10.6 Common Problems of the Eye

A free GCSE Biology lesson for AQA (8461) from OBA School: short and long sight, ray diagrams, and treatments: glasses, contact lenses, laser surgery and lens replacement. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Describe myopia (short sight) and hyperopia (long sight) and their causes
• Interpret ray diagrams showing these defects and how spectacle lenses correct them
• Describe new technologies for treating eye defects
• Evaluate the advantages and disadvantages of each treatment

Key words

• Myopia: Short sightedness: near objects are clear, distant objects are blurred.
• Hyperopia: Long sightedness: distant objects are clear, near objects are blurred.
• Concave lens: A diverging lens, thinner in the middle. Spreads light rays out. Corrects myopia.
• Convex lens: A converging lens, thicker in the middle. Bends light rays together. Corrects hyperopia.
• Laser surgery: Using a laser to reshape the cornea so it refracts light by the right amount.

Myopia (short sight)

In myopia the lens is too thick (refracts light too much) or the eyeball is too long. Light from a distant object is focused in front of the retina, so the image on the retina is blurred.

Hyperopia (long sight)

In hyperopia the lens is too thin (does not refract light enough) or the eyeball is too short. Light from a near object would be focused behind the retina. Long sight often develops with age as the lens becomes less elastic.

• Can see clearly; Myopia Near objects; Hyperopia Distant objects
• Cause; Myopia Lens too thick / eyeball too long; Hyperopia Lens too thin / eyeball too short
• Image focused; Myopia In front of retina; Hyperopia Behind retina
• Spectacle lens; Myopia Concave (diverging); Hyperopia Convex (converging)

Exam tip: link the letters: myOpia – cOncave. Hyperopia needs a convex lens.

Treatments and new technologies

• Spectacles (glasses); How it works Concave or convex lenses in a frame; Advantages Cheap, safe, easy to change; Disadvantages Can break, steam up, get lost; some dislike the look
• Contact lenses; How it works Thin lenses on the cornea; hard or soft; Advantages Hardly visible; good for sport; Disadvantages Risk of eye infection; need careful cleaning; some are uncomfortable
• Laser eye surgery; How it works Laser reshapes (thins) the cornea to change how it refracts light; Advantages Quick; often no glasses needed afterwards; Disadvantages Costly; risk of damage or infection; not suitable for everyone; cannot be reversed
• Replacement lens surgery; How it works Natural lens replaced by a clear plastic lens; Advantages Treats severe defects; also used for cataracts; Disadvantages Higher risk: infection, damage to retina; costly

Worked example: comparing costs

Glasses cost £150 and need replacing every 2 years. Laser surgery costs £2 100 once. After how many years would the surgery have cost the same as glasses?
Glasses cost £150 ÷ 2 = £75 per year.
£2 100 ÷ £75 per year = 28 years.

Answer: About 28 years

Common mistakes

• Swapping the lenses. Myopia needs a concave lens; hyperopia needs a convex lens.
• Saying short-sighted people cannot see near objects. They see near objects clearly but distant objects are blurred.
• Saying laser surgery changes the lens. It reshapes the cornea.
• Saying the image forms “behind” the retina in myopia. It forms in front of the retina.

Revision questions

Try these, then check your answers below each one.

Question 1. A person with myopia (short sight) cannot clearly see… (Choose from: in dim light, near objects, distant objects, colours.)

Answer: distant objects

Working: In myopia, light from distant objects focuses in front of the retina, so distant objects are blurred.

Question 2. Which lens corrects hyperopia (long sight)? (Choose from: Convex (converging), Flat glass, A tinted lens, Concave (diverging).)

Answer: Convex (converging)

Working: A convex lens starts converging the rays before they enter the eye.

Question 3. Which part of the eye is reshaped in laser eye surgery?

Answer: cornea

Working: Laser surgery reshapes the cornea so it refracts light by the right amount.

Related lessons

• Previous lesson: 10.5 The Eye
• Next lesson: 10.7 Required Practicals: The Human Nervous System
• In this chapter: 10.1 Principles of Homeostasis
• In this chapter: 10.2 The Structure and Function of the Human Nervous System
• In this chapter: 10.3 Reflex Actions

Continue in the full course

This lesson is section 10.6 (AGCBH1006) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.