Learn Science [Form 2]

Chapter 1 - Lesson 6

Figure 1.12 Formation of an image on the retina

SCIENCE ALERT!
Formation of an image on the retina:

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Okay. So let's take a recap!

1.6 The Sense of Sight

Structure of the human eye

Eye ➡ is a sensory organ of sight.
        ➡ is sensitive to light.

The spherical human eyes are held by muscles in the bony sockets of the skull.

Three pairs of muscles control the movements of the eyeballs.

The tear gland produces tears to clean the eyes and kill microorganisms.

The wall of the eyeball is made up of three layers:
• the sclera
• the choroid
• the retina

Sclera ➡ is the outer layer of the eyeball.
              ➡ is white, tough and opaque.

Choroid ➡ is the middle layer of the eyeball.
                 ➡ has black pigments and a lot of blood vessels.

Retina ➡ is the innermost layer of the eyeball.
              ➡ has many receptors that are sensitive to light. These are called photorceptors (cones and rods).

Parts of the eye and its functions:

◇ Conjunctiva
➡ The thin, transparent, self-repairing membrane that protects the cornea.
◇ Cornea
➡ The curved, transparent layer at the front of the eye is a continuation of the sclera.
➡ Allows light to enter the eye. Helps to focus light onto the retina by bending the light rays passing through it.
◇ Aqueous humour
➡ Helps refract light and focus the image on the retina.                                     
➡ Helps maintain the shape of the eye and the pressure in the eye.
◇ Pupil
➡ Allows light to pass into the eye.
◇ Iris
➡ Controls the size of the pupil and hence the amount of lught entering the eye.
◇ Eye lens
➡ Bends and focuses light to form an image on the retina.                  
➡ The thickness of the lens can be altered to focus near and distant objects.
◇ Suspensory ligaments
➡ Hold the lens in place and connect it to the ciliary body.
◇ Ciliary body
➡ Contracts and relaxes to change the thickness of the lens. This changes the focal length of the lens.
◇ Vitreous humour
➡ The jelly-like material found between the lens and the retina.                                       ➡ Helps keep the shape of the eye spherical.                                      
➡ Helps refract light onto the retina.
◇ Retina
➡ Detects light stimuli and sends information in the form of nerve impulses to the brain.
◇ Yellow spot (fovea)
➡ This part of the retina is the most sensitive to light.                                          
➡ Detects the images of objects formed and gives the clearest vision.
◇ Blind spot
➡ This point on the retina is not sensitive to light.                        
➡ Images falling on this spot cannot be detected because there is no receptor cells on this spot.                        
➡ It is the spot where the optic nerve leaves the eyeball.
◇ Choroid
➡ The capillaries supply nutrients and oxygen to the eye.                   
➡ The black pigments absorb light and prevent reflection of light.
◇ Sclera
➡ Protects and shape the eye.
◇ Optic nerve
➡ Sends nerve impulses from the retina to the brain to be interpreted.

How do we see?

1. Light rays falling on the ibject is reflected in all directions.
2. Some reflected rays enter the eye.
3. Light rays entering the eye are refracted by the cornea, aqueous humour, eye lens and vitreous humour.
4. An inverted image is formed on the retina.
5. Nerve impulses from the retina are sent to the brain by the optic nerve.
6. The brain interprets the nerve impulses and allows the observer to see the object the right way up.

The nearer the object to the eye is, the bigger the image that is formed on the retina.

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Is the past few lessons, good? Some of you may study this before but yeah. I would advise you to not just memorize but understand each thing here. As my experience, if you just memorize without understanding it, you will easily forget what you have memorized. But if you understand it, you will easily remember the things. So yeah. Just a tip from me due to my experience. =)

New update! Just add some notes at the end. Hope you like it. ☺😊😀

~ CutieKittyMe