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William V. Good, Chuan Hou, Anthony M. Norcia; Sweep VEP vernier acuity for the detection of amblyopia. Journal of Vision 2002;2(10):51. doi: 10.1167/2.10.51.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The study of eye diseases in preverbal children is hampered by the fact that there is no test that correlates well with Snellen acuity. Grating acuity overestimates and correlates imprecisely with Snellen acuity. Vernier acuity is often more affected than grating acuity in patients with amblyopia and other diseases, however, there is no well-developed behavioral test for vernier acuity in preverbal children. We therefore studied electrophysiological tests of vernier acuity in verbal patients with amblyopia.
Methods: Acuity thresholds were measured in 18 amblyopia and 28 normal subjects using the following stimuli: off/on gratings presented at 15 Hz; off/on gratings presented at 3.76 Hz; pattern reversal gratings at 7.6 Hz; vernier alignment/misalignment gratings presented at 3.76 Hz; 2-frequency vernier alignment/misalignment gratings presented at 3.76/6.01 Hz; and Snellen acuity using a LogMar chart. Swept parameter stimuli were presented in a loosely randomized fashion and consisted of short trials (10–16 secs.) with stimulus ranges of 0.25–4.0 arc minutes for vernier acuity, and 32 to 2 cpd for grating stimuli. Signal averaging was done for 8 trials per stimulus condition. Interocular acuity differences and Z scores were calculated for each stimulus condition.
Results: One-frequency vernier acuity more closely correlated with Snellen acuity than 2-frequency vernier acuity measures or than any of the grating acuity stimuli. One frequency vernier acuity was more likely to identify eyes with amblyopia when Z scores were compared to the various other stimuli. Of all the grating stimuli, 7.6 Hz grating acuity thresholds showed the best correlation with Snellen acuity thresholds.
Conclusions: Off-on grating acuity is less affected than VEP vernier acuity in our patient group. VEP vernier acuity losses more closely approximate Snellen acuity losses than any of the grating stimuli acuity thresholds. The sweep VEP is a promising tool to measure vernier acuity thresholds in amblyopic patients.
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