A cataract is any opacity in the natural
(of an eye)
that results in blurred/reduced vision. The extent and severity of cataracts
can vary considerably.
Further explanation of terminology "Opacity",
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/transparent
or as opaque/solid/i.e. "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. These 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
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
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 the diagram
of the eye, and definitions
of parts of the eye, a description
of the human retina, and definitions
of parts of the retina, and the section of short definitions
of clinical and surgical procedures re. eyes and human visual system.
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