Saccades are the minute lateral eye movements the eye makes that allow you to see. Since photoreceptor cells in the retina are activated by a change in the light, the eye must make these movements to keep these receptors firing and providing visual information to the primary visual cortex located in the occipital lobe of the brain.
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-- visual cortex
Some monks who practice one point meditation have reported their vision temporarily blurring out when these movements stop.