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R. Hamilton, J. Calvert, M. S. Bradnam, A. Chowdhury, G. N. Dutton, A. Evans, V. Manahilov, D. L. McCulloch, J. Roy; Using ssVEPs to Assess Contrast Sensitivity and Acuity and to Demonstrate Visual Impairment to Parents/Carers. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3757.
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Reduced contrast sensitivity (CS) may occur in children with neurological impairment. The aim of the study was to develop an objective, efficient method of testing CS in infants and children, to produce a set of clinical norms and to develop a pictorial method of demonstrating reduced acuity/contrast to parents based on clinical findings.
The ‘step VEP’ acuity test previously developed was modified to measure VEP CS. CS was measured from 118 infants and children and 12 adults and compared with CS measured using conventional methods. Software (ImageJ, NIH) was written to degrade an image according to acuity/CS findings.
Over 83% (103/118) of infants and children completed the CS VEP test, giving a threshold. VEP CS values correlated well with standard measures of CS. A function was established to predict subjective CS from the VEP CS. VEP CS rises in infancy and early childhood, reaching adult levels at an age of 3 years, 9 months. Subjective measures of CS were fully developed by school age, at least for high spatial frequencies (Functional Acuity Contrast Test). Sensitivity to low and medium spatial frequencies, as well as performance on the Pelli-Robson test, continued to develop through childhood, reaching adult levels by 8-15 years. A program was successfully written to accept acuity and CS input data and to generate a degraded image demonstrating the effects of reduced vision.
The VEP CS test is an objective and efficient method of assessing CS in infants as young as one month of age. Clinically, it combines well with the high-contrast acuity version. The image degradation software will allow parents and teachers of each child to understand their vision loss and to guide care and education strategies accordingly.
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