5.9 Defects of the eye
6 exam questions worth 14 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
0 / 14
Which type of lens is used to correct short-sightedness?
Choose one answer.
Correct Not quite: the answer is Concave
Mark scheme
B (concave)
Model answer
B: a concave (diverging) lens.
Explain why a person with long-sightedness cannot see near objects clearly.
Mark scheme
- light (from near objects) is focused behind the retina (1)
- because the lens is too thin / does not refract light enough / eyeball is too short (1)
Model answer
The lens is too thin, or the eyeball too short, so light from near objects is not refracted enough and would be focused behind the retina, giving a blurred image.
Describe how a concave lens corrects myopia. You may refer to a ray diagram in your answer.
Mark scheme
- in myopia light is focused in front of the retina (1)
- the concave lens spreads out / diverges the light (before it enters the eye) (1)
- so the eye focuses the light (further back,) on the retina (1)
Model answer
In myopia, light from distant objects is focused in front of the retina. A concave lens diverges the rays slightly before they enter the eye, so the cornea and lens bring them to a focus further back, exactly on the retina.
A person with myopia is deciding whether to have laser eye surgery or to wear contact lenses.
Evaluate the two treatments.
Mark scheme
- laser surgery reshapes the cornea (1)
- laser surgery: permanent / no need for lenses or glasses afterwards (1)
- laser surgery: risks, e.g. infection / dry eyes / vision could be made worse / cannot be reversed / expensive (1)
- contact lenses: no surgery / can be removed / cheaper at first (1)
- contact lenses: risk of eye infection / need cleaning / ongoing cost (1)
- a justified conclusion (1)
Max 4; must include a point for each treatment for full marks
Model answer
Laser surgery reshapes the cornea, so it is a permanent fix and the person would not need lenses again, but it costs a lot at once, cannot be reversed and carries risks such as infection or dry eyes. Contact lenses avoid surgery and can be stopped at any time, but they must be cleaned carefully, can cause eye infections and cost money every month. If the person's eyesight is stable and they accept the small risk, surgery is better long term; otherwise contact lenses are the safer choice.
Describe what a cataract is and how it is treated.
Mark scheme
- (a cataract is) a cloudy area in the lens (1)
- treated by replacing the lens with an artificial lens (1)
Model answer
A cataract is a cloudy patch in the lens that blurs vision. It is treated by surgically replacing the lens with an artificial one.
Explain why a person with red-green colour blindness cannot tell red from green.
Mark scheme
- one type of cone (cell) does not work properly / is missing (1)
- cones detect colour / the red- or green-sensitive cones (1)
Model answer
Cones in the retina detect colour. In red-green colour blindness the red-sensitive or green-sensitive cones do not work properly, so the person cannot tell these colours apart.
Found a mistake?