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J Calvert, M S. Bradnam, V Manahilov, R Hamilton, D L. McCulloch, A Mackay, G N. Dutton; Assessment of contrast sensitivity in infants and children with neurological impairment: A novel test using steady-state visual evoked potentials (ssVEPs). Journal of Vision 2005;5(8):294. doi: 10.1167/5.8.294.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Children with neurological impairment often have visual dysfunction, including reduced contrast sensitivity. However, a lack of co-operation or developmental delay can make subjective testing slow and inaccurate. We have previously developed an automated objective visual acuity test using ssVEPs (Bradnam et al. 1994, 2001; Mackay, 2003, 2003a & b). In the present study we report a similar technique to objectively and rapidly assess contrast sensitivity thresholds.
Methods: The rationale for our technique is to acquire the most important information as quickly as possible, before the child loses co-operation. This is accomplished by real-time analysis of the individual's ssVEP, which determines the subsequent contrast levels to be presented. The stimulus presentation technique is based on an adaptive staircase method, usually used in psychophysical experiments. The starting point is a high contrast pattern, large initial steps in contrast allow the threshold region to be identified and subsequent smaller steps allow an accurate threshold to be established.
Results: The stimulus parameters and presentation protocol were optimized in order to obtain a rapid and accurate contrast threshold. The contrast range, contrast step size, stimulus presentation algorithm, spatial frequency, temporal frequency, scalp recording sites and length of recording time before accepting ‘no response’ were all investigated. As a result, it takes less than three minutes to estimate a contrast sensitivity threshold, with the threshold estimates being comparable to psychophysical estimates.
Conclusions: The use of ssVEPs, combined with sensitive objective signal detection and a staircase stimulus presentation is an effective strategy for determining contrast sensitivity.
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