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The Human Eye & Defects of Vision Worksheet

Class 10 Science · about 40 minutes · open the simulation at jugnix.com/simulations/human-eye

NameClassDate

By the end you will: explain accommodation, find the near and far points, and choose and calculate the lens that corrects myopia, hypermetropia and presbyopia.

A. Explore with the simulation

  1. With no corrective lens (0 D), choose each eye and record how near and how far it sees sharply.

    EyeNear pointFar pointEye lens power range (D)
    Normal
    Short-sighted
    Long-sighted
    Old-age eye

  2. Normal eye: look Far away, then at the Book (25 cm). How does the eye lens power change? What makes it change?

  3. Short-sighted eye, Far away: where does the image form? Find the corrective lens that makes it sharp. Is it convex or concave?

  4. Long-sighted eye, Book 25 cm: where does the image form? Find the lens that makes it sharp.

  5. Old-age eye: give it +3 D reading glasses. How far can it now see sharply? Why do some people wear bifocals?

B. Calculate (then check in the simulation)

  1. A student can't see clearly beyond 80 cm. What kind of lens, and what power, do they need?

  2. A person's near point is 75 cm. Find the power of the reading glasses that let them read at 25 cm.

  3. The eye lens is 2.5 cm from the retina. Find the eye's power when it looks at a far object, and when it looks at a book 25 cm away.

  4. A prescription says −2.5 D. What is the focal length, and which defect does it correct?

C. Think it through

  1. Give two causes each of myopia and hypermetropia.

Answer key (for teachers and parents)

  1. Normal: 25 cm to far away, 40–44 D · Short-sighted: about 17 cm to 50 cm, 42–46 D · Long-sighted: 1 m to far away, 39–41 D · Old-age eye: 1 m to far away, 40–41 D.
  2. It rises from 40 D to 44 D. The ciliary muscles squeeze the lens fatter so it bends light more. This is accommodation.
  3. In front of the retina. A −2 D lens makes it sharp (far point becomes far away). Negative power: a concave lens.
  4. Behind the retina. A +3 D (convex) lens brings the near point to 25 cm.
  5. From 25 cm only out to about 33 cm, so far things blur through reading glasses. Bifocals have a top half for distance and a bottom half (+ lens) for reading.
  6. Myopia. f = −80 cm = −0.8 m, so P = 1 ÷ (−0.8) = −1.25 D, a concave lens.
  7. Hypermetropia. P = 1/0.25 − 1/0.75 = 4 − 1.33 = +2.67 D (f ≈ +37.5 cm), a convex lens.
  8. Far: P = 1 ÷ 0.025 = 40 D. At 25 cm it needs an extra 1 ÷ 0.25 = 4 D, so 44 D.
  9. f = 1 ÷ (−2.5) = −0.4 m = −40 cm. A concave lens for myopia (far point 40 cm).
  10. Myopia: eyeball too long, or the eye lens too strongly curved (focal length too short). Hypermetropia: eyeball too short, or the eye lens too weak (focal length too long).

Free to print and share for teaching. Made with the interactive simulation at jugnix.com/simulations/human-eye.