Cataracts are where the lens in the eye becomes cloudy and opaque. This reduces visual acuity by reducing the light that enters the eye.

The job of the lens is to focus light coming into the eye onto the retina at the back of the eye. It is held in place by suspensory ligaments attached to the ciliary body. The ciliary body contracts and relaxes to focus the lens. When the ciliary body contracts it releases tension on the suspensory ligaments and the lens thickens. When the ciliary body relaxes it increases the tension in the suspensory ligaments and the lens narrows. The lens is nourished by the surrounding fluid and doesn’t have a blood supply. It grows and develops throughout life.

Most cataracts develop over years with advanced age in the presence of risk factors. Congenital cataracts occur before birth and are screened for using the red reflex during the neonatal examination.


Risk Factors

  • Increasing age
  • Smoking
  • Alcohol
  • Diabetes
  • Steroids
  • Hypocalcaemia



Symptoms are usually asymmetrical as both eyes are affected separately. It presents with:

  • Very slow reduction in vision
  • Progressive blurring of vision
  • Change of colour of vision with colours becoming more brown or yellow
  • Starbursts” can appear around lights, particularly at night time


A key sign for cataracts is the loss of the red reflex. The lens can appear grey or white when testing the red reflex. This might show up on photographs taken with a flash.

TOM TIP: It is useful in exams to distinguish the causes of visual problems based on the symptoms. Cataracts cause a generalised reduction in visual acuity with starbursts around lights. Glaucoma causes a peripheral loss of vision with halos around lights. Macular degeneration causes a central loss of vision with a crooked or wavy appearance to straight lines.



If the symptoms are manageable then no intervention may be necessary.

Cataract surgery involves drilling and breaking the lens into pieces, removing the pieces and then implanting an artificial lens into the eye. This is usually done as a day case under local anaesthetic. It usually gives good results.

It is worth noting that cataracts can prevent the detection of other pathology such as macular degeneration or diabetic retinopathy. Once cataract surgery is performed these conditions may be detected. Therefore, the surgery may treat the cataract but they may still have poor visual acuity due to other causes.



Endophthalmitis is a rare but serious complication of cataract surgery. It is inflammation of the inner contents of the eye, usually caused by infection. It can be treated with intravitreal antibiotics injected into the eye. This can lead to loss of vision and loss of the eye itself.


Last updated April 2019