In diabetes mellitus, which mechanism contributes to cataract formation?

• A. Vitamin C deficiency in the lens
• B. Inflammation from hyperglycemia
• C. Elevated lens glucose with shunting to the aldose reductase pathway and sorbitol accumulation causing osmotic damage
• D. Decreased lens protein synthesis

Answer: (C)

When blood glucose is high, more glucose enters the lens and is converted to sorbitol by aldose reductase. The lens has relatively low sorbitol dehydrogenase activity and limited permeability to sorbitol, so it accumulates inside the lens. This buildup creates an osmotic gradient that pulls water into the lens, causing swelling and disruption of the orderly arrangement of crystallin proteins. The resulting osmotic stress and structural disruption lead to opacities, i.e., cataracts, in diabetes.

This is the main driver of diabetic cataracts. Vitamin C deficiency in the lens isn’t the mechanism here, inflammation from hyperglycemia isn’t the primary cause of lens opacities, and decreased lens protein synthesis isn’t how these cataracts typically develop.