PURPOSE. Results in several studies have suggested that the visual evoked p
otential (VEP) amplitude can vary with stimulus duration. The purpose of th
is study was to determine whether acuity estimates obtained by extrapolatio
n of the sweep VEP are altered by this adaptation effect.
METHODS. Sweep VEP data were obtained from 16 healthy observers under binoc
ular viewing conditions. Data were acquired with a commercially available V
EP unit using standard electrode recording techniques. Three sweeps (high s
patial frequencies , medium spatial frequencies, and low spatial frequencie
s) were run. The subjects' visual acuity at the monitor distance was 6/6 fo
r the high spatial frequency sweep. For the medium and low spatial frequenc
y sweeps, the subjects were dioptrically blurred to 6/15 (medium spatial fr
equencies) or 6/30 (low spatial frequencies) at the monitor distance. Each
sweep consisted of six spatial frequencies (contrast 80%; temporal frequenc
y (TF) = 7.5 Hz; screen luminance = 100 candela [cd]/m(2)). For each spatia
l frequency, the stimulus duration was 8 seconds, partitioned into 1-second
bins. A minimum of eight sweeps were obtained per subject. An acuity estim
ate nas obtained for each second's data by fitting a line to the high spati
al frequencies (excluding noise) and extrapolating this line to the x-axis.
With this technique, estimates could not be obtained for 29 of 384 possibl
e acuities.
RESULTS. The sweep VEP acuities for the 16 subjects did not change signific
antly over the 8 seconds of data collection for the high, medium, or low sp
atial frequency sweep (repeated measures analysis of variance [ANOVA]: high
, P = 0.25; medium, P = 0.50; low, P = 0.23). In any given subject, there w
as a 1- to 2-octave range in acuity estimates over the 8 seconds of stimulu
s presentation (high, 1.23 +/- 0.417 octaves; medium, 1.41 +/- 0.593 octave
s; low, 1.52 +/- 0.475 octaves; mean +/- SD).
CONCLUSIONS. These results suggest that there is not a significant change i
n sweep VEP acuity estimates over an 8-second stimulus presentation. Thus,
neural adaptation does not significantly affect the clinical use of the swe
ep VEP.