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Conditions · Head and neck

Cataract !

A cataract is clouding of the lens inside the eye that slowly blurs vision; it is the leading cause of blindness worldwide and is treated with surgery.

Updated 2026-10-29

Structures involved

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In biochemistry

Microorganisms that cause it

In histology

In embryology

In the clinical exam

In physiology

Why it happens

What it is

Clouding of the eye's lens that scatters light and gradually blurs vision. It is the leading cause of blindness worldwide, and that blindness is reversible with surgery.

Who gets it

Very common with age, and the main cause of reversible blindness in Latin America and worldwide. Access to surgery, rather than the disease itself, decides how much blindness it causes.

Causes

  • Age-related changes in lens proteins (the commonest)
  • Diabetes mellitus
  • Corticosteroid use, systemic or topical
  • Eye trauma, uveitis, previous eye surgery, radiation
  • Congenital: genetic, intrauterine infection (rubella), metabolic disease

Risk factors

  • Older age
  • Diabetes
  • Long-term corticosteroids
  • Smoking and heavy alcohol use
  • High ultraviolet (sunlight) exposure
  • High myopia, family history

Pathophysiology

The lens is clear because its proteins are tightly ordered and well hydrated. With age, oxidative stress, glycation in diabetes or drugs, the proteins aggregate and the fibres lose transparency. Light is scattered and absorbed, which reduces contrast, causes glare and blurs vision; the nucleus may also harden and change refraction.

Classification

  • Nuclear: central yellow-brown, myopic shift
  • Cortical: spoke-like opacities, glare
  • Posterior subcapsular: near the back surface; steroids and diabetes; trouble reading and with bright light
  • Congenital or paediatric
  • Traumatic or secondary

Symptoms and signs

  • Gradual, painless blurred or cloudy vision
  • Glare and halos, especially at night and when driving
  • Faded colours, need for more light
  • Frequent changes in glasses prescription; better near vision in some («second sight»)
  • Double vision in one eye
  • In infants: white pupil (leukocoria) or squint

Diagnosis

Clinical
Visual acuity and glare testing; slit-lamp examination through a dilated pupil shows the type and density of opacity; the red reflex is dimmed. The fundus is examined to exclude other causes of poor vision.
Tests
Before surgery: biometry (eye length and corneal curvature) to choose the intraocular lens power. Glucose and diabetes review where relevant.
Imaging
Ultrasound B-scan when the lens is too dense to see the retina. OCT of the macula if macular disease is suspected.

Differential diagnosis

  • Uncorrected refractive error
  • Age-related macular degeneration
  • Diabetic retinopathy or macular oedema
  • Glaucoma
  • Corneal opacity or dystrophy

Goal of treatment

Restore functional vision by removing the cloudy lens when it limits daily life, and prevent amblyopia in children.

Treatment

Conservative
Early stage: updated glasses, brighter lighting and anti-glare measures. No drug reverses a cataract.
Surgical
Cataract extraction with an artificial intraocular lens implant, usually by phacoemulsification through a small incision; manual small-incision surgery is a lower-cost alternative widely used in limited-resource settings.
Surgical
Congenital visually significant cataract: early surgery followed by optical correction and amblyopia therapy.
Procedure
Laser capsulotomy (Nd:YAG) for posterior capsule opacification after surgery.

Complications

  • Untreated: progressive blindness, falls, lens-induced glaucoma or inflammation
  • Posterior capsule opacification (common, treated by laser)
  • Endophthalmitis (rare, serious)
  • Cystoid macular oedema
  • Retinal detachment, raised intraocular pressure
  • Amblyopia in children

Prognosis

Surgery is one of the most successful operations in medicine: most people regain good vision quickly. Results are poorer when there is coexisting retinal or optic nerve disease.

Prevention

  • Sun protection with UV-blocking glasses and hats
  • Not smoking and moderating alcohol
  • Good diabetes control
  • Avoiding unnecessary long-term corticosteroids
  • Eye protection against injury; red reflex check in all newborns

Test yourself

Think of the answer, then tap the question to see it.

What is the most common risk factor for cataract?

Age; diabetes, corticosteroids, smoking and ultraviolet exposure add to the risk.

Which type of cataract is associated with corticosteroid use?

Posterior subcapsular cataract.

What is the standard treatment for a visually significant cataract?

Surgical removal of the lens with an intraocular lens implant, usually by phacoemulsification.

Why is a congenital cataract an urgent problem?

It blocks visual input during the critical period and causes deep amblyopia unless treated early.

What is the commonest late complication after cataract surgery and how is it treated?

Posterior capsule opacification, treated with Nd:YAG laser capsulotomy.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Cataract (StatPearls (NCBI Bookshelf), 2024).

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