Cataract
- Lesion
A cataract is a cloudy lens; it is the leading cause of blindness in the world and is cured by surgery.
What it is
The lens is a capsule of epithelium and long fibres packed with crystallin proteins that must stay clear. With age, ultraviolet light, diabetes, steroids, radiation, trauma, inflammation or inherited and congenital causes, crystallins aggregate, fibres swell and break, and light scatters. Cataracts are named by where the opacity lies. A very mature cataract can leak lens proteins, provoking inflammation or blocking the outflow channels and causing glaucoma.
Step by step
- Lens fibres live for life with no turnover of their crystallin proteins.
- Oxidation, glycation and ultraviolet damage alter crystallins.
- Altered proteins aggregate and fibres lose their regular packing.
- Light scatters and the lens yellows; vision blurs and glare increases.
- Very mature lenses liquefy and leak proteins that can inflame the eye or block drainage.
Types of cataract
| Type | Location | Main causes |
|---|---|---|
| Nuclear | Centre of the lens | Ageing, ultraviolet, smoking |
| Cortical | Outer fibres, spoke-like | Ageing, diabetes |
| Posterior subcapsular | Just inside the back capsule | Corticosteroids, diabetes, radiation, uveitis |
| Congenital or infantile | Variable | Rubella, galactosemia, trisomies, inherited |
| Traumatic | Variable, often rosette-shaped | Blunt or penetrating injury |
Clinical notes
- Cataract surgery with an intraocular lens is one of the most effective procedures; cataract remains a leading cause of avoidable blindness in Colombia.
- In diabetes, sorbitol from the polyol pathway draws water into the lens.
Test yourself
Think of the answer, then tap the question to see it.
Which type of cataract is typical of long-term corticosteroid use?
Posterior subcapsular cataract.
What causes phacolytic glaucoma?
Lens proteins leaking from a hypermature cataract, with macrophages that clog the trabecular meshwork.
Which congenital infection classically causes cataract?
Rubella (congenital rubella syndrome).
Elsewhere in DurgiPedia
- The lens and zonules through life
- Steroid eye drops: glaucoma, cataract and infection
- Coloboma, congenital cataract and congenital glaucoma
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Cataract (StatPearls (NCBI Bookshelf), 2026).
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Representative model, for educational purposes only.