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D. Newsham, P.C. Knox, R. Cooke; Control of Fixation in Preterm Children . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2933.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Preterm children (<32 weeks) are at risk of a variety of cerebral lesions. We have previously demonstrated that preterms make significantly more antisaccade errors and have longer latency when executing vergence, in comparison to full term controls. A lack of inhibitory control affecting the ability to suppress reflexive saccades results in increased antisaccade errors. In ADHD it has also been shown to increase intrusive saccades. We therefore decided to investigate the control of fixation in preterm children. Methods: Fixation was examined in 14 preterm children aged 9–10 years with normal IQ (>85) who were free from major neurological deficits, plus 11 full term age matched controls. Subjects binoculary viewed a fixation target (small dark square 0.3° x 0.3°) straight ahead and at eccentricities of 2° and 5°, each for 10s for 20 trials. Their head was stabilised and their eye movements were recorded by infrared oculography. The output of the eyetracker was digitised and written to hard disk for off–line analysis Results: The number of saccadic intrusions, square wave jerks and blinks were counted for each trial, and the mean rate per second of each event calculated. The mean intrusive saccade rate was significantly higher in the preterm group (0.26±0.07; mean±sd) compared to full terms (0.16±0.05; p<0.001). The mean rate of square wave jerks was slightly, but not significantly, higher for the preterms (0.11±0.09) compared to the full term group (0.07±0.03; p=0.139). The blink rate was also higher for preterms (0.26±0.13) in comparison to full terms (0.18±0.08; p=0.05). Conclusions: The preterm children had an increased rate of saccadic intrusions. The frontal eye fields (FEF) have an active role in the control of fixation. The presence of an increased rate of saccadic intrusions is consistent with our previous findings of greater antisaccade errors and longer vergence latency and may be further evidence of a diffuse deficit affecting the frontal cortical region. The increased blink rate may be attributed to the fact that both voluntary saccades and blinks are both under partial control of the FEF.
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