Presbyopia
Presbyopia is an age-related defect in which the power of accommodation decreases and near vision becomes difficult.
In one line: Age goes up, near focus goes down.
Practice This ConceptUnderstand it
As a person grows older, the ciliary muscles weaken and the eye lens loses flexibility. The near point shifts farther away, so reading nearby text becomes difficult. In many cases, bifocal lenses or suitable combinations of lenses are used for correction.
Example
Formula and rule
Presbyopia is corrected by lenses that help near vision, often bifocal lenses when distance vision is also affected.
See it worked out
Follow the example line by line, then use the same method on new questions.
Worked example
- 1A 55-year-old person can watch television clearly but cannot read a medicine label at 25 cm.
- 2The near point has shifted farther away, so reading glasses are needed to aid near focus.
Method you can reuse
- 1State that the problem appears with age.
- 2Mention weakened ciliary muscles and reduced lens flexibility.
- 3Say that the near point moves away.
- 4Explain that reading becomes difficult.
- 5Add that bifocal or suitable corrective lenses are used.
Sketch it in your answer
Draw a normal near-vision path and a presbyopic eye where the near image would fall behind the retina. Show a bifocal lens option if needed.
Check yourself
Answer the question in your head before opening the answer.
Try it yourself
Why do many older people need reading glasses even if they can see far objects clearly?
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Common wrong answer
A common wrong answer is to describe presbyopia as a defect of distant vision.
Why it loses marks: It mainly affects near vision.
Don't mix this up
Exam tip
Write it in the exam
Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.
How CBSE asks it
- 1
Enough for 1 mark
Presbyopia is an age-related defect in which the power of accommodation decreases and near vision becomes difficult.
- 2
Add for 2 marks
Example: An older teacher may be able to see the blackboard clearly but need reading glasses for a small-print book.
- 3
Add for 3 marks
As a person grows older, the ciliary muscles weaken and the eye lens loses flexibility.
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