The Eye

• What is the function of the sclera?

  The sclera is the tough, supporting wall of the eye.
• What is the function of the cornea?

  The cornea is the transparent outer layer found at the front of the eye.

  It refracts light into the eye.
• What is the function of the iris?

  The iris contains muscles that control the diameter of the pupil and how much light enters the eye.
• What is the function of the lens?

  The lens focuses the light on to the retina.
• What is the function of the optic nerve?

  The optic nerve carries impulses from the receptors on the retina to the brain.
• What is the retina?

  The retina contains receptors sensitive to light intensity and colour.
• What controls the shape of the lens?

  The shape of the lens is controlled by the ciliary muscles and senseory ligaments.
• What happens when light receptors detect bright light?

  A reflex is triggered that makes the pupil smaller.

  The circular muscles in the iris contract and radial muscles relax.

  This reduces the amount of light that can enter the eye.
• What happens when light receptors detect dim light?

  A reflex is triggered which makes the pupil larger.

  The circular muscles in the iris relax and radial muscles contract.

  This makes the pupil wider and increases the amount of light that can enter the eye.
• How does you eye look at near objects?

  The ciliary muscles contract, which slackens the suspensory ligaments.

  The lens becomes thicker (more curved).

  This increases the amount by which is refracts light.
• How does you eye look at distant objects?

  The ciliary muscles relax, which allows the suspensory ligaments to pull tight.

  This makes the lens thinner (less curved).

  It refracts light by a smaller amount.
• What does long-sighted/hyperopia mean?

  When people are unable to focus on near objects.

  This happens when the lens is the wrong shape and doesn't refract enough light.

  You can use a convex lens to fix this (lens which curves outwards)

  The lens refracts the light rays so they focus on the retina.
• What does short-sighted/myopia mean?

  Unable to focus on distant objects.

  When eye refracts too much light.

  You can use a concave lens to correct this so the light rays focus on the retina (a lens that curves inwards)
• What are contact lenses?

  Thin lenses that sit on the surface of the eye.

  They are light weight and almost invisible.

  They are more convenient for sports.
• What are the 2 types of lenses?

  Soft lenses are more comfortable but have higher risk of eye infections.

  Hard lenses have less risk of infection
• What is laser eye surgery?

  A laser can be used to vaporise tissue and change the shape of the cornea.

  Slimming it down makes it less powerful and can improve short sight.

  Making it more powerful will improve long sight.

  The surgeon can precisely control how much tissue is removed.
• What is a disadvantage of laser eye surgery?

  The eye can get infected or can react in a way that makes your vision worse.
• What is replacement lens surgery?

  The natural lens of the eye is removed and an artificial lens, made of plastic is inserted in its place.

  The risks are possible damage to the retina because it involves work inside the eye. (This leads to becoming blind)