The sensory experience which brings into awareness objects in the environment through the act of seeing is referred to as vision or visual sensation.

1. SENSATION
Vision

2. Sensation
 Sensation is the process of receiving stimulus energies from the external
environment. Stimulus consist of physical energies i.e. light, sound, and heat.
 Stimulus is detected by specialized receptor cells in the sense organs, which are in
eyes, nose, ear, skin and tongue.
 Stimulus Receptor cells Electrochemical impulse Brain
(Physical energy) (Transduction) (Cerebral cortex)

3. Senses

4. Vision
 Stimulus for vision is a wave form of radiant energy, that is, light radiates from its
source in waves, which we can call light waves.
 Light has three major characteristics;
1. Wave amplitude indicates its intensity. The amplitude or intensity is its
brightness.
2. Wave length is the distance between any point in a wave and the corresponding
point on the next cycle. It’s the attribute of light energy that determines the hue or
color.
3. Wave purity (whether there is more than one type of wave) produces the
psychological experience of saturation. It is made up of light waves all of one
length or color.

5. Structure of eye
Human eyes are 2 inches apart. Because of this, each eye sees the world from a
slightly different perspective. Our brain takes the information it receives from each
eye and correlates the two images to interpret depth and distance known as
binocular fusion.
Each eye consist of three concentric layers, each with its own characteristics,
appearance, structure and primary functions.
1. Outermost layer consist of sclera and cornea.
2. The middle layer (choroids), contains, aqueous humor, ciliary bodies, Iris, Pupil,
Lens and the vitreous chamber.
3. Innermost layer is retinal layer consist photoreceptors (Rods and codes), Fovea,
Blind spot, optic nerve and optic chiasma.

7. Outer Layer
Sclera : The outer layer of the eyeball is a tough, white membrane called the sclera
(the white of the eye). Sclera is 1mm thick and tough because of the pressure of
aqueous humor.
Cornea: The slight bulge in the sclera at the front of the eye is a clear, thin, dome-
shaped tissue called the cornea. Light enters the eye through the cornea, the clear,
curved layer in front of the iris and pupil. The cornea serves as a protective covering
for the front of the eye and also helps focus light on the retina at the back of the eye.

8. The middle layer (Choroids coat)
 The choroid provides oxygen and
nourishment to the outer layers of the
retina.
 This thin layer of tissue is made up almost
entirely of blood vessels. These blood
vessels supply oxygen and nutrients to the
outer part of the retina. In short, the
choroid is the life source that keeps the
retina healthy and functioning.

9.  Pupil: The pupil is the black opening in the middle of the colored part of your eye
(iris). The pupil gets bigger or smaller in response to changes in light. Muscles in
the iris control the size of the pupil.
Iris and ciliary bodies: The ciliary body produces the fluid in the eye called aqueous
humor. It also contains the ciliary muscle, which changes the shape of the lens when
your eyes focus on a near object. This process is called accommodation.

10. Inner layer ( Retinal coat)
 Retina contains photoreceptors, the rods and cones which contains chemical that
absorb light waves.
 When they absorb light waves, these chemicals break down, generate a tiny
electrical force. If a large enough force is generated, the threshold of neighboring
cells is reached and nerve impulse are triggered. These impulses then move to brain.
 The most critical function of the eye is to convert the information about the world,
which is being carried by light waves into neural signals, that the brain can process.

11.  Photoreceptors: Photoreceptors are
specialized cells for detecting light.
 There are two types of photoreceptors:
Rods and cones.
 Rod cells are highly sensitive to light and
function in night vision. Rods are more
than 115 million in the side area of retina
handling low illuminative vision.
 Cone cells are capable of detecting a wide
spectrum of light photons and are
responsible for color vision. They are
packed in the center of retina as they are
about 6 million. This area is called Fovea,
it is our area for sharpest vision.

12.  Blind spot: This region contains no receptor
cells at all. Contributing no photoreceptors and
is therefor insensitive to light, creating a blind
spot where optic nerve leaves the eye.
 Optic Nerve: The optic nerve is located in the
back of the eye and connects the eye to the
brain. Impulses produced by the retina are sent
to the brain via the optic nerve, where the
impulses are developed into images.

13.  Optic Chiasma: Place in the brain
where some of the optic nerve fibers
coming from one eye cross optic
nerve fibers from the other eye.
 This enables vision from one side of
both the eyes to be appreciated by the
occipital cortex of the opposite side.

14. • Cornea
• Iris
Pupil
• Ciliary
muscles
• Lens
Retina
• Photoreceptors
• Optic Nerve
Occipital
Cortex