Correcting eye defectsSpec 2.17B
| Defect | Correction |
|---|---|
| Long-sightedness | A convex lens (glasses or contact lenses) bends light inwards before it enters the eye, so it focuses on the retina instead of behind it. |
| Short-sightedness | A concave lens (glasses or contact lenses) spreads the light out before it enters the eye, so it focuses on the retina instead of in front of it. |
| Long- or short-sightedness (other option) | Laser eye surgery changes the shape of the cornea, so that light is focused on the retina. |
| Cataracts | Surgery removes the cloudy lens and replaces it with an artificial lens. |
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What does the iris do?
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It controls how much light enters the eye.
What is the difference between rod and cone cells?
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Rods work in dim light and do not detect colour. Cones detect colour and work in bright light.
What causes cataracts?
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The lens becomes cloudy, so less light reaches the retina.
What type of lens corrects short-sightedness?
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A concave lens.
Why can some people not tell red and green apart?
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One or more types of cone cell are missing or not working properly.