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The eye and vision defects - Coggle Diagram
The eye and vision defects
The eye
It is a sense organ
Image B5, 1
Sclera - tough, supporting wall
Iris - contains muscles that allow it to control the diameter of the pupil and therefore how much light enters
Pupil - whole in the middle
Lens - focuses light onto the retina
Ciliary muscles and suspensory ligaments - controls the lens' shape
Optic nerve - carries impulses from the receptors on the retina to the b
Cornea - transparent outer layer at the front of the eye. It refracts light into the eye
Retina - contains receptor cells sensitive to light intensity and colour
Iris reflex
Very bright light can damage the retina so you have a reflex to protect it
2) The opposite process happens in dim light. The radial muscles contract while the circular muscles relax making the pupils wider
1) When light receptors detect bright light a reflex is triggered which makes the pupil smaller. The circular muscles in the iris contract and the radial muscles relax. This reduces the amount of light that can enter the eye
Focusing on near and distant object
The eye focuses light on the retina by changing the shape of the lens - accommodation
To look at near objects:
1) Ciliary muscles contract, which slakens the suspensory ligaments
2) The lens becomes fat (more curved)
3) This increases the amount by which it refracts light
To look at far objects = opposite
Long / short-sighted
Long sighted people are unable to focus on near objects
2) Images of near objects are brought into focus
3) You can use glasses with a convex lens (a lens which curves outwards) to correct it. The lens refracts the light rays so they focus on the retina
1) Occurs when the lens is the wrong shape and doesn't refract (bend) the light enough or the eyeball is too short
4) The medical term for long-sightedness is hyperopia
Short sighted people are unable to focus on distant objects
1) This occurs when the lens is the wrong shape and refracts the light too much or the eyeball is too long.
2) The images of distant objects are brought into focus in front of the retina.
3) You can use glasses with a concave lens (a lens which curves inwards) to correct it, so that the light rays focus on the retina.
4) The medical term for short-sightedness is myopia.
Treatments
Laser eye Surgery
Bad eyesight can sometimes be corrected with laser eye surgery.
A laser can be used to vaporise tissue, changing the shape of the cornea (and so changing how strongly it refracts light into the eye).
Slimming it down makes it less powerful and can improve short sight. Changing the shape so that it's more powerful will improve long sight.
The surgeon can precisely control how much tissue the laser takes off, completely correcting the vision. However, like all surgical procedures, there is a risk of complications, such as infection or the eye reacting in a way that makes your vision worse than before
Replacement lense surgery
Sometimes long-sightedness may be more effectively treated by replacing the lens of the eye (rather than altering the shape of the cornea with laser eye surgery).
In replacement lens surgery, the natural lens of the eye is removed and an artificial lens, made of clear plastic, is inserted in its place.
As it involves work inside the eye, replacing a lens carries higher risks than laser eye surgery, including possible damage to the retina (which could lead to loss of sight
Contact lenses
Contact lenses are thin lenses that sit on the surface of the eye and are shaped to compensate for the fault in focusing.
They're popular because they are lightweight and almost invisible. They're also more convenient than glasses for activities like sports.
The two main types of contact lenses are hard lenses and soft lenses. Soft lenses are generally more comfortable, but carry a higher risk of eye infections than hard lenses.