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At least 667 records · Page 37Linked to original sources
PubMed2005

Six-month variability of the dark-adapted pupil diameter.

PURPOSE: To determine the individual variability of the dark-adapted pupil diameter over 6 months using a standardized dark-adaptation protocol. SETTING: Texas Tech University Health Sciences Center, Lubbock, Texas, USA. METHODS: This prospective observational cohort study comprised volunteers with no history of ocular disease, surgery, or injury other than requirement for refractive correction. The right eye was tested. A standardized dark-adaptation protocol was used that controlled for accommodation and patient alertness. Infrared, still digital photographs were taken after 10 minutes of dark adaptation at 1 lux and were analyzed using digital image software. Testing was performed at baseline in the afternoon, at 3 months in the afternoon, and at 6 months in the morning. Lifestyle factors such as diet and exercise were not controlled. RESULTS: Mean intersession differences were 0.04 mm (95% confidence interval [CI]: -0.68-0.146), 0.15 mm (95% CI: -0.001-0.297), and 0.09 mm (95% CI: -0.048-0.236) for baseline-3 month, baseline-6 month, and 3 month-6 month comparisons, respectively. None of these differences was significantly different from zero (P>.05, 2-tailed Student t tests). The likelihood that the mean intersession difference was >.25 mm was negligible for all comparisons (P=.9996, .9099, and .9829 respectively, 1-tailed Student t tests). CONCLUSION: When a consistent dark-adaptation protocol that controls for alertness and accommodation is used, normal young individuals showed no significant variation in the dark-adapted pupil diameter over a 6-month period.

Accommodation, Ocular↗
PubMed2002

The dependence of binocular contrast sensitivities on binocular single vision in normal and amblyopic human subjects.

We have measured monocular and binocular contrast sensitivities in response to medium to high spatial frequencies of vertical sinusoidal grating patterns in normal subjects, anisometropic amblyopes, strabismic amblyopes and non-amblyopic esotropes. On binocular viewing, contrast sensitivities were slightly but significantly increased in normal subjects, markedly increased in anisometropes and esotropes with anomalous binocular single vision (BSV) and significantly reduced in esotropes and exotropes without BSV. Application of a prismatic correction to the strabismic eye in order to achieve bifoveal stimulation resulted in a significant reduction in contrast sensitivity in esotropes with and without anomalous BSV, in exotropes and in non-amblyopic esotropes. Control experiments in normal subjects with monocular viewing showed that degradative effects of the prism occurred only with high prism powers and at high spatial frequencies, thus establishing that the reduced contrast sensitivities were the consequence of bifoveal stimulation rather than optical degradation. Displacement of the image of the grating pattern by 2 deg. in normal subjects and anisometropes by a dichoptic method to simulate a small angle esotropia had no effect on the contrast sensitivities recorded through the companion eye. By contrast, esotropes showed similar reductions in contrast sensitivity to those obtained with the prism experiments, confirming a fundamental difference between subjects with normal and abnormal ocular alignments. The results have thus established a suppressive action of the fovea of the amblyopic eye acting on the companion, non-amblyopic eye and indicate that correction of ocular misalignments in adult esotropes may be disadvantageous to binocular visual performance.

Accommodation, Ocular↗
PubMedDate not supplied

Are optical aberrations during accommodation a significant problem for refractive surgery?

PURPOSE: To study the limits to a perfect ideal customized wavefront correction due to the change of aberrations during accommodation. METHODS. We measured the dynamic changes of ocular aberrations during accommodation in normal eyes with a real-time Hartmann-Shack wavefront sensor. Those results were used in computer simulations to predict the benefit of a perfect customized correction. RESULTS: Due to the continuous changes of the aberrations over time, an ideal perfect static correction will not provide stable aberration-free optics. For example, when the eye accommodates to near objects, due to the changing aberrations, the eye will become aberrated again. An alternative correction using the aberration pattern for a slightly accommodated condition could provide a better-correction in a larger accommodative range, although at the cost of non-perfect correction for far vision. CONCLUSIONS: Due to the dynamic nature of ocular optics, a static perfect correction, for instance performed in customized refractive surgery, would not remain perfect for every condition occurring during normal accommodation.

Accommodation, Ocular↗
PubMed1990

A review of non-retinal ocular complications of diabetes mellitus.

Significant attention is paid to the retinal complications of diabetes mellitus and their potentially devastating effects on vision. Diabetes mellitus, however, is a multisystem disease, and diabetic eye disease is an end-organ response to the effects of the condition on the human system. Each portion of the eye is susceptible to the harmful effects of diabetes. This article reviews diabetic effects on non-retinal ocular structures and provides references for those interested in pursuing further studies on diabetic eye disease.

Accommodation, Ocular↗
PubMed2005

Ocular compensation for alternating myopic and hyperopic defocus.

During development, the eye grows under visual feedback control, as shown by its compensating for defocus imposed by spectacle lenses. Under normal conditions the sign and magnitude of defocus vary with viewing distance, accommodative status and other factors. To explore how periods of myopic and hyperopic defocus are integrated over time we presented rapidly alternating episodes of myopic and hyperopic defocus by sequentially illuminating a nearby scrim and the wall beyond it to chick eyes wearing lenses that put the far point between the two surfaces. We found that equal periods of myopic and hyperopic defocus generally led to compensatory hyperopia, showing that myopic defocus had a disproportionate effect. Furthermore, the degree of hyperopia depended on the frequency of alternation: low frequencies (1 cycle/30 min) resulted in more hyperopia, whereas at high frequencies (1 cycle/s) the myopic and hyperopic defocus nearly cancelled each other. If similar temporal integration effects apply to humans, they may help explain why brief accommodation events may not influence lens-compensation and why a child's total reading time may be a poor predictor of myopic progression.

Accommodation, Ocular↗
PubMed2004

Day to day variability of the dark-adapted pupil diameter.

PURPOSE: To determine the individual variability of the dark-adapted pupil diameter over 2 testing sessions using a standardized dark-adaptation protocol. SETTING: Texas Tech University Health Sciences Center, Lubbock, Texas, USA. METHODS: In this prospective observational cohort study, 40 volunteers with no history of ocular disease, surgery, or injury other than requirement for refractive correction were included. The right eye was tested. A standardized dark-adaptation protocol was used that controlled for accommodation and patient alertness. Infrared, still digital photographs were taken after 5 and 10 minutes of dark adaptation and analyzed independently by 2 investigators using digital-image software. Two test sessions were performed 1 to 7 days apart. Lifestyle factors such as sleep, diet, and exercise were not controlled. RESULTS: The mean subject age was 31.5 years (range 20 to 49 years). There were 20 men; 27 subjects wore correction for myopia, and 13 wore no correction. The mean interval between test sessions was 2 days (range 1 to 7 days). The mean difference and 95% confidence intervals for pupil diameter difference between sessions were as follows: 5-minute readings, +0.032 mm (-0.030 to +0.094); 10-minute readings, -0.006 mm (-0.059 to +0.047); mean of 5- and 10-minute readings, +0.013 mm (-0.038 to +0.064). Using the paired t test, the pupil diameter did not differ significantly between sessions in 5-minute dark adaptation (P =.2980), 10-minute dark adaptation (P =.8263), or the mean (P =.6049). CONCLUSION: Using a consistent dark-adaptation protocol that controlled for alertness, individuals aged 20 to 49 years showed no significant variation in dark-adapted pupil diameter when tested twice in 1 week.

Accommodation, Ocular↗
PubMed1984

Saccadic anomalies: vergence induces large departures from ball-and-socket behavior.

The configuration of muscular forces, which maintains a given orientation of the eye, varies with vergence state. As a consequence, changes in vergence produce both static and dynamic violations of simple ball-and-socket behavior: during strong convergence, the entire eye is displaced temporally within its orbit at steady state by as much as 200 microns; and the axis of ocular rotation for small horizontal saccades is consistently displaced forward within the globe by an average of about 1 mm. These phenomena occur regardless of whether vergence is maintained by accommodation or by binocular disparity. Hence, systematic errors of as much as a full degree can arise in measurement of vergence movement, unless monitoring methods are used which are insensitive to translational motion. The observed displacement on the axis of rotation for saccades may be involved in subjective shrinkage of visual targets during convergence ("experimental micropsia ").

Accommodation, Ocular↗
PubMed1993

Characteristics of early onset esotropia.

Some 115 patients with a reported onset of esotropia within the first six months of life were studied retrospectively to assess ocular findings and the evolution of any changes with time. All patients had been treated by one ophthalmologist and one orthoptist since 1972. Of the 115 patients, 27% had an accommodative element associated with the esotropia. Patients with an accommodative esotropia had higher levels of hypermetropia when compared to the non-accommodative group, but there were no other distinguishing characteristics. The groups exhibited a large variation in angle size, ranging from four to 45 degrees at the initial visit. The presence of fusion, amblyopia and the degree of hypermetropia had no significant effect on the course of the squint. Amblyopia was noted in 67% of cases and appeared to stabilise at a later-than-expected age, with 66% of patients with amblyopia stabilising between eight and 11 years. Surgical intervention had no effect on the incidence of amblyopia at the initial or final visits.

Accommodation, Ocular↗
PubMed1986

The elucidation and use of the effect of near fixation in congenital nystagmus.

It has frequently been reported that the spontaneous ocular oscillation in congenital nystagmats is less intense for near viewing than during distance fixation. The reason for this effect was sought, and the influences of monocular adduction, convergence and accommodation acting separately and synergistically were assessed. The frequent assumption that nystagmus intensity (amplitude and frequency) is determined by convergence angle (either symmetrical or asymmetrical) was confirmed, and it was found that binocular viewing was not necessary. An identical effect on nystagmus intensity could be created for distance fixation by the use of base-out prisms, and these were prescribed for constant wear in two congenital idiopathic nystagmats. Although nystagmus intensity was constantly reduced, no concomitant increase in binocular contrast sensitivity or Snellen visual acuity occurred.

Accommodation, Ocular↗
PubMed1997

[Why and how to correct myopia?].

The myopia and its aggravation depend on genetic and environmental factors. Experiences performed on monkeys and chickens indicate that the quality of the image affects the growth on the ocular globe in the young animal by modifying biochemical conditions at the retinal level. If near work seems to be a factor associated to the myopia, the role of sustained accommodation on the evolution of the former is not evident. The correction of the myopia by glasses can be made with the help of different materials that will be chosen according to the importance of the myopia, the morphology of the face, the priority of the esthetics or the security.

Accommodation, Ocular↗
PubMed1984

Visual stabilization of posture. Physiological stimulus characteristics and clinical aspects.

Visual stabilization of posture is critically dependent on stimulus characteristics as well as on the performance of the visual system. The purpose of the present investigation was to obtain quantitative data in man by means of posturography of fore-aft and lateral body sway in relation to different visual stimulus characteristics. Visual acuity, when decreased logarithmically, causes a linearly increasing postural instability, twice as prominent for fore-aft than for lateral sway. Any measurable visual contribution for fore-aft sway ceases with an acuity lower than 0.03 and for lateral sway with an acuity lower than 0.01. The central area of the visual field as compared with the peripheral retina dominates postural control. The foveal region exhibits a powerful contribution, in particular for lateral sway. A partial but significant visual stabilization is preserved with a visual input rate between 1 to 4 Hz flicker frequency. As soon as continuous motion perception becomes involved with frequencies higher than 4 Hz, visual stabilization gradually improves with a saturation at frequencies higher than 16 Hz. Lateral body sway activity and eye-object distance are linearly related: body sway decreases with increasing distance corresponding to the linear decrease of net retinal displacement with increasing eye-object distance. Aspects of 'afferent' and 'efferent' visual motion perception, which involve fore-aft and lateral body sway differently, are evaluated. The clinical relevance is demonstrated in patients with oculomotor disturbances. The results are discussed with respect to the variety of related clinical disorders, which involve reduction in visual acuity, field defects, accommodation disturbances and ocular oscillations.

Accommodation, Ocular↗
PubMed1994

Neuro-ophthalmic findings in botulism type B.

In June 1989, the largest recorded outbreak of food-borne botulism occurred in the United Kingdom. Twenty-seven patients were affected during the outbreak with type B botulism. A case note review of 14 patients admitted with this condition was performed and the neuro-ophthalmic findings are presented. Patients with severe disease presented with a combination of ocular and bulbar symptoms; in mild cases dysphagia was noted first and visual disturbance followed within 24 hours. Clustering of cases and bilaterality of cranial nerve signs aided in the diagnosis. Accommodative paresis and sixth cranial nerve palsy were frequent early signs. When there was respiratory paralysis and ventilatory failure, it occurred within 12 hours of the onset of a third cranial nerve palsy.

Abducens Nerve↗
PubMed2003

Further evidence that chick eyes use the sign of blur in spectacle lens compensation.

Young animals compensate for defocus imposed by positive or negative spectacle lenses by adjusting the elongation rate of their vitreous chambers, thus matching the length of the eye with the focal length of the eye's optics combined with the spectacle lenses. The ability to compensate for either negative or positive lenses could rely on the ability to distinguish between myopic and hyperopic blur, or it could rely on the fact that positive lenses would bring nearby objects into focus, thereby reducing the amount of blur, whereas negative lenses would not. This study asks whether eyes emmetropize using the magnitude of blur or the sign of blur as a directional cue. We fitted chick eyes with positive lenses while imposing a substantial amount of blur, either (a) by having them wear lenses only when restrained in the center of a cylinder, the walls of which were beyond their far-point or (b) by having them wear mild diffusers over positive lenses. We found good refractive compensation in both situations in a large number of birds. Furthermore, we found that mild diffusers worn on top of positive lenses differentially affected the two ocular components of refractive compensation: there was less choroidal thickening, but more inhibition of ocular elongation, compared to wearing positive lenses alone. These findings argue both that the eye can discern the sign of the blur and that choroidal and ocular-elongation components of the refractive compensation do not respond identically to visual inputs.

Accommodation, Ocular↗
PubMed2003

Presbyopia among normal individuals.

BACKGROUND: To define ocular variables that might affect the need for early use of reading glasses. METHODS: A retrospective, non-randomized clinical trial was conducted at an aero-medical center. The charts of 100 healthy male pilots who suffered from presbyopia were reviewed. All subjects had undergone a complete eye examination every year for 30 years. Ocular parameters measured at the ages of 20, 30, 40, 45, and 50 years were recorded. Individuals were divided into two groups: those who needed reading glasses at the age of 45 years or earlier (group 1) and those who had needed reading glasses after 45 years of age (group 2). RESULTS: Of all the ocular variables examined each year, two differed significantly between the two groups. Refraction at age 20 was 0.1+/- 0.3 D in group 1 and 0.0 +/- 0.3 D in group 2 ( P <0.05). Amplitude of accommodation at age 20 was 9.5 +/- 1.2 D in group 1 and 9.9 +/- 1.0 D in group 2 ( P <0.05). CONCLUSION: Hyperopia and low amplitude of accommodation at the age of 20 might predispose to early development of presbyopia in normal individuals.

Accommodation, Ocular↗
PubMed1995

Ocular adverse effects of neuropsychiatric agents. Incidence and management.

Neuropsychiatric agents may adversely affect the eye in various ways. The more frequently encountered effects include corneal oedema and pigmentary changes in the lens and cornea which are induced by phenothiazine derivatives; thioridazine-induced retinopathy; tricyclic antidepressant-induced accommodation interference and glaucoma; and lithium carbonate-induced exophthalmos and papilloedema. Several adverse effects, such as corneal oedema, retinopathy and glaucoma, are vision-threatening, and patients often fail to describe their symptoms properly. A more precise understanding of these conditions is essential for prompt diagnosis and appropriate treatment.

Accommodation, Ocular↗
PubMed2006

Monochromatic ocular wave aberrations in young monkeys.

High-order monochromatic aberrations could potentially influence vision-dependent refractive development in a variety of ways. As a first step in understanding the effects of wave aberration on refractive development, we characterized the maturational changes that take place in the high-order aberrations of infant rhesus monkey eyes. Specifically, we compared the monochromatic wave aberrations of infant and adolescent animals and measured the longitudinal changes in the high-order aberrations of infant monkeys during the early period when emmetropization takes place. Our main findings were that (1) adolescent monkey eyes have excellent optical quality, exhibiting total RMS errors that were slightly better than those for adult human eyes that have the same numerical aperture and (2) shortly after birth, infant rhesus monkeys exhibited relatively larger magnitudes of high-order aberrations predominately spherical aberration, coma, and trefoil, which decreased rapidly to assume adolescent values by about 200 days of age. The results demonstrate that rhesus monkey eyes are a good model for studying the contribution of individual ocular components to the eye's overall aberration structure, the mechanisms responsible for the improvements in optical quality that occur during early ocular development, and the effects of high-order aberrations on ocular growth and emmetropization.

Accommodation, Ocular↗
PubMedDate not supplied

Clinical experience with the Tracey technology wavefront device.

PURPOSE: In refractive surgery, measuring the total ocular profile of refraction gives more vital information than measuring the cornea alone. We report the first clinical experiments with spatially resolved refractometry using ray tracking principles. Tracey technology was developed in Ukraine by the Institute of Biomedical Engineering in cooperation with the Vardinoyannion Eye Institute of Crete. METHODS: The Tracey-1 device was evaluated in comparison with conventional videokeratoscopes. Seven pseudophakic eyes of 7 patients and two phakic eyes were measured thirty (30) consecutive times (consecutively) each to test reproducibility. Measurements were provided in zones 0 to 5 (6) mm. For each zone, parameters of astigmatism were calculated and mean value and standard deviation were derived. RESULTS: Standard deviation on the order of 0.14 D was derived. CONCLUSION: The Tracey Technology wavefront device provides information on the refraction distribution at the first principal plane of the ocular optical system. For the instrument to provide measurements that are directly applicable to clinical practice, the data should be transposed to the corneal plane. The Tracey device can be utilized for the measurement of accommodative amplitude and range. Further development of the instrument is requred to increase its accuracy.

Accommodation, Ocular↗