Eyes & Vision

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.
NICE NG77 is explicit that access to cataract surgery must not be restricted on the basis of visual acuity: referral is based on the impact on vision and quality of life.
Surgery, day-case 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, alongside biometry once surgery is planned to calculate intraocular lens power.

Management

Confirm the cataract and assess impact

Assess acuity, glare, contrast, reading, mobility, driving and ocular comorbidity; refer urgently for sudden visual loss, a painful red eye or childhood leukocoria rather than attributing these to an uncomplicated cataract.^1,2,5,6

Support function while symptoms are mild

Update spectacles, improve task lighting and address falls or driving risk while symptoms remain manageable; explain that these measures do not reverse the lens opacity.²

Refer using shared decision-making

Refer when the cataract affects vision or quality of life after discussing benefits, risks, recovery, refractive expectations and the consequences of not operating; do not use a visual-acuity threshold to deny access.^1,7

Plan and perform lens replacement

Complete ocular risk assessment and biometry, then offer phacoemulsification with intraocular-lens implantation using an appropriate anaesthetic and an individualised plan for complex eyes or second-eye surgery.^1,3,4

Protect recovery and recognise complications

Give the current postoperative eye-drop regimen and safety-netting. New or worsening pain, redness, photophobia or vision loss needs prompt ophthalmology assessment; later blurred vision may be posterior capsule opacification but requires assessment before laser treatment.^1,7,8,9

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.
Do not withhold referral because visual acuity is 'not bad enough': NICE NG77 explicitly prohibits using visual acuity thresholds to restrict access to surgery.

Illustrations

Light scattering by an opacified lensDiagram comparing light passing cleanly through a transparent lens versus scattering through a cataractous lens with disordered protein aggregates.PassFinals · original

Clinical appearance of a mature cataractClose clinical photograph showing the dense white lens opacity of a mature cataract filling the pupillary area.Imrankabirhossain, Wikimedia Commons · CC-BY-SA-4.0

Key sources

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.