Webster's New World Medical Dictionary

virus, attenuated
A virus that has been weak-
ened. A vaccine against a viral disease can be made
from an attenuated, less virulent strain of the virus:
a virus that is capable of stimulating an immune
response and creating immunity but not of causing
illness.
visceral leishmaniasis
See 
leishmaniasis.
visceral pericardium
The inner layer of the
pericardium.
vision, central
See 
central vision.
vision, macular
See 
central vision.
vision, phantom
See 
phantom vision.
vision therapy
The use of special eye exercises
to address eye defects, such as strabismus. Some
vision therapists claim that eye exercises can help
people with neurological or learning disabilities.
Vision therapy is not proven for the latter use,
although some patients do report improvement.
visual acuity
The clarity or clearness of vision, a
measure of how well a person sees.
visual acuity test
See 
eye chart test.
visual field test
A test that measures the extent
and distribution of the field of vision. A visual field
test may be done via a number of methods, includ-
ing termed confrontation, tangent screen exam, and
automated perimetry. These tests are not painful or
uncomfortable. Many diseases can adversely affect
the visual field, including glaucoma, strokes, high
blood pressure (hypertension), diabetes, multiple
sclerosis, and overactivity of the thyroid gland
(hyperthyroidism). Medications, including the anti-
malarial drugs chloroquine (brand name: Atabrine)
and hydroxychloroquine (brand name: Plaquenil),
can also affect the visual field.
visual nerve
See 
optic nerve.
visual nerve pathways
See 
optic nerve 
pathways.