Encyclopedia of Health and Medicine

C
cataract Cloudiness and discoloration of the
LENS. Cataracts become increasingly common with
advancing age, affecting half of all people age 80
and older. Cataracts were once a leading cause of
age-related blindness. Today ophthalmologists surgically
remove cataracts and replace the lens with
a prosthetic intraocular lens (IOL) that restores
vision.
Cataracts result from protein deposits that accumulate
within the lens. These deposits disperse
light in much the same way cracks in a window
might splinter sunlight shining through. The fragmented
light creates areas of accentuated brightness,
causing the halos and sensitivity to lights at
night. The opacity of the cataract interferes with
the refractive function of the lens, causing blurry
or hazy vision. The yellow or gray discoloration of
the lens common with mature or “ripe” cataracts
filters the lightwaves that enter the EYE, particularly
affecting those in the spectrum of blue. The
location of the cataract on the lens determines the
nature and extent of VISION IMPAIRMENT.
Age-related cataracts Most cataracts develop as
a function of aging. Protein structures within the
body, including the lens of the eye, begin to
change. The lens becomes less resilient. Such
changes make it easier for proteins to clump
together, forming areas of opacity that eventually
form cataracts. Nuclear cataracts form in the
nucleus (gelatinous center) of the lens and are the
most common type of age-related cataract. Cortical
cataracts form in the cortex, or outer layer, of
the lens and often do not affect vision.
Congenital cataracts Infants may be born with
cataracts. A congenital cataract affecting only one
eye typically is idiopathic (without identifiable
cause); congenital cataracts affecting both eyes
often suggest genetic disorders such as DOWN SYN-
DROME. A congenital cataract that is in the line of
vision (on the visual axis) can cause significant
vision impairment or blindness because the pathways
for vision develop in the infant’s first few
months of life. Ophthalmologists usually remove
such cataracts as soon as possible. Other congenital
cataracts may be small and located so they are
inconsequential to vision; ophthalmologists generally
take an approach of watchful waiting with
these.
Cataracts of diabetes GLUCOSE, which can be
present in high blood levels with DIABETES, interacts
with the protein structure of the lens, causing
protein clumping. People who have type 1
(INSULIN-dependent) diabetes are at greatest risk
for cataracts of diabetes, which often develop at a
young age. People who have type 2 diabetes or
insulin resistance also are at increased risk. Developing
cataracts account in part for the vision disturbances
that are among the symptoms of
diabetes. Treatment for cataracts of diabetes is the
same as for age-related cataracts.
Symptoms and Diagnostic Path
Because cataracts develop slowly, symptoms
become gradually noticeable. Symptoms usually
affect only one eye (though cataracts may develop
concurrently in both eyes) and may include
• blurry or hazy vision
• double vision
• halos around lights at night
• difficulty seeing at night
• colors appearing faded or dull, or difficulty perceiving
shades of blue and purple
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