A cataract is a clouding of the lens in the eye leading to a decrease in vision. Cataracts often develop slowly and can affect one or both eyes. The most common symptoms are blurred vision, halos around lights, light sensitivity, and dull and fading colors. As cataracts worsen, they can cause vision loss that interferes with daily activities like reading, driving, watching TV, and recognizing faces. While cataracts are most common in older adults, they can occur at any age due to genetics, diseases, medications, injuries, or radiation exposure. Understanding the main cause of cataracts is important for prevention and treatment.
What is a cataract?
The lens is a clear part of the eye behind the colored iris that helps focus light onto the retina at the back of the eye, allowing us to see. A cataract forms when the proteins in the lens clump together, clouding small areas that progressively grow larger over time. The cloudy areas block light from passing through the lens and focusing correctly on the retina, causing blurred vision.
Cataracts develop in the lens capsule, which is a thin membrane that encloses and supports the lens. As we age, the lens capsule can become less elastic, preventing nutrients from reaching the lens and allowing proteins to clump. The lens also contains a high concentration of proteins called crystallins, which are packed closely together in an organized way to keep the lens clear. Oxidation from factors like sunlight, smoking, and diabetes can damage the crystallins, causing them to clump and form cataracts.
Types of cataracts
There are three main types of cataracts:
Nuclear cataracts
Form in the center of the lens (the nucleus) and cause the nucleus to become yellow or brown. This is the most common type of cataract.
Cortical cataracts
Form at the edge of the lens (in the cortex) and look like white wedge-shaped spokes coming from the outside edge of the lens.
Posterior subcapsular cataracts
Form at the back of the lens near the retina and initially affect reading vision.
Cataracts can be age-related, called senile cataracts, or congenital meaning present at birth. Traumatic cataracts can form after an injury to the eye. Secondary cataracts can result from diseases, medications, or long-term unmanaged diabetes. Radiation exposure is another cause.
What is the main cause of cataracts?
Aging is the most common cause of cataracts. The natural aging process affects the lens over time, disrupting the organized proteins and causing clumping and cloudiness. The lens slowly loses elasticity and the ability to alter shape and focus light properly. Risk increases significantly after age 60. More than half of people age 80 or older have cataracts or have undergone cataract surgery, according to National Eye Institute statistics.
While aging itself is the primary factor, certain age-related changes create risks:
- Oxidation damage – lifelong exposure to ultraviolet light and effects of oxygen create free radicals that damage lens proteins.
- Protein alteration – lens proteins can become altered and unstable over decades.
- Loss of antioxidants – antioxidant protective enzymes in the lens decrease with age.
- Dehydration – reduced water content in the lens leads to protein clumping.
Genetics can also play a role, with some people inheriting a tendency to develop cataracts earlier in life, between ages 40-60. Specific gene mutations have been identified that cause early onset cataracts.
Other causes and risk factors
While aging is the primary factor, many other medical conditions, environmental exposures, medications, and lifestyle choices can accelerate cataract development. Common causes and risk factors include:
Ultraviolet light exposure
Prolonged UV exposure from sunlight causes chemical changes and oxidative stress in the lens. People living in areas with bright sunlight year-round tend to develop cataracts earlier. Wearing UV-blocking sunglasses delays onset.
Smoking
Tobacco use releases toxins that enter the lens and oxidatively damage lens proteins. Smokers develop cataracts about 10 years earlier than non-smokers.
Alcohol
Heavy alcohol consumption has been shown in studies to double the risk of developing cataracts.
Diabetes
Poorly controlled blood sugar leads to higher glucose levels in eye fluids. Abnormal glucose levels damage lens proteins through glycation and oxidation, causing clumping and opacity. Cataracts tend to develop earlier and progress faster in diabetics.
Eye injury
A blunt force injury, puncture wound, electric shock, or radiation exposure can instantly damage the lens structure and cause a traumatic cataract.
Medications
Some medications such as oral, topical, or inhaled steroids like prednisone; statin cholesterol medications; and certain antipsychotics increase risk, especially with long-term use.
Inflammation
Chronic inflammatory conditions like uveitis and autoimmune disorders can cause inflamed blood vessels to release oxidative products into eye fluids.
Eye surgeries
Previous eye surgeries like glaucoma surgery, corneal transplantation, or retinal surgery can increase later risk of cataract formation.
Radiation treatment
Cancer patients who undergo external beam radiation therapy to the eye/orbit or total body irradiation have increased risk of developing cataracts within 5-10 years.
Poor nutrition
Low intake of antioxidants like vitamin C, vitamin E, lutein, and zeaxanthin may contribute by allowing greater oxidative damage to the lens over time.
Conclusion
While many factors can increase risk, advancing age remains the predominant cause of cataracts in the majority of cases. Age brings changes to the lens like loss of flexibility, protein destabilization, and a reduction in protective antioxidants. These changes allow proteins in the lens to clump and precipitate out, creating areas of opacity that gradually impair vision. The good news is that cataract surgery to remove the cloudy natural lens and replace it with an artificial intraocular lens is one of the most successful and commonly performed surgeries worldwide. Understanding the major drivers of cataract development allows ophthalmologists to recommend lifestyle changes and eye protection strategies that may slow their progression.