Overview: A cataract is an opacity of the eye's crystalline lens that reduces the passage of light to the retina and degrades visual clarity. It most commonly develops with age, but may also arise from injury, metabolic disease, medication use, or congenital factors. Vision loss from a cataract is usually gradual and painless; in some cases the lens changes cause a temporary increase in near-focus (a myopic shift), making distant objects harder to see. For information on the anatomy involved, see the lens and its structure.

Typical signs and symptoms

Early symptoms can be subtle and may include blurred vision, increased sensitivity to glare, faded colors, difficulty with night driving, frequent prescription changes in eyeglasses, and halos around lights. If only one eye is affected, patients may notice reduced depth perception and difficulties judging distances. Cataract-related visual loss can progress to severe impairment or legal blindness if left untreated; this is why assessment and follow-up are important (see blindness risks).

Causes and types

Cataracts are classified by their location in the lens and by origin. Common types include nuclear sclerotic cataract (central hardening and yellowing), cortical cataract (spoke-like opacities at the lens periphery), and posterior subcapsular cataract (opacities at the back of the lens that often affect reading and bright-light vision). Causes and contributing factors include:

  • Age-related protein changes in the lens (the most common cause).
  • Systemic diseases such as diabetes mellitus.
  • Prolonged exposure to ultraviolet radiation and environmental factors.
  • Long-term corticosteroid use and certain medications.
  • Eye injury, inflammation, or previous eye surgery.
  • Congenital genetic conditions present at birth.

Diagnosis and clinical course

Ophthalmic diagnosis relies on a clinical eye examination including visual acuity testing, slit-lamp biomicroscopy to inspect the lens, and measurement of how the lens opacity affects vision. A dilated fundus examination and intraocular pressure checks are often performed to assess other eye health factors. The rate of progression varies: some cataracts remain stable for years, while others worsen over months.

Treatment and surgical options

No medication is proven to reverse established lens opacities. When vision interferes with daily activities, the standard treatment is surgical removal of the cloudy lens and replacement with an artificial intraocular lens (IOL). Modern techniques most commonly use phacoemulsification: the lens is fragmented with ultrasound and aspirated through a small incision, then an IOL is implanted. Different IOL types (monofocal, multifocal, toric) can be selected to address distance, near, or astigmatic refractive needs. Information about surgical approaches is available at surgical treatment and at operation procedure.

Prevention, prognosis and special considerations

Preventive measures focus on modifiable risks: protecting the eyes from excessive UV exposure, managing systemic conditions such as diabetes, avoiding smoking, and using steroids only when medically necessary. After uncomplicated surgery visual outcomes are generally excellent and most patients achieve substantial improvement. A common late issue is posterior capsule opacification, a secondary clouding that can be treated with a quick outpatient laser procedure.

Historical and public health perspective

Cataract surgery is one of the oldest known surgical procedures and remains one of the most frequently performed operations worldwide. It is a major public health intervention because cataracts are a leading treatable cause of vision impairment. Advances in lens technology and surgical technique have steadily improved safety, recovery time, and the quality of postoperative vision.

Key distinctions: congenital cataracts differ from age-related types in timing and management; traumatic cataracts follow injury and may be accompanied by other ocular damage; and secondary cataracts can result from systemic disease or medication. For a brief overview of how astigmatism and near-vision issues can be affected by lens changes, see myopia and refractive shifts.