Correction of Vision Defects - UNSOLVED PRACTICE SET

Q7. Explain how a concave lens corrects myopia. Where does the lens form the virtual image of a distant object, and how does this help the myopic eye?

Q8. Explain how a convex lens corrects hypermetropia. Where does it place the virtual image of a nearby object so that the hypermetropic eye can focus on it?

Q9. What are bifocal lenses? Which two defects do they correct simultaneously? Describe how the different regions of the lens work.

Q10. A student's prescription reads: Right eye −1.5 D, Left eye +2.0 D.
(a) What defect does each eye have?
(b) What type of lens is used for each eye?
(c) What is the focal length of each lens?

Q11. What is LASIK surgery? How does it permanently correct myopia without spectacles? What part of the eye is modified?

Q12. A person with both myopia and presbyopia is prescribed bifocal glasses. The top portion is −2.5 D and the bottom portion is +1.5 D. Explain what each portion corrects and how the person uses the glasses in daily life.

Q13. Explain how each of the following vision defects is corrected with the appropriate lens, including ray diagram descriptions:
(a) Myopia — use a concave lens; describe what virtual image it forms and where,
(b) Hypermetropia — use a convex lens; describe what virtual image it forms and where,
(c) Presbyopia — explain why bifocals are used and how they differ from single-vision glasses, and
(d) Astigmatism — briefly explain the role of cylindrical lenses.

Q14. Riya is a Class 10 student in Bengaluru who has been diagnosed with myopia (far point = 1.5 m) in her right eye.
(a) Calculate the power of the corrective lens for her right eye.
(b) What type of lens does she need?
(c) Her optometrist also notices early hypermetropia in her left eye (near point = 50 cm). Calculate the power of the corrective lens for her left eye for reading at 25 cm.
(d) Will a single type of lens work for both eyes? Explain.
(e) What lifestyle advice would you give Riya to prevent her myopia from worsening?

Q15. Compare spectacles, contact lenses, and LASIK surgery as methods of correcting vision defects. Your comparison must cover: 

(a) how each works physically (which part of the optical system it modifies), 

(b) the advantages of each method,
(c) the disadvantages or risks of each,
(d) which method is permanent and which is temporary, and
(e) why LASIK is not suitable for people whose prescription is still changing (e.g. teenagers). Include at least one reference to how these options are available in India today.

Q16. Arun cannot see objects beyond 1.5 m.
(a) State his far point.
(b) Calculate the power of the lens needed to correct his distance vision. (Object at ∞, image at −1.5 m.) 

(c) What is the focal length? 

(d) After correction, what is his effective far point? (e) Would a +3 D lens help him — explain why or why not.

Q17. Meena's near point has receded to 75 cm due to presbyopia. She wants to read her phone at 20 cm.
(a) Using the lens formula with u = −20 cm and v = −75 cm, find the required focal length.
(b) Calculate the power of the corrective lens.
(c) What type of lens is this?
(d) She also has a distance problem (far point = 3 m). Calculate the power of the lens for distance vision.
(e) Should she use bifocals? Justify.

Q18. A doctor examines three patients and records these findings:   Patient A: cannot see beyond 50 cm.   Patient B: near point is at 80 cm.   Patient C: near point 60 cm, far point 1 m.
(a) Identify the defect for each patient.
(b) For Patient A: calculate the corrective lens power.
(c) For Patient B: calculate the corrective lens power (reading at 25 cm, image at −80 cm).
(d) For Patient C: calculate both lens powers needed for bifocals.