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A J Wilkins

Publications and source records attributed to A J Wilkins.

At least 19 recordsLinked to original sources
PubMed1999

A review of the management of 323 consecutive patients seen in a specific learning difficulties clinic.

Visual correlates of specific learning difficulties (SpLD) include: binocular instability, low amplitude of accommodation, and Meares-Irlen Syndrome. Meares-Irlen Syndrome describes asthenopia and perceptual distortions which are alleviated by using individually prescribed coloured filters. Data from 323 consecutive patients seen over a 15 month period in an optometric clinic specialising in SpLD are reviewed. Visual symptoms and headaches were common. 48% of patients were given a conventional optometric intervention (spectacles, orthoptic exercises) and 50% were issued with coloured filters, usually for a trial period. 40% of those who were given orthoptic exercises were later issued with coloured overlays. 32% of those who were issued with coloured overlays were ultimately prescribed Precision Tinted lenses. Approximately half the sample were telephoned more than a year after the last clinical appointment. More than 70% of those who were prescribed Precision Tints were still wearing them daily, and results for this intervention compared favourably with data for non-tinted spectacles. The data suggest that many people with SpLD need optometric care and that the optometrist needs to be skilled in orthoptic techniques and cognisant of recent research on coloured filters.

Accommodation, Ocular↗
PubMed1999

Treatment of photosensitive epilepsy using coloured glasses.

A recently introduced optometric technique, colorimetry, enables the perceptual effects of ophthalmic tints to be evaluated subjectively, optimized, and then prescribed in tinted spectacles. The new technique is beneficial in reducing visual stress in patients with dyslexia and migraine. We describe an open trial designed to ascertain: (1) whether the colorimetry assessment, as it is now given, is safe for the investigation of photosensitive patients in optometry clinics where colorimetry equipment is most readily available, but where EEG control is not practical; (2) what proportion of patients with photosensitive epilepsy is likely to benefit to the extent already described in individual cases; (3) whether a tint selected by colorimetry could be shown to reduce the incidence of paroxysmal epileptiform EEG activity in response to flicker and patterns, thereby validating the subjective methods and corroborating the reported seizure reduction. Twenty-four females and nine males (aged 12-43 years) took part. All the patients had suffered visually-provoked seizures, had exhibited a photoparoxysmal response on at least one previous EEG recording, and had received a diagnosis of photosensitive epilepsy. Twenty-two were currently experiencing seizures. A further EEG was recorded in all except seven cases: a routine resting record, followed by hyperventilation. Colorimetry was performed after hyperventilation and before photic stimulation. Twenty-three (70%) reported beneficial effects during colorimetry and were prescribed glasses. There was a preponderance of lenses with a rose or purple colour, in contrast to patients with dyslexia. Seventeen of the 23 patients were available at follow-up, an average of 2.4 years later. Thirteen (57%) reported benefits, and said they were still using the lenses. In six of the 13 the benefits were pronounced, including a reduction of dizziness from fluorescent lighting, elimination of aura when using computer screens etc. Only in three cases was there a reduction in seizures that could reasonably be attributed to the use of lenses; in two of these cases no medications were prescribed, and in the third the medications remained unchanged for four years, two before and two after the introduction of the glasses. In an additional four cases a reduction in seizures was observed but medication had been changed. There was a modest reduction in EEG photosensitivity with the coloured lenses but also to an equivalent or lesser extent with grey in all of the eight patients examined in this way. One patient had seizures during colorimetry, but the seizures were not accompanied by scalp EEG changes.

Adolescent↗
PubMed1997

Neuropsychological correlates of sustained attention in schizophrenia.

We employed a simple and relatively undemanding task of monotone counting for the assessment of sustained attention in schizophrenic patients. The monotone counting task has been validated neuropsychologically and is particularly sensitive to right prefrontal lesions. We compared the performance of schizophrenic patients with age- and education-matched controls. We then explored the extent to which a range of commonly employed neuropsychological tasks in schizophrenia research are related to attentional impairment as measured in this way. Monotone counting performance was found to be correlated with digit span (WAIS-R-HK), information (WAIS-R-HK), comprehension (WAIS-R-HK), logical memory (immediate recall) (Weschler Memory Scale, WMS), and visual reproduction (WMS). Multiple regression analysis also identified visual reproduction, digit span and comprehension as significant predictors of attention performance. In contrast, logical memory (delay recall) (WMS), similarity (WAIS-R-HK), semantic fluency, and Wisconsin Card Sorting Test (perseverative errors) were not correlated with attention. In addition, no significant correlation between sustained attention and symptoms was found. These findings are discussed in the context of a weakly modular cognitive system where attentional impairment may contribute selectively to a range of other cognitive deficits.

Adolescent↗
PubMed1997

What brings intentions to mind? An in situ study of prospective memory.

In a naturalistic study, we aimed to uncover the relationship between thinking about and remembering intentions. Electronic badges allowed us to track the activities of subjects within their work environment. Over two weeks, subjects were asked to respond using a button on their badges (1) every two hours (Time task); (2) whenever they were in a particular room (Place task). In addition, whenever they thought about the task, they were asked to indicate this with their badges. Although subjects thought about the Time task more, they forgot to respond more often than in the Place task. In the Time task, there was a marked absence of thoughts about the task following successful remembering. When subjects remembered the Place task, thoughts increased with proximity to the target location. In both tasks, thoughts about intentions occurred more in places such as stairwells than in locations where people tended to settle. On the basis of these findings, possible mechanisms for prospective memory are discussed.

Cues↗
PubMed1996

A preliminary investigation into the aetiology of Meares-Irlen syndrome.

A recent double-masked placebo-controlled trial has confirmed that some children experience a reduction in symptoms of eyestrain and headache when they read through individually prescribed coloured filters and has shown that this benefit cannot be solely attributed to a placebo effect. People who are helped by coloured filters in this way have been described as having "Meares-Irlen syndrome'. We investigated the mechanism of this benefit by studying the optometric and visual perceptual characteristics of the children in the double-masked study. This population had normal refractive errors and heterophorias (none of the subjects had strabismus). They demonstrated slightly, but significantly, reduced amplitudes of accommodation and vergence and poor stereo-acuity. However, these factors seemed to be correlates of Meares-Irlen syndrome rather than the underlying cause. Pattern glare, a sensitivity to striped patterns (e.g. lines of text), was prevalent in our sample and was significantly associated with the subjects' symptoms. The spatial contrast sensitivity function was normal.

Adolescent↗
PubMed1996

Gratings that induce perceptual distortions mask superimposed targets.

Masking is known to depend upon the relationship between the spatial-frequency content of target and mask. This relationship has been held constant in three experiments in order to investigate the separate contribution of the spatial parameters of the mask, in this case a grating with square-wave luminance profile. Thresholds for the detection of a probe target were highest when the background grating upon which the probe was superimposed had a spatial frequency of about 4 cycles deg-1 (experiment 1) and a duty cycle of 50% (experiment 3). In experiment 2, the thresholds were strongly affected by the size of the background grating even though the size of the target was small in proportion to the grating and remained constant. The increase in threshold was linearly related to the area of visual cortex to which the grating projected. The spatial parameters of gratings that maximise masking are therefore the same as those that have been shown to be optimal for the induction of perceptual distortions, suggesting a possible physiological mechanism for both the masking and the distortions.

Adult↗
PubMed1996

Rate of Reading Test: its reliability, and its validity in the assessment of the effects of coloured overlays.

A simple reading test that can be undertaken by disabled readers is described. The test is suitable for use in the optometric clinic, taking less than 2 minutes to administer per passage. Test-retest scores are acceptably reliable. The test reveals increases in the speed of reading when coloured overlays are used both (1) in children who have made long-term use of coloured overlays for reading, and (2) in children who will subsequently do so.

Child↗
PubMed1995

Thresholds for detection of a target against a background grating suggest visual dysfunction in migraine with aura but not migraine without aura.

Square-wave gratings with particular spatial characteristics induce visual illusions. Patients with migraine are particularly susceptible to these illusions and report discomfort. Their discomfort tends to be greater when the gratings are illuminated by red light, a tendency not shown by controls. Gratings that induce illusions have been found to impair the recognition of optically superimposed targets in headache-free control subjects. We measured the impairment of target detection under illuminants of various chromaticities in migraineurs with and without aura and in matched controls. Migraineurs with aura had significantly higher thresholds for target detection than either migraineurs without aura or controls; in addition, the effect of chromaticity was slightly more pronounced in both migraine groups than in the control group. These findings are consistent with a recent suggestion that migraine with aura might give rise to subclinical damage to the primary visual cortex.

Adult↗
PubMed1995

Optometric correlates of Meares-Irlen syndrome: a matched group study.

People who report visual perceptual distortions, typically when reading, that are alleviated by using coloured filters are described as suffering from 'Meares-Irlen Syndrome'. A recent double-masked placebo-controlled trial showed that this condition cannot be solely explained as a placebo effect and that the beneficial filter is idiosyncratic and sometimes needs to be highly specific. Several mechanisms have been suggested for Meares-Irlen Syndrome including ocular motor (binocular and accommodative) anomalies, a sensitivity to patterned stimuli (pattern glare), and a deficit of the transient visual sub-system. We investigated these hypotheses by comparing 16 children, who reported the symptoms described above and who showed a sustained benefit from coloured filters, with 25 control children who came from the same school and were matched for age, reading performance and intelligence. The 'Meares-Irlen Syndrome' group had slightly, but significantly, reduced vergence and accommodative amplitudes and stereo-acuity; they also demonstrated significantly more pattern glare. The two groups did not differ significantly in their visual acuities, refractive error, dissociated or associated heterophoria, AC/A ratio, or ability to perceive 20 Hz flicker. It appears that certain ocular motor factors are correlates of Meares-Irlen Syndrome, rather than the primary underlying cause of the symptoms. The results support the hypothesis that pattern glare may be involved in the mechanism of Meares-Irlen Syndrome.

Accommodation, Ocular↗
PubMed1994

Semantic memory is both impaired and anomalous in schizophrenia.

The integrity of semantic memory in schizophrenia was examined in a reaction time task requiring subjects to verify words as members or non-members of a conceptual category, where the words differed in their degree of semantic relationship to the category. Compared to matched normal controls, 28 schizophrenic patients were impaired on the task, showing slower responses in all conditions. In addition, their performance was anomalous in that they took longest to respond to items that were outside the category but semantically related to it, in contrast to the controls who took the longest to respond to ambiguous words at the borderline of the category. The pattern of 'yes' and 'no' responses of the patients was anomalous in a similar way. In both speed and accuracy of responding, the findings indicate that there is an outward shift of semantic category boundaries in schizophrenia.

Adult↗
PubMed1994

Double-masked placebo-controlled trial of precision spectral filters in children who use coloured overlays.

We selected 68 children who reported benefit from individually chosen sheets of coloured plastic placed upon the page when reading, and who used these regularly without prompting. These children viewed text illuminated by coloured light in an apparatus that allowed the separate manipulation of hue (colour) and saturation (depth of colour), at constant luminance. Many of the children reported improvements in perception when the light had a chromaticity within a limited range, which was different for each individual. A pair of plastic spectacle lenses ('experimental' lenses) was dyed so as to provide the appropriate chromaticity under conventional white (F3) fluorescent light. An additional pair was prepared having very similar colour but with a chromaticity outside the range in which perception was reported to improve ('control' lenses). Each pair was provided for 1 month in random order. The children kept diaries (36 completed) recording symptoms of eye-strain and headache. The children and those responsible for their assessment were unable reliably to distinguish 'experimental' from 'control' lenses. Nevertheless, symptoms were less frequent on days when the 'experimental' lenses were worn (P < 0.003).

Adolescent↗
PubMed1992

The common cold, pattern sensitivity and contrast sensitivity.

Results from two studies involving challenge with respiratory syncytial viruses showed that volunteers who developed colds were more sensitive to a visually distracting pattern presented prior to virus challenge than were volunteers who did not get a cold. Volunteers with sub-clinical infections reported more illusions after virus challenge than they had done before, whereas uninfected volunteers and those with colds tended to report fewer illusions on the second test. These effects did not occur when volunteers were challenged with either a coronavirus or rhinovirus. Overall, the results confirm that behavioural measures may be related to susceptibility to subsequent illness, and that viral infections may influence visual perception. They also show that the effects vary according to the nature of the infecting agent, which agrees with results from studies looking at other aspects of behaviour.

Adolescent↗
PubMed1992

Colorimeter for the intuitive manipulation of hue and saturation and its role in the study of perceptual distortion.

A simple optical method for mixing coloured light is described. The observer has intuitive and approximately independent control over hue and saturation at constant brightness. The method facilitates colour matching by unpracticed observers. It allows children with reading difficulties to select a colour that reduces perceptual distortion of text. The chromaticity coordinates of this colour vary from one observer to another but can be very specific. Complementary colours can exacerbate the distortions and induce pain. For the majority of children reporting beneficial perceptual effects, the u' coordinate is less than 0.25.

Adolescent↗
PubMed1991

A tint to reduce eye-strain from fluorescent lighting? Preliminary observations.

The rapid modulation of light from fluorescent lamps is responsible for eye-strain and headaches. The modulation is greater at certain wavelengths than at others, and it can therefore be reduced by wearing tinted spectacles. A tint was designed: (1) to minimize the luminous pulsation of light from conventional halophosphate fluorescent lamps; (2) to avoid as much as possible any concomitant increase in the pulsation from triphosphor lamps; (3) to interfere with colour perception as little as possible; and (4) to have a cosmetically acceptable colour appearance. The four design criteria conflict. A compromise design is described, together with case histories of patients who appear to have benefited from the use of the tint.

Adult↗