Dissociated visual development: electrodiagnostic studies in infants who are 'slow to see'

The Effects of Brain Damage on Visual Functioning in Children

This article reviews the research literature on the direct effects of brain damage on the visual functioning of children and the electrodiagnostic tests used to diagnose them. Although the studies documented that brain damage affects visual functioning, they suggested that the prognosis for good functional vision after remedial intervention is more optimistic than was previously thought. They also found that electrodiagnostic testing is a valuable tool, but that the use of a combination of tests yields a more complete picture of the effects than does any single test.

Electrodiagnostic Testing of Visually Impaired Children under Sedation

The use of chloral hydrate as a sedative to enable electrodiagnostic testing of hyperkinetic children is discussed, and procedures for the administration of chloral hydrate are described. Case examples are presented to illustrate that assessment during the sleep-induced state enables further counseling regarding spasmus nutans, optic nerve hyoplasia, and Leber's congenital amaurosis. Management based on comparative electroretinogram and visual-evoked-response recordings is emphasized.

Delayed visual maturation associated with auditory neuropathy/dyssynchrony

Delayed visual maturation is a term used to describe infants who initially seem blind but subsequently have a marked improvement. The mechanism of visual loss and the subsequent improvement remains unknown. Auditory neuropathy/dyssynchrony is a condition of hearing impairment associated with absent or severely abnormal brainstem auditory evoked potentials but normal cochlear functions as measured by otoacoustic emissions. In this report, a 9-month-old infant who had no visual fixation for the first 3 months of life and congenital hearing impairment is described. Her brainstem auditory evoked potential study at 2.5 months of age showed no response to click stimuli presented at 90 dB nHL, whereas her otoacoustic emissions were normal. Subsequently, her vision and hearing improved. A brainstem auditory evoked potential study at 9 months of age showed reproducible waveforms. This case suggests the need for a detailed hearing evaluation of children with delayed visual maturation. Furthermore, this case highlights the need for follow-up brainstem auditory evoked potential testing prior to pursuing any audiologic intervention.

Maturation of the pattern-reversal VEP in human infants: a theoretical framework

Visual evoked potentials to pattern reversal (PR-VEPs) are used to assess the integrity and maturation of the visual pathways in infants and young children. To establish normal ranges and to facilitate interpolation, we consider the maturation rate of PR-VEPs using published normative data. Curves based on the logistic function (a sigmoid model) are introduced and compared with three other models: (1) the power law function; (2) the sum of two decaying exponentials; and (3) a two-stage linear model. Although methods vary somewhat, remarkable consistency among laboratories is found for the maturation of the major positivity (P1) of PR-VEP. The P1 occurs at approximately 260 ms in neonates and is quite variable. It matures rapidly before 12-14 weeks of age and becomes much less variable. The logistic model provides a parsimonious description of P1 maturation with most rapid maturation at around 6 weeks of age for large patterns and around 9 weeks for small patterns. As inter-laboratory agreement is generally good, the normal ranges based on this model could be used in centres, which do not have their own normative databases for infant VEPs.

Transient nystagmus in delayed visual maturation

Two infants who presented with wide-amplitude and high-frequency nystagmus and lack of visual awareness in the first 3 months of life were studied. No ocular abnormalities were found. Neurodevelopmental examination, visual evoked potentials and electroretinograms were normal. One infant underwent MRI which resulted in normal findings. Two months later both patients showed increased visual responsiveness and a gradual reduction of the nystagmus amplitude. By 5 months of age nystagmus was no longer detectable and both infants appeared to be visually, developmentally, and neurologically normal. Follow-up at 3 years of age for subject 1 and at 11 months for subject 2 showed that both the infants maintained the normal ophthalmological and neurological assessments. We diagnosed delayed visual maturation with oculomotor involvement.

Prognostic value of visual evoked potentials (VEP) in infants with visual inattentiveness

Visual evoked potentials elicited by strobe flash (fVEPs) were recorded in 56 infants (3 months to 15 months of age) with visual inattentiveness but without prechiasmal problems. Their visual status was reexamined one or more years later when 41 children were found to be visually competent (Group NB) and 15 were blind (Group B). We also evaluated a group of 32 age-matched children who had no visual symptoms (Group C). It was found that well organized VEP waveforms over one or both hemispheres (Types U and S), or those with a characteristic negative shift (Type N) suggest favorable prognosis. Integrated voltage of the VEP correlated well with long-term prognosis for visual recovery. The vertex VEP also (had) provided some predictions for visual prognosis. Overall results indicate good prognosis if related to sufficient voltage and complexity of the VEP components.

Delayed visual maturation in infants: a disorder of figure-ground separation?

Delayed visual maturation (DVM) is characterised by visual unresponsiveness in early infancy, which subsequently improves spontaneously to normal levels. We studied the optokinetic response and recorded pattern reversal VEPs in six infants with DVM (aged 2-4 months) when they were at the stage of complete visual unresponsiveness. Although no saccades or visual tracking with the eyes or head could be elicited to visual objects, a normal full-field rapid buildup OKN response occurred when viewing biocularly or during monocular stimulation in the temporo-nasal direction of the viewing eye. Almost no monocular OKN could be elicited in the naso-temporal direction, which was significantly poorer than normal age-matched infants. No OKN quick phases were missed, and there were no other signs of "ocular motor apraxia." VEPs were normal in amplitude and latency for age. It appears, therefore, that infants with DVM are delayed in orienting to local regions of the visual field, but can respond to full-field motion. The presence of normal OKN quick-phases and slow-phases suggests normal brain stem function, and the presence of normal pattern VEPs suggests a normal retino-geniculo-striate pathway. These oculomotor and electrophysiological findings suggest delayed development of extra-striate cortical structures, possibly involving either an abnormality in figure-ground segregation or in attentional pathways.

Visual system electrodiagnosis in neurologic disease of childhood

Electrodiagnostic examination of the visual system includes visual evoked potentials and electroretinography. These tests can be applied to all ages. Pitfalls in the clinical ophthalmologic examination of children, such as optic nerve pallor and pigmentary retinopathy, can be clarified by these tests. Investigation of neurodegenerative disease may be directed to the most likely defect by results of visual evoked potential testing and electroretinography. The child who is unable to meaningfully communicate sensory experience can be objectively evaluated by these studies. Familiarity with the applications and limitations of these tests will allow the examiner to choose the appropriate setting and time to apply each of them.

Cortical visual impairment in children

Cortical visual impairment (CVI) in children is most commonly caused by peri- or post-natal hypoxia-ischemia, but may also occur following other insults, e.g., trauma, epilepsy, infections, drugs or poisons, and certain neurologic diseases. The disorder differs considerably in etiology, physical findings, and, perhaps, prognosis, from the cortical blindness seen in adults. The same event that causes CVI by damaging the geniculate and/or extrageniculate visual pathways may also damage other areas of the brain, or the retina, optic nerves, or chiasm. Thus, children with CVI often have other neurological problems. Diagnosis may require the participation of a multidisciplinary team and the use of special visual testing techniques. Due to the uncertainty concerning the prognosis in CVI, clinicians should remain optimistic about the child's potential for some vision recovery.

The visual-evoked response in infants with central visual impairment

We studied ten children with central visual impairment with a known neurologic defect and an abnormal visual-evoked response who had results of repeat electrophysiologic testing evaluated at the Children's Hospital of Philadelphia from December 1989 through July 1991. Central visual impairment is defined as poor visual function with a normal anterior visual pathway. Age at first examination ranged from 5 to 48 months with a followup of two to 31 months. Repeat visual-evoked response testing showed improvement in seven patients and no change in three. Grating acuity as measured by the Teller acuity card procedure, performed in nine of ten patients, improved in seven, showed no change in one, and declined in one. We found a potentially favorable prognosis for those infants with central visual impairment, despite an initially abnormal visual-evoked response. We used a clinical approach to this disorder to improve diagnostic categorization and prognostic capabilities in central visual impairment.

Visual function in children with developmental disabilities

Vision involves a process of maturation that occurs in early childhood. Early recognition of visual disorders such as amblyopia is necessary to assure prompt treatment and optimize visual potential. This is especially important in children with developmental disabilities, in whom there is a high prevalence of such problems. Certainly, the type of ocular disorder varies according to the type of disability. But individual ophthalmic assessment is important, regardless of diagnosis, to identify treatable conditions that may improve or maximize visual function. In addition, ophthalmic examination may reveal distinctive anomalies in cases in which the etiology of disability has been difficult to establish. The present level of expertise and technology allows a comprehensive ophthalmic assessment to be performed, regardless of a child's level of impairment or ability to cooperate.

The visually inattentive preterm infant

A retrospective study was made of 16 premature infants who were visually inattentive despite normal eye findings and a lack of factors predisposing them to cerebral blindness. A comparison of this study group with other premature infants who were visually attentive revealed a much greater incidence of upper motor neuron disease and mental retardation in the study infants.

Sporadic aniridia and Wilms' tumor: visual function evaluation of three cases

The visual function of three infants with sporadic aniridia associated with Wilms' tumor and a deletion of the short arm of chromosome 11 was evaluated with electrophysiological tests. The patients presented nystagmus and photophobia. The electroretinograms (ERGs) were normal, as in other sporadic cases, but at variance with the familial cases. The latency of the flash visual evoked potentials (FVEPs) became shorter with time but remained longer than in age-matched controls, suggesting a delay in maturation of the nervous system. Poor visual function in our cases did not appear to be the result of gross retinal anomalies, as shown by the normal ERG, nor of an hypoplasia of the optic nerve. Contact lenses that provide an artificial pupil decreased photophobia and nystagmus and are therefore highly recommended to increase patient comfort.

Delayed visual maturation. A longitudinal clinical and electrophysiological assessment

Delayed visual maturation is an idiopathic condition characterized by visual inattention during infancy. The authors followed longitudinally nine children with an initial diagnosis of delayed visual maturation and compared their electroretinograms (ERGs) and visual evoked potentials with those of age-matched controls. Eight of the nine patients consistently had normal visual evoked potentials to flash and to pattern stimulation. All of the children had normal ERGs. Visually mediated behavior gradually developed in all of these children when they were between 3 and 8 months of age (mean, 5.5 months). Five patients also were delayed in other spheres of development. Visual evoked potentials are helpful in formulating a visual prognosis for children with delayed visual maturation.

Cortical visual impairment following birth asphyxia

Visual defects are often poorly recognized in children with multiple neurologic problems due to perinatal hypoxic-ischemic encephalopathy. We report the clinical, radiologic, and electrodiagnostic characteristics of 20 children with cortical visual impairment secondary to birth asphyxia. Clinical diagnosis often was delayed. Ten patients recovered vision during the first two years of life. Four infants had coexisting damage to the pregeniculate visual pathway. Useful investigations included cranial computed tomography and visual evoked potential mapping. Electroencephalographic abnormalities were nonspecific. The classical definition of cortical blindness must be modified for children.

Electroretinography: application to clinical studies of infants

The electroretinographic (ERG) responses of normal human infants have been studied in scotopic conditions. The relation of stimulus intensity to the amplitude of the b-wave of the ERG undergoes developmental changes during infancy. The maximum amplitude that can be obtained gradually increases to approach adult values by age 12 months. Sensitivity, however, is equivalent to that of adults at age five to six months. Latencies reach adult values at the end of the first year. Some results of ERG testing of infant patients with retinal disorders are compared to the normal results. As previously reported for animals and human adults with retinal disorders, amplitude, sensitivity and latency are not always equally compromised by the retinal diseases of infants.

Albinism

Albinism is the term applied to a heterogeneous group of genetically determined disorders characterized by hypopigmentation and affecting the eyes. After describing the clinical features of albinism in general, the authors discuss the various forms of oculocutaneous albinism, ocular albinism, and albinoidism that are of interest to the ophthalmologist. Emphasis is placed on the ocular features of each form. The visual pathway abnormalities and the clinical management of albinism are discussed.

Delayed visual maturation

Sixteen blind babies who were considered to be showing the characteristics of delayed visual maturation were studied prospectively. The diagnosis was made on clinical grounds, and the criteria for this are discussed. All of these infants developed visual responses between 4 and 6 months of age and had normal or near normal visual acuities by 1 year of age. Long term follow up, however, has shown neurological abnormalities in some of these children.

Pediatric neuro-ophthalmology

The author discusses an extended list of the ophthalmic signs and symptoms of neurologic disease (some of which were once considered to be benign or isolated eye problems) under the general categories of vision problems, pupil signs, eye movement disorders, fundus abnormalities, and eyelid abnormalities.

Visual development in infancy and childhood

This article considers the development of vision in normal children, emphasizing new evaluative techniques that may eventually play an important role in clinical practice, and follows with a discussion of abnormal development, where recent discoveries in the laboratory and in clinical observation have already led to significant advances in the treatment of children with ophthalmologic problems.

Delayed visual maturation

Three infants, recognised as blind during the first 4 months of life, were found to be normal on neurological and ophthalmological examinations. Visual electro-diagnostic studies showed normal retinal responses, but delayed conduction velocities and impaired visually-evoked responses over the occipital cortex. After age 6 months, normal vision developed gradually and all abnormalities disappeared.