Disorders of the Lens Practice Test

The key idea is the sorbitol (polyol) pathway in the lens and how it links to diabetic cataracts. In high glucose conditions like diabetes, aldose reductase converts glucose into sorbitol using NADPH. The lens has relatively low activity of sorbitol dehydrogenase, so sorbitol tends to accumulate. Since sorbitol is osmotically active, its buildup draws water into lens cells, causing osmotic swelling, disruption of lens fibers, and opacity over time—leading to cataracts. Additionally, consuming NADPH for this reaction reduces antioxidant capacity in the lens, increasing susceptibility to oxidative damage, which can further contribute to cataract formation. Other enzymes listed are not directly part of this pathway in the lens.