Reduced accommodation in children with Down syndrome.

PURPOSE: To examine the accommodative accuracy and amplitude in children with Down syndrome. Accommodation is usually assumed to be good in children and is rarely measured. METHODS: A dynamic retinoscopy technique was developed that allows rapid and reliable measures of accuracy and amplitude of accommodation in infants and children. RESULTS: Use of the dynamic technique with a small sample of schoolchildren with Down syndrome shows that 80% have reduced amplitude of accommodation, in comparison to a control group of developmentally normal children. CONCLUSIONS: Optometric management of children with Down syndrome should include consideration of accommodation.

Accommodation and refractive error in children with Down syndrome: cross-sectional and longitudinal studies.

PURPOSE: To examine the relationship between defective accommodation and refractive errors in children with Down syndrome. METHODS: Children with Down syndrome aged 4 to 85 months were seen at their homes as part of an ongoing study of visual development. Seventy-five children contributed cross-sectional data and 69 children longitudinal data. Accommodation was measured using a modification of Nott dynamic retinoscopy technique, and refractive error measurements were obtained using Mohindra retinoscopy. RESULTS: Accommodation was poor, regardless of the refractive error present. The total accommodation produced by the children was related to the refractive error at the time of the test, with the degree of accommodation deficit increasing with the amount of positive refractive error. The longitudinal results showed that although children with Down syndrome did not accommodate accurately, the amount of accommodation elicited did not reflect their maximum amplitude of accommodation. Each child showed a consistent degree of underaccommodation for a given stimulus. Spectacles to correct hypermetropia did not improve the accommodative response. CONCLUSIONS: In children with Down syndrome, underaccommodation is substantial, even when there is no, or a fully corrected, refractive error. The accommodation system of children with Down syndrome may have the physical capacity to respond to a given stimulus, but the neural control of the system has an anomalous set point. Spectacles do not remedy the situation. This has important implications, especially for children in a learning environment, because near vision is consistently out of focus.

The effect of age, size of target, and cognitive factors on accommodative responses of children with Down syndrome.

PURPOSE: To investigate possible factors that may be implicated in the poor accommodative responses of individuals with Down syndrome. This article evaluates the effect of age, angular size of target, and cognitive factors on accommodation. METHODS: Seventy-seven children with Down syndrome who are participating in an ongoing study of visual development were assessed. One hundred thirty-one developmentally normal children took part in a previous study and provided control data. Accommodation was measured using a modified Nott dynamic retinoscopy technique. RESULTS: Children with Down syndrome showed considerably poorer accommodative responses than normally developing children. No target used in the present study produced an improved response in children with Down syndrome. Age, angular subtense of target, and cognitive factors could not fully account for the poor accommodation in children with Down syndrome. CONCLUSIONS: Poor accommodation is a common feature of Down syndrome, regardless of the target used. The etiology of the deficit has yet to be established. It is imperative that educators and clinicians are aware that near vision is out of focus for these children.

The Cardiff acuity test used for measuring visual acuity development in toddlers.

The Cardiff acuity test was used in estimating the binocular and monocular visual acuity norms of 231 toddlers between 12 and 36 months. Mean binocular acuity increased from 4.5 to 1.2 min arc and monocular acuity from 4.5 to 1.4 min arc over the age range. Interocular acuity difference was not significant and for 99% of the children, the difference in acuity estimate was < or = 1/3 octave. Success rates ranged from 96 to 100% for binocular tests but fell to a range of 41-91% for monocular testing. Acuity assessment was fast and the intraobserver reliability was high. Age norms of visual acuity useful in clinical settings are presented for toddlers between the ages of 12 and 36 months.

Emmetropisation in human infancy: rate of change is related to initial refractive error.

Animal studies show that the rate of recovery from experimentally induced refractive errors is related to the level of ametropia induced. The present study examined the rate of emmetropisation occurring in a sample of 22 human infants refracted by near retinoscopy during the first six months of life and then again between 12 and 17 months old. None of the subjects were myopic. Regression analysis revealed that emmetropisation occurred more rapidly in the presence of high refractive errors (P < 0.005 and P = 0.001 for hyperopia and astigmatism respectively). These data confirm the findings of the animal studies and suggest that non-reducing hyperopia and astigmatism in the second year of life may require correction.

Heart defects and ocular anomalies in children with Down's syndrome.

AIMS: To investigate whether ocular anomalies are associated with congenital heart defects in children with Down's syndrome. METHODS: 58 children with Down's syndrome were entered into a retrospective observational study. Children were assigned to heart defect groups based on medical records. Optometric tests had previously been carried out at the homes of the children. RESULTS: A relation between congenital cardiac defects, myopia, and nystagmus was observed. Heart problems were not related to accommodative insufficiency, hyperopia, or strabismus. CONCLUSION: In children with Down's syndrome heart defects were associated with both myopia and nystagmus.

The modified frisby stereotest.

BACKGROUND: The Frisby stereotest commonly is used in clinical practice to estimate stereoacuity. Assessment of the presence or absence of stereopsis is valuable particularly in toddlers because of the difficulties encountered in this age group with assessment of other aspects of visual function, such as monocular visual acuities. METHODS: The present study describes two modifications to the Frisby stereotest: 1) the introduction of a nonstereo practice plate; and 2) the use of an auditory "reward" for correct identification of the target. These modifications aim to increase the success rate of the test and provide a means to discriminate between testable and untestable children. Subjects were 165 children aged between 0.5 and 47 months. RESULTS: The modifications improved the age range over which results could be obtained with the Frisby test, allowing infants as young as 7 months to complete testing. By 12 months of age, more than 60% of children were able to complete testing. The modifications also allowed the examiner to distinguish untestable children from those without stereopsis. CONCLUSIONS: By simple modification of the Frisby stereotest, the authors have increased the ease with which the Frisby stereotest can be used to assess stereoacuity in infants and children and provided a means by which children unable to cooperate with testing can be distinguished from those without stereopsis.

How to help children with neurodevelopmental and visual problems: a scoping review.

Children with visual impairment and a condition affecting their neurodevelopment (children with VND) may require extensive and specialised help but evidence on the most effective strategies for visual improvement is lacking. We defined a PICO format (Population, Intervention, Comparator, Outcome) for a scoping review and systematically searched 13 databases. Two reviewers assessed the abstracts for inclusion and a third arbitrated in cases of disagreement. We abstracted data from included studies. We found 4450 abstracts from which we identified 107 papers for inclusion. Of these, 42 related to interventions involving a change in visual input or function: 5 controlled trials, 8 before and after studies and 29 case reports. The strongest evidence supported the provision of spectacles to improve distance or near vision and the use of ultraviolet light as environmental modification for training. Less strong but suggestive evidence supported training/practice routines to improve acuity or oculomotor control. Interventions exist to help children with VND and current recommendations that they are assessed by a vision specialist are supported by the evidence. More information is needed on the effectiveness of training/practice programmes which may promote improved function, and of environmental modifications to facilitate engagement of children with VND with the surroundings.

Investigating and managing the child with special needs.

Children with disabilities are much more at risk of eye and vision problems than are able children. These problems can take the form of 'optical' defects such as refractive errors and poor accommodation. Thus children with all forms of special needs not only have a right to Optometric services, but have a greater need than the rest of the population. This paper presents recent data on the defects found specifically in children with Down's Syndrome, (but likely to occur in other children) and provides general guidelines for Optometrists working with children with special needs.

Practical applications of the contrast sensitivity function.

The contrast sensitivity function, as a statement of visual capabilities over a wide range of object sizes, has proved to be a valuable tool in the study of visual mechanisms. This paper examines the more clinical applications of the function which may be of interest to practising optometrists. These applications include the assessment of binocularity and aids to the recognition of conditions not picked up by more conventional tests.

Rivalry with continuous and flashed stimuli as a measure of ocular dominance across the visual field.

Two measures of sensory ocular dominance were compared. Both involved dichoptic presentation of orthogonal gratings--a situation which results in binocular rivalry. The gratings were presently briefly in experiment 1 and continuously in experiment 2 and by the predominance of one grating over the other a quantitative estimation of ocular dominance was obtained in both cases. Comparison of the results showed that (a) binocular rivalry suppression was present for exposures of 250 ms and (b) the briefly presented gratings were a more sensitive test for ocular dominance than conventional continuously presented stimuli. The variation of dominance over the horizontal meridian of the visual field was considered. For many subjects a consistent different in the ocular dominance in the two halves of the visual field, and therefore of the cortex, was found. Some showed dominance of the ipsilateral eye in each hemisphere while others showed dominance of the contralateral eye. It was found that there is, in fact, a continuum of types of dominance pattern amongst individuals.

Visual fitness to drive after stroke or head injury.

The visual requirements for driving in Britain are outlined and how they might be compromised following stroke or head injury examined. The role of the optometrist in assessing such patients who wish to resume driving is discussed. Topics discussed include legal considerations, the relationship between visual problems and driving ability and the vision-testing techniques that are most appropriate for use with the brain injured. An illustrative case history is presented.

Reading performance with low vision aids: relationship with contrast sensitivity.

Reading performance and contrast sensitivity were measured in 30 subjects with low vision due to a variety of pathologies. The Pepper test was used to quantify reading rate and accuracy with the subject's own prescribed optical reading low vision aid. It was found that both reading rate and accuracy were repeatable measures. Reading rates were found to be correlated with contrast sensitivity at 0.5 c/deg (r = 0.62). Multiple regression analysis also showed that the best predictor of reading rate was contrast sensitivity at 0.5 c/deg and that no other components of the contrast sensitivity function helped to explain more of the variance. This indicates that primarily low spatial frequencies are necessary for reading with optical low vision aids, as has been found previously for reading with a close circuit TV system.

Genetic and environmental factors in orientation anisotropy: a field study in the British Isles.

Visual acuity for the detection of gratings at four orientations was measured for groups of ten boys and ten girls aged five to seven years, from the following four populations: Scots in Glasgow, Pakistanis in Glasgow, Gaels in Stornoway (Outer Hebrides) and East Anglians in Littleport (Cambridgeshire fenlands). The Glaswegians, both Scottish and Pakistani, showed the normal pattern of anisotropy, with poorest acuity for oblique orientations; the East Anglians showed no significant anisotropy; while the Gaels were unusual in showing poorest horizontal acuity. A group of fourteen Pakistani children in Stornoway differed slightly from a matched group of Gaels. The group differences bore little relation to the visual environments, and were probably due to genetic or cultural factors. The relatively poor horizontal acuity of the Gaels was not correlated with astigmatism. Sex differences were also found, with the boys showing higher mean acuity and a higher ratio between vertical and oblique acuity.

A new illusion and possible links with the Münsterberg and Fraser illusions of direction.

In the course of an investigation of the Münsterberg illusion, a new illusion has been produced. The illusion is reduced to its simplest form and possible links to the original Münsterberg and Fraser illusions are suggested.

Further studies of the Café Wall and Hollow Squares illusions.

The effect of varying the contrast on the apparent convergence is measured for both the Café Wall and the Hollow Squares (Taylor-Woodhouse) illusions. The apparent convergence is dependent on the contrast, and also on the size of the stimulus, and varies in the same way for both illusions. This strengthens the argument that the illusions are not independent, as Taylor and Woodhouse originally claimed. McCourt has discussed brightness induction as a basis of the Café Wall illusion. Consideration of this theory leads to some interesting examples of interactions of the two illusions, and to a further, very strong, variation of the illusion in a real-life situation.

Assessment of techniques for measuring contrast sensitivity in children.

Contrast sensitivity was measured in 10 children aged from 3 to 11 years using 4 psychophysical techniques in order to establish the best method of measurement for clinical use. Of the four methods, staircase, ascending continuous, modified Von Bekesy and two-alternate forced-choice, the staircase was selected as the most appropriate clinical technique and monocular contrast sensitivity functions of normal children were measured.