In preverbal children, it is difficult to assess visual acuity accurately. If nystagmus waveforms can be used to predict visual acuity in these young patients, then they would be a useful additional clinical tool. Existing acuity predictors were assessed in 10 adults with idiopathic early onset nystagmus. The most reliable predictor in this group of patients was mean velocity of the waveform. The mean velocity of the waveform may be used in preverbal children to give an estimate of best potential visual acuity in adulthood, and estimated best potential visual acuity at the current age.