Sight, more than any of our senses, helps us navigate the world
around us. In a single glance, lasting a fraction of a second,
our eyes work with our brains to tell us the size, shape, color,
and texture of an object. They let us know how close it is,
whether it's standing still or coming toward us, and how quickly
it's moving. The eyes are small compared with most organs, but
their structure is incredibly complex. They work together to
perceive depth, enabling us to judge distance and the size of
objects to help us move around them. They also work with the
brain, muscles, and nerves to produce complicated visual images
and messages. And they constantly adapt to the changing
environment — for example, adjusting so that we can easily move
around in a nearly dark room or bright sunlight. To understand
how the eyes work, it's important to know about their structure
and about conditions and diseases that can interfere with
vision. How Eyes Work Only part of the eye is visible in a
person's face. The whole eye — t