Contrast sensitivity threshold measured by sweep-visual evoked potential in term and preterm infants at 3 and 10 months of age

Visual Acuity alterations in heavily impaired Congenital Zika Syndrome (CZS) children

Introduction

This study aimed to assess visual acuity (VA) in Congenital Zika Syndrome (CZS)-children to evaluate visual loss. To that end we evaluated 41 CZS - children, from Rio de Janeiro using Teller Acuity Cards.

Methods

To asses VA, we evaluated 41 CZS - children, from Rio de Janeiro using Teller Acuity Cards. The children had Zika virus-infection confirmed by reverse transcription-polymerase chain reaction (RT-PCR) or clinical evaluation.

Results

In 39 out of 41 (95%) children, the VA scores were below normative values, while in 10 cases, VA was only marginally below normal; in the remaining 29 cases, VA was more than 0.15 logMAR below the lower limit. There was no correlation between VA and the cognitive domain tasks, although there was a correlation between VA and motor domain tasks. Thirty-seven children performed at least one task in the cognitive set, while fourteen children did not perform any task in the motor set. Children with VA above the lower limit performed better in the cognitive and motor tasks.

Discussion

We concluded that ZIKV- infected children with CZS were highly VA impaired which correlated with motor performance, but not with cognitive performance. Part of the children had VA within the normal limits and displayed better performance in the cognitive and motor sets. Therefore, even if heavily impaired, most children had some degree of VA and visual function.

Technical Innovation for Visual Assessment of Preterm Newborns in a Neonatal Intensive Care Unit: Exploratory Study

Objective

The present study is aimed at assessing heart rate variability (HRV) and its correlation with visual acuity (VA) assessment of preterm newborns (PTNB) in neonatal intensive care units.

Method

Cross-sectional study analyzing HRV during assessment of VA with the aid of a Polar RS800CX heart rate monitor (Polar Electro Oy, Finland). HRV was analyzed according to time and frequency domains and the chaos domain used the autocorrelation coefficient and entropy. The sample consisted of hospitalized PTNB, and static analysis included simple regression diagnosis.

Results

A total of 14 PTNB were included in the sample. VA varied between 0.23 and 1.60 cpd, and only five PTNB obtained below-expected values for age. Statistical analysis demonstrated a negative correlation between VA and time domain (SDDN and SD2) and a positive correlation between frequency domain (heart rate and hertz), but in simple linear regression analysis, these variables did not influence VA.

Conclusion

The results of the study demonstrate that visual acuity was inversely correlated with SDNN and SD2 and during stimulation, showing that the higher the visual performance, the lower the autonomic modulation response.

Alterations in visual acuity and visual development in infants 1-24 months old either exposed to or infected by Zika virus during gestation, with and without microcephaly

PURPOSE

To evaluate visual acuity and visual acuity development in children from the state of São Paulo, Brazil, who were exposed to the Zika virus (ZIKV) gestationally.

METHODS

Children who had been exposed to ZIKV during gestation and age-matched control subjects received visual acuity and funduscopic examination. ZIKV exposure was confirmed by maternal quantitative polymerase chain reaction testing or serology assay. The ZIKV group was divided into two subgroups: exposed (ZE), with only the mother having confirmed ZIKV infection, and infected (ZI), with confirmed infection. Visual acuity development was compared with prior norms and quantified by measuring visual acuity correlation with age.

RESULTS

A total of 110 children were included: 47 who had been exposed to ZIKV (ZE, 23; ZI, 24) and 63 controls. Abnormal visual acuity was found in 5 of 24 ZI children. Of the 4 children with microcephaly, only 2 had visual acuity loss (only 1 also had abnormal funduscopic findings). There was significant correlation between age and visual acuity in both the control group (R2 = 0.8; P < 0.0000) and the ZE subgroup (R2 = 0.6; P < 0.0000). However, visual acuity did not correlate with age in the ZI subgroup (R2 = 0.04; P = 0.38). Furthermore, the increment in octaves/month was much lower in the ZI subgroup.

CONCLUSIONS

Our data indicate that visual acuity losses only occur in infants who suffered gestational-infection, not simply exposure. Lack of correlation between age and visual acuity in the ZI subgroup suggests a slowing of visual development even in the absence of microcephaly. This result may have broad implications for the deleterious effects of ZIKV on the central nervous system.

Maturation of Binocular, Monocular Grating Acuity and of the Visual Interocular Difference in the First 2 Years of Life

The sweep visual evoked potential method (sVEP) is a powerful tool for measurement of visual acuity in infants. Despite the applicability and reliability of the technique in measuring visual functions the understanding of sVEP acuity maturation and how interocular difference of acuity develops in early infancy, as well as the availability of normality ranges, are rare in the literature. We measured binocular and monocular sVEPS acuities in 481 healthy infants aged from birth to 24 months without ophthalmological diseases. Binocular sVEP acuity was significantly higher than monocular visual acuities for almost all ages. Maturation of monocular sVEP acuity showed 2 longer critical periods while binocular acuity showed three maturation periods in the same age range. We found a systematic variation of the mean interocular acuity difference (IAD) range according to age from 1.45 cpd at birth to 0.31 cpd at 24 months. An additional contribution was the determination of sVEP acuity norms for the entire age range. We conclude that binocular and monocular sVEP acuities have distinct growth curves reflecting different maturation profiles for each function. Differences in IAD range shorten according to age and they should be considered in using the sVEP acuity measurements for clinical diagnosis as amblyopia.

Visual Acuity and Contrast Sensitivity Development in Children: Sweep Visually Evoked Potential and Psychophysics

PURPOSE

The purpose of this study was to investigate the development of visual acuity (VA) and contrast sensitivity in children as measured with objective (sweep visually evoked potential) and subjective, psychophysical techniques, including signal detection theory (SDT), which attempts to control for differences in criterion or behavior between adults and children. Furthermore, this study examines the possibility of applying SDT methods with children.

METHODS

Visual acuity and contrast thresholds were measured in 12 children 6 to 7 years old, 10 children 8 to 9 years old, 10 children 10 to 12 years old, and 16 adults. For sweep visually evoked potential measurements, spatial frequency was swept from 1 to 40 cpd to measure VA, and contrast of sine-wave gratings (1 or 8 cpd) was swept from 0.33 to 30% to measure contrast thresholds. For psychophysical measurements, VA and contrast thresholds (1 or 8 cpd) were measured using a temporal two-alternative forced-choice staircase procedure and also with a yes-no SDT procedure. Optotype (logMAR [log of the minimum angle of resolution]) VA was also measured.

RESULTS

The results of the various procedures were in agreement showing that there are age-related changes in threshold values and logMAR VA after the age of 6 years and that these visual functions do not become adult-like until the age of 8 to 9 years at the earliest. It was also found that children can participate in SDT procedures and do show differences in criterion compared with adults in psychophysical testing.

CONCLUSIONS

These findings confirm a slightly later development of VA and contrast sensitivity (8 years or older) and indicate the importance of using SDT or forced-choice procedures in any developmental study to attempt to overcome the effect of criterion in children.

Sensory processing disorder in children ages birth-3 years born prematurely: a systematic review

This systematic review of multidisciplinary literature synthesizes evidence of the prevalence and patterns of sensory processing disorder (SPD) in children ages birth-3 yr born preterm. Forty-five articles including physiological, behavioral, temperament, and SPD research met the inclusion criteria and provided 295 findings related to SPD-130 (44%) positive (evidence of SPD) and 165 (56%) negative (no evidence of SPD). The majority of findings related to sensory modulation disorder (SMD; 43% positive). The most prevalent subcategory of SMD was sensory overresponsivity (82% of findings positive). Evidence of sensory underresponsivity and sensory-seeking SMD, sensory discrimination disorder, and sensory-based motor disorder was limited. This study supports the education of neonatologists, pediatricians, and caregivers about the symptoms and potential consequences of SPD and helps justify the need for follow-up screening for SPD in children ages birth-3 yr born preterm. Research using measures based on sensory processing theory is needed.

Sweep visually evoked potentials and visual findings in children with West syndrome

BACKGROUND

West syndrome (WS) is a type of early childhood epilepsy characterized by progressive neurological development deterioration that includes vision.

AIM

To demonstrate the clinical importance of grating visual acuity thresholds (GVA) measurement by sweep visually evoked potentials technique (sweep-VEP) as a reliable tool for evaluation of the visual cortex status in WS children.

METHODS

This is a retrospective study of the best-corrected binocular GVA and ophthalmological features of WS children referred for the Laboratory of Clinical Electrophysiology of Vision of UNIFESP from 1998 to 2012 (Committee on Ethics in Research of UNIFESP n° 0349/08). The GVA deficit was calculated by subtracting binocular GVA score (logMAR units) of each patient from the median values of age norms from our own lab and classified as mild (0.1-0.39 logMAR), moderate (0.40-0.80 logMAR) or severe (>0.81 logMAR). Associated ophthalmological features were also described.

RESULTS

Data from 30 WS children (age from 6 to 108 months, median = 14.5 months, mean ± SD = 22.0 ± 22.1 months; 19 male) were analyzed. The majority presented severe GVA deficit (0.15-1.44 logMAR; mean ± SD = 0.82 ± 0.32 logMAR; median = 0.82 logMAR), poor visual behavior, high prevalence of strabismus and great variability in ocular positioning. The GVA deficit did not vary according to gender (P = .8022), WS type (P = .908), birth age (P = .2881), perinatal oxygenation (P = .7692), visual behavior (P = .8789), ocular motility (P = .1821), nystagmus (P = .2868), risk of drug-induced retinopathy (P = .4632) and participation in early visual stimulation therapy (P = .9010).

CONCLUSIONS

The sweep-VEP technique is a reliable tool to classify visual system impairment in WS children, in agreement with the poor visual behavior exhibited by them.

Visual impairment in children with spastic cerebral palsy measured by psychophysical and electrophysiological grating acuity tests

BACKGROUND

This study measured grating visual acuity in 173 children between 6-48 months of age who had different types of spastic cerebral palsy (CP).

METHOD

Behavioural acuity was measured with the Teller Acuity Cards (TAC) using a staircase psychophysical procedure. Electrophysiological visual acuity was estimated using the sweep VEP (sVEP).

RESULTS

The percentage of children outside the superior tolerance limits was 44 of 63 (69%) and 50 of 55 (91%) of tetraplegic, 36 of 56 (64%) and 42 of 53 (79%) of diplegic, 10 of 48 (21%) and 12 of 40 (30%) of hemiplegic for sVEP and TAC, respectively. For the sVEP, the greater visual acuity deficit found in the tetraplegic group was significantly different from that of the hemiplegic group (p<0.001). In the TAC procedure the mean visual acuity deficits of the tetraplegic and diplegic groups were significantly different from that of hemiplegic group (p<0.001). The differences between sVEP and TAC means of visual acuity difference were statistically significant for the tetraplegic (p<0.001), diplegic (p<0.001), and hemiplegic group (p=0.004).

DISCUSSION

Better visual acuities were obtained in both procedures for hemiplegic children compared to diplegic or tetraplegic. Tetraplegic and diplegic children showed greater discrepancies between the TAC and sVEP results. Inter-ocular acuity difference was more frequent in sVEP measurements.

CONCLUSIONS

Electrophysiologically measured visual acuity is better than behavioural visual acuity in children with CP.

Effects of prematurity on the development of contrast sensitivity: testing the visual experience hypothesis

In order to investigate the effects of visual experience on early visual development, the current study compared contrast sensitivity across infants born with different degrees of moderate-to-late prematurity. Here the logic is that at any given postterm age, the most premature infants will have the oldest postnatal age. Given that postnatal age is a proxy for visual experience, the visual experience hypothesis predicts that infants who are more premature, yet healthy, should have higher sensitivity. Luminance (light/dark) and chromatic (red/green) contrast sensitivities (CS) were measured in 236 healthy infants (born -10 to +2 weeks relative to due date) between 5 and 32 weeks postterm age from due date and 8-38 weeks postnatal from birth date. For chromatic CS, we found clear evidence that infants who were most premature within our sample had the highest sensitivity. Specifically, 4-10 additional weeks of visual experience, by virtue of being born early, enhanced chromatic CS. For luminance CS, similar but weaker results were seen. Here, only infants with an additional 6-10 weeks of visual experience, and only at later age points in development, showed enhanced sensitivity. However, CS in preterm infants was still below that of fullterm infants with equivalent postnatal age. In sum, these results suggest that chromatic CS is influenced more by prematurity (and possibly visual experience) than luminance CS, which has implications for differential development of parvocellular and magnocellular pathways.

A clínica da psicofísica

Apresentamos a Psicofísica como uma ciência aplicada nas investigações e nas abordagens e diagnósticos clínicos. Inicialmente, introduzimos algo dos aspectos epistemológicos e teóricos da área, passamos para as abordagens que a Psicofísica pode apresentar na aplicabilidade clínica e, por fim, discutimos os avanços recentes da aplicação clínica, apresentamos as experiências de nosso laboratório de pesquisa clínica em psicofísica, finalizando com as perspectivas de ampliação do uso da psicofísica para investigações clínicas de funções perceptuais mais complexas.

Responses to a modified visual cliff by pre-walking infants born preterm and at term

The purpose of this study was to examine, using a modified visual cliff apparatus, possible perceptual differences at crawling age between infants born preterm and infants born at term without documented visual or motor impairments. Sixteen infants born at term and 16 born preterm were encouraged to crawl to their caregivers on a modified visual cliff. Successful trials, crossing time, duration of visual attention, duration of tactile exploration, motor strategies, and avoidance behaviors were analyzed. A significant surface effect was found, with longer crossing times and longer durations of visual attention and tactile exploration in the condition with the visual appearance of a deep cliff. Although the two groups of infants did not differ on any of the timed measures, infants born at term demonstrated a larger number of motor strategies and avoidance behaviors by simple tally. This study indicates that infants born at term and those born preterm can perceive a visual cliff and adapt their responses accordingly.

Chromatic and luminance contrast sensitivity in fullterm and preterm infants

In order to investigate the contributions of visual experience vs. preprogrammed mechanisms on visual development, the current study compared contrast sensitivity in preterm vs. fullterm infants. If development is tied to time since conception, preterm infants should match the developmental trajectories of fullterm infants when plotted in postterm age. By contrast, if development is influenced by visual experience, preterm and fullterm infants should match when plotted in postnatal age. Luminance (light/dark) and chromatic (red/green) contrast sensitivities (CS) were measured in 25 preterm (born, on average, 6.6 weeks early) and 77 fullterm infants, between 1 and 6 months postterm. In the first few months, luminance CS was found to be predicted by postterm age, suggesting that preprogrammed development is sufficient to account for luminance CS. By contrast, chromatic CS exceeded that predicted by postterm age, which suggests that time since birth confers a benefit on chromatic CS. The preterms' 6.6 weeks of additional time since birth is roughly equivalent to 3.7 weeks of development in chromatic CS. In sum, these results suggest that chromatic CS is more influenced by early postnatal visual experience than luminance CS, which may have implications for development of parvocellular and magnocellular pathways.

The technique, validity and clinical use of the sweep VEP

Vision scientists have concentrated on studying two visual functions when it comes to assessing the sensory visual development in human: visual acuity and contrast sensitivity. The methods used to measure these visual functions can be either behavioral or electrophysiological. A relatively new technique for measuring the visual acuity and contrast sensitivity electrophysiologically is the sweep visual evoked potential (sVEP). This paper is a review of the literature on the sVEP technique: stimulus parameters, threshold determination, validity and reliability of sVEP are discussed. Different studies using the sVEP to study the development of visual acuity, contrast sensitivity, and vernier acuity are presented. Studies have demonstrated that the sVEP is a potentially important tool for assessing visual acuity and contrast sensitivity in non-verbal individuals with disorders affecting their visual system.

Electrophysiological evidence for impairment of contrast sensitivity in mercury vapor occupational intoxication

Contrast sensitivity (CS) was evaluated in 41 former workers from a lamp manufacturing plant who were on disability retirement due to exposure to mercury and 14 age-matched controls. The CS was measured monocularly using the sweep visual evoked potential (sVEP) paradigm at 6 spatial frequencies (0.2, 0.8, 2.0, 4.0, 15.0, and 30 cpd). Statistical difference (p<0.05) was found between the controls and the patient right and left eyes for 2.0 and 4.0 cpd. According the results in those spatial frequencies the eyes were classified in best and worst. Statistical differences were found between the controls and the best eyes for 2.0 and 4.0 cpd and for 0.8, 2.0, and 4.0 cpd for their worst eyes. No correlation was found between CS results and the time of exposure (mean=8.9 yr+/-4.1), time away from the mercury source (mean=6.0 yr+/-3.9), urinary mercury level at the time of work (mean=40.6 microg/g+/-36.3) or with the mercury level at the CS measurement time (mean=1.6 microg/g+/-1.1). We show the first evidence of a permanent impairment in CS measured objectively with the sVEP. Our data complement the previous psychophysical works reporting a diffuse impairment in the CS function showing a CS reduction in the low to middle spatial frequencies. In conclusion, non-reversible CS impairment was found in occupational exposure to mercury vapor. We suggest that CS measurement should be included in studies of the mercury effects of occupational exposure.

Visão de cores no primeiro ano de vida

Procedimentos comportamentais que permitem inferir capacidades sensoriais ou perceptuais em bebês e crianças baseiam-se, na sua maior parte, na descoberta seminal feita no fim da década de 1950 pelo psicólogo Robert Fantz. Desde o nascimento, há uma preferência do bebê por dirigir o olhar para estímulos complexos a fixá-lo em cenas monótonas. Baseado no novo conhecimento, o grupo liderado por Davida Teller na Universidade de Washington desenvolveu uma metodologia de avaliação psicofísica da visão em bebês, o que possibilitou grande avanço no estudo do desenvolvimento e da maturação de várias funções visuais básicas, como acuidade visual, visão de cores, visão de contrastes, estereopsia e visão de movimento. A presente revisão examina essa literatura, mostrando como é avaliada a visão em bebês e o que se conhece até o momento sobre a capacidade dos recém-nascidos de ver cores.

Estimativa da sensibilidade ao contraste espacial de luminância e discriminação de cores por meio do potencial provocado visual transiente

O potencial provocado visual (VEP) é uma resposta cortical registrável na superfície do couro cabeludo, que reflete a atividade dos neurônios de V1. é classificado, a partir da freqüência temporal de estimulação, em transiente ou de estado estacionário. Outras propriedades do estímulo parecem provocar uma atividade seletiva dos diversos grupos de neurônios existentes em V1. Desse modo, o VEP vem sendo usado para estudar a visão humana acromática e cromática. Diversos trabalhos usaram o VEP para estimar a sensibilidade ao contraste de luminância no domínio das freqüências espaciais. Mais recentemente, há estudos que empregaram o VEP para medir os limiares de discriminação de cores. O VEP transiente pode complementar as medidas psicofísicas de sensibilidade ao contraste espacial de luminância e de discriminação cromática, e constitui um método não invasivo para estudar a visão de indivíduos com dificuldades de realizar testes psicofísicos.

Medidas psicofísicas e eletrofisiológicas da função visual do recém nascido: uma revisão

O sistema visual apresenta muitas funções ao nascimento. O processo de amadurecimento destas funções demanda um tempo variado. Neste trabalho, inicialmente descreveremos como a psicofísica e a eletrofisiologia visual tem colaborado para a medida e o estudo do desenvolvimento de três funções visuais: acuidade visual, sensibilidade ao contraste e visão de cores. Num segundo momento, discutimos sobre como a medida e o desenvolvimento destas funções podem estar prejudicados em patologias que afetam o sistema visual, como a prematuridade e a paralisia cerebral.