A 58-year-old man needs to hold his newspaper at arm's length to read it. His distance vision is normal. The primary mechanism responsible for this condition is:
- A Age-related loss of elasticity of the crystalline lens ✓
- B Progressive flattening of the corneal curvature
- C Weakness of the extraocular muscles
- D Elongation of the anteroposterior axis of the eyeball
Correct answer: A. Age-related loss of elasticity of the crystalline lens
Explanation
Presbyopia results from age-related stiffening and loss of elasticity of the lens substance, so contraction of the ciliary muscle produces less change in lens curvature and near point recedes. Distance vision remains unaffected because emmetropia does not require accommodation. Corneal flattening, extraocular muscle weakness, and axial elongation are not mechanisms of presbyopia; axial elongation actually causes myopia.
Reference: Ganong's Review of Medical Physiology, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.