Q1. [4] medium exam-ready
Read the following and answer the questions that follow:
Dr. Sharma, an ophthalmologist, examines three patients in one morning. Patient A, aged 14, complains that she cannot read the whiteboard at school from the back rows. Patient B, aged 45, says he has to hold his newspaper at arm's length to read it comfortably. Patient C, aged 65, tells the doctor that she struggles to see both nearby and distant objects clearly and has been prescribed special glasses with two different lens types.
(i) Identify the vision defect each patient is suffering from. [1]
(ii) For Patient A, state the position of the image formed on the eye relative to the retina and the type of corrective lens prescribed. [1]
(iii) For Patient B, explain why the light from a nearby object is not focused on the retina. What type of lens corrects this? [2]
Generated by claude-sonnet-4-6 · 2026-06-26 01:09 · grounding rag
Model Answer
(i) Defects:
- Patient A (14 yrs): Myopia (short-sightedness)
- Patient B (45 yrs): Hypermetropia (far-sightedness)
- Patient C (65 yrs): Presbyopia
(ii) In Patient A's myopic eye, the image of a distant object is formed in front of (before) the retina. A concave lens (diverging lens) of suitable power is prescribed to correct this defect.
(iii) In Patient B's hypermetropic eye, the focal length of the eye lens is too long, or the eyeball is too small. As a result, light rays from a nearby object are focused at a point behind the retina instead of on it. A convex lens (converging lens) provides the additional focusing power needed to bring the image onto the retina, correcting the defect.
Source: Chapter 10, Section 10.2 – Defects of Vision and Their Correction
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Explanation
- (i) Each patient maps to a textbook defect: difficulty seeing the board = myopia; holding things far to read = hypermetropia; trouble with both near and distant + bifocals = presbyopia.
- (ii) For myopia, the key phrase examiners look for is "image formed in front of/before the retina" + "concave lens." Both parts needed for the 1 mark.
- (iii) This is 2 marks, so you need reason (focal length too long OR eyeball too small → image behind retina) AND correction (convex/converging lens). Missing either costs a mark.