What is the mechanism of diabetic cataract formation?

• A. Oxidative stress from free radicals leads to protein cross-linking
• B. Sorbitol accumulation causes osmotic water influx and lens swelling
• C. Calcium deposition in the lens capsule
• D. Inflammation of the lens fibers

Answer: (B)

In diabetic cataracts the key process is the polyol pathway. High glucose in the lens is reduced to sorbitol by aldose reductase. The lens has limited activity of sorbitol dehydrogenase, so sorbitol accumulates inside the lens. Sorbitol is osmotically active, drawing water into lens fibers, which causes osmotic swelling and disruption of crystallin proteins. This swelling and protein changes lead to opacity characteristic of cataracts in diabetics.

So, the accumulation of sorbitol and the resulting osmotic water influx directly explain why diabetes promotes lens opacification. While oxidative stress and other factors can contribute to lens damage, they do not account for the primary mechanism described here. Calcium deposition in the lens capsule and inflammation of lens fibers are not the main drivers of diabetic cataract formation.