Cerebral visual impairment in children

Much of the brain is devoted to vision. Damage causes visual problems ranging from profound impairment, to cognitive visual problems only. A child with cerebral blindness may have intact perception of movement. The principal cognitive visual pathways comprise the dorsal and the ventral streams. The dorsal stream runs between the occipital lobes (which process incoming visual data), the posterior parietal lobes (which process the whole visual scene and give attention to component parts), the motor cortex (which facilitates movement through the visual scene) and the frontal cortex (which directs attention to chosen parts of the visual scene). The ventral stream runs between the occipital lobes and the temporal lobes (which enable recognition of people and objects, facilitate route finding and serve visual memory). Damage to these pathways disrupts these functions in a variety of combinations. This paper reviews cerebral visual impairment in children, the differential diagnosis and the management.

Spatial localization in esotropia: does extraretinal eye position information change?

PURPOSE

To investigate the accuracy of spatial localization in children with a specific type of convergent strabismus, fully accommodative esotropia.

METHODS

Two groups of children, with right and left fully accommodative esotropia, respectively, pointed at targets located centrally and eccentrically on a computer touchscreen without being able to see their hands. The size and the direction of the horizontal pointing responses were recorded under two conditions: when their eyes were aligned (wearing spectacles) and when they were squinting (not wearing spectacles). A group of children without strabismus but with hypermetropia were assessed as controls.

RESULTS

For both fully accommodative groups, the pointing responses to the central target shifted in the direction of the nonsquinting eye when deviations were manifest. No difference was found for the eccentric targets. No difference was found for the hypermetropia group with any target.

CONCLUSIONS

These results are consistent with an alteration in the extraretinal eye position information (efference copy, extraocular muscle proprioception, or both) that is used in spatial localization.

Reduced accommodative function in dyskinetic cerebral palsy: a novel management strategy

A 9-year-old boy with dyskinetic cerebral palsy secondary to neonatal encephalopathy is described. He presented with blurring of near vision which had begun to impact on his school work. Objective assessment of accommodation showed that very little was present, although convergence was almost normal. The near-vision symptoms were completely removed and reading dramatically improved with the provision of varifocal spectacles. Varifocal lenses provide an optimal correction for far, intermediate (i.e. for computer screens), and near distances (i.e. for reading). Managing this type of patient with varifocal spectacles has not been previously reported. It is clearly very important to prescribe an optimal spectacle correction to provide clear vision to optimize learning.

Periventricular leukomalacia: an important cause of visual and ocular motility dysfunction in children

The immature visual system in infants born preterm is vulnerable to adverse events during the perinatal period. Periventricular leukomalacia affecting the optic radiation has now become the principal cause of visual impairment and dysfunction in children born prematurely. Visual dysfunction is characterized by delayed visual maturation, subnormal visual acuity, crowding, visual field defects, and visual perceptual-cognitive problems. Magnetic resonance imaging is the method of choice for diagnosing this brain lesion, which is associated with optic disk abnormalities, strabismus, nystagmus, and deficient visually guided eye movements. Children with periventricular leukomalacia may present to the ophthalmologist within a clinical spectrum from severe cerebral visual impairment in combination with cerebral palsy and mental retardation to only early-onset esotropia, normal intellectual level, and no cerebral palsy. Optimal educational and habilitational strategies need to be developed to meet the needs of this group of visually impaired children.

Transorbital optic nerve sheath ultrasonography in normal children

AIM

Early diagnosis of acute intracranial hypertension is essential to enable prompt, optimal treatment. The optic nerve sheath diameter (ONSD) is increased in raised ICP and there has been recent interest in the use of ultrasound to diagnose and indirectly monitor raised ICP by ONSD measurement. The advantages of the technique include its non-invasiveness, wide availability, portability, low cost and the absence of ionizing radiation. This prospective study was designed to establish the range of normal values for ONSD in infants and children up to 15 years of age.

PATIENTS AND METHODS

One hundred and two children attending the hospital for other reasons were recruited to the study. Three measurements of the ONSD were taken for each eye, 3 mm behind the optic nerve head using a 7 MHz sector probe.

RESULTS

The range for ONSD was 2.1-4.3 mm, mean 3.08 (SD 0.36). There were no significant differences on ONSD measurement between boys and girls (P = 0.59) or between right and left eyes (P=0.66). When the data were grouped and analysed, a correlation between increasing age and increasing ONSD was seen (r2=0.48), with the greatest increase occurring in the first 2 months of life.

CONCLUSION

Using the technique described here, our results suggest that an ONSD of greater than 4 mm in infants less than 1 year, and 45 mm or greater in older children, should be regarded as abnormal.

Effect of oral administration of vitamin C on human aqueous humor ascorbate concentration

AIM

To study oral administration of vitamin C on human aqueous humour ascorbate concentration.

METHODS

High performance liquid chromatography (HPLC) coupled with electrochemical detector (ECD) was used. The effect of oral administration of various doses of ascorbic acid, 0 (control), 1.0, 1.5, 2.0, 3.0, and 5.0 g, on its concentration in aqueous humour, obtained from volunteer cataract patients was studied.

RESULTS

The concentration of ascorbic acid in aqueous humour of control group (without administration of vitamin-C tablet or drug containing ascorbic acid was (254 +/- 119) mg.L-1. This study revealed that the administration of 2.0 g of ascorbic acid saturate the aqueous humour and further increase in the dose (3.0 g and 5.0 g) did not increase its concentration in aqueous humour, although its concentration was increased in plasma.

CONCLUSION

Oral administration of 2.0 g of Vc is sufficient to saturate the aqueous humour where it may be helpful in controlling the intra-ocular pressure.

Evidence of cognitive visual problems in children with hydrocephalus: a structured clinical history-taking strategy

Damage to the occipital cortex in children can result in many complex disorders of cognitive visual function. A series of clinical questions, developed from the specific problems of a cohort of children with cortical visual impairment, was asked of the parents of 200 children with no history of cerebral pathology, aged 5 to 12 years. One hundred and ninety-two parents gave reliable consistent responses. The results show a progressive improvement in performance with age, culminating in few 11- and 12-year olds having frequent problems, apart from 8% having frequent difficulty with orientation in new surroundings and 2% having problems with simultaneous perception tasks. The parents of 52 children (aged 5 to 17 years) with shunted hydrocephalus were then asked the same set of questions. Evidence of cognitive visual problems was identified in 27 of these children of whom 16 manifested multiple difficulties. The disabilities identified by our study comprised problems with: shape recognition, simultaneous perception, perception of movement, colour perception, orientation, object recognition, and face recognition. The range, nature, and combinations of these disorders are presented in this paper.

Prognostic value of flash visual evoked potentials in preterm infants

This paper investigates the prognostic value of flash visual evoked potentials (VEPs) recorded in preterm infants at birth and at term age with respect to severe neurological outcome. Flash VEPs were recorded in 81 preterm infants at birth (i.e. <35 weeks' gestation) and repeated in 56 of these infants at term age. The preterm infants were assigned to either a healthy or at-risk subgroup based on clinical birth factors. Normal ranges of flash-VEP latencies, amplitudes, and number of components present were obtained from the subgroup of healthy preterm infants and from 68 term infants tested postnatally. The flash-VEP results of the entire preterm group were compared with the normal ranges and any abnormalities noted. Seven preterm infants in the at-risk group died, six of whom had abnormal flash VEPs before term age. Of the five infants from the at-risk group diagnosed with cerebral palsy (CP), three had abnormal flash VEPs before term age. Thus the sensitivity and specificity of the flash VEP with respect to survival was 86% and 89% respectively, and with respect to the development of CP was 60% and 92%. The abnormal features of the flash VEP associated with adverse outcomes comprised a delayed N3 component before term age and the absence of a positive component (P2) at term age.

Evolution of a form of pure alexia without agraphia in a child sustaining occipital lobe infarction at 2 1/2 years

The progress of cognitive visual dysfunction over an 8-year period of a child who sustained bilateral occipital-lobe infarctions at the age of 2 1/2 years is described. She survived with normal intelligence and went on to attend mainstream school. She manifested many features of cognitive visual impairment and, in particular, developed a form of pure alexia without agraphia. She achieved some letter-by-letter reading but no sight vocabulary development, including to her own name. She learned to write imaginatively employing phonetically true spelling but cannot read what she has written. Her progress and the difficulties encountered during the management of her condition are discussed in this first case report of the evolution of pure alexia without agraphia in childhood. The features of this syndrome in the developing child who has never developed the capacity to read are contrasted with that seen in affected adults.

An inner city preschool visual screening programme: long-term visual results

AIMS

The aim of this study was to investigate the long-term outcome of the treatment of amblyopia as a sequel to preschool screening, which has not hither-to been described.

METHODS

All patients originally referred from a preschool screening programme were recalled for examination by letter. 255 patients were reviewed at least 4 years after discharge of which 88 were definitely amblyopic at presentation and 107 were not amblyopic at presentation and were used as controls.

RESULTS

79% of the amblyopes improved or maintained visual acuity after discharge but this was reduced to 42% after an age induced increase (estimated from the controls) was compensated for. The mean drop in visual acuity in the amblyopic eyes which deteriorated was 0.23 (SD 0.15) logMAR units. Stepwise multiple linear regression showed that the best single predictor of post-discharge deterioration in visual acuity was the improvement in visual acuity seen during treatment (R2 = 19%). Eccentric fixation at time of follow up (increasing R2 to 47%) and good presenting acuity (further raising R2 to 57%) contributed additional information, and were both associated with greater post-discharge deterioration in visual acuity.

CONCLUSIONS

The majority of amblyopes who attended for follow up maintained or improved their visual acuities after discharge. Those patients who demonstrated deterioration of their amblyopia had usually improved well during the programme and were often fixating eccentrically at follow up.

Clinical characteristics of microtropia--is microtropia a fixed phenomenon?

BACKGROUND/AIMS

Microtropia is believed to be a static condition, in which accepted achievable levels of vision are those of 6/12-6/9 maximum, with the inability to achieve "normal" levels of stereopsis. The aim of this paper was to present the results of treatment of 30 consecutively presenting primary microtropes, and assess their outcomes using a more active treatment strategy than that conventionally used.

METHODS

Visual acuity, stereoacuity, fixation, and the presence of a central suppression scotoma were assessed in all patients before, during, and after treatment, which comprised wearing maximum refractive correction, and an occlusion strategy aiming for equal visual acuity.

RESULTS

Equal visual acuity of 6/5 Snellen was achieved in 43% of the 30 patients, while 87% achieved 6/9 Snellen or better visual acuity in the microtropic eye. Stereoacuity of better than 60" of arc was attained in 37%, and foveal fixation on visuscopy in 55%. The treatment outcome was not affected by the patient's age, initial visual acuity, or the amount of anisometropia. A change in the patient's diagnosis was noted in 50%, with nine patients recovering completely.

CONCLUSIONS

The results show that microtropia is not static. Equal 6/5 vision is attainable, as is high grade stereoacuity. The pattern of fixation may change during treatment and elimination of the microtropia is possible in some cases. There is a requirement for management protocols to be changed in order to treat this condition more effectively.

Recovery in microtropia: implications for aetiology and neurophysiology

AIMS/BACKGROUND

The basis of binocular single vision in microtropia remains a matter of contention. This paper discusses the implications of recovery, in a group of primary microtropes following treatment, in relation to current concepts on the aetiology of the condition and proposed retinocortical correspondence.

METHODS

Nine previously untreated primary microtropes whose condition resolved, were reviewed in detail to assess the patterns of change in retinal correspondence, uniocular fixation, stereoacuity, and visual acuity in response to treatment.

RESULTS

Anomalous retinal correspondence (ARC), a central scotoma, reduced or absent stereoacuity, amblyopia, and uniocular eccentric fixation were present in all patients before treatment. Following treatment, all cases attained normal retinal correspondence (NRC), elimination of the central scotoma, stereo acuity levels of between 20 and 40 seconds of arc, 6/5 Snellen visual acuity in both eyes, and foveal fixation in both eyes.

CONCLUSION

A hypothesis is put forward that for the patients described, a period of normal development is likely to have preceded the onset of microtropia, during which the retinocortical "foundations" for NRC were established. Precise pairing of foveo-foveal receptive fields was not abolished by the presence of amblyopia and a central scotoma, but this relation was temporarily suspended and binocular single vision was sustained via the neural substrate of paired receptive fields over a wide retinocortical area.