Eye tracking white sclera (limbus tracking). It presents another challenge for vertical eye movements due to obstruction of eyelids. Eye-tracking setups vary greatly: some are head-mounted, some require the head to be stable (for example, with a chin rest), and some function remotely and automatically track the head during motion. Most use a sampling rate of at least 30 Hz. Although 50/60 Hz is more common, today many video-based eye trackers run at 240, 350 or even 1000/1250 Hz, speeds needed in order to capture fixational eye movements or correctly measure saccade dynamics. Eye movements are typically divided into fixations and saccades
Eye development Eye development Eye formation in the human embryo begins at approximately three weeks into embryonic development and continues through the tenth week. Cells from both the mesodermal and the ectodermal tissues contribute to the formation of the eye. Specifically, the eye is derived from the neuroepithelium, surface ectoderm, and the extracellular mesenchyme which consists of both the neural crest and mesoderm. Neuroepithelium forms the retina, ciliary body, iris, and optic nerves. Surface ectoderm forms the lens, corneal epithelium and eyelid. The extracellular mesenchyme forms the sclera, the corneal endothelium and stroma, blood vessels, muscles, and vitreous. The eye begins to