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Results for “ACCOMMODATION (OCULAR)”

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PubMedDate not supplied

Prior topical anesthesia reduces time to full cycloplegia in Chinese.

PURPOSE: To investigate the effect of prior anesthesia on the time to full cycloplegia in young Chinese subjects. METHODS: The amplitude of accommodation was monitored over a 50-minute interval after the application of 1% cyclopentolate hydrochloride with a pretreatment of 0.4% benoxinate (oxybuprocaine) or 0.9% saline solution (control). Using a nonlinear mathematical model, the rate of accommodative loss (k) and the time required for 95% of total cycloplegia (T95%) were determined. RESULTS: Statistical analysis revealed a significantly faster rate of accommodative loss (P < .0001) after prior anesthesia (0.129 +/- 0.05) compared with the controls (0.103 +/- 0.04). T95% was noted at 26.43 +/- 10.22 minutes after prior anesthesia, which was significantly shorter (P < .0001) than that after the saline treatment (35.28 +/- 16.51 minutes). CONCLUSIONS: Prior application of topical anesthetic can shorten the time to full cycloplegia for people, such as the Chinese, with dark irides.

Accommodation, Ocular↗
PubMed2003

Refractive abnormalities in childhood.

The knowledgeable pediatrician can make a significant contribution to the management of refractive errors by aiding in the early recognition of abnormalities, making appropriate referrals, and reinforcing the ophthalmologist's recommendations to the family. If this article has focused the reader's attention and caused a few rays of light to fall on an important subject, it has achieved its purpose.

Accommodation, Ocular↗
PubMedDate not supplied

Dynamic retinoscopy: the missing data.

Dynamic retinoscopy is a well described but often overlooked technique that allows rapid assessment of accommodative ability. The key to the technique is the neutralization of the retinoscopic reflex that occurs when the patient accommodates on a target adjacent to the retinoscope. This clinical tool can provide critical data that can help solve treatment dilemmas, such as when a child presents with high hyperopia or when a patient presents at any age with possible accommodative insufficiency. In this review, performance of dynamic retinoscopy will be detailed, with the applicability of the technique demonstrated with use of case examples.

Accommodation, Ocular↗
PubMedDate not supplied

Compensation procedures for the anisometropic presbyope.

When changing to bifocal lenses from distance anisometropic lenses, presbyopic patients may experience diplopia when attempting to do close work. Prescription failure can be dramatically reduced by utilizing the procedures outlined in this article. Why would a patient experience diplopia when attempting to read with bifocals? The diplopia may simply be a result of the optical difference in power between the two lenses. Anisometropia creates a disparity in the size of the retinal image as well as a prismatic imbalance when looking away from the optical center. A practical approach to coping with these problems is recommended.

Accommodation, Ocular↗
PubMedDate not supplied

Refractive emergency.

Explore the source record for details and available documents.

Accommodation, Ocular↗
PubMedDate not supplied

Spasm of the near reflex: a spectrum of anomalies.

Spasm of the near reflex has been characterized as the variable appearance of pseudomyopia, convergent strabismus and miosis. These characteristics may appear together or separately. In addition, abnormalities of accommodation may appear not only as pseudomyopia, but may also be manifest in cases with significant hypermetropia in which the patient is unable to relax accommodation even when plus lenses are used. The intent of this review is to identify the various clinical presentations of anomalies of the entire near reflex as well as the component parts. The relationship to functional and organic disorders are discussed as well as the related neuroanatomy. We suggest that one may more readily understand the clinical manifestations as a spectrum of anomalies of the near reflex rather than a multitude of disconnected entities.

Accommodation, Ocular↗
PubMedDate not supplied

Visual complaints from healthy children.

It is common for healthy children with specific visual complaints to be seen for eye examinations. After a complete eye examination has ruled out pathologic conditions as the cause of these complaints, it is appropriate for the clinician to explore the possibility that normal entoptic or physiologic visual phenomena might have provoked the child's report of vision problems. Some of these normal visual experiences are frequent causes of children's complaints of vision problems, such as physiologic diplopia, relaxation of the near synkinesis during reading, and vitreous body floaters. Some complaints are common, even though the underlying entoptic or physiologic phenomenon may be speculative or obscure, such as the report that objects look bigger or smaller than they actually are. When the clinician encounters such situations, the parents and the child will be much more satisfied by an explanation of the normal system anatomy and physiology than by the simple reassurance that everything is all right.

Accommodation, Ocular↗
PubMed2000

On the linearity of accommodation dynamics.

Available experimental data on the gain and phase lags in the closed-loop accommodation responses to stimuli whose dioptric vergence changes sinusoidally with time are examined. It is shown that both phase lags and gain change almost linearly with the temporal frequency of the stimulus. This implies that the phase lags correspond to a frequency-independent time delay and that, if the system is linear, the impulse response should take a symmetrical (sin x/x)(2) form, with a corresponding standard form of step response. Comparison of this derived step response with the quasi-exponential results found experimentally underlines the limitations of attempting to generalize dynamic accommodation performance from responses obtained with predictable sinusoidally-changing stimuli and the application of a linear model. Consideration of the frequency response which would lead to an exponential step response supports the argument that, although the gain results obtained with sinusoidal stimuli are reasonably representative of those applying with other forms of stimulus, the predictable nature of sinusoidally-changing stimuli makes the derived phase lags inapplicable to non-predictable step or other stimuli. Other limitations in linear models of the response are discussed.

Accommodation, Ocular↗
PubMed2000

Why we need reading-glasses before a zimmer-frame.

Accommodative loss represents the fastest human biological decrement. Why? To examine this, the shape of the eye-lens during accommodation or its relaxation is analysed with special reference to age-related changes. The capsule is viewed as a force transmitter: the distribution of forces along centripetal capsular arcs and the resulting stresses and strains are calculated. The effect of zonular 'shifts' is considered. Age-related accommodative loss can be modelled successfully if changes in mechanical properties are linked to those in lenticular and capsular shape.

Accommodation, Ocular↗
PubMed2000

Developmental compensation of imposed astigmatism is not initiated by astigmatic accommodation in chickens.

PURPOSE: It is not clear whether emmetropization is confined to spherical refractive errors, or whether astiqmatic errors are also corrected via visual feedback. Experimental results from the animal model of the chicken are equivocal since compensation of imposed astimatic defocus was found in some but not all studies. Astigmatism could only be compensated by changes in the geometry of the cornea or lens. One has tested whether astigmatic spectacle lenses induce astigmatic accommodation as a possible first step of long-lasting compensation. METHODS: Thirty-five chickens were treated with cylinder lenses (+3/0D or -3/0D) for 5 h. Refractions were determined at 1.38 m distance without cycloplegia in hand-held chicks before attaching the lenses, with the lenses on (0 h), and after 3 and 5 h, and after removal of the lenses. Spheres (S), cylinders (C) and axes (A) were determined using infrared photoretinocopy in three axes (the 'PowerRefractor', equipped with a 135 mm lens). RESULTS: (1) The performance of the 'PowerRefractor' was tested in the chickens with trial lenses and gave correct refractions. (2) Astigmatic trial lenses induced refractive errors as expected from their powers in the case of +3/0D lenses: (S) +3.26 +/- 0.93D, (C) -3.45 +/- 0.87D). In the case of -3/0D lenses, slightly more hyperopic spheres were induced (refractions (S) +4.5 +/- 0.48D) but the cylinders were still as expected (-3.25 +/- 0.49D). The axes of astigmatism were correctly reproduced, since rotating the lenses changed the axes of the induced cylinders as expected. (3) Neither after 3 nor after 5 h of lens wear were there significant changes in the axes or the magnitude of astigmatism. Directly after removal of the lens, the refractions did not differ from their start-up values (with +3/0D lenses: (S) +3.31 +/- 1.05D vs. +3.22 +/- 0.76D, (C) -1.19 +/- 1.77D vs. -0.65 +/- 0.94D, (A) 96 +/- 49 vs. 113 +/- 45 deg; with -3/0D lenses: (S) 2.63 +/- 1.12D vs. 2.97 +/- 0.94D, (C) -1.11 +/- 1.15D vs. -0.53 +/- 0.56D, (A) 78 +/- 24 vs. 131 +/- 35 deg). CONCLUSIONS: The most intuitive mechanism for compensation of astigmatic refractive errors, astigmatic accommodation, could not be demonstrated in chickens. In light of this finding, it seems unlikely that a visually controlled mechanism is operating during development to reduced astigmatism by changing corneal or lenticular growth.

Accommodation, Ocular↗
PubMed2001

Closed-loop and open-loop accommodative vergence eye movements.

We examined accommodative vergence eye movements under conditions in which feedback about retinal-image slip was and was not present (i.e. closed-loop and open-loop conditions). We found that (a) in both conditions the two eyes started to move at the same time; (b) in the open-loop condition, vergence continued in both eyes; and (c) in the closed-loop condition, vergence continued in the occluded eye only, and the magnitude and velocity exceeded that of the occluded eye in the open-loop condition by a factor of two.

Accommodation, Ocular↗
PubMed2001

Dynamics of the accommodation response to abrupt changes in target vergence as a function of age.

The dynamic accommodation responses to small, abrupt changes in an accommodation stimulus were studied in two experiments. In the first, responses of 19 subjects with ages distributed between 18 and 49 years were measured for step stimuli of +/- 1.05 D. In the second, responses to small step stimuli (+/- 0.75, +/- 1.75 D) were recorded for a group of six 'young' (mean age 22, range 16-26 years) and six 'old' (mean age 42, range 36-48 years) subjects. In both experiments, the low target vergences always lay within the accommodation range of all subjects. Whether the data were analysed in terms of simple reaction and response times, or in terms of the frequency response, no marked systematic changes with age were found in the dynamics of the response in either of the experiments. It is concluded that, for small stimuli within the amplitude of accommodation, the response dynamics over the adult age range studied remain remarkably constant, even though the amplitude progressively reduces with age as complete presbyopia is approached.

Accommodation, Ocular↗
PubMed2001

Isolated short-wavelength sensitive cones can mediate a reflex accommodation response.

Both long- and middle-wavelength sensitive cones mediate the reflex accommodation signal but the contribution from the short-wavelength sensitive cones is unknown. A short-wavelength sensitive cone contribution could extend the range of the signed defocus signal from chromatic aberration. The aim was to determine whether isolated short-wavelength sensitive cones mediate reflex accommodation independently of long- and middle-wavelength sensitive cones. Accommodation was monitored continuously (eight subjects) to a sine-wave grating (3 cpd; 0.53 contrast) moving with a sum of sines motion in a Badal optometer. Two illumination conditions were used: a 'blue' condition that isolated short-wavelength sensitive cones, and a 'white' control condition that stimulated all three cone types. Of the eight subjects, two responded equally in the 'white' and 'blue' condition, four gave reduced responses in the 'blue' condition and two failed to respond in both conditions. The mean response in the 'blue' condition was reduced by 50% compared to the 'white' condition. Further analysis indicated that four of the eight subjects gave responses that were considerably greater than noise (S.D.>1.82) when short-wavelength sensitive cones were isolated. Some subjects can accommodate using only S-cones.

Accommodation, Ocular↗
PubMed2001

Fixation disparity and accommodation for stimuli closer and more distant than oculomotor tonic positions.

Both the vergence and the accommodative system have individual tonic positions (also referred to as dark vergence and dark focus, respectively) where the static response may be expected to be most accurate. This was confirmed by measuring fixation disparity with nonius lines and accommodation with an autorefractometer for foveal stimuli at viewing distances of 460, 100, 60, 40, and 30 cm. Multiple regression analysis was used at each viewing distance to predict fixation disparity from dark vergence, dark focus, accommodative gain and accommodative convergence: these accommodative measures had little effect on the inter-individual variability of near fixation disparity nor on the linear slope of fixation disparity as a function viewing distance.

Accommodation, Ocular↗