Epidemiology

16 million people worldwide have cataracts; it is the most common cause of reversible loss of useful vision.

Incidence

• 200,000 cataract removals in the UK per annum.¹
• Congenital cataract occurs in 3/10,000 population cumulatively over 5 years.²

Age is a major factor in cataract development. The Framingham eye study reported 492 cases per 100,000 in those aged >80 years.³

Risk factors

• Diabetes
• Eye trauma
• Uveitis
• Long term steroid use
• Smoking
• UV exposure
• Metabolic disorders e.g. galactosaemia in children

Aetiology

Three types of age related cataracts occur:

• Nuclear sclerosis; this cataract is formed by new layers of fibre (added with ageing) compressing the lens nucleus.
• Cortical; new fibres are added to outside of lens, which age and produce cortical spokes. These may not produce symptoms unless on visual axis or entire cortex is affected when it is "mature".
• Posterior subcapsular; opacities in the central posterior cortex. This may occur in younger patients and may cause glare ± deterioration in near vision.

The most common cause of congenital cataract is infection; rubella (the most common), rubeola, chickenpox, cytomegalovirus, herpes simplex, herpes zoster, poliomyelitis, influenza, Epstein-Barr virus, syphilis and toxoplasmosis. Other causes are metabolic and genetic syndromes.

Presentation

This depends upon the size and location of the opacity and whether one or both eyes are affected.

• Opacities can be seen as defects in the red reflex obtained when the ophthalmoscope is held 60 cm from the eye. This is best seen with a dilated pupil.
• Lens may appear brown or white when a bright light is shone on the eye.

Check that:

• Visual acuity is not improved by viewing test through pinhole.
• Patient can indicate where a light is placed.
• Pupillary reactions are normal.

Differential diagnosis

• Macular degeneration
• Presbyopia
• Retinal disease

Management

In older patients with undemanding visual needs, it may be enough to recommend the use of a strong reading light placed above and behind the patient.

Phacoemulsification

This is the most widely used, safest and most effective technique. There is no absolute threshold of visual acuity at which surgery is indicated.⁴ It all depends upon the impact of the cataract on the patient's quality of life. Now no longer need to wait for the cataract to "ripen" so that contents are liquid and can be easily aspirated.

• Incision approximately 3 mm in diameter is made in the sclera.
• Round hole of approximately 5 mm diameter is made in lens capsule.
• Hard lens nucleus is liquefied by ultrasonic probe inserted through the hole and extracted.
• Soft lens fibres are aspirated.
• Replacement lens is placed folded into the now empty capsular bag where it unfolds.
• Hole heals without sutures.

This can be performed on day-case basis either with a locally injected anaesthetic or even anaesthetic eye drops. Post-operative care includes use of topical antibiotics and steroids with avoidance of strenuous activity.

A technique now reserved for specific situations is the intracapsular method where the whole lens is extracted in its capsule. In this technique, which has been used widely in the past, very thick glasses are required as no intraocular lens is present. These cause significant visual problems including objects being apparently nearer than they really are, loss of visual field and a ring of blindness. Contact lenses are better but can be a problem with the elderly. Multi-focal (non-accommodative) intraocular lenses can be implanted during surgery and provide good vision.⁵

Complications^6,7

Early complications

• Posterior capsule rupture (most common - approximately 3%).
• Trauma to iris.
• Wound gape or prolapse of iris.
• Anterior chamber haemorrhage.
• Rupture of lens capsule with loss of vitreous.
• Vitreous haemorrhage.
• Choroidal haemorrhage.
• Hypopyon (least common).
• Post-operative infection (endophthalmitis) occurs in around 0.13% of cases, presenting with red eye and loss of vision. Occasionally low grade infection presents late with refractory uveitis. This can be avoided by intraoperative antibiotic prophylaxis.⁸

Late complications

• Posterior capsule opacification - is a late complication in 20%. Most common finding.
• Cystoid macular oedema (more frequently diagnosed by angiography).
• Uveitis.
• Retinal detachment.
• Open angle glaucoma.
• Closed angle glaucoma.
• Bullous keratopathy (a rare complication).
• Increased risk of age-related macular degeneration requiring photodynamic therapy.⁹

Thickening of the lens capsule frequently occurs over time causing gradual deterioration of vision. This is treated by splitting the capsule with a laser.

Prognosis

95% of patients with otherwise healthy eyes achieve post-operative corrected acuity of 6/12.¹ Diabetic retinopathy and diabetes are the major risk factors that affect prognosis.¹⁰