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T. Pansell, S. Giovagnoli, R. Bolzani, B. Zhang, J. Ygge; Hyper Acuity Target Improve Fixation Stability. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2830.
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© ARVO (1962-2015); The Authors (2016-present)
A slow oscillation of eye position (±0.5 deg, 0.1 Hz) was recently described when analyzing fixational eye movements by means of a Fourier transformation (poster Zhang et al., ARVO 2009). The underlying purpose of this eye movement is not known. This study investigated the influence of hyper acuity targets on this ocular oscillation. Many studies have reported that the visual hyperacuity, the ability to perceive visual information presented under the threshold of visual acuity is mainly related to the magnocellular system, which is supposed to be of advantage for visual stabilization. Our hypothesis is that the fixation of a hyper-acuity target is more stable than the fixation of a super threshold target.
Eye movements were recorded binocularly (VOG, Chronos Vision; 100 Hz) in seven healthy subjects during a fixation task. Three targets were used in a randomized procedure for each subject in three tests (180 sec). i) hyper-acuity target (dot obtained by a number of concentric circles with distances between each other under the visual acuity threshold) ii) visible target (dot made by concentric circles with distances each other over the visual acuity threshold), and iii) solid target (control target, a grey dot). All the targets had the same luminosity (23 cd/m²), size (visual angle 0.9 deg) and were presented at the same eye-screen distance (50 cm). The subjects were instructed to fixate the target.
Significant differences were found in the characteristics of the oscillation between the targets (F=2.49; p< .05). The oscillation was faster and the amplitude was smaller in response to the hyper acuity target compared to the other two targets. The faster oscillation might be caused by a constant eye velocity in a narrower fixation area.
These results suggest that the oscillation of fixational eye movements is more stable when fixating a hyper acuity target. Fixation is more stable when only the magnocellular system is stimulated compared to when both the parvocellular and mangocellular systems are involved.
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