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Reduced binocular beat visual evoked responses and stereoacuity in patients with Duane syndrome
J J Sloper1, C Garnham, P Gous
1Moorfields Eye Hospital, London, United Kingdom. john.sloper@dial.pipex.com
Purpose:
To study the effects that the abnormal eye movements of patients with Duane retraction syndrome have on the development of binocular function.
Methods:
Pattern reversal visual evoked responses (VEPs) to 15-minutes-of-arc and 60-minutes-of-arc checks and binocular beat VEPs to diffuse sinusoidally modulated 18- and 20-Hz stimuli were recorded in 10 patients with Duane retraction syndrome who maintain binocular function by using an abnormal head posture. Visual acuity, stereoacuity, and eye movements were measured. The results have been compared to those from 10 normal subjects.
Results:
The patients with Duane retraction syndrome had reduced stereoacuity compared to the normal control group (TNO mean, 82.5 seconds of arc compared to 37.5 seconds of arc; Titmus mean, 143 seconds of arc compared to 44 seconds of arc). The binocular beat VEPs showed a significantly reduced difference beat response at 2 Hz in the patients with Duane syndrome compared to normal subjects (mean signal-to-noise ratio 2.40 +/- 1.05 compared to 4.30 +/- 2.66; t = 2.21, df = 18, P < 0.05). Binocular enhancement of the P100 pattern reversal amplitude to 15-minute checks was increased in these patients, because of a reduction of the monocular P100 amplitudes compared to the normal group.
Conclusions:
Patients with Duane syndrome who maintain binocular function using an abnormal head posture have reduced stereoacuity and show electrophysiological evidence of reduced cortical binocular interaction.
