Cataract

Labelled Diagram of the Eye

Labelled diagram of the structure of the retina

A cataract is any opacity in the natural crystalline lens (of an eye) that results in blurred or reduced vision. The extent and severity of cataracts can vary considerably.

Further explanation of terminology "Opacity", "Opacities", "Opaque":

Note that an "opacity" is an area or region that is "opaque" - meaning that it appears to be solid rather than transparent because light does not pass through that area, but simply reflects or scatters from its surface. In the context of cataracts, some - but not all (see list below) - opacities tend to appear to have a white-ish colour.

However, in common usage of the word "opaque", objects of any colour may be described colloquially as either 'clear ', meaning transparent, or as 'opaque', meaning apparently 'solid', that is "not see-through", or of course "semi-opaque" (mostly "solid" but a bit of light gets through), etc..


There are many different types of cataracts. They may be classified according to the cause, age of onset, or characteristics of the cataract.

Examples include (in alphabetical order):

  • Brunescent cataract - dark brown and very dense.
  • Congenital cataract - present since birth.
  • Cortical cataract - distinctive due to the presence of spoke-like opacities.
  • Glass-blowers' cataract - an e.g. of cataracts due to direct or indirect injury to the lens of the eye such as may result from excessive expose of the eyes to certain types of radiation.
  • Mature cataract - characterised by a totally opaque lens, hence the pupil of the eye appears to be white.
  • Morgagnian cataract - longstanding and severely opaque.
  • Nuclear sclerotic cataract - due to increasing density and yellowing of the centre of the lens, may be associated with increased myopia, hence distance vision affected to a greater extent than near-vision.
  • Senile cataract - age-related, a common cause of visual impairment in the elderly.
  • Subcapsular cataract (anterior or posterior) - may be associated with increased sensations of glare, near-vision may be affected to a greater extent than distance vision.

Conventional treatment of cataracts is by surgical extraction.

More about Ophthalmology:

This section includes short definitions of many diseases, disorders, and conditions of the eyes and visual system.
For definitions of other terms in this category, choose from the list to the left (but note that this is not a complete/exhaustive list).

Other related pages include

For further information see also our pages of books about ophthalmology.

The following books may also be of interest:

The Aging Eye (Harvard Medical School)
MCQ Companion to the Eye (Textbook)
The Secret of Perfect Vision: How You Can Prevent and Reverse Nearsightedness
What Your Doctor May Not Tell You About(TM) Glaucoma: The Essential Treatments and Advances That Could Save Your Sight

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