Slide 1

Question of the day:Name the 3 main layers of the eye, and their function.

Instructions: Write your name on the outside of the booklet.Refer to your notes Write the answer in your booklet. There is no need to re-write the question in your notebook. But, write the date on the right hand side, above each answer. The formation of an imageThe Formation of an Image on the Retina:

Light rays always travel in a STRAIGHT LINE.

Rays from the top of the candle enter the eye through the PUPIL opening and then hit the LENS. Once they hit the lens the rays are bent in such a way that they end up IN FOCUS directly on the RETINA

The same happens to the light rays from the bottom of the candle. What do you notice about the image on the retina?

It is UPSIDE DOWN!!All of the rods and cones located on the RETINA are then stimulated and send that message through the optic nerve to our brain. The brains then flips the image around so we see the candle right side up.

4The final image:

Specialized receptors and BRAIN AREAS process different COMPONENTS of vision.

THEN the brain PUTS ALL THE INFORMATION BACK TOGETHER

The Eye and the Image: Steps in seeingThe CorneaLight enters the eye through the cornea (the transparent front part of the eye that covers the iris and pupil).The cornea actually contributes most of the eye's FOCUSING POWER, BUT its focus is fixed.

2. The Iris and pupil

Controlling light levels:

Your eyes are very SENSITIVE and can be DAMAGED by harsh light.

The IRIS is a SMOOTH MUSCLE (sphincter) responsible for controlling how much LIGHT enters the eye.

The PUPIL is the opening left by the iris (not really a part)

In a DARK room where there is not much light the pupil will become LARGE to allow a lot of light in. On a very sunny day when there is a lot of light the pupil will become SMALLER to allow LESS light in.

If the pupil is a hole that lets light into the eye, why does it appear black?It appears black because light rays entering the pupil are absorbed by tissues inside the eye.

The pupil dilates (gets wider) in response to extreme emotional situations such as fear or pain. The same thing happens in response to loads on working memory and attention.Such stimuli awakens your fight or flight response of your CNS. Brain chemicals (neurotransmitters) such as adrenaline cause immediate physical reactions. 3. The Lens (Changing lens thickness)CILIARY muscles are attached to the lens, when CONTRACTED they pull the lens thin

Far Objects:

When looking at objects FAR AWAY the CILIARY muscles contract and the lens becomes THIN, this way the rays appear on the retina and the image is clear.

Close Objects:

When objects are CLOSE the CILIARY muscles RELAX and make the lens FAT allowing the rays to project on the retina and the image is clear.

Why do we need glasses?

Our RETINA is like the screen of an overhead projector. If the image does not LAND on the screen properly it will look BLURRED.

Light rays will bend and land SHARPLY on the retina (screen) only if the RETINA is the proper DISTANCE from the lens.

If you are Far-Sighted (hypermetropia)

The eyeball is too SHORT and the rays are projected BEHIND the retina so vision is blurred.

This can be corrected by placing a CONVEX lens (glasses) in front of the eye.

If you are Near-Sighted (myopia)

The eyeball is too long and the image appears IN FRONT of the retina so vision is blurred.

This can be corrected by placing a CONCAVE lens (glasses) in front of the eye.

Normal View Myopia

Near SightedFar SightedHyperopia

Convex lens: pre-bends light INWARD to shorten the focal pointConcave lens: pre-bends light OUTWARD to lengthen the focal pointSeeing Color:

The type of photoreceptors responsible for seeing color are the CONES.

There are 3 types of cones, each with a heightened sensitivity to either RED, GREEN, or BLUE.

Every colour we see is some combination of these three colors.Colorblindness is the inability to distinguish between certain colors and is caused by a chemical disorder in the cones.