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WV Good, C Hou, AM Norcia; Sweep VEP Pattern Reversal Grating Acuity is Superior to On/Off Grating Acuity for the Detection of Amblyopia . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2938.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Sweep VEP grating acuity thresholds can be measured with an on/off stimulus, or with a sinusoidal pattern reversal stimulus. We compared thresholds for these 2 types of grating stimuli in amblyopic observers to determine which is most sensitive for detection of amblyopia. Methods:Thresholds were measured in amblyopic subjects and normal subjects with the following stimuli: on/off gratings presented at 15 Hz and 3.76 Hz and pattern reversal gratings presented at 7.5 Hz. Subjects ranged in age from 4 years to 50 years, with best corrected Snellen acuities in the amblyopic eye of 20/30 to 20/400 (average 20/50). 11 subjects had anisometropic amblyopia and 3 had strabismic amblyopia. Swept parameter stimuli were presented in a loosely randomized fashion and consisted of short trials (10 seconds) with stimulus ranges from 32 to 2 cycles per degree. Signal averaging was done for 8 trials per stimulus condition. Mean thresholds for each stimulus type were computed allowing comparison of the amblyopic and fellow eye. Thresholds were compared to Snellen acuities. We also compared grating acuities in dominant vs. non-dominant eyes of normal viewers. Results:All 3 grating acuities underestimate Snellen acuity, however, the magnitude of underestimation was least for pattern reversal. In fact, the 3.76 on/off stimulus failed to show any interocular acuity difference (amblyopic vs fellow eye). The fellow eye acuities were equal across all 3 stimulus conditions. In normal subjects, thresholds for the 3.76 and 15 Hz on/off stimulus were higher (better) than for the 7.5 Hz pattern reversal stimulus, but only in the dominant eye. Conclusion:On/off grating acuity measures are less sensitive than 7.5 Hz pattern reversal measures for the detection of amblyopia. This is especially true in the case of 3.76 Hz on/off thresholds, which fail to detect any difference between amblyopic and fellow eyes. Caution is recommended when using on/off grating acuity thresholds to detect amblyopia. The relative sparing of vision with 3.76 Hz on/off stimuli suggests sparing of some high spatial frequency cortical mechanisms in amblyopia.
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