In cases of diabetes, what substance accumulates in the lens leading to early cataract formation?

In individuals with diabetes, sorbitol accumulates in the lens of the eye, which contributes to the early development of cataracts. This accumulation occurs due to the conversion of glucose to sorbitol via the enzyme aldose reductase, part of the polyol pathway. When plasma glucose levels are elevated, as they are in diabetes, excessive amounts of glucose enter the lens, leading to increased sorbitol levels.

Sorbitol is relatively impermeable to the lens, meaning that once it accumulates, it cannot exit easily. This osmotic imbalance causes water to be drawn into the lens, leading to swelling and changes in lens transparency, which are characteristic of cataract formation. Therefore, the pathway involving sorbitol is critical in understanding the biochemical changes that promote cataract development in diabetic patients.

While glucose is the precursor in this process, it is the accumulation of sorbitol that directly impacts lens structure and function, making it the key substance associated with early cataract formation in diabetes.