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Eyes

Rest of human body

Did you know???: Average humans blinks about 15,000 a day.

4. Aqueous Humour

5. Vitreous Humour

10. Ciliary Body

11. Ciliary Muscle

13. Optic Nerve

Light focussing

Changing Shape of Lens

Detecting Light

Perception: very complex process involving both eyesight and using brain to make sense of image received by eyes.
Vision testing: normally for professional called optometrist.
Sometimes, optometrist gives you to a ophthalmologist, physician expert in eye care .

Human vision

Outer surface of eye = where light enters,
Made of transparent layer of tissue of cornea.
Light pass through cornea yet is tough enough to protect the inner eye.

1. Cornea

Transparent part of eye covering iris and pupil (about thick as credit card to protect inner) to decide how much light enters.
Enough to send strong pain signal if anything touches.
Light enters are refracted by cornea.

Heals itself, if get scratched.
Helps direct light enter.
Without refractive properties of cornea = can't focus.

Created by circular band of muscle called iris. Iris’s color = eye color.

2. Pupil

Upon entering, it reaches pupil.

Pupil = eye’s dark circle, a hole letting light pass into eye.
Upon passing cornea, light reach pupil.
The dark circle in eye is actually a hole letting light pass into eye.
Created by circular bond of muscle called iris.

3. Iris

Control pupil size and how much light enters
In unclear light, it opens and pupil dilates/becomes wider to let more light.
For bright light, iris closes and pupil contracts/shrinks to let less light.
In dim light, iris opens and pupil dilates/gets wider letting more light.

4. Aqueous Humour

Transparent water-like fluid similar to blood plasma.
Provides nutrition to cornea and lens, maintains eye in pressurized state
Clear fluid between sclera and lens

5. Vitreous Humour

Jelly like material maintains shape of eyeball
Transmit light to retina

6. Lens

Lens = clear, curved and flexible structure at front of eye behind pupil.
Making image on retina
Focus light rays entering through pupil.👇

8. Retina

Find back of eye acting as projection for light rays entering.
Images reaching retina is turned upside down by brain.

Back of the eye

9. Sclera

White layer of eyeball at front of eye
Continuous with cornea.

Maintain eyeball shape and protect from injury.

10. Ciliary Body

Found behind eyaball
Part of eye connect iris to choroid
Consist of ciliary muscle
Changes lens shape when eye focus
Clear fluid, that fills the space between cornea ad iris.

11. Ciliary Muscle

Circular structure being extension of iris, the color of the eye.
Produces the fluid called aqueous humor.
Change shape of lens when eye focus on near object.

12. Choroid

Dense network of blood vessels located between retina and sclera.
Supplies nutrition to posterior, layers of retina.

13. Optic Nerve

Bundle of more than 1 million nerve fiber carrying visual messages from eye to brain.
Located back of eye →→→→
Damaging it, causes vision loss
Type of vision loss or how severe it is depends on where damage

is.

14. Tear Duct

Small tube located beside eye
Drain tear from eyes
Wash over eyes to keep them

Light focussing

As mentionned most light focused oneye is done by cornea.
The entire eye is a focussing system that involves the cornea, lens and even spaces in front and behind the lens that are filled with a watery fluid.

Changing Shape of Lens

Your eye includes a convex lens. The lens is able to adjust its focal length (focus) due, unlike the cornea, it's attached to a tiny circle of muscles called "ciliary muscles" that changes its shape.

When muscle contract the lens expand into a more spherical or thicker shape.
The lens now strongly refract light, which helps you focus on very ear object.
When circular muscle is relaxed, the lens becomes flatter and thinner. It's excellent to see distant objects.

Detecting Light

To see, light rays must be absorbed by photoreceptors.
Cells in the retina that are sentstive to light.
Photoreceptorrs include cells and cone cells

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