Bifocal lens is used to correct the eye defect of

Analysis

The question asks for the specific eye defect that is corrected by the use of a bifocal lens. To answer this, we must understand the nature of common eye defects and the lenses used to treat them.

Concept Explanation

Eye defects occur when the eye's ability to focus light on the retina is impaired. Here is a breakdown of the common defects:

1. Myopia (Short-sightedness): The person can see near objects clearly but distant objects appear blurred. It is corrected using a concave (diverging) lens.
2. Hypermetropia (Long-sightedness): The person can see distant objects clearly but near objects appear blurred. It is corrected using a convex (converging) lens.
3. Astigmatism: This occurs when the cornea or lens has an irregular curvature, causing blurred vision at all distances. It is corrected using cylindrical lenses.
4. Presbyopia: This is an age-related condition where the eye loses its ability to focus on near objects due to the hardening of the lens. Because elderly people often suffer from both presbyopia (difficulty with near vision) and sometimes other distance vision issues, they require a lens that combines both convex and concave powers. This is known as a bifocal lens.

Step-by-Step Solution

• Step 1: Evaluate the function of a bifocal lens. A bifocal lens contains two parts: the upper part for distance vision and the lower part for reading (near vision).
• Step 2: Match the defect to the lens. Since presbyopia involves the loss of near-focusing ability (often occurring alongside distance vision issues in older adults), the bifocal lens is the standard medical solution.
• Step 3: Compare with other options. • Astigmatism requires cylindrical lenses. • Hypermetropia requires convex lenses. • Myopia requires concave lenses.
• Step 4: Conclude that presbyopia is the correct match for bifocal lenses.

Conclusion

The correct option is D.

Exam Tip

To remember this easily, think of the word "Presbyopia" as the "old age" defect. When people get older, they often need "two" (bi-) focuses—one to look at the road while driving and one to read their newspaper. Hence, Bi-focal for Presbyopia.