A 30-year-old woman operated for parathyroid adenoma presents with blurred vision. Slit lamp examination shows multiple small white punctate opacities in both the anterior and posterior subcapsular cortex of each lens. Serum calcium is 7.0 mg/dL. This cataract results from:
- A Accumulation of galactitol causing osmotic swelling of lens fibres
- B Increased permeability of the lens capsule with altered electrolyte balance in lens fibres ✓
- C Deposition of copper in the posterior capsule
- D Reactive oxygen damage to lens crystallins by ultraviolet radiation
Correct answer: B. Increased permeability of the lens capsule with altered electrolyte balance in lens fibres
Explanation
Hypocalcaemia, whether from tetany or thyroid surgery, produces punctate subcapsular opacities involving both anterior and posterior cortex. Low calcium alters membrane permeability and disturbs the electrolyte equilibrium of the lens fibres. Galactitol accumulation explains galactosaemic cataract, copper deposition gives the sunflower cataract of chalcosis, and ultraviolet oxidative damage contributes to age-related nuclear sclerosis, not the symmetric subcapsular pattern of tetanic cataract.
Reference: Parsons' Diseases of the Eye, 23rd ed.
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