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AM Mackay, R Hamilton, MS Bradnam; Faster Acuity Assessment in Children- A New, Electrophysiological Test . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1811.
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© ARVO (1962-2015); The Authors (2016-present)
Introduction: Visual Evoked Potentials (VEPs) can be used to objectively assess infant and child acuity. VEP acuity threshold is usually either defined as the smallest check evoking a measurable transient response, or by extrapolation of steady-state response amplitudes to a range of checks (sweep VEP). A third possible definition is the smallest check to which a steady-state VEP (ssVEP) can be detected. Purpose: To develop fully automated software to assess visual acuity threshold by finding the smallest check which evokes a ssVEP. Methods: A range of reversing checkerboards were used with sizes ranging from 480' to 1.5'. Software was developed to present the stimuli at a rate of 7.78 reversals per second. On-going analysis meant that recording to a particular stimulus was continued only until a response was found. It was possible to pause analysis during periods of inattention. Fourier analysis was performed on both averaged and un-averaged recordings and response significance (at the 99.5% level) was determined by calculation of signal-to-noise-ratio and circular T2 statistics respectively. A successive approximation technique was used to quickly establish the VEP acuity threshold. If a response was detected by either of the statistical methods within 25s of stimulus onset, then a smaller stimulus was presented. If no signal was detected then a failure was logged and a larger stimulus presented. When two failures had been recorded, the acuity was defined using the smallest check to which a response was successfully detected. Transient VEP recording (1.1 reversals per second) to the same stimulus sizes has been our clinical method for paediatric acuity estimation for the last seven years. The automated test has recently been introduced in parallel. Total test duration for acuity assessment between the two methods was prospectively studied. A Mann-Whitney U test for unpaired data was performed to describe any time differences. This preliminary analysis evaluates 20 subjects, ten for each method, attending our paediatric vision clinic and matched in terms of age, acuity and diagnosis. Results: The median test duration for the groups assessed by transient VEP and the new automated test respectively were seven minutes 34 seconds and two minutes 29s. The difference was significant (p=0.002). Conclusions: It has been possible to create software that automatically finds a visual acuity threshold with minimal user input. The software has been established in clinical practice and is around four times faster than the same technique based on transient VEPs.
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