Paradoxical robust visual evoked potentials in young patients with cortical blindness

Abstract

The objective of this study was to review retrospectively cases of clinically blind children in whom robust pattern visual evoked potentials (VEPs) were recorded. VEP records from a 10-year period (1990-2000) were reviewed. We searched for charts of children who were clinically cortically blind, but in whom assessment of visual acuity, using visual evoked potentials (VEPs), was normal or close to normal. The majority (77.5%) of VEP and behavioral acuity measures were concordant (subset analysis). Of the 1,113 VEP records, 9 cases (<1% of records reviewed) had clinically compromised vision with fair to good levels of visual function using VEPs. The commonality among the cases was the presence of suspected cortical visual impairment with seizures and developmental delay. VEP acuity cannot be correlated unequivocally with visually guided behaviour. In specific cases, particularly cases with developmental delay and neuroradiographic abnormalities, a child who is behaviorally blind with no clinical evidence of vision may show robust VEPs even to small patterns. This finding might be consistent with a defect of the visual association cortex.

VEP estimation of visual acuity: a systematic review

“…Furthermore, a normal VEP SF limit in combination with poor acuity may indicate dysfunction of higher visual processing areas rather than NOVL; such patients may benefit from eventrelated potential threshold measures [226]. In a very small number of extreme cases, patients with no behavioural vision at all can present with extant and even normal pattern VEPs [202,227].…”

“…VEP SF limits for transient VEPs and behavioural acuity were qualitatively described in 100 paediatric patients (3 months-8 years) with predominantly neurological impairments: 69/89 were ''in agreement'', 14/89 (with predominately primary ocular abnormalities) had VEP SF limits which fell short of their behavioural acuity and 6/89 had VEP SF limits which exceeded their behavioural acuity [202].…”

Persistence of Cortical Sensory Processing during Absence Seizures in Human and an Animal Model: Evidence from EEG and Intracellular Recordings

“…Nonetheless, they are in fact in agreement with a number of studies, ranging from single unit recordings in animals [71] to human EEG [72] and neuroimaging [73] experiments, which demonstrate the persistence of brain responses to sensory stimulations during non-rapid eye movement sleep, suggesting that the brain can still process external stimuli during thalamocortical oscillations that make the subject unresponsive. In addition, in patients with cortical blindness, unaware of the visual stimulus, vERPs can be recorded [74]. More recent studies combining EEG and fMRI in human indicate that auditory cortical responses persist during non-rapid eye movement sleep, except during spindles [75], [76] and the negative going phase of the slow-wave oscillations during which responses become less consistent or even absent [76].…”

Cerebral Visual Impairment in Children

“…In addition, pattern-evoked visual potentials may also be useful in longitudinal assessment of visual function in children with CVI (Watson et al 2007 ), but besides parallel courses of PL, visual acuity and VEP development, disparities in PL and VEP can also be found (Lim et al 2005 ). Apparently, a smaller number of spared neurons in V1 is required for generating P1 than are needed to 'see' the same stimulus pattern and discriminate pattern components (Celesia et al 1982 ;Wygnanksi-Jaffe et al 2009 ). Nearly normal P1 responses after pattern stimulation have been recorded in adults with bilateral destruction of V1 and resulting severe visual disability, characterised by a visual acuity 1.3logMAR (<0.05).…”