Complete Guide to Cataract Surgery

What are cataracts?

Cataracts refer to the changes in the lens of the eye (the crystalline structure that sits just behind your pupil, the black opening in the centre of your iris), causing it to become less transparent. The normally clear lens develops semi-opaque or fully opaque areas.

In the healthy eye, light enters through the cornea (the clear window at the front of the eye), then passes through the pupil and the lens. The lens helps focus light rays on to the light-sensitive cells within the retina at the back of your eye.

Over months or years, cataracts become worse and start to affect vision. Eventually, surgery will be required to remove and replace the affected lens. Glasses will not correct the problem.

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Cataracts are most commonly as a result of ageing, and become increasingly prevalent after the age of 60.

The word cataract comes from the Latin cataracta meaning ‘waterfall or floodgate’ and refers to the white appearance of the pupil in advanced cataracts.

The UK’s National Health Service (NHS) performs around 300,000 cataract extractions each year. Additional cases are performed in the private sector, particularly those patients seeking a premium multifocal IOL. Premium IOLs are designed to restore both distance and reading vision, and are not available on the NHS.

How common are cataracts?

The North London Eye Study found that the prevalence of cataract increases with age. Visually impairing cataracts were present in:

In the UK, age-related cataracts will affect around 50% of those aged 65 years or older to some degree. This number rises to 70% in those aged 85+.

Even though cataracts typically affect those age 60 and above (age-related cataracts), they can also occasionally affect young children and even babies (known as childhood and congenital cataracts).

The most common cause of cataracts is ageing. Cataracts are, in addition, a little more common in women. There is also some variation according to ethnicity, with a lower age of incidence in Indian and Bangladeshi patients.

On a worldwide scale, cataracts are the leading cause of preventable blindness. Cataracts are responsible for 51% of all world blindness (which in 2010 represented 20 million people) and as such are an international priority for the World Health Organization (WHO).

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Types of cataracts

There are various types of cataracts, depending on the location of the opacity within the lens. Some are very slow to develop, gradually reducing vision over a number of years, whereas others can progress more quickly, even within weeks or months:

Nuclear cataract

Most commonly associated with
ageing, these lens changes start as a
yellowing deep in the central nucleus
of the lens, later becoming brown
(known as brunescence). They
cause a general reduction in
visual clarity, and a yellow
hue to colours.

Cortical cataract

White, spoke-like opacities that are
found in the lens cortex, the outer
part that surrounds the nucleus.
Cortical cataracts begin in the
periphery and then progress
inwards to the centre.

Subcapsular cataract

Appear at the back of the lens and
often produce initial problematic
symptoms of glare from bright lights,
e.g. car headlights, before progressing
on to general vision reduction. People
with diabetes or those taking high
doses of steroid medications have a
greater risk of developing a
subcapsular cataract.

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The surgical approach for the various types of cataract is the same, removing both the central nucleus and lens cortex. Hence any lenticular opacity it will be removed during the extraction of the natural lens, irrespective of its location.

Removing the nucleus and surrounding cortex will leave the lens’ clear surrounding bag in place, known as the capsule. An intraocular lens (IOL) implant is placed within this remaining capsular bag.

The power of the lens is calculated so as to restore clear distance vision. Reading (30 to 50 cm away) and intermediate (~60 cm to 1.0 metre) vision can also be provided through the use of a premium multifocal or accommodating IOL. Bifocal and trifocal IOL designs are increasingly popular.

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Surgeon David Allamby FRCS(Ed), FRCOphth
 David Allamby