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Shuang Song, Ethan A. Rossi, Charlotte Wickham, Austin Roorda, David R. Brillinger, Dennis M. Levi; Fixational eye movements for normal and strabismic amblyopic observers. Journal of Vision 2010;10(7):456. doi: 10.1167/10.7.456.
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© ARVO (1962-2015); The Authors (2016-present)
An adaptive optics scanning laser ophthalmoscope (AOSLO) was used to record fixational eye movements in normal and strabismic amblyopic observers, allowing direct viewing of retinal movements and fixation locations. Fixational eye movements were modeled as a stochastic process governed by a potential function. This model integrates various aspects of fixational eye movements, e.g., velocity, fixation position, and time, in a natural way. We applied this approach to both normal and strabismic amblyopic observers to characterize their fixational eye movements quantitatively. Retinal movements were recorded using the AOSLO (at 30 Hz) while subjects fixated a small target generated by selectively modulating the amplitude of the laser beam. Cross correlation was used to estimate relative positions of different frames. The gradient of the potential function assumed to have the form of a quadratic polynomial in the domain of a plane (i.e. fixation position) was fitted to microsaccade and drift velocities (at different times following a microsaccade) for normal subjects; a chain model of microsaccades was developed to characterize fixation patterns on multiple loci for the strabismic amblyopes. We estimated microsaccade rate as a function of location, using a Poisson point process approximation. Our results confirm that microsaccades, on average, correct for fixation inaccuracy. Microsaccades occur more frequently and tend to move faster towards the target at relatively large displacements, as predicted by the microsaccade rate map and the potential function. Drift is modeled as a Brownian motion with constant rate over time plus an error-correcting component initially following a microsaccade. The unstable eccentric fixational eye movements in strabismic amblyopia are characterized by frequent intrusive saccades with large amplitudes and high speeds. The strabismic amblyopic fixation pattern on multiple loci is task dependent, with less eccentric but unstable fixation induced by challenging tasks, and relatively stable fixation by small highly visible static targets.
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