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 sur-
gically remove cataracts and replace the lens with
a prosthetic intraocular lens (IOL) that restores
vision.
Cataracts result from protein deposits that accu-
mulate within the lens. These deposits disperse
light in much the same way cracks in a window
might splinter sunlight shining through. The frag-
mented light creates areas of accentuated bright-
ness, 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, particu-
larly 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. Corti-
cal 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 path-

ways for vision develop in the infant’s first few

months of life. Ophthalmologists usually remove

such cataracts as soon as possible. Other congeni-

tal cataracts may be small and located so they are

inconsequential to vision; ophthalmologists gener-

ally take an approach of watchful waiting with

these.

Cataracts of diabetes GLUCOSE, which can be

present in high blood levels with DIABETES, inter-

acts 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. Devel-

oping cataracts account in part for the vision dis-

turbances 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 per-
  ceiving shades of blue and purple

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