THE EFFECTS OF AFFERENT STIMULATION ON CONGENITAL NYSTAGMUS FOVEATIONPERIODS

Visual acuity in congenital nystagmus (CN) patients is related primari ly to the duration of ''foveation periods'', during which the image of the target is relatively stationary in the foveal area, Thirteen indi viduals with CN were studied to test the hypothesis that somatosensory stimulation (vibration or electrical) of either the forehead or the n eck damps CN and improves visual acuity. We identified characteristics of the nystagmus waveform that were likely to be important in determi ning visual acuity and combined these measures into an ''acuity functi on'' (NAFP) that correlated well with visual acuity (r(2) = 0.91). Sta tistically significant changes in NAFP were used to assess the effects of afferent stimulation; positive effects were found in nine subjects , Vibratory stimulation (especially on the neck) was found to be more effective than electrical stimulation. CN amplitude reduction alone wa s neither necessary nor sufficient to improve acuity. Foveation durati on was the single most important factor determining acuity, Based on o ur findings, afferent stimulation should be considered as an alternati ve or additional treatment to improve visual acuity in CN patients.