Power of Accommodation - UNSOLVED PRACTICE SET

Q7. Define the power of accommodation of the eye. What part of the eye is responsible for this ability?

Q8. What is meant by 'near point' and 'far point' of the eye? State the values for a normal human eye. 

Q9. Explain what happens to the shape and focal length of the eye lens when you shift your gaze from a distant mountain to a nearby book.

Q10. Why do ciliary muscles need to work harder when reading a book compared to watching a cricket match at a distance? What long-term effect can excessive close work have on the eyes?

Q11. A student studies for hours close to her book (about 15 cm away). Is this within the range of clear vision? What might happen to her eyes over time if this is a regular habit?

Q12. Explain why the power of accommodation decreases with age. What condition results from this, and how is it different from myopia or hypermetropia?

Q13. Explain the power of accommodation of the human eye in detail. Your answer must cover:
(a) the mechanism — how the ciliary muscles and suspensory ligaments change the shape of the lens,
(b) what happens when focusing on a near object vs a far object (describe each case),
(c) the near point and far point of a normal eye with exact values,
(d) why accommodation is needed (the lens alone cannot produce sharp images of all distances without it), and
(e) how this mechanism is fundamentally different from how a camera focuses.

Q14. A student uses a mobile phone in a dark room, holding it 10 cm from her eyes, for 3 hours every night.
(a) Is 10 cm within the normal range of clear vision? Explain.
(b) What strain does this place on the ciliary muscles?
(c) What long-term vision problem might this cause, and why?
(d) Doctors recommend the 20-20-20 rule: every 20 minutes, look at something 20 feet away for 20 seconds. Explain the optical benefit of this rule.
(e) What is the recommended reading distance for optimal eye health and why?

Q15. Compare the focusing mechanism of the human eye with that of a camera through the following points:
(a) how each changes focus — does the eye change lens shape or lens position?
(b) does a camera change lens shape or lens position?
(c) the speed of accommodation in a healthy young adult vs a camera autofocus system,
(d) why the human eye loses accommodation with age (hardening of the crystalline lens) while a camera does not, and
(e) what the term 'presbyopia' means and how it relates to the loss of accommodation.

Q16. A normal eye has a near point of 25 cm and far point at infinity.
(a) Using the lens formula 1/v−1/u=1/f with v = +2.5 cm (image on retina, approximate) and u = −25 cm, estimate the focal length of the eye lens when focused at near point.
(b) Repeat for far point: v = +2.5 cm, u = −∞. Find f.
(c) Calculate the power of the eye lens in each situation (P = 1/f in metres).
(d) Calculate the range of power (accommodation range) = P_near − P_far.

Q17. A person's near point has shifted to 40 cm due to ageing.
(a) If they try to read at 25 cm, will they be able to focus? Why not?
(b) What power of convex lens is needed so that an object at 25 cm appears to be at 40 cm (their near point)? Use: 1/v − 1/u = 1/f with u = −25 cm, v = −40 cm.
(c) What is the focal length of this lens?
(d) What eye condition is this and what is the lens type used?

Q18. A student's range of accommodation gives her eye lens a minimum power of 60 D (far point) and maximum power of 64 D (near point).
(a) Calculate the accommodation range in dioptres.
(b) Calculate the focal length at each extreme.
(c) What is the near point distance if the image is formed at v = 2.5 cm when P = 64 D? (Use: 1/v − 1/u = 1/f to find u.)
(d) Comment on whether this is a normal near point.