodation as well as to static accommodation. The relationship between accommodation velocity and firing rate was studied for 15 identified EW neurons during sine-wave tracking of targets moving in depth. All of these cells showed a clear relationship between firing rate and accommodation velocity. Overall, this group of identified EW neurons showed a velocity sensitivity of 1.2 (spikes/s)/(diopter/s) and an estimated neural time constant of 380 ms. 6. Eleven neurons encountered near to preganglionic EW neurons could not be antidromically activated by stimulation of the oculomotor nerve. These neurons had statistically higher gains with respect to the near response; indeed, there was no overlap between the gains of these neurons and the gains of preganglionic EW neurons. Upon dissociation of vergence from accommodation, they were found to be related to either vergence or to vergence and accommodation but not solely to accommodation.

Accommodation, Ocular↗