Why the cornea has no blood vessels
The cornea is the clear, curved window at the front of the eye. Unlike most living tissue, it has no blood vessels running through it. That keeps the path for light relatively clear: vessels and the cells in blood could scatter light before it reaches the retina.
The cornea still needs oxygen to power its cells. With the eye open, oxygen from the air dissolves in the thin tear layer covering the surface, then diffuses into the cornea. When the eyelids are closed, oxygen can also reach it from fluid inside the eye, though less directly from the air.
What blinking does for the surface
A blink spreads tears across the cornea, smoothing its optical surface and helping keep it moist. Tears also carry dissolved substances and help wash away small particles. During screen use, people often blink less frequently or incompletely, so the tear layer can break up and leave patches of the surface exposed.
That dryness irritates the cornea’s densely packed sensory nerves, producing burning, grittiness, or a sensation like sand. It can also make vision briefly blur because an uneven tear layer bends light less consistently. The discomfort is therefore not simply a sign that the cornea is running out of oxygen: the immediate problem is often a disrupted, drying surface. A full blink restores the tear coating—and, with it, a smoother window for light.
