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E. Gowen, R.V. Abadi; Saccadic Intrusions and Voluntary Saccadic Behaviour . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1972.
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Purpose: To identify and describe the nature of saccadic intrusions and their relationship to voluntary saccadic behaviour. Methods: Horizontal, binocular fixation eye movements to a stationary target in primary position were measured in thirty-one normal, randomly chosen subjects (age range, 21-55 yrs) using an infrared recording system (Skalar Medical, The Netherlands). Four voluntary saccade tasks, consisting of pro, overlap, gap (200ms) and antisaccades were then conducted on 10 of the group who displayed fixational instabilities in order to examine latencies, biases and errors. Saccades were centrifugal and 4° in amplitude around the central fixation point. The target was identical in all experiments and consisted of two concentric circles, containing an inner cross subtending 0.3° and an outer cross subtending 3.0° . Student T tests at the 5% level were used to determine significant differences. Results: Twenty five of the thirty one subjects displayed saccadic intrusions on primary gaze. The saccadic intrusions were involuntary, conjugate, horizontal uniplanar saccadic interruptions of fixation which took one of two forms: Square wave intrusions (monophasic and biphasic) and saccadic pulses (single and double). Amplitudes and frequencies ranged between 0.1 - 1.5° (mean=0.5°±0.2°) and 5-55 per minute (mean=26.4±17.2 per minute) respectively. No significant correlation was found between saccadic intrusion frequency and the latency and errors for each of the four volitional saccade tasks. Conclusions: Saccadic intrusions are a common fixational phenomenon to be found in normal populations. Volitional saccadic behaviour does not appear to be affected by the presence of saccadic intrusions nor does it appear to influence saccadic intrusions.
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