Cataract — Causes, Symptoms & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

A cataract is the progressive opacification (clouding) of the crystalline lens of the eye, which lies behind the iris and pupil. The lens focuses light onto the retina to form clear images. When the transparent lens proteins aggregate and denature — due to age, UV exposure, oxidative damage, or other factors — the lens becomes increasingly opaque, scattering and blocking light transmission and causing progressive visual impairment. Cataracts are the leading cause of blindness and visual impairment worldwide, accounting for 51% of global blindness — approximately 95 million people. The vast majority (90%) are age-related (senile) cataracts. Other types include congenital cataracts (present at birth — a paediatric emergency requiring prompt surgery to prevent amblyopia), secondary cataracts (from steroid use, trauma, or systemic disease), and radiation cataracts. Cataract surgery — phacoemulsification with intraocular lens implantation — is the most commonly performed elective surgical procedure in the world and is highly effective (over 98% restoration of useful vision in uncomplicated cases).

Age-related cataracts develop from cumulative UV-B radiation exposure, oxidative damage to lens proteins, and the natural ageing of the avascular lens (which cannot repair itself). Risk factors: advancing age (most important — affects 50% of those over 70, 70% over 80); ultraviolet B radiation exposure (occupational outdoor work, tropical latitude, lack of UV-protective eyewear); smoking (doubles cataract risk — dose-dependent); diabetes mellitus (causes sorbitol accumulation in the lens — nuclear and posterior subcapsular cataracts, at younger age); systemic corticosteroid use (posterior subcapsular cataracts — even inhaled steroids at high doses); prior ocular surgery, trauma, or intraocular inflammation (uveitis); high myopia; family history; obesity; alcohol excess; and nutritional deficiencies (vitamin C and E, lutein, zeaxanthin). Congenital cataracts: TORCH infections (rubella), genetic syndromes (Down's, Galactosaemia), or idiopathic.

Cataracts develop gradually over months to years, causing progressive visual impairment. Classic symptoms: blurred or misty vision that does not improve with glasses prescription change; glare and halos around lights (especially oncoming headlights at night — particularly troublesome when driving); reduced vision in bright light (posterior subcapsular cataracts — sunlight direct); reduced contrast sensitivity (difficulty distinguishing objects from similar backgrounds); faded, yellowish, or brownish colour perception (nuclear cataracts affect colour perception — patients may not notice until the cataract is treated); monocular diplopia (double vision in one eye); and frequent changes in spectacle prescription (nuclear cataracts cause a myopic shift — 'second sight,' temporarily improving reading vision without glasses before worsening). Visual impairment may affect driving (unable to meet DVLA standards), reading, and independent living. Congenital cataracts may present with leukocoria (white pupillary reflex — as seen in photographs), nystagmus (abnormal eye movements), or strabismus (squint).

Cataract is diagnosed through a comprehensive ophthalmic examination. Visual acuity (Snellen chart): measures vision at distance and near; assesses functional impact. Slit-lamp biomicroscopy: the gold standard — the ophthalmologist views the lens under magnification using a slit-lamp, characterising the cataract by type (nuclear, cortical, posterior subcapsular, or mixed), density (Lens Opacity Classification System III — LOCS III grading), and location. Dilated fundal examination: performed with pupil dilation to fully assess the lens and examine the retina (to exclude coexisting retinal disease — macular degeneration, diabetic retinopathy, epiretinal membrane — which would limit post-operative visual gain). Visual function questionnaire: assesses impact on daily activities (driving, reading, face recognition). Biometry (IOL Master or Lenstar): measures axial length, corneal curvature, and anterior chamber depth to calculate the power of the intraocular lens (IOL) implant needed for post-operative emmetropia (clear distance vision). Endothelial cell count (specular microscopy): assesses corneal endothelial health, particularly relevant for diabetics, prior uveitis, or Fuchs' dystrophy.

No medical treatment (drops, tablets, or diet) has been proven to reverse or halt cataract progression. Spectacles and improved lighting: optimise remaining visual function in early cataracts — adequate for mildly symptomatic cases. Cataract surgery (phacoemulsification): the definitive and only effective treatment. Performed as a day case under topical anaesthetic (eye drops) in most cases (30 minutes). A small incision is made at the corneal edge, the anterior lens capsule is opened (capsulorrhexis), the cataractous lens nucleus is emulsified with ultrasound and aspirated, and the lens cortex is removed. An artificial intraocular lens (IOL) is implanted in the lens capsule: monofocal IOL (single focal length — corrects distance or near vision; spectacles needed for the other distance); multifocal IOL (corrects both distance and near, reducing spectacle dependence — risk of glare and halos); toric IOL (corrects pre-existing astigmatism). FLACS (femtosecond laser-assisted cataract surgery): laser performs some steps (capsulorrhexis, lens softening) with potentially greater precision. Manual small incision cataract surgery (MSICS): more commonly used in low-income settings. Surgical complications (rare with modern techniques): posterior capsule rupture (2%), infection (endophthalmitis — 0.05%), cystoid macular oedema, and posterior capsule opacification (PCO — occurs in 20-40% of patients within 2-5 years, causing return of blurred vision; treated with YAG laser capsulotomy — a quick painless outpatient procedure). Congenital cataracts: urgent surgery within weeks of birth, followed by aggressive amblyopia treatment (patching).

Untreated cataracts cause progressive visual impairment leading to blindness — cataracts account for 51% of global blindness and remain the leading preventable cause worldwide. Severe visual impairment from cataracts significantly increases falls, hip fractures, and road traffic accidents in elderly patients. Hypermature cataracts cause secondary complications including phacolytic glaucoma (liquefied lens proteins leak through the capsule and block trabecular meshwork drainage) and phacomorphic angle-closure glaucoma (intumescent lens pushes the iris forward, occluding the drainage angle) — both are sight-threatening emergencies requiring urgent surgery. Dense bilateral cataracts in neonates and young infants cause stimulus deprivation amblyopia: if untreated beyond 6-8 weeks of age, permanent irreversible suppression of the visual cortex occurs that cannot be reversed by later successful surgery. Post-operative complications: posterior capsule opacification (20-40% within 2-5 years — treated by YAG laser capsulotomy), endophthalmitis (0.05% — sight-threatening infection requiring emergency intravitreal antibiotics), and cystoid macular oedema.

UV-B protection is the most evidence-based preventive measure: wear quality sunglasses with UV400 protection (blocking 99-100% of UVA and UVB) in bright sunlight — particularly in high-altitude or tropical environments; wide-brimmed hats provide additional corneal and lens protection. Smoking cessation significantly reduces cataract risk — smokers have 2-3x the cataract risk of non-smokers. Optimal blood glucose control in diabetes substantially delays the onset and slows progression of diabetic cataracts. Minimise systemic and inhaled corticosteroid use — use the lowest effective dose and monitor for posterior subcapsular cataracts with annual ophthalmic review if on long-term steroids. Nutritional support: a diet rich in antioxidants — vitamin C (citrus, strawberries), vitamin E (nuts, seeds, vegetable oils), lutein and zeaxanthin (dark leafy greens, eggs) — is associated with reduced cataract risk in observational studies. Wear protective eyewear in occupational and sports settings with risk of eye trauma.

See a GP or optician if you notice progressive blurring of vision, increased glare from lights (especially when driving at night), or frequent changes to your glasses prescription. Opticians routinely screen for cataracts during eye examinations — adults should have eye examinations every 2 years (annually over 60). Referral for surgical assessment is appropriate when cataracts significantly affect visual function for daily activities — driving, reading, work, or safety. In the UK, referral thresholds include vision below 6/18 or significant functional impairment. For congenital cataracts (leukocoria — white pupil in a baby's photograph or examination), seek immediate ophthalmological referral — within days — as delay causes irreversible amblyopia. Seek urgent ophthalmic assessment for sudden deterioration in vision, eye pain, or redness after cataract surgery (potential endophthalmitis — a surgical emergency).