Cataracts

Overview

•Leading cause of reversible blindness globally; most common elective surgical procedure in the NHS

•Age-related cataract affects the majority by age 75; congenital cataract occurs in ~1-3 per 10,000 live births

Aetiology

•Age-related - cumulative oxidative stress causes crystallin protein aggregation and light scatter

•Diabetes mellitus - polyol pathway accumulates sorbitol, draws water into lens fibres

•Corticosteroids (systemic or topical) - cause posterior subcapsular cataract (PSC)

•Trauma - direct capsule/fibre disruption

•Congenital - intrauterine infections (TORCH, especially rubella), Down/Marfan/Lowe syndromes, galactosaemia

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Posterior subcapsular cataract (PSC) - associated with steroid use and diabetes - causes disproportionate difficulty with reading and bright-light conditions; consider in younger patients with visual symptoms.

Presentation

•Gradual painless visual blurring - cardinal symptom

•Glare and haloes - around headlights/sunlight; early and prominent in PSC

•Monocular diplopia - persists when fellow eye covered; irregular refraction through opacified lens

•Myopic shift - nuclear sclerosis increases refractive index; may cause 'second sight' (improved near vision)

•Colour fading/yellowing - nuclear brunescence

•Examination - diminished or absent red reflex on fundoscopy; slit-lamp confirms opacity

•Congenital - absent/white red reflex (leukocoria) on NIPE screening, failure to fix/track, squint, nystagmus

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Leukocoria (white pupillary reflex) in a child is a red flag - retinoblastoma must be excluded. All children with leukocoria require same-day urgent ophthalmology referral.

Investigations

•Visual acuity (Snellen chart) - quantifies impairment; referral should NOT be based on acuity alone (NICE NG77)

•Red reflex (direct ophthalmoscope) - reduced, absent, or asymmetric suggests media opacity

•Slit-lamp biomicroscopy - confirms morphology and extent of opacity

•Glare testing - functional loss under bright light may exceed Snellen acuity

•Biometry (IOL Master) - pre-operative IOL power calculation

Management

•No effective medical treatment to halt or reverse progression

•Conservative - update spectacle prescription, improve lighting, magnifying aids

•Gold standard surgery: phacoemulsification with intraocular lens (IOL) implantation - day case under local anaesthesia; ~95% achieve 6/12 or better post-operatively

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NICE NG77: referral for cataract surgery must be based on impact on daily activities, safety (e.g. driving, falls), and quality of life - NOT on Snellen acuity alone.

•Congenital cataract - surgery urgently within first weeks of life for dense unilateral cataract to prevent deprivation amblyopia; followed by optical correction and patching of fellow eye

•Driving post-operatively - must meet DVLA standard of at least 6/12 in the better eye (with correction) before resuming driving

Complications

•Posterior capsule opacification (PCO) - most common late complication ('secondary cataract'); treated with outpatient Nd:YAG laser capsulotomy

•Endophthalmitis - rare but serious intraocular infection; acute painful red eye and visual loss post-operatively; emergency requiring intravitreal antibiotics

•Cystoid macular oedema - post-operative macular thickening; treated with topical NSAIDs or steroids

•Posterior capsule rupture - intraoperative complication; may require further intervention

•Retinal detachment - small but increased risk, particularly in myopes

•Deprivation amblyopia - irreversible if congenital cataract not treated before end of critical visual development period