Webster's New World Medical Dictionary

RNA interference
The process by which the
introduction of double-stranded RNA into a cell
interferes with the expression of genes. Abbreviated
RNAi.
RNA polymerase
The enzyme that makes the
very large molecule RNA, by joining together many
smaller molecules, using DNA as a template.
RNAi
RNA interference.
robotic surgery
Surgery performed using a
high-tech robotic system to perform the actual
operation. Robotic surgery is most commonly used
for prostate surgery, hysterectomy, heart valve and
blood vessel repair, pediatric surgery, and urologic
surgery.
Rochalimaea quintana
See 
Bartonella 
quintana.
rocker bottom feet
A type of congenital anom-
aly of the feet in which the bottom of the foot is
rounded, resembling the bottom of a rocking chair,
and the calcaneus (heel bone) is unusually promi-
nent. This anomaly usually occurs with other con-
genital defects and suggests the presence of a
chromosomal abnormality.
Rocky Mountain spotted fever
An acute febrile
(feverish) disease that was initially recognized in
the Rocky Mountain states. Abbreviated RMSF. RMSF
is caused by Rickettsia rickettsii, transmitted by
hard-shelled (ixodid) ticks, and occurs only in the
Western hemisphere. Anyone frequenting tick-
infested areas is at risk for RMSF. Onset of symp-
toms is abrupt, with headache, high fever, chills,
muscle pain, and then a rash. The rickettsiae grow
within damaged cells lining blood vessels, which
may become blocked by clots. Blood vessel inflam-
mation (vasculitis) is widespread in a person with
RMSF. Early recognition of RMSF and prompt antibi-
otic treatment is important to prevent death. Also
known as spotted fever, tick fever, and tick typhus.
rod
A specialized light-sensitive cell (photorecep-
tor) in the retina that provides side vision and the
ability to see objects in dim light (night vision). See
also 
cone cell.