The Human Eye Informative Speech
Good morning, everyone.
Take a moment and look around the room. You can see colors, shapes, movement, distance, and
details almost instantly. You can recognize a familiar face, read a sentence, notice a bright light,
and judge whether something is near or far. We use our eyes constantly, yet most of us rarely
stop to think about how remarkable they are.
So, how does the human eye turn light into the images we see?
Today, I want to take you through the basic science of the human eye, from the moment light
enters the eye to the moment your brain interprets what you are looking at.
The first thing to understand is that vision begins with light.
Light reflected from an object enters the eye through a transparent outer surface called the
cornea. The cornea is not simply a protective covering. It does much of the initial bending, or
refraction, of incoming light.
After passing through the cornea, light travels through the pupil. The pupil is the opening in the
center of the iris, the colored part of the eye. The iris controls how much light enters. In bright
conditions, the pupil becomes smaller. In dim conditions, it becomes larger.
You can actually observe this response yourself. If you move from a bright outdoor area into a
dark room, it takes a little time for your eyes to adjust. One reason is that the pupils widen to allow
more light into the eye.
After the pupil, light reaches the lens.
The lens helps focus incoming light onto the retina at the back of the eye. Unlike a camera lens
that moves as a whole, the human lens changes shape. Tiny muscles and fibers surrounding it
alter its curvature so that we can focus on objects at different distances.
This ability is called accommodation.
Try looking at your hand and then at something far away. Your visual system has to adjust its
focusing system as your viewing distance changes. When we are young, the lens is generally
flexible enough to change shape easily. With age, it gradually becomes less flexible, which
contributes to the common need for reading glasses known as presbyopia.
Now we reach one of the most important parts of the eye: the retina.
