Cataract: Causes, Symptoms and Surgery

Cataract: Causes, Symptoms and Surgery

A cataract is an opacity — a clouding — of the crystalline lens of the eye, which sits directly behind the iris and pupil. The lens is normally transparent, focusing light precisely onto the retina to produce a clear image. When the lens proteins denature and aggregate with age, the lens gradually becomes cloudy, progressively impairing vision.

Cataracts are a leading cause of vision impairment and blindness worldwide. The World Health Organization estimates that 94 million people have distance vision impairment or blindness due to cataract; this figure does not mean that 94 million people are blind. Cataract surgery can improve vision, but its benefits and risks depend on the individual eye and any other eye conditions. Discuss the expected outcome with your eye doctor; this guide does not promise a universal success rate.

How Cataracts Form

Age-Related Cataract (Most Common)

The natural lens is composed of tightly packed crystallin proteins arranged in a precise structure that maintains transparency. With ageing, several processes disrupt this structure:

• Oxidative damage — accumulated damage from ultraviolet radiation, metabolic activity, and free radicals crosslinks lens proteins, causing them to aggregate into opaque clusters
• Loss of molecular chaperones — proteins that normally prevent misfolding decline with age
• Lens fibre compaction — older fibres are compressed to the centre (nucleus) as new fibres form at the periphery, creating the harder, yellow nuclear sclerosis of age-related cataract

Age-related cataracts typically progress slowly over years and are bilateral, although one eye is usually more advanced.

Types of Age-Related Cataract

Nuclear cataract — the most common type; cloudiness begins in the central nucleus; causes progressive myopic shift (worsening near-sightedness), yellowing and browning of colours, and reduced contrast; patients may paradoxically find they no longer need reading glasses in early stages ("second sight").

Cortical cataract — peripheral, spoke-like opacities in the lens cortex radiate towards the centre; causes glare and light scatter, particularly at night.

Posterior subcapsular cataract (PSC) — opacity at the back of the lens, directly in the visual axis; produces the most symptoms earliest; disproportionate glare, halos, and difficulty reading; associated with steroid use and diabetes.

Non-Age-Related Cataracts

• Diabetic cataract — chronic hyperglycaemia causes osmotic changes in the lens; cataracts occur earlier and progress faster in diabetic patients
• Steroid-induced cataract — systemic, topical, or inhaled corticosteroids accelerate PSC cataract formation; established cataract should not be assumed to reverse when corticosteroids are reduced or stopped; medication changes require the prescribing clinician’s advice
• Traumatic cataract — blunt or penetrating eye injury; can cause rapid lens opacification
• Congenital cataract — present at birth; caused by genetic mutations, intrauterine infections (rubella), or metabolic disorders; requires urgent treatment to prevent amblyopia (lazy eye) from disrupting visual development
• Secondary cataract — associated with uveitis, high myopia, or after vitreoretinal surgery

Symptoms

Cataract symptoms depend on the type and location of the opacity:

Progressive blurring of vision — the most common complaint; vision becomes foggy or hazy, like looking through a frosted window; bright conditions may paradoxically help (constricted pupil reduces peripheral scatter) or worsen vision (for PSC cataracts, bright light makes the pupil constrict against the central opacity)

Glare and halos — bright lights (car headlights at night, sunlight) produce glare and coloured halos; a major safety concern for driving

Reduced contrast sensitivity — difficulty distinguishing objects of similar colour or against complex backgrounds; affects daily tasks before visual acuity worsens significantly

Colour desaturation — colours appear washed out or yellowed; patients often only appreciate this after surgery, when they suddenly see vivid blues again

Monocular diplopia — double or multiple images in one eye, caused by irregular refraction through the opaque lens

Frequent glasses prescription changes — particularly the myopic shift of nuclear cataract

Difficulty reading or with near work — especially with PSC cataracts

Diagnosis

Cataract is diagnosed by ophthalmoscopic examination following pupillary dilation:

• Slit-lamp examination — the slit lamp illuminates and magnifies the anterior segment, allowing characterisation of the cataract type, location, density (grading), and extent
• Visual acuity — Snellen chart; best corrected visual acuity (BCVA)
• Contrast sensitivity testing — BCVA alone underestimates functional impairment; contrast sensitivity better predicts daily visual function
• Glare testing — assessing vision under glare conditions to quantify disability
• Retinal assessment — ophthalmoscopy through dilated pupil to exclude co-existing macular degeneration, glaucoma, or diabetic retinopathy that might limit post-operative visual improvement

Treatment

Non-Surgical Management

Early cataracts causing mild symptoms can often be managed conservatively:

• Updated spectacle prescription
• Anti-glare coatings on glasses
• Bright lighting for reading
• Larger-print books

These measures are temporising — cataracts are progressive and surgery is the only definitive treatment.

Cataract Surgery — Phacoemulsification

When is surgery indicated?

Surgery is recommended when cataract-related visual impairment is affecting the patient's daily life and activities — not when the cataract reaches a certain density on examination. Indications include:

• Vision that interferes with work, driving, or leisure activities
• Inability to achieve satisfactory vision with spectacle correction
• Significant glare affecting safety or quality of life
• Anisometropia (large difference between eyes) after unilateral surgery

The procedure:

Modern cataract surgery takes 10–20 minutes under local anaesthetic (topical eye drops or a peribulbar injection). No general anaesthesia is required in the vast majority of patients. It is performed as a day case.

1. A 2.2–2.8 mm clear corneal incision is made (self-sealing; no stitches required)
2. A circular opening (capsulorhexis) is made in the front of the lens capsule
3. Ultrasound energy is applied via a phacoemulsification probe to emulsify (break up and aspirate) the hard lens nucleus
4. The remaining soft cortex is aspirated
5. The clear posterior capsule remains in place as a scaffold
6. A foldable artificial intraocular lens (IOL) is inserted through the small incision and unfolds within the capsular bag, where it remains permanently
7. The incision is hydrated and self-seals; no sutures required

Recovery: vision begins improving within hours; final vision stabilises over 2–4 weeks.

Intraocular Lens (IOL) Options:

The choice of IOL determines what spectacle correction (if any) will be needed after surgery:

IOL Type	Function	Spectacle Dependence Post-Surgery
Monofocal IOL (standard)	Fixed focus at one distance (usually distance)	Glasses for near/intermediate work
Toric IOL	Corrects astigmatism in addition to spherical refraction	Reduces or eliminates distance spectacles in astigmatic patients
Extended depth of focus (EDOF)	Extends range of clear vision from distance to intermediate	Reduced dependence; glasses often still needed for close reading
Multifocal IOL (premium)	Multiple focal zones; designed for distance, intermediate and near	Spectacle independence in the majority; may reduce contrast sensitivity
Trifocal IOL (premium)	Optimised for distance, intermediate and near	May reduce spectacle use across distances; halos, glare and reduced contrast are possible; selection depends on ocular health and visual needs

Laser-Assisted Cataract Surgery (LACS): A femtosecond laser can assist with selected steps of cataract surgery. Conventional phacoemulsification and laser-assisted surgery generally have comparable visual acuity and refractive outcomes. Suitability is assessed individually; a complex case or a premium IOL does not by itself establish a better outcome with laser assistance.

Complications

Cataract surgery is generally safe, but complication rates differ by the event, patient risk factors and follow-up period. A single rate below 1% does not describe all possible complications:

• Posterior capsule rupture — most significant intra-operative complication (1–2%); may require anterior vitrectomy
• Posterior capsule opacification (PCO) — the most common late complication (up to 25%); secondary clouding of the posterior capsule, treated simply with a 5-minute YAG laser capsulotomy
• Endophthalmitis — sight-threatening infection (<0.1%); the risk is reduced, not eliminated, by appropriate intracameral antibiotic prophylaxis at the end of surgery
• Cystoid macular oedema — postoperative retinal swelling causing visual blurring; usually self-resolving or responsive to anti-inflammatory drops
• Refractive surprise — IOL power calculation error; may require spectacle correction or lens exchange

Cataract Surgery in China

Before arranging cataract surgery in China, confirm the receiving centre’s available services and the options appropriate for your eyes:

• Assessment and surgery: slit-lamp evaluation, biometry (IOL power calculation with optical coherence biometry), corneal topography, and surgery booking
• IOL selection: discuss whether a monofocal, toric, EDOF, multifocal or trifocal lens is suitable; confirm the exact lens model, availability, cost and trade-offs
• Laser-assisted cataract surgery: ask whether this option is available and what additional benefits, limitations and costs apply
• Bilateral surgery timing: discuss whether separate-day or same-day surgery is appropriate and available, including the risks and follow-up requirements
• Cost: obtain a written, itemised hospital quote and clarify separately charged coordination services before committing; this guide does not establish comparative savings.
• Full English navigation from pre-operative assessment through surgery and follow-up

Contact a PriumCare care navigator to arrange a cataract assessment or surgical consultation.

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Sources and editorial correction

• Clinical source.
• Clinical source.

Editorial source correction: 25 October 2026. This targeted correction addresses the specific claims documented above; it is not a clinical review of the whole article. No named medical reviewer is claimed. Original publication date is retained.

Further targeted source clarification

Editorial source check: 25 October 2026. This update checks only the specific residual claims linked below; it is not a whole-article medical review and does not add a named clinical reviewer. The original publication date is retained.

• ESCRS cataract recommendations: IOL selection and laser assistance