An illiterate 62-year-old farmer reports he can now read newspaper print without glasses, something he could not do two years ago. Examination shows grade III nuclear sclerosis bilaterally. This phenomenon of 'second sight' is explained by:
- A Cortical hydration causing a hypermetropic shift
- B Posterior subcapsular thinning reducing corneal power
- C Increase in refractive index of the nucleus causing a myopic shift ✓
- D Zonular relaxation flattening the lens equator
Correct answer: C. Increase in refractive index of the nucleus causing a myopic shift
Explanation
Progressive nuclear sclerosis raises the refractive index of the nucleus, increasing its converging power and producing index myopia. The patient can again read at near without glasses, hence 'second sight'. As the cataract matures the vision declines. Cortical cataracts cause irregular refraction and astigmatism rather than a uniform myopic shift, which rules out option A.
Reference: Parsons' Diseases of the Eye, 23rd ed.
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Written and medically reviewed by the StethoPrep medical team.