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Crystalline lens position dynamics during mixed saccadic/convergence eye movements


Purpose : The dynamics of the crystalline lens position during eye movements can shed light on some properties of the accommodation mechanism, such as ciliary muscle operation. While previous works revealed lens wobbling after pure saccadic movements and used this effect to study ciliary muscle tension in accommodation steady states, this experiment explores lens position stability following pure convergence or mixed convergence-saccadic eye movements, which could eventually be used to gain information about ciliary muscle dynamics.

Methods : We used a high-speed Purkinje-meter (Tabernero et al., Sci.Rep. 6: 25551, 2016) to record Purkinje image videos at 376 fps in 4 normal young subjects when they performed different types of eye movements: Saccades for both far and near fixation, pure convergence, and mixed convergence-saccade movements. Fixation/accommodation stimuli were two pairs of 1-deg Maltese crosses, 9-deg laterally apart, at 3 m and 30 cm from the subject, and viewed under unrestricted binocular conditions. For each frame, the 4th (lens back) and 1st (corneal front) Purkinje images were determined together with the pupil center and size.

Results : Lens wobbling was observed after pure saccades with amplitude consistent with previous studies: 150 ± 72 mm for near and 125 ± 57 mm for far fixation. On the contrary, no wobbling was detected after convergence/accommodation or mixed saccade-convergence movements. This lack comes from the different nature of the movements: saccades are fast and cease abruptly, producing an inertial movement of the lens, whereas convergence movements are slower and stop progressively, preventing lens wobbling. Combined movements have a mixed structure, starting with a fast initial component followed by a slow progressive tail end that precludes noticeable inertial movements of the lens.

Conclusions : Crystalline lens wobbling was only observed after pure saccadic movements. During and after accommodation/convergence, lens position changes smoothly without showing any significant oscillation. A similar situation occurs for combined saccadic and accommodation eye movements.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

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