The eye and correcting vision defects. Flashcards
What is the eye ?
The eye is a sense organ.
What are the 9 parts of the eye?
The Sclera, the Cornea, the Pupil, the Lens, the Ciliary muscle, the Iris, the Optic nerve, the Retina and the Suspensory ligaments.
What is the Sclera?
It is the tough, supporting wall of the eye.
What is the Cornea?
It is the transparent outer layer found at the front of the eye. It refracts light into the eye.
What is the Iris?
The Iris contains muscles that allow it to control the diameter of the Pupil and how much light enters it.
What is the Lens?
It focuses the light onto the Retina.
What does the Retina contain?
It contains receptor cells sensitive to light intensity and colour.
What do the Ciliary muscles and suspensory ligaments control?
The shape of the lens.
What does the Optic nerve do ?
It carries impulses from the receptors on the retina to the brain.
Why do we have an Iris reflex ?
Very bright light can damage the retina - so you have a reflex to protect it.
What is the Iris reflex ?
- When light receptors in the eye detect very bright light, a reflex is triggered that makes the pupil smaller. The circular muscles in the iris contract and the radial muscles relax. The reduces the amount of the light that can enter the eye.
- The opposite process happens in dim light. This time the radial muscles contract and the circular muscles relax, which makes the pupil wider.
What is accommodation ?
When the eye focuses light on the retina by changing the shape of the lens.
What happens when the eye is focusing on near objects?
- The ciliary muscles contract, which slackens the suspensory ligaments.
- The lens becomes fat ( more curved )
3 . This increases the amount by which it refracta light.
What happens when our eye is focusing on distant objects?
- The ciliary muscles relax, which allows the suspensory ligaments to pull tight.
- This makes the lens go thin ( less curved )
- so it refracts light by a smaller amount.
What is long - sightedness and how can you fix it ?
- It occurs when the lens is the wrong shape and doesn’t refract the light enough it the eyeball is too short.
- The image of near object are brought into focus behind the retina.
- You can use glasses with a convex lense ( a lens that curves outwards) to correct it. The lens refracts the light rays so they focus in the retina.
What is the medical term for long- sightedness?
Hyperopia
What is short - sightedness and how can you fix it ?
- It occurs when the lens is the wrong shape and refracts the light too much or the eyeball is too long.
- The image of distant objects are brought into focus in front of the retina.
- You can use glasses with concave lenses ( lens which curve inwards) to correct it, so the light rays focus in the retina.
What is the medical term for short- sightedness ?
Myopia
What alternate treatments are there for vision defects apart from glasses ?
Contact lenses, Laser eye surgery and Replacement lens surgery.
What are contact lenses ?
They are thin lenses that sit on the surface of the eye and are shaped to compensate for the fault of focusing. They are popular because lightweight and invisible. They are also not convenient for activities like sports.
What are the two types of contact lenses?
Hard and soft lenses.
Soft lenses are usually more comfortable, but carry a higher risk of eye infections than hard lenses.
What is Laser eye surgery ?
A laser can be used to vaporise tissue, changing the shape of the cornea ( so changing how strongly it refracts light into the eye) Slimming it down can make it less powerful and can improve short sight. The surgeon can precisely control how much tissue the laser takes off, completely correcting the vision. However, there are complications, such as infection or eye. reaction in a way that make your vision worse than before.
What is the replacement of lens 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 master eye surgery. In replacement lens surgery, the natural lens is the eye is removed and an artificial lens, made from clear plastic, is inserted in its place. As it involves work inside the ye, replacing the lens carries higher risks than laser eye surgery, including possible damage to the retina ( could lead to loss of sight)
