The document discusses the anatomy and function of the human eye. It describes how the eye has evolved over 50 million years from tree-dwelling ancestors into its modern form. The eye functions similarly to a camera, using a lens to focus light and specialized cells in the retina to process visual images that are sent to the brain. Understanding how the eyes, retina and brain work together allows us to better interpret visual messages and cues communicated through eye contact and expression.

1. LESSON 5
Eye
TOPICS COVERED
How eye works.
Eyes in Photograph.
OBJECTIVES
Notice how eyes communicate – your own and others around you. By studying how the
eyes, retina and mind work, you will be in a better position to understand and analyse
how complex messages are received. . This Lesson will deal with the fascinating process
of how eyes direct images to the brain.
By the end of this chapter you should know:
. The major components of the eye, retina, and their functions.
. How eye contact in a visual message directs meaning and mood.
My eyes make pictures when they are shut.
Samuel Taylor Coleridge.

2. Study your eyes in a mirror for a moment.
What do you see? You see ancient, prehistoric eyes. In fact, the configuration of two eyes set in the
front of the head, protected by a heavy layer of surrounding bone, and sending their dual images to a
brain that fuses the double view into a single, coherent picture is at least 50 million years old.
Over countless generations, modern humans eventually emerged from treedwelling animals (Figure
3.1). Our Ice Age ancestors had the same brain size, shape, and functions as the reader of this line of
text. Although minuscule in comparison to evolutionary time changes, the 50,000-year-old life span
of the contemporary human nevertheless has adapted to the requirements of its modern age. Such
complex and unanticipated evolutionary skills as driving a car or piloting an airplane are possible
only because of the way the eye and brain function together to control the rest of the body.
Windows to the soul
As Leonardo da Vinci once wrote, "The sense which is nearest to the organ of perception functions
most quickly, and this is the eye, the chief, the leader of all other senses" More than 70 percent of all
the sensory receptors in the human body are in the eyes. Hearing, smelling, tasting, and touching all
take a backseat. Given such an important sense, the eyes should never be subjected to unnecessary
harm. In an American Academy of Pediatrics report it was estimated that seventy children in 1999
became permanently blind because of a fireworks-related injury. In another publication the Academy
found that being struck by a pitched ball while playing baseball is the leading cause of sports- related
eye injuries in children.

3. A camera is like an eye.
Just how does the eye work?
The eye is a fantastic piece of natural engineering. It copes with extremes of light and dark, capable
of focusing from inches to infinity, and has a design life of 70-plus years.
The eye is an instrument that collects light and focuses it to the rear surface of the eyeball. Since the
invention of the camera, the eye has been compared to its simple mechanism for focusing and
capturing "light drawings" on film. This analogy isn't surprising because knowledge of the physical
workings of the eye helped in the camera's development. The essential parts of the still or motion
picture photographic process are housed within a protective box or carrying
case; the eye is protected by an outgrowth of the skull. A visual artist often uses a drop of solution to
clean the glass elements of the lens from dust and smudges; the eye has a built-in lens-cleaning
system with its salty tears. The shutter regulates the amount of time film is exposed to light; the
eyelids open and shut so that vision is possible. The aperture is an opening that Jets light enter the
camera; the pupil performs the same function in the eye. In still and motion picture photography, as
with the eye, the lens focuses the outside image to a point at the back of the dark chamber. In
photography, a sheet of thin, light-sensitive emulsion records the picture, as photo receptors in the
back of the eye process the light rays. Photographers process and print their images in a darkroom or
on a computer; humans process their images within the visual cortex region of the brain.

4. EYE, RETINA, AND THE BRAIN
As with light, much is communicated through the eyes.
By studying how the eyes, retina, and mind work, we are better able to notice how eyes
communicate complex messages. Is a person in a visual message looking confidently into the camera
and is relaxed with the image-taking process, looking away from the lens as if embarrassed or
covering the eyes completely as if to ward off the photographer? These drastically different visual
messages are more easily noticed with a basic understanding of how the eyes direct images to the
brain.
 At Least 50 Million Years Old
Eyes Evolved for Walking
and Safe Eating
The only transparent tissue in the body the cornea - the most
sensitive to touch, and the best protected (by the lids)
The grey ring around the dark brown iris is known as “arcus”. It
can be the sign that someone’s diet has too much cholesterol!
The Pupil - not just a hole
The pupil appears black due to the dark pigment beneath the retina absorbing light as it
enters.

5. The quantity of light entering through the pupil is controlled by the iris.
The iris is has two muscles - one to constrict the pupil, the other to pull it open.
A technique called ophthalmoscopy shines a light through the pupil and lets us to look along the
same path as the light is traveling. No longer does the pupil appear black - all is revealed.
Careful inspection of the structures within the eye can indicate so much about a person’s general
health and, of course, the health of their eyes:
· Here is only place in the body where the condition of the blood vessels can be checked -
without needing invasive surgery.
· The condition of the optic nerve, taking over a million nerve fibres to the visual centres in the
brain, can be inspected.
·
·
Critical vision and colour vision are carried out at the fovea of the eye.
A diagrammatic representation of the blood supply in the retina is available.
The eyes in photographs