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Results for “ACCOMMODATION, OCULAR”

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At least 613 records · Page 34Linked to original sources
PubMed2006

Neural correlates of the dependence of compensatory eye movements during translation on target distance and eccentricity.

To stabilize objects of interest on the fovea during translation, vestibular-driven compensatory eye movements [translational vestibulo-ocular reflex (TVOR)] must scale with both target distance and eccentricity. To identify the neural correlates of these properties, we recorded from different groups of eye movement-sensitive neurons in the prepositus hypoglossi and vestibular nuclei of macaque monkeys during lateral and fore-aft displacements. All neuron types exhibited some increase in modulation amplitude as a function of target distance during high-frequency (4 Hz) lateral motion in darkness, with slopes that were correlated with the cell's pursuit gain, but not eye position sensitivity. Vergence angle dependence was largest for burst-tonic (BT) and contralateral eye-head (EH) neurons and smallest for ipsilateral EH and position-vestibular-pause (PVP) cells. On the other hand, the EH and PVP neurons with ipsilateral eye movement preferences exhibited the largest vergence-independent responses, which would be inappropriate to drive the TVOR. In addition to target distance, the TVOR also scales with target eccentricity, as evidenced during fore-aft motion, where eye velocity amplitude exhibits a "V-shaped " dependence and phase shifts 180 degrees for right versus left eye positions. Both the modulation amplitude and phase of BT and contralateral EH cells scaled with eye position, similar to the evoked eye movements during fore-aft motion. In contrast, the response modulation of ipsilateral EH and PVP cells during fore-aft motion was characterized by neither the V-shaped scaling nor the phase reversal. These results show that distinct premotor cell types carry neural signals that are appropriately scaled by vergence angle and eye position to generate the geometrically appropriate compensatory eye movements in the translational vestibulo-ocular reflex.

Accommodation, Ocular↗
PubMed1992

Functional roles of the lateral suprasylvian cortex in ocular near response in the cat.

The lateral suprasylvian (LS) area, an extrastriate visual area in the cat, has been suggested to play an important role in processing motion in 3-dimensional visual space. In addition, the LS area is related to all three components of the ocular near response, i.e. lens accommodation, pupillary constriction, and ocular convergence: microstimulation in this area evoked these intra- and extraocular movements, and neuronal discharges associated with these movements were also found. Anatomical pathways, direct and indirect, from this area to premotor nuclei in the brainstem are known to exist. The present paper reviews studies useful for assessing the functional roles played by the LS area in triggering and modulating component movements in the ocular near response.

Accommodation, Ocular↗
PubMed1993

The outcome of strabismus surgery in childhood esotropia.

The results of squint surgery in 118 children with non-paralytic childhood esotropia are analysed. A 'favourable outcome', defined as a final alignment within +/- 10 dioptres of straight, or within +/- 20 dioptres of straight if there was evidence of binocular single vision, was achieved in 86 (72.9%) children. The factors affecting the final outcome are discussed, including age of onset, age at the time of surgery, pre-operative and post-operative amblyopia, refractive error, anisometropia, the surgical procedures used, and post-operative ocular alignment.

Accommodation, Ocular↗
PubMedDate not supplied

Differential retinal-defocus magnitude during eye growth provides the appropriate direction signal.

INTRODUCTION: The rate of ocular growth can be modified by the imposition of either plus or minus lenses before the eyes, which creates changes in retinal defocus. Several hypotheses with relatively complicated mechanisms have been proposed to explain these changes, but the underlying mechanism has remained elusive. MATERIAL AND METHODS: Our new analysis using schematic models, however, provides a relatively simple and logically-consistent explanation of how retinal defocus magnitude alone during ocular growth gives the requisite sign for an appropriate change in ocular growth rate. RESULTS: During a normal genetically-determined incremental increase in axial length, the presence of either an imposed plus or minus lens results in an increase or decrease, respectively, of the blur circle magnitude. Neuromodulators in the retina are proposed to regulate the sensitivity to retinal-image contrast by means of a local feedback mechanism, and the alteration in retinal-image contrast associated with the change in blur circle causes an increase or decrease, respectively, in the rate of release of neuromodulators as well as the rate of proteoglycan synthesis, the latter being associated with the structural integrity of the sclera. CONCLUSION: This provides the critical sign, as well as amplitude, information needed to modulate appropriately the rate of eye growth, to result in a decrease or increase, respectively, in the rate of ocular growth.

Accommodation, Ocular↗
PubMed1954

Dynamic retinoscopy.

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Accommodation, Ocular↗
PubMed2005

Dynamic control of ocular disaccommodation: first and second-order dynamics.

Velocity and acceleration characteristics provide valuable information about dynamic control of accommodation. We investigated velocity and acceleration of disaccommodation (near-far focusing) from three starting positions. Peak velocity and peak acceleration of disaccommodation increased with the proximity of starting position however for a given starting position they were invariant of response magnitude. These results suggest that all disaccommodation responses are initiated towards a constant primary destination and are switched mid-flight to attain the desired final position. Large discrepancies between the primary destination and desired final position appear to produce overshoots and oscillations of small responses from proximal starting positions.

Accommodation, Ocular↗