80 research outputs found
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Independent and reciprocal accommodation in anisometropic amblyopia
Accommodation is considered to be a symmetrical response and to be driven by the least ametropic and nonamblyopic eye in anisometropia. We report the case of a 4-year-old child with anisometropic amblyopia who accommodates asymmetrically, reliably demonstrating normal accommodation in the nonamblyopic eye and antiaccommodation of the amblyopic eye to near targets. The abnormal accommodation of the amblyopic eye remained largely unchanged during 7 subsequent testing sessions undertaken over the course of therapy. We suggest that a congenital dysinnervation syndrome may result in relaxation of accommodation in relation to near cues and might be a hitherto unconsidered additional etiological factor in anisometropic amblyopia
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Convergence and accommodation development is pre-programmed in premature infants
Purpose This study investigated whether vergence and accommodation development in pre-term infants is pre-programmed or is driven by experience.
Methods 32 healthy infants, born at mean 34 weeks gestation (range 31.2-36 weeks) were compared with 45 healthy full-term infants (mean 40.0 weeks) over a 6 month period, starting at 4-6 weeks post-natally. Simultaneous accommodation and convergence to a detailed target were measured using a Plusoptix PowerRefII infra-red photorefractor as a target moved between 0.33m and 2m. Stimulus/response gains and responses at 0.33m and 2m were compared by both corrected (gestational) age and chronological (post-natal) age.
Results When compared by their corrected age, pre-term and full-term infants showed few significant differences in vergence and accommodation responses after 6-7 weeks of age. However, when compared by chronological age, pre-term infants’ responses were more variable, with significantly reduced vergence gains, reduced vergence response at 0.33m, reduced accommodation gain, and increased accommodation at 2m, compared to full-term infants between 8-13 weeks after birth.
Conclusions When matched by corrected age, vergence and accommodation in pre-term infants show few differences from full-term infants’ responses. Maturation appears pre-programmed and is not advanced by visual experience. Longer periods of immature visual responses might leave pre-term infants more at risk of development of oculomotor deficits such as strabismus
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Asymmetrical accommodation in hyperopic anisometropic amblyopia
Background/Aims: To investigate the presence of asymmetrical accommodation in hyperopic anisometropic amblyopia.
Methods: Accommodation in each eye and binocular vergence were measured simultaneously using a PlusoptiX SO4 photorefractor in 26 children aged 4 to 8 years with hyperopic anisometropic amblyopia and 13 controls (group age-matched) whilst they viewed a detailed target moving in depth.
Results: Without spectacles, only 5 (19%) of anisometropes demonstrated symmetrical accommodation (within the 95%CI of the mean gain of the sound eye of the anisometropic group), whereas 81% demonstrated asymmetrical accommodation. Of those, 15 (58%) showed aniso-accommodation and 6 (23%) demonstrated “anti-accommodation” (greater accommodation for distance than for near). In those with anti-accommodation the response gain in the sound eye was (0.93 ±0.20) whilst that of the amblyopic eye showed a negative accommodation gain of (-0.44 ±0.23). Anti-accommodation resolved with spectacles. Vergence gains were typical in those with symmetrical and asymmetrical accommodation.
Conclusion: The majority of hyperopic anisometropic amblyopes demonstrated non-consensual asymmetrical accommodation. Approximately one in four demonstrated anti-accommodation
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Intermittent exotropia: are we underminusing by not overminusing?
In this invited commentary, the authors discuss whether the use of minus lenses to aid control of intermittent exotropia has an alternative method of action. Conventional theory suggests that the lenses induce accommodation and therefore accommodative convergence to reduce the angle of deviation. We discuss evidence which suggests that convergence is induced to control the primary deviation and that the minus lenses allow this control by correcting refractive blur caused by additional vergence accommodation
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Neural correlates of true and false memory in mild cognitive impairment
The goal of this research was to investigate the changes in neural processing in mild cognitive impairment. We measured phase synchrony, amplitudes, and event-related potentials in veridical and false memory to determine whether these differed in participants with mild cognitive impairment compared with typical, age-matched controls. Empirical mode decomposition phase locking analysis was used to assess synchrony, which is the first time this analysis technique has been applied in a complex cognitive task such as memory processing. The technique allowed assessment of changes in frontal and parietal cortex connectivity over time during a memory task, without a priori selection of frequency ranges, which has been shown previously to influence synchrony detection. Phase synchrony differed significantly in its timing and degree between participant groups in the theta and alpha frequency ranges. Timing differences suggested greater dependence on gist memory in the presence of mild cognitive impairment. The group with mild cognitive impairment had significantly more frontal theta phase locking than the controls in the absence of a significant behavioural difference in the task, providing new evidence for compensatory processing in the former group. Both groups showed greater frontal phase locking during false than true memory, suggesting increased searching when no actual memory trace was found. Significant inter-group differences in frontal alpha phase locking provided support for a role for lower and upper alpha oscillations in memory processing. Finally, fronto-parietal interaction was significantly reduced in the group with mild cognitive impairment, supporting the notion that mild cognitive impairment could represent an early stage in Alzheimer’s disease, which has been described as a ‘disconnection syndrome’
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Children’s accommodation to a variety of targets – a pilot study
Background: Previous research indicates that a significant proportion of children underaccommodate
at 1/3 m. Accommodation may vary with task demand, so children may accommodate
appropriately if required, for example, when reading small print. This study explores the range
of accommodative responses elicited in typical children, under naturalistic conditions, to a range
of targets.
Method: We identified 24 typically developing children from the University of Reading Child
Database. Primary-school children attending UK Year 2 (age 6-7 years) or Year 6 (age 10-11
years) with minimum distance visual acuity of 0.200 logMAR and near visual acuity of 0.100
logMAR were recruited for participation. A remote haploscopic photorefractor was used to assess
naturalistic, sustained, binocular accommodative responses to a variety of targets. At 33 cm,
accommodative targets included individual letters, age-appropriate text in large print equivalent
to early primary-school books, small N5 equivalent print, a visual search task (“Where’s Wally?”), a
clown picture containing a range of spatial frequencies, and a children’s cartoon. Participants were
given minimal instructions for task completion. The target presentation order was counterbalanced.
The results reported in this study were obtained during a longer testing session involving
different target types and fixation distances.
Results: The accommodative response observed with each target varied across participants to
both the clown target and single letters of a size used in school reading books the accommodative
responses were 2.4±0.48 D (range 0.85-2.97 D) and 2.47±0.37 D (range 1.48-3.09 D), respectively.
The accommodative response to N5 print (3.06±0.52 D) was statistically better than all
other targets other than the visual search and larger print tasks (P<0.05).
Conclusions: Even to demanding N5 text, accommodation is variable between participants, but is
better than that to less demanding targets. Tasks experienced by children in everyday or clinical
situations will stimulate an unknown amount of accommodation for near fixation
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The effects of acute wild blueberry supplementation on the cognition of 7-10 year old schoolchildren
Purpose: Previous evidence suggests consumption of flavonoids, a sub-class of polyphenols, is associated with improved cognitive function across the lifespan. In particular, acute intervention of a flavonoid-rich wild blueberry (WBB) drink has been shown to boost executive function (EF), short-term memory and mood 2-6 h post-consumption in 7-10 yr old children. However, confirmation of the aspects of EF and memory susceptible to WBB ingestion is required, particularly during childhood, a critical period of neurological development. In addition, the child literature on berry-flavonoid supplementation and cognition highlights the potential for such interventions to elicit positive benefits to real world educational scenarios, such as reading; a complex ability which relies upon aspects of cognition already known to improve following WBB.
Methods: Here we examined which aspects of EF and memory are susceptible to acute WBB, as well as investigating whether acute WBB could further benefit reading ability. Fifty-four healthy children, aged 7-10 yrs, consumed a 200ml WBB drink (253mg anthocyanins) or a matched placebo according to a randomised, single-blind, parallel groups design. Verbal memory (Auditory Verbal Learning Task; AVLT), EF (Modified Attention Network Task; MANT), and reading efficiency (Test of Word Reading Efficiency-2; TOWRE-2) were assessed at baseline and 2 h post consumption.
Results: For the MANT, significantly quicker RTs were observed for WBB participants when compared to placebo participants on 120 ms trials, without cost to accuracy. Furthermore, WBB participants showed enhanced verbal memory performance on the AVLT, recalling more words than placebo participants on short delay and memory acquisition measures post-consumption. Despite these significant improvements in cognitive performance, no significant effects were observed for reading measures.
Conclusion: Consumption of WBB was found to significantly improve memory and attentional aspects of EF. This indicates that a flavonoid-rich blueberry product, equivalent to 240 g or 1½ cups of fresh blueberries can provide acute cognitive benefits in children. These findings support accumulating evidence that flavonoid-rich products are beneficial for healthy brain function, particularly during critical developmental periods. However, the lack of findings relating to reading ability suggested acute WBB may not be sufficient to elicit benefits to reading. Chronic supplementation and other more sensitive reading measures should be considered for examining the effects of WBB on such a complex skill in the future
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Change in convergence and accommodation after two weeks of eye exercises in typical young adults
Abstract: Introduction
Although eye exercises appear to help heterophoria, convergence insufficiency and intermittent strabismus, true treatment effects can be confounded by placebo, practice and encouragement factors. This study assessed objective changes in vergence and accommodation responses in typical naïve young adults after two weeks of exercises compared to control conditions to assess the extent of treatment effects occur above other factors.
Methods
156 asymptomatic young adults were randomly assigned to 6 exercise groups or 2 no-treatment groups. Treatment targeted i) accommodation, ii)vergence, iii) both, iv) convergence>accommodation, v)accommodation>convergence, or vi) a placebo. All were re-tested under identical conditions, except for the second control group who were
additionally encouraged during testing. Objective accommodation and vergence were assessed to a range of targets moving in depth containing combinations of blur, disparity and proximity/looming cues.
Results
Response gain improved more for less naturalistic targets where more improvement was possible. Convergence exercises improved vergence for near across all targets (P=.035). Mean accommodation changed similarly,but non-significantly. No other treatment group differed significantly from the non-encouraged control group, while encouraging effort produced significantly increased vergence (P=.004) and accommodation (P=.005) gains in the other control group.
Conclusions
True treatment effects were small, only significantly better after vergence exercises to a non-accommodative target, and were rarely related to response they were designed to improve. Exercising accommodation without convergence made no difference to accommodation to cues
containing detail. Additional effort improved objective responses the most, so should be controlled carefully in research, and considered when auditing treatment
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Using a runway paradigm to assess the relative strength of rats' motivations for enrichment objects
Laboratory animals should be provided with enrichment objects in their cages; however, it is first necessary to
test whether the proposed enrichment objects provide benefits that increase the animals’ welfare. The two main
paradigms currently used to assess proposed enrichment objects are the choice test, which is limited to determining
relative frequency of choice, and consumer demand studies, which can indicate the strength of a preference but are complex to design. Here, we propose a third methodology: a runway paradigm, which can be used to assess the strength of an animal’s motivation for enrichment objects, is simpler to use than consumer demand studies, and is faster to complete than typical choice tests. Time spent with objects in a standard choice test was used to rank several enrichment objects in order to compare with the ranking found in our runway paradigm. The rats ran significantly more times, ran faster, and interacted longer with objects with which they had previously spent the most time. It was concluded that this simple methodology is suitable for measuring rats’ motivation to reach enrichment objects. This can be used to assess the preference for different types of enrichment objects or to measure reward system processes
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Accommodation and vergence response gains to different near cues characterize specific esotropias
Aim. To describe preliminary findings of how the profile of the use of blur, disparity and proximal cues varies between non-strabismic groups and those with different types of esotropia.
Design. Case control study
Methodology. A remote haploscopic photorefractor measured simultaneous convergence and accommodation to a range of targets containing all combinations of binocular disparity, blur and proximal (looming) cues. 13 constant esotropes, 16 fully accommodative esotropes, and 8 convergence excess esotropes were compared with age and refractive error matched controls, and 27 young adult emmetropic controls. All wore full refractive correction if not emmetropic. Response AC/A and CA/C ratios were also assessed.
Results. Cue use differed between the groups. Even esotropes with constant suppression and no binocular vision (BV) responded to disparity in cues. The constant esotropes with weak BV showed trends for more stable responses and better vergence and accommodation than those without any BV. The accommodative esotropes made less use of disparity cues to drive accommodation (p=0.04) and more use of blur to drive vergence (p=0.008) than controls. All esotropic groups failed to show the strong bias for better responses to disparity cues found in the controls, with convergence excess esotropes favoring blur cues. AC/A and CA/C ratios existed in an inverse relationship in the different groups. Accommodative lag of >1.0D at 33cm was common (46%) in the pooled esotropia groups compared with 11% in typical children (p=0.05).
Conclusion. Esotropic children use near cues differently from matched non-esotropic children in ways characteristic to their deviations. Relatively higher weighting for blur cues was found in accommodative esotropia compared to matched controls
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