What causes cataracts

Understanding Cataracts

A cataract is a clouding of the eye's normally clear lens, progressively blocking light from reaching the retina. The lens contains water and proteins arranged to keep it clear and allow light to pass through. As cataracts develop, these proteins clump together, scattering light and causing blurry or dimmed vision. Most cataracts develop slowly over years, though some progress more rapidly.

Age-Related Cataracts

The most common type develops as part of normal aging. Over decades, lens proteins undergo oxidative damage and chemical modifications. Water content in the lens changes, and proteins cross-link and precipitate. These cumulative changes typically begin around age 60, though individual variation is significant. Some people develop visually significant cataracts by age 70-80, while others maintain clear lenses longer.

Ultraviolet Radiation and Environmental Factors

UV radiation exposure significantly increases cataract risk. The sun's UVA and UVB rays penetrate the lens, generating reactive oxygen species that damage proteins. Long-term cumulative exposure without eye protection accelerates cataract formation. People living at high altitudes or near the equator with intense sunlight exposure show higher cataract prevalence. Cigarette smoking also increases risk by promoting oxidative stress in the lens.

Metabolic and Systemic Causes

Diabetes mellitus substantially increases cataract risk. High blood glucose levels alter lens metabolism, increase sorbitol accumulation through the polyol pathway, and promote protein glycation. Diabetics often develop cataracts at younger ages than non-diabetics. Other metabolic conditions like myotonic dystrophy also increase susceptibility. Hypocalcemia and hypoparathyroidism can cause subcapsular cataracts through calcium imbalances.

Medications and Toxins

Corticosteroids, particularly when used long-term, significantly increase posterior subcapsular cataract risk. The mechanism involves protein cross-linking in the posterior lens. Phenothiazine antipsychotics, tamoxifen, and topiramate have also been associated with cataract formation. Ionizing radiation and certain chemical exposures increase cataract risk occupationally.

Traumatic and Congenital Factors

Eye trauma can cause cataracts acutely or progressing over years after injury. Congenital cataracts present at birth result from intrauterine infections (rubella, varicella), genetic mutations, metabolic disorders, or unknown causes. Early congenital cataracts require prompt intervention to prevent permanent vision loss through amblyopia.