Congenital cataracts are cloudy areas in the lens of a baby’s eye, present at birth or developing within the first year of life. They affect roughly 1.6 to 3 per 10,000 births, depending on how broadly the condition is defined. The causes range from inherited gene mutations to infections during pregnancy, but the majority of cases have no identifiable cause at all. A large meta-analysis of published data found that about 62% of congenital cataracts are classified as idiopathic, meaning no specific trigger can be pinpointed.
Genetic Mutations Are the Leading Known Cause
When a cause can be identified, inherited gene mutations are the most common explanation, accounting for roughly 22% of all congenital cataract cases. Most of these follow an autosomal dominant pattern, meaning a child only needs to inherit one copy of the faulty gene from one parent to develop the condition. Less commonly, cataracts follow a recessive pattern, requiring a defective gene from both parents.
The genes involved typically produce proteins essential for keeping the lens clear. The largest group are the crystallin genes, which code for proteins that make up about a third of total lens protein content. Mutations in these genes (including CRYAA, CRYBB2, CRYGC, and CRYGD, among others) disrupt the orderly arrangement of lens proteins, causing them to clump and scatter light instead of transmitting it. Mutations in CRYAA can also be associated with other eye abnormalities like unusually small corneas or iris defects, while mutations in several other crystallin genes tend to cause cataracts alone with no additional eye or body problems.
Another important group of genes code for connexin proteins, which form tiny channels between lens cells that allow nutrients and signals to pass through. Mutations in one connexin gene (GJA8) cause cataracts and, in about half of reported cases, also lead to an abnormally small cornea or glaucoma. A related connexin gene (GJA3) produces only cataracts with no other complications.
Because so many different genes can be involved, the appearance of inherited cataracts varies widely. They can be nuclear (centered in the middle of the lens), lamellar (affecting a shell-like layer), polar (at the front or back of the lens), or scattered in punctate or pulverulent patterns. The specific gene mutation often influences which morphological type develops.
Infections During Pregnancy
Certain maternal infections can cross the placenta and damage the developing lens during pregnancy. The best-known culprit is rubella. Before widespread vaccination, rubella was a leading infectious cause of congenital cataracts, and research estimates that about 10% of congenital cataracts in some populations are still attributable to rubella infection. The virus disrupts lens cell growth during the first trimester, when the eye is forming most rapidly.
Other infections in the TORCH group also carry risk. Herpes simplex virus (both type I and type II) has been detected in children with congenital cataracts across multiple studies. Cytomegalovirus (CMV) often causes inflammation in the retina and surrounding tissue, changing the chemical environment around the lens and promoting cataract formation. Toxoplasma gondii, a parasite typically acquired through undercooked meat or contaminated soil, has been linked to congenital cataracts in both animal models and human case reports. Overall, TORCH infections are detected in a meaningful minority of affected infants, with one large survey finding a 17.2% positivity rate for these infections among pregnant women in a major urban population.
Chromosomal and Syndromic Causes
Congenital cataracts sometimes appear as one feature of a broader genetic syndrome rather than as an isolated eye problem. Down syndrome (caused by an extra copy of chromosome 21) is one of the more common associations. Patau syndrome, caused by an extra copy of chromosome 13, also frequently involves cataracts along with severe developmental abnormalities.
Lowe syndrome is a rarer X-linked condition that produces a distinctive triad: dense congenital cataracts, intellectual disability, and kidney tubule dysfunction. Because it is X-linked recessive, it almost exclusively affects boys, while mothers who carry the gene may show subtle lens changes visible only on a detailed eye exam.
In these syndromic cases, the cataract is typically discovered alongside other developmental concerns, which helps guide genetic testing and a broader evaluation of the child’s health.
Medications and Environmental Exposures
Maternal use of corticosteroids during pregnancy has been linked to congenital cataracts in the baby. Corticosteroids are well established as a cause of cataracts in adults who take them long-term, and evidence suggests that prenatal exposure can have a similar effect on the developing lens. The nonhereditary, non-infectious causes (which include drug exposures and other environmental factors) collectively account for about 11.5% of congenital cataract cases.
Why Most Cases Remain Unexplained
For decades, the conventional wisdom was that congenital cataracts split roughly into thirds: one-third genetic, one-third environmental, and one-third unknown. Newer pooled data paints a different picture. Idiopathic cases actually make up closer to two-thirds of all congenital cataracts. This likely reflects the limits of current genetic testing and the difficulty of identifying subtle prenatal exposures. Many of these “unexplained” cases may eventually turn out to have genetic roots as testing becomes more comprehensive, but for now, most families receive no definitive answer about why their child’s cataract developed.
Why Early Detection Matters
Regardless of the cause, the timing of treatment is what most influences a child’s long-term vision. A cloudy lens blocks patterned light from reaching the retina, and without that stimulation, the visual pathways in the brain fail to develop normally. This leads to amblyopia, sometimes called “lazy eye,” which can become permanent if not addressed during a narrow window of brain development.
For cataracts affecting only one eye, surgery within the first 6 to 8 weeks of life significantly reduces amblyopia risk. When both eyes are involved, the window extends slightly, with surgery recommended within 8 to 12 weeks. Even with early surgery, amblyopia remains common: about 53% of children who have a one-sided cataract removed before 8 weeks still develop some degree of amblyopia, compared to 79% when surgery is delayed past 12 months. For bilateral cataracts, early surgery cuts the rate from 72% to 39%.
After surgery, children typically need glasses or contact lenses to replace the focusing power of the removed lens, along with ongoing amblyopia therapy (often patching the stronger eye) during the first several years. The therapeutic window for amblyopia treatment narrows considerably after age 6, making consistent follow-up during early childhood essential for the best possible visual outcome.