Webster's New World Medical Dictionary

blind
Unable to see. See also 
blindness.
blinded study
A clinical trial of drugs in which
the test participants do not know whether they are
receiving the product being tested or a placebo
(dummy). This blinding is intended to ensure that
the study results are not affected by the power of
suggestion (the placebo effect). See also 
double-
blinded study.
blindness
Loss of useful sight. Blindness can be
temporary or permanent, and there are many
causes of blindness. Damage to any portion of the
eye, the optic nerve, or the area of the brain that is
responsible for vision can lead to blindness. Also
known as visually handicapped, visually impaired,
and visually challenged. See also 
blindness, legal.
blindness, legal
A degree of blindness that enti-
tles a person to certain benefits according to the law.
The definition of legal blindness varies from country
to country. In the US, the definition of legal blindness
that is used to determine eligibility for government
disability benefits is as follows: 
1
visual acuity of
20/200 or worse in the better eye with corrective
lenses (20/200 means that a person must be at 20
feet from an eye chart to see what a person with nor-
mal vision can see at 200 feet); or 
2
visual field
restriction to 20 degrees diameter or less (tunnel
vision) in the better eye. Note that these criteria do
not necessarily indicate a person’s ability to function.
blindness, night
See 
nyctanopia.
blindness, river
See 
river blindness.
blister
A collection of fluid underneath the top
layer of skin (epidermis). There are many causes of
blisters, including burns, friction forces, and dis-
eases of the skin. Also known as bleb and bulla.