A 68-year-old man reports that he can now read newspaper print without the glasses he has worn for years. Refraction shows his myopia has increased by 1.50 D in both eyes over six months. Slit lamp examination reveals grade III nuclear sclerosis. The change in refraction is best explained by:
- A Increased refractive index of the lens nucleus ✓
- B Axial elongation of the globe
- C Keratoconus
- D Ciliary muscle spasm
Correct answer: A. Increased refractive index of the lens nucleus
Explanation
Nuclear sclerosis raises the refractive index of the lens nucleus, increasing its converging power and shifting the refraction toward myopia, called index myopia. Elderly patients experience 'second sight', reading without glasses because their acquired myopia offsets presbyopia. Axial elongation occurs in childhood myopia, not new onset at 68 years, and the slit lamp finding localizes the change to the lens rather than the cornea or ciliary muscle.
Reference: Parsons' Diseases of the Eye, 23rd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.