Avaliação da acuidade visual de recém-nascidos pequenos para a idade gestacional pelos métodos do potencial visual evocado de varredura e cartões de acuidade de Teller / Evaluation of Visual Acuity in Small-for-Gestational-Age Newborns Using Sweep VEP and Teller Acuity Card Methods

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Objective: To evaluate the effects of intra-uterine malnutrition on grating visual acuity (VA) using Sweep VEP and Teller Acuity Cards (TAC). Method: Binocular grating acuity was evaluated in 41 newborns with gestational age 37 weeks. Twentythree were born with appropriate weight for gestational age (AGA age: 14.3 ± 7.5 weeks) and 18 were born small for gestational age (SGA age: 10.7 ± 4.1 weeks). Visual acuity was determined using both psychophysical (Teller Acuity Cards) and electrophysiological (sVEP) techniques. For the TAC evaluation, cards having calibrated black and white square waves gratings at spatial frequencies (SFs) between 0.23 and 19 cycles/degree were presented 55 cm from the subject. The test began with the lowest SF card in random orientation to which the experimenter was blind. Subsequent cards were presented in order of increasing SF until an incorrect response was made, at which time the prior (lower-SF) card was presented again. Visual acuity was defined as the average of the SF values for 4 reversals. For the sVEP recordings, the PowerDIVA VEP system (Brosnahan et al., 1998) was used to generate all stimuli and analyze the evoked responses. Stimuli were spatial luminance sinewave gratings presented on a 21-inch monochromatic high-resolution monitor (1600x1200 pixels) with an average luminance of 161.1 cd/m2. Gratings were phase-reversed at either 3, 6 or 10 Hz. The electroencephalogram was recorded using 3 active electrodes (O1,Oz,O2) related to the reference electrode at vertex. During each 10-sec sVEP trial a linear sweep of increasing SF was presented. Sweep ranges were selected according to the subjects age. For each condition (each TF), a minimum of 3 trials were used to estimate thresholds, but the majority of measures were the result of a vector average of 5 to 10 trials. For each condition, the acuity estimate used derived from the channel with the highest acuity with statistically significant signal-to-noise ratio (>3:1) and stable phase during the high-SNR portion of the response. Results: There were no statistical differences in visual acuity between the two groups (SGA and AGA) for either method (sVEP or TAC). For the sVEP, acuities were not statistically different for the different TFs. There were also no statistical differences between groups for the sVEP measures of amplitude, phase, noise or signal-to-noise ratio. Intra-group analysis of the sVEP measures at the three TFs revealed statistical differences for amplitude, noise and signal-to-noise ratio, but only for SGA group. However, the SGA subjects less than or equal to 8 weeks of age showed a tendency for higher amplitudes and SNR for 3Hz temporal frequency compared to AGA subjects, and these same SGA subjects showed tendency for larger phase values (slower responses) compared to AGA. However, phase development rate was faster for SGA than for AGA for all temporal frequencies. Conclusion: There were no significant alterations of visual acuity in SGA babies, but the data from suprathreshold measures are consistent with the hypothesis that intrauterine malnutrition results in slower visual responses between retina and cortex. The data obtained so far suggest that such affects are transient, affecting primarily the younger group of infants, and that the visual system in SGA infants has sufficient plasticity to recover rapidly to normal levels. More data is needed to validate this interpretation of the results.

ASSUNTO(S)

desnutrição fetal neonates teller acuity cards visual acuity fetal malnutrition visual evoked potential recém-nascidos acuidade visual potenciais visuais evocados cartões de acuidade de teller

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