reflex is protective and helps to spread
the tear film evenly over the cornea to
enable clear vision.
eye, artificialA prosthesisto replace an
eyethat has been removed. It is worn
for cosmetic reasons. Some movement
of the artificial eye may be achieved by
attaching the muscles that normally
move the eye to the remaining conjunc-
tival membrane (see conjunctiva) or to a
plastic implant in the eye socket.
eye, disorders ofMany eyedisorders
are minor, but some can cause loss of
vision unless treated. (See also cornea,
disorders of; retinal detachment.)
Squintis sometimes present at birth.
Rarely, babies are born with microph-
thalmos. Other congenitaldisorders that
affect the eye are nystagmus, albinism,
and developmental abnormalities of the
cornea and retina.
Conjunctivitisis the most common eye
infection and rarely affects vision. Tr a -
chomaor severe bacterial conjunctivitis
can impair vision. Corneal infections
can lead to blurred vision or corneal
perforationif not treated early. Endoph-
thalmitis (infection within the eye) can
occur as a result of eye injury or infec-
tion elsewhere in the body.
Narrowing, blockage or inflammation
of the blood vessels of the retinamay
cause partial or total loss of vision.
Malignant melanomaof the choroidis
the most common cancerous tumour of
the eye. Retinoblastomais a cancerous
tumour of the retina that most com-
monly affects children.
Various vitamindeficiencies (particu-
larly of vitamin A) can affect the eye.
This may lead to xerophthalmia, night
blindness, or, ultimately, keratomalacia.
Uveitismay be caused by infection or
an autoimmune disordersuch as anky-
losing spondylitisand sarcoidosis.
Macular degenerationof the retina is
common in the elderly, as is cataract.
Glaucoma, in which the pressure in-
side the eyeball becomes raised, can
lead to permanent loss of vision. In reti-
nal detachment, the retina lifts away
from the underlying layer of the eye.
Ametropia is a general term for any
focusing error, such as astigmatism,
myopia, or hypermetropia. Presbyopiaisthe progressive loss with age of the
ability to focus at close range. Ambly-
opiais often due to squint.
eye-dropsMedication in solution used
to treat eye disordersor to aid in diag-
nosis. Examples of drugs given in this
form are antibiotic drugs, corticosteroid
drugs, antihistamine drugs, and drugs
used to dilate or constrict the pupil.
eye, examination ofAn inspection of
the structures of the eyes, either as part
of a vision testor to make a diagnosis
when an eye disorderis suspected.
An eye examination usually begins
with inspection of the external appear-
ance of the eyes, lids, and surrounding
skin. A check of eye movements is usu-
ally performed and the examiner looks
for squint. A check of the visual acuity in
each eye using a Snellen chartfollows.
Refractiontesting (using lenses of dif-
ferent strengths) may be performed to
determine what glasses or contact lens-
es, if any, may be needed. A test of the
visual fieldsmay be performed, espe-
cially in suspected cases of glaucomaor
neurological conditions. Colour vision
may be checked because loss of colour
perception is an indication of certain
disorders of the retinaor optic nerve. To
check for abrasions or ulcers, the con-
junctivaand corneamay be stained with
fluorescein. Applanation tonometryis
an essential test for glaucoma.
The ophthalmoscopeis an instrument
used to examine the inside of the eye,
particularly the retina. The slit-lamp
microscope, with its illumination and
lens magnification, allows examination
of the conjunctiva, cornea, front cham-
ber of the eye, iris, and lens. For a full
view of the lens and the structures
behind it, the pupilmust be widely
dilated with eye-drops.
eye, foreign body inAny material on
the surface of the eyeor under the lid,
or an object that penetrates the eyeball.
A foreign body may cause irritation,
redness, increased tear production, and
blepharospasm. In some cases, a foreign
body left in the eye may cause a reac-
tion that results in permanent loss of
sight in both eyes.
Foreign bodies on or in the conjuncti-
va can usually be flushed out withEYE, ARTIFICIAL EYE, FOREIGN BODY INE