A cataract is an opacification or clouding of the lens. It is the most common cause of blindness worldwide.
Cataracts can affect people of all ages, but they are particularly prevalent in elderly patients. Cataracts are found in 75% of people over 65 years old.1
The lens helps to focuslight onto the retina.
There are 3 main anatomical structures of the lens relevant to cataracts:
Lens nucleus – middle aspect of the lens
Lens cortex – outer aspect of the lens
Lens capsule – the membrane surrounding the lens
Aetiology and Risk Factors
There are many risk factors for developing cataracts. Through a variety of disease processes, risk factors contribute to lens opacification.
The majority of cataracts are associated with age-related changes.
Other risk factors include:
Common Types of Cataracts
There are 3 main types of cataracts, classified according to the part of the lens affected.
Sclerosis of the lens nucleus
Common in old age
Symptoms include myopia (short-sightedness) and colours appearing dull
Myopia occurs as sclerosis changes the lens refractive index. Patients experiencing this symptom will often say that they previously needed reading glasses, but no longer require them.
Opacifications of the lens cortex
On ophthalmoscopy, the opacifications look like the spokes of a wheel around the edge of the lens.
Vision is often unaffected
Posterior subcapsular cataracts
Opacifications in the posterior aspect of the lens capsule
Typically affect younger patients and individuals taking steroids
Patients complain of glare when looking at lights (this can cause issues when driving at night).
Progresses more rapidly than other types of cataracts
Progressive blurring of vision
Glare when looking at lights
Colours appearing dull
Reduced red reflex (elicited by shining a light into the eye)
Diagnosis is made using history and clinical examination. Slit-lamp examination with dilated pupils can be used to the support diagnosis.
Cataracts often begin small with mild symptoms and progress over several years.
NICE recommends refraining from surgical management until symptoms inhibit lifestyle.
Controlling risk factors such as diabetes, smoking, steroid use and UV exposure may slow down the development of cataracts.
Phacoemulsification with an intraocular lens implant is the most common cataract surgery:
The opacified lens is broken down using ultrasound and the fragments are aspirated. A new lens is then implanted.
Often conducted under local anaesthetic.
Prior to surgery, ocular biometry is conducted to measure the corneal curvature and the shape of the eye. It is used to choose a suitable replacement lens.
If not managed appropriately, cataracts can cause lossofvision.
Posterior capsule opacification is very common. Patients present months to years after cataract surgery complaining that it seems like their cataract is returning. It is treated with a capsulotomy, where lasers are used to make a hole in the capsule to allow light to pass through.
Endophthalmitis is an infection of the aqueous and/or vitreous humour. It is a rare,severe complication and can result in visual loss. It is treated with intraocular antibiotic injections.
Congenital cataracts are present from birth.
Associated with infection (typically congenital rubella syndrome) and genetic predisposition.