Bma Illustrated Medical Dictionary

in turn. The effect of different lenses on

the beam of light determines whether

glasses are needed for various refractive

errors, such as hypermetropia, myopia,

or astigmatism. Retinoscopy is particu-

larly useful for assessing babies or

young children.

retractorA surgical instrument used to

hold an incision open or to hold back

surrounding tissue.

retrobulbar neuritisA form of optic

neuritisin which the optic nerve be-

comes inflamed behind the eyeball.

retrogradeMoving backwards or in an

opposite direction to normal. For exam-

ple, in retrograde ejaculation, semen is

forced into the bladder rather than out

through the tip of the penis (see ejacu-

lation, disorders of).

retrolental fibroplasiaAlso called

retinopathyof prematurity, a condition

that mainly affects the eyes of prema-

ture infants. The usual cause is high

concentrations of oxygenbeing given as

part of the treatment for respiratory dis-

tress. Excess oxygen causes the tissues

at the margin of the retinato shut down

their blood vessels. When oxygen con-

centrations return to normal, the affected

tissues may send strands of new vessels

and fibrous scar tissue into the vitreous

humour. This may interfere with vision

and cause retinal detachment. Laser

treatmentmay be used.

retroperitoneal

fibrosisInflam-

mation and scarring

of tissues at the

back of the abdom-

inal cavity. The

fibrosis often blocks

the ureters, pre-

venting urine flow

from the kidneys.

In severe cases,

this results in kid-

ney failure. Most

cases occur in mid-

dle-aged men and

are of unknown

cause, but long-

term treatment with

the drug methy-

sergidecan cause

the condition.

retrosternal painPain in the central

region of the chest, behind the sternum.

Causes include irritation of the oesoph-

agus, angina pectoris, or myocardial

infarction. (See also chest pain.)

retrovirusA type of virus whose genetic

material is RNArather than DNAand

that uses an enzyme called reverse tran-

scriptase to produce DNA from the RNA

template. The DNA can then be incor-

porated into its host cells. A notable

example of a retrovirus is HIV(human

immunodeficiency virus).

Rett’s syndromeA brain disorder,

thought to be a genetic disorder, that

only affects girls. Symptoms usually

occur when the child is 12–18 months

old. Acquired skills, such as walking and

communication skills, disappear and the

girl becomes progressively handicapped,

perhaps with signs of autism. There are

repetitive writhing movements of the

hands and limbs, and inappropriate out-

bursts of crying or laughter. There is no

cure for Rett’s syndrome and sufferers

need constant care and attention. Par-

ents of an affected child should receive

genetic counselling.

reverse transcriptase inhibitorsA

class of drugs used in the treatment of

diseases, including HIVinfection, that

are caused by retroviruses. The drugs

affect the ability of the virus to reproduce

by blocking reverse transcriptase, a key

RETRACTOR REVERSE TRANSCRIPTASE INHIBITORS

R

RETINOSCOPY

Beam

of light Lens

Retinoscope