Ocular signs may be the first indication of serious neurological
disease.
Alternatively, the eyes may be responsible for
“neurological” symptoms such as headache.
Palsies of the third, fourth, and sixth cranial nerves all
cause paralytic squints, in which the angle of squint varies with
the direction of gaze.
Adult patients may also complain of
double vision. It is important to exclude palsies of these three
nerves when examining patients who have a squint, double
vision, or both. In any patient with diplopia you should
consider the possibility of ocular myasthenia gravis, which can
mimic many different conditions.
Third nerve palsy
Patients with a third nerve palsy may present with a variety of
symptoms, depending on the cause of the palsy.
These include
a drooping eyelid, double vision (if the lid does not cover the
eye), or headache in the distribution of the ophthalmic division
of the trigeminal nerve.
On examination there is characteristically a ptosis (paralysed
levator muscle of the eyelid) and the eye is turned out because
of the action of the unaffected lateral rectus muscle that is
supplied by the sixth nerve.
The eye is sometimes turned
slightly downwards because of the unopposed action of the
unaffected superior oblique muscle supplied by the fourth
nerve.
The pupil is dilated if the parasympathetic fibres of the
third nerve supplying the sphincter pupillae have been
damaged.
Important causes of a third nerve palsy include intracranial
aneurysms, compressive lesions in the cavernous sinus, diabetes
mellitus, and trauma.
If there is pain and a dilated pupil, a
compressive lesion must be excluded urgently, as life saving
curative treatment may be needed for what could be a fatal
lesion, such as an aneurysm.
Fourth nerve palsy
This is often difficult to diagnose.
Patients may complain of a
combination of vertical and torsional diplopia, which may be
worse during activities such as walking down stairs or reading.
There may be a compensatory head tilt, with the head tilted
away from the side of the lesion and the chin depressed.
The
fourth nerve is long and therefore is particularly susceptible to
injury.
A patient with bilateral fourth nerve palsies following a
head injury may complain only of difficulty in reading.
This occurs as a result of difficulty during depression and
convergence of the eyes because both superior oblique
muscles are paralysed.
This diagnosis is easily missed if a careful history is not
taken, and it should be considered in any patient who
complains of difficulty in reading after a head injury.
Sixth nerve palsy
This is probably the best known of the palsies of the three
nerves of ocular motility.
The eye on the affected side cannot
be abducted.
The patient develops horizontal diplopia that
worsens when they look towards the side of the affected
muscle.
Management of paralytic squint
A detailed ophthalmic, neurological, and general medical
assessment is essential in order to make an accurate diagnosis.
If diplopia is a problem, opaque sticky tape may be placed over
the patient’s glasses or a patch may be placed over the eye.
Adults will not develop amblyopia. Temporary prisms can be
put on the glasses if the angle is not too large.
For long term
treatment, permanent prisms (which are clearer than
temporary prisms) may be incorporated into a prescription for
glasses.
Later, an operation may be performed to straighten the eyes.
Botulinum toxin may be injected into the extraocular muscles as
a diagnostic or therapeutic procedure in paralytic squint.
Facial nerve palsy
Seventh nerve palsy
Facial weakness caused by a seventh nerve palsy is common
(called a Bell’s palsy). In many cases no cause is found and the
palsy improves spontaneously.
If the eyelids do not close
properly, corneal exposure, ulceration, and eventually scarring
and blindness may occur. Ocular assessment should include the
following.
Testing of corneal sensation
The cornea is innervated by the ophthalmic branch of the
fifth nerve, which may also be affected by the pathology that
is causing the seventh nerve palsy.
If the corneal sensation is
impaired, patients cannot feel foreign bodies or when their
corneas are ulcerating.
They should be referred to an
ophthalmic surgeon, as there is a high risk of corneal
scarring.
When the seventh nerve is affected the patient is
unable to close the eye and there is inadequate lubrication
of the cornea.
Testing of Bell’s phenomenon
(Not to be confused with a Bell’s palsy.)
Normally when the
eyes are closed the eyes move up under the upper lids.
This
“Bell’s phenomenon” can be tested by observing the position of
the cornea while the patient closes their eyes.
If the cornea
does not move up under the paralysed lid, the patient is at a
high risk of developing corneal exposure.
Staining the cornea with fluorescein
Staining of the cornea when fluorescein is used indicates that
the cornea is drying out.
If there is only a tiny amount of stain,
the eye is white and unremarkable on external examination,
and the visual acuity is normal, the patient may be managed in
the short term with tear drops and ointment.
If the staining
persists or if the eye becomes red then the patient should be
referred immediately to an ophthalmologist.
The cornea may
need to be protected by frequent lubrication and by sewing
together the lateral parts of the eyelids or lowering the upper
eyelid with botulinum toxin.
Seventh nerve palsy
The aim of treatment is to prevent corneal exposure and
ulceration with subsequent complications of infection and
perforation.
Simple initial measures include frequent ocular
lubrication with artificial tears and ointments and lid taping to
physically close the eyelids.
Recent studies have shown that
steroids are probably effective, and that the drug aciclovir
combined with prednisone is possibly effective in improving
facial function.
In more severe cases it may be necessary to
reduce the size of the palpebral aperture surgically by
performing a lateral tarsorrhaphy or by inserting an inert gold
weight into the upper eyelid.
Nerve reconstructive surgery can
restore innervation to the facial muscles in severe cases.
Sympathetic pathway
Horner’s syndrome
In a patient with
Horner’s syndrome the sympathetic nerve
supply to the eye is disturbed.
The clinical features are as
follows.
●
A small pupil that is reactive to light
(unlike the small pupil
caused by pilocarpine eye drops) because the sympathetically
innervated dilator muscle of the pupil is paralysed.
●
A drooping eyelid. The muscles that raise the eyelid are
innervated by the third nerve and also by the sympathetic
nerve supply.
Therefore lesions of either the third nerve or
the sympathetic nervous system supplying these muscles
cause a ptosis, although in the latter case it is only slight.
●
Lack of sweating on the same side of the face
is because of
sympathetic denervation and depends on the position of the
lesion.
The ocular movements are completely normal, as the
extraocular muscles are not sympathetically innervated.
Optic disc
The swollen optic disc
There are many causes of a swollen optic disc, the best known
of which is raised intracranial pressure resulting in the
development of papilloedema.
The absence of papilloedema,
however, does not exclude raised intracranial pressure.
The
history and examination of the patient should lead to the
suspicion of raised intracranial pressure, and a swollen optic
disc is merely a helpful sign.
The vision of patients with
papilloedema usually is not affected until late in the course of
the condition.
Most causes of a swollen disc are serious from either the
ocular or systemic point of view, and patients should be
referred promptly.
If a patient has a swollen optic disc the
following features suggest a diagnosis other than raised
intracranial pressure.
Impaired vision
Vision usually is impaired only late in the course of
papilloedema.
Impaired vision may indicate giant cell arteritis
and the patient may or may not have aching muscles, malaise,
headaches, tenderness over the temporal arteries, and
claudication of the jaw muscles when eating.
The disc is
characteristically swollen and pale because the small vessels that
supply the head of the optic nerve are inflamed and occluded.
By this time vision will be severely affected.
It is important to
exclude giant cell arteritis in any patient over 60 with visual
disturbance or a swollen optic disc, as urgent treatment with
steroids is needed to prevent blindness in the other eye.
Disturbance of the visual fields
The visual fields of a patient with raised intracranial pressure
usually are normal.
A field defect usually indicates some other
diagnosis, such as compression of the optic nerve.
A pale disc
The disc of a patient with raised intracranial pressure is often
hyperaemic.
It is only in longstanding papilloedema that the
disc becomes atrophic and pale.
The disc is also pale if the
swelling results from ischaemia of the optic nerve, as in giant
cell arteritis.
Retinal exudates and haemorrhages
These are present in papilloedema and are usually found
around the disc.
If there are many exudates or haemorrhages
in the retina, diagnoses such as retinal vein occlusion,
malignant hypertension, diabetes, and vasculitis should be
considered.
In all patients the blood pressure should be
measured and the urine tested for the presence of sugar, blood,
and protein.
Conditions that may mimic swelling of the optic disc
●
Longsightedness
(hypermetropia), in which the margin of
the optic disc does not look clear.
A clue lies in the
patient’s glasses, which make the patient’s eyes look
larger.
●
Drusen of the head of the optic nerve
These colloid bodies of
the head of the nerve makes the margin of the disc look
blurred.
●
Developmental abnormalities of the head of the nerve
These may
be difficult to diagnose.
Management
Patients with true papilloedema will need neurological
investigation.
Patients with pseudopapilloedema and other
acquired causes of optic disc swelling (for example, retinal
venous occlusion, uveitis, optic neuritis, ischaemic optic
neuropathy, optic nerve compression, and optic nerve
tumours) will need full ophthalmic and neurological
examination and investigation.
The pale optic disc
There are many causes of a pale optic disc and it is vital to
make the correct diagnosis, as many of them are treatable.
These include compressive lesions, glaucoma, vitamin
deficiency, the presence of toxic substances (for example, lead
or some drugs), and infective conditions such as syphilis.
It is
also important to identify whether the cause is hereditary, as
genetic counselling, and occasionally, metabolic treatments are
available (for example, a diet free of phytanic acid and plasma
exchange may prevent the progression of ocular disease in
Refsum’s disease).
Headaches and the eye
Most patients who present with a history of “headache” around
the eye do not have serious disease.
The following features in
the history and examination should raise suspicion of serious
disease.
●
The nature of the headache
Headaches that cause sleep
disturbance or that are worse on waking or with coughing,
suggest raised intracranial pressure. Temporal tenderness in
patients over the age of 60 with symptoms of aching muscles
and malaise suggest giant cell arteritis.
●
Visual disturbance
If there is a change in visual acuity that
cannot be corrected by a pinhole test, serious disease
should be suspected.
A history of haloes around lights
(caused by transient oedema of the cornea when the
intraocular pressure rises) suggests attacks of angle closure
glaucoma.
●
A red eye
In acute glaucoma the eye is usually red, injected,
and tender, and the acuity is diminished. The pain is deep
seated and may be associated with vomiting.
Inflammation of the iris and ciliary body also cause a red eye and a deep pain.
Primary open angle glaucoma does not present with severe
pain.
●
Defective ocular movements
Restricted ocular movements on
the same side as the pain may indicate serious disease,
including orbital cellulitis (from infected sinuses),
inflammatory lesions in the orbit, and compressive lesions
causing nerve palsies (for example, a posterior
communicating aneurysm causing third nerve palsy and pain
around the eye).
●
Abnormal pupils
An abnormal pupil on the side of the
headache should suggest a compressive lesion (for example,
a painful Horner’s syndrome caused by an internal carotid
artery aneurysm).
Pupillary abnormalities and ocular motility
problems may be present in so called “cluster headaches” and
“ophthalmoplegic migraine,” although these are relatively
benign conditions.
However, patients with headache around
the eye, together with ocular motility or pupillary
abnormalities, should be investigated to exclude serious
lesions.
●
Swelling, atrophy, or cupping of the optic disc
A patient with
headaches around the eye in addition to any of these
symptoms should be referred. The swelling and atrophy may
be due to a compressive lesion and pathological cupping
suggests a chronic form of glaucoma.
