Cataract

This is an eye disorder. Clouded lens is the most characteristic sign of cataracts. The lens loses transparency when its specific proteins’ structure changes and they clump together. These accumulations “scatter” light. The formation of accumulations is promoted by prolonged or repeated exposure to high-energy radiation, such as X-rays, ionizing radiation. During the exposure, the amount of reduced glutathione is reduced, which, when lacking, leads to the oxidation of crystallins. Additionally, in the lens affected by cataracts, the concentration of calcium ions increases from 10 to 100 times. Calcium ions promote the binding of a specific 43,000 MW protein to the lens fiber cell plasma membrane. The 43,000 MW protein attached to the membrane becomes the center for the attachment of oxidized crystallins, leading to the formation of protein accumulations. Cataracts also occur due to changes in the osmotic properties of the lens fluid. It has been observed that cataracts are common in individuals with diabetes mellitus or congenital galactosemia. In such cases, monosaccharides, such as glucose or galactose, are reduced by aldose reductase present in the lens, whose cofactor is NADPH. There is insufficient cofactor for glutathione reductase to reduce glutathione. During the reduction of monosaccharides, sorbitol is formed from glucose, and dulcitol from galactose. These compounds accumulate in the lens, increasing the osmotic pressure of the fluid inside it, causing water to flow into the lens. It hydrates the crystallins and enhances their ability to scatter light. Additionally, glucose binds to the N-terminal amino acids of crystallins, glycosylating them. Glycosylated crystallins also scatter light.

Source | Glossary of Most Commonly Used Biomedical Terms and Concepts | Lithuanian University of Health Sciences | Academician Professor Antanas Praškevičius, Professor Laima Ivanovienė