Bma Illustrated Medical Dictionary

affects the brain or the nerves supplying

the eye muscles, such as stroke, a brain

tumour,encephalitis, or multiple sclerosis.

ophthalmoscopeAn instrument used

to examine the inside of the eye.

ophthalmoscopyA noninvasive proce-

dure in which an ophthalmologist (a

doctor specializing in eye disorders)

uses an ophthalmoscopeto examine the

inside of the eye. The ophthalmoscope

is used first to direct a beam of light

into the eye and then to examine the

light-sensitive retina; the retinal blood

vessels; the head of the optic nerve; and

the jelly-like vitreous humour.

opiateAny drug derived from, or chemi-

cally similar to, opium.

opioidA type of analgesic drug(pain-

killer) used to treat moderate to severe

pain. Opioids, also knows as narcotic

drugs, may be abused for their euphoric

effects; abuse may cause tolerance(the

need for greater amounts of a drug to

get the same effect), and physical and

psychological drug dependence. Com-

monly used opioids include codeine,

diamorphine, morphine, and pethidine.

opiumA substance obtained from the

unripeseed pods of the poppy plant

PAPAVER SOMNIFERUM. Opium has an

analgesic effect and may also cause

sleepiness and euphoria. Opium and its

derivatives, such as codeineand diamor-

phine, are known as opioid.

opportunistic infectionInfection by

organisms that rarely have serious or

widespread effects in people of normal

health, but which can cause serious ill-

ness or widespread infection in a person

whose immune systemis impaired. In

most patients with AIDS, death is due

to opportunistic infections, especially

pneumocystis pneumonia. Many fungal

infections, such as candidiasis, and some

viral infections, such as herpessimplex,

are opportunistic infections. Treatment

is with appropriate antimicrobial drugs.

oppositional defiant disorderA type

of behavioural disorder that usually

appears in childhood or early adoles-

cence. Typically, a child shows hostile,

argumentative behaviour that includes

loss of temper, defiance of rules, and

swearing. To some extent such behaviour

is common in adolescence, but when

law-breaking or violence occur the con-

dition is deemed to be pathological.

optic atrophyA shrinkage or wasting

of the optic nerve fibres due to disease

or injury to the optic nerve, resulting in

partial or complete loss of vision. Optic

atrophy may occur without prior signs

of nerve disease, such as inflammation.

optic discThe area on the retinawhere

nerve fibres from the eyeball join the

optic nerve. The optic disc is also known

as the blind spot due to its lack of light-

sensitive cells.

opticianA person who fits and sells

glassesor contact lenses. An ophthalmic

optician, or optometrist, also examines

the eyes to test for myopia, presbyopia,

hypermetropia,or astigmatism. People

with suspected eye disorders are referred

to a specialist called an ophthalmologist.

(See also ophthalmology;optometry.)

optic nerveThe 2nd cranial nerve; the

nerve of vision. The 2 optic nerves each

consist of about 1 million nerve fibres

that transmit impulses from the retina

to the brain. The optic nerves converge

behindthe eyes, where fibres from the

inner halves of the retina cross over.

Nerve fibres from the right halves of

both retinas go to right side of the

occipital lobes in the brain; those from

the left halves go to the left side.

Disorders of the optic nerve include

optic neuritisand papilloedema. The latter

is caused by pressure on the nerve from

disease in the orbitor a brain tumour.

optic neuritisInflammation of the optic

nerve, often causing sudden loss of part

of the visual field. Attacks are sometimes

OPHTHALMOSCOPE OPTIC NEURITIS

O

Ophthalmoscope Ophthalmologist

OPHTHALMOSCOPY