Cataracts
Progressive opacification of the crystalline lens scatters and blocks incoming light, causing gradual, painless blurring of vision that only surgery (replacing the lens) can reverse, because the damaged protein structure cannot be cleared or treated medically.
In a nutshell
Cataracts are structural opacification of lens crystallin proteins that scatters light, causing gradual painless blurring, glare and haloes rather than sudden or painful visual loss. Because the damaged protein cannot be treated medically, surgery to remove and replace the lens is curative.
Classic presentation
An older patient with gradual, painless blurring of vision over months to years, glare in bright light or from oncoming headlights, haloes around lights and difficulty with night driving.
Key points
- The mechanism is physical light scattering by denatured, aggregated lens protein: there is no inflammatory or infective component, so no medical treatment reverses it.
- Painless and gradual onset distinguishes cataract from the acute, often painful causes of visual disturbance such as angle closure or uveitis.
- The location of opacity, not just its amount, determines symptoms: posterior subcapsular cataracts cause disproportionate glare and near-vision loss for their size.
- A nuclear cataract can transiently improve near vision, 'second sight', by altering the lens's refractive power before vision deteriorates further.
- Surgery, phacoemulsification with intraocular lens implantation, is curative because it physically removes the light-scattering material.
First-line investigation
Visual acuity testing with slit-lamp examination to confirm lens opacity and characterise its type, guiding the decision and timing for surgery.
First-line management
Conservative measures, such as updated spectacles and better lighting, for mild symptoms, progressing to cataract surgery with intraocular lens implantation once vision significantly affects daily life.
Exam traps
- A painful red eye is not a cataract: do not attribute pain to lens opacity; look for a coexisting sight-threatening diagnosis.
- Leukocoria (white pupil) in a child is retinoblastoma until excluded, not simply a paediatric cataract.
- Sudden visual loss is not how cataracts present: gradual decline over months to years is the expected pattern.
Educational content pending clinical review. Not medical advice.