Acute disturbance of vision in a non-inflamed eye demands an
accurate history, as the patient may have only just noticed a
longstanding visual defect.
Acute visual disturbance of
unknown cause requires urgent referral.
Symptoms and signs
In many cases the diagnosis can be made from the history.
Symptoms of floaters or flashing lights suggest a vitreous
detachment, a vitreous haemorrhage, or a retinal detachment.
Horizontal field loss usually indicates a retinal vascular
problem, whereas a vertical defect suggests a neuro-ophthalmic
abnormality at or posterior to the optic chiasm.
If there is
central field loss (“I can’t see things in the centre of my vision”
or “I can’t see people’s faces”) there may be a disorder at the
macula or within the optic nerve.
Associated systemic
symptoms should be elicited. Severe headache and jaw
claudication in an older person may suggest giant cell arteritis.
A previous history of migraine, diabetes mellitus,
cerebrovascular disease, valvular heart disease, carotid artery
disease, or multiple sclerosis may give clues to the underlying
aetiology of the acute visual loss.
It is important to take a
careful history regarding the onset of acute visual loss, as a
patient may sometimes only notice that one eye has
(longstanding) reduced vision when they inadvertently cover
the good eye. The visual acuity gives a strong clue to the diagnosis.
Poor
visual acuity such as count fingers (CF), hand movements
(HM), perception of light only (PL) or no perception of light
(NPL) suggest a severe insult to the retina or optic nerve (for
example, a vascular occlusive event).
Obstruction of the red reflex on ophthalmoscopy suggests a
vitreous haemorrhage, although the patient may have a preexisting
cataract.
The appearance of the macula, remaining
retina, and head of the optic nerve will indicate the diagnosis if
there has been haemorrhage or arterial or venous occlusion in
these areas.
If there is any uncertainty about the cause of acute visual
loss, then the patient should be referred to an eye specialist
immediately.
Many of the causes are treatable if detected at an
early stage.
Posterior vitreous detachment
Posterior vitreous detachment is the most common cause of the
acute onset of floaters, particularly with advancing age, and is
one of the most common causes of acute visual disturbance.
History The patient presents complaining of floaters. In
posterior vitreous detachment, the vitreous body collapses and
detaches from the retina.
If there are associated flashing lights
it suggests that there may be traction on the retina, which may
result in a retinal hole and a subsequent retinal detachment.
Examination The visual acuity is characteristically normal,
and there should be no loss of visual field.
Management Patients with an acute posterior vitreous
detachment should have an urgent (same day) ophthalmic
assessment, so that any retinal breaks or detachment can be
identified and treated at an early stage.
The patient may
require a further visit one to two months later to exclude
subsequent development of a retinal hole.
Vitreous haemorrhage
History The patient complains of a sudden onset of floaters,
or “blobs,” in the vision.
The visual acuity may be normal or, if
the haemorrhage is dense, it may be reduced.
Flashing lights
indicate retinal traction and are a dangerous symptom.
Haemorrhage may occur from spontaneous rupture of vessels,
avulsion of vessels during retinal traction, or bleeding from
abnormal new vessels.
If the patient is shortsighted, retinal
detachment is more likely.
If there is associated diabetes
mellitus the patient may have bled from new vessels and the
vitreous haemorrhage may herald potentially sight threatening
diabetic retinopathy.
Examination The visual acuity depends on the extent of
the haemorrhage.
Projection of light is accurate unless the
haemorrhage is extremely dense.
Ophthalmoscopy shows the
red reflex to be reduced; there may be clots of blood that move
with the vitreous.
Management The patient should be referred to an
ophthalmologist to exclude a retinal detachment.
Ultrasound
examination of the eye may be useful, particularly if the
haemorrhage precludes a view of the retina.
Underlying causes
such as diabetes must also be excluded.
If a vitreous
haemorrhage fails to clear spontaneously the patient may
benefit from having the vitreous removed (vitrectomy).
Retinal detachment
Retinal detachment should be suspected from the history.
It is
only when the detachment is advanced that the vision and the
visual fields are affected and the detachment becomes readily
visible on direct ophthalmoscopy.
History The patient may complain of a sudden onset of
floaters, indicating pigment or blood in the vitreous, and flashing lights caused by traction on the retina.
These, however,
are not invariable and the patient may not present until there is
field loss when the area of detachment is sufficiently large or
a deterioration in visual acuity if the macula is detached.
Retinal detachment is more likely to occur if the retina is thin
(in the shortsighted patient) or damaged (by trauma) or if the
ocular dynamics have been disturbed (by a previous cataract
operation).
Traction from a contracting membrane after
vitreous haemorrhage in a patient with diabetes can also cause
a retinal detachment.
Examination Visual acuity is normal if the macula is still
attached, but the acuity is reduced to counting fingers or hand
movements if the macula is detached.
Field loss (not complete
in the early stages) is dependent on the size and location of the
detachment.
Direct ophthalmoscopy will not detect the
abnormality if the detachment is small; detached retinal folds
may be seen in larger detachments.
Management The patient should be referred urgently.
Only
small retinal holes with no associated fluid under the retina can
be treated with a laser, which causes an inflammatory reaction
that seals the hole.
True detachments usually require an
operation to seal any holes, reduce vitreous traction, and if
necessary drain fluid from beneath the neuroretina.
A vitrectomy may be required, which is carried out using fine
microsurgical cutting instruments inserted into the eye with
fibreoptic illumination.
This may be combined with the use of
special intraocular gases (for example, sulphur hexafluoride)
or silicone oil to keep the retina flat.
If gas is used the patient
may have to posture face down for several weeks after surgery
in cases of retinal detachment, and must not travel by air (the
intraocular gas expands at altitude) until most of the gas in the
eye has been absorbed.
Arterial occlusion
History The patient complains of a sudden onset of visual
disturbance, often described as a “greyout” of the vision or as a
“curtain” descending over the vision, in one or both eyes.
This may be temporary (amaurosis fugax) if the obstruction
dislodges or permanent if tissue infarction occurs.
Examination In retinal artery occlusion the visual acuity
depends on whether the macula or its fibres are affected.
There
may be no direct pupillary reaction if there is a complete
occlusion with a dense relative afferent pupil defect.
The extent
of visual field loss depends on the area of retina affected.
The
retinal artery and its branches supply the inner two thirds of
the neuroretina, and the outer third is supplied by the choroid.
The arteries may be blocked by atherosclerosis, thrombosis, or
emboli, and the attacks may be associated with a history of
transient ischaemic attacks if the aetiology is embolic.
When
the retina infarcts it becomes oedematous and pale and masks
the choroidal circulation except at the macula, which is
extremely thin hence the “cherry red spot” appearance.
Ophthalmoscopy may be normal initially, before oedema is
established, and indeed the retinal appearance may return to
normal after the oedema resolves.
Plaques of cholesterol or
calcium occasionally may be seen in the vessels.
In posterior
ciliary artery occlusion there is infarction of the optic nerve
head, which has a pale swollen appearance with peripapillary
haemorrhage.
This appearance may be mistaken for
papilloedema.
Papilloedema, however, is usually bilateral and
the visual acuity is not affected until late in its development.
Management Giant cell arteritis must be excluded by the
history and examination, and by checking the erythrocyte
sedimentation rate.
Rapid onset of second eye involvement can
occur in giant cell arteritis and this condition is an ophthalmic
and medical emergency.
Immediate high dose intravenous
steroid therapy is indicated.
Emboli from the carotid arteries
and heart should be excluded.
Attempts may be made to open
up the arterial circulation in acute cases by ocular massage,
rapid reduction in intraocular pressure medically, anterior
chamber paracentesis, or by carbon dioxide rebreathing to
cause arterial dilatation.
Factors predisposing to vascular
disease (for example, smoking, diabetes, and hyperlipidaemia)
should be identified and dealt with.
Venous occlusion
History The visual acuity will be disturbed only if the occlusion
affects the temporal vascular arcades and damages the macula.
Patients may otherwise complain only of a vague visual
disturbance or of field loss.
The arteries and veins share a
common sheath in the eye, and venous occlusion most
commonly occurs where arteries and veins cross, and in the
head of the nerve.
Thus raised arterial pressure can give rise to
venous occlusion.
Hyperviscosity (for example, in myeloma)
and increased “stickiness” of the blood (as in diabetes mellitus)
will also predispose to venous occlusion.
This leads to
haemorrhages and oedema of the retina. Occlusion of the
central retinal vein within the head of the nerve leads to
swelling of the optic disc.
Examination Visual acuity will not be affected unless the
macula is damaged.
There may be some peripheral field loss if
a branch occlusion has occurred.
Ophthalmoscopy shows
characteristic flame haemorrhages in the affected areas, with a
swollen disc if there is occlusion of the central vein.
An afferent
pupillary defect and retinal cotton wool spots imply an
ischaemic, damaged retina and are a bad prognostic sign.
Management Hypertension, diabetes mellitus,
hyperviscosity syndromes, and chronic glaucoma must be
identified and treated if present.
It is important to consider
systemic investigation for inherited and acquired
coagulopathies in young patients with retinal venous occlusive
disease.
Antiplatelet therapy should be considered if there are
no contraindications.
There is evidence that involvement of a
physician in the care of patients with retinal occlusive disease
can reduce the chance of second eye involvement and serious
systemic vascular disease.
If the retina becomes ischaemic it stimulates the formation
of new vessels on the iris (rubeosis) and subsequent
neovascularisation of the angle may lead to secondary
glaucoma.
This may occur several months after the initial
venous occlusion.
Such rubeotic glaucoma is a serious
condition and has the potential to render the eye both blind
and painful.
Fluorescein angiography may be useful.
This involves the injection of intravenous fluorescein and sequential fundus photography with light filters to identify areas of poor
perfusion and fluorescein leakage.
Laser treatment is used to
ablate the ischaemic retina in an attempt to prevent new vessel
formation.
Disciform macular degeneration
History The patient notices a sudden disturbance of central
vision.
Straight lines may seem wavy and objects may be
distorted, even seeming larger or smaller than normal.
Eventually, central vision may be lost completely.
This central
area of visual distortion or loss moves as the patient tries to
look around it.
The layer under the neuro retina is the black
retinal pigment epithelium.
Most commonly with increasing
age (the patient is normally over 60) and in certain conditions
(for example, high myopia) neovascular membranes may
develop under this layer in the macular region.
These
membranes may leak fluid or bleed and cause an acute
disturbance of vision.
Examination Visual acuity depends on the extent of macular
involvement.
If the patient looks at a grid pattern (Amsler chart)
the lines may seem distorted in the central area, although the
peripheral fields are normal.
On fundal examination the macula
may look normal or there may be a raised area within it.
Haemorrhage in the retina is red but it appears black if it is
under the retinal pigment epithelium.
There may be associated
deposits of yellow degenerative retinal products (drusen).
Management Some cases are treatable with a laser that
occludes these neovascular membranes.
The abnormal areas of
leaking blood vessels are identified by the use of intravenous dye
injection in combination with fundus photography (fluorescein
angiography and indocyanine green angiography).
A patient who has had a subretinal neovascular membrane in one eye that
has destroyed central vision is at risk of the same thing
occurring in the other eye.
The problem with laser treatment is
that it may cause immediate worsening of vision, with benefit
only in the long term.
Trials are still underway to determine the
role of radiation therapy in preventing the progression of the
neovascular membranes.
A recent development in the treatment
of choroidal neovascularisation is the use of photodynamic
therapy (PDT).
Optic or retrobulbar neuritis
History The patient is usually a woman aged between
20 and 40, who complains of a disturbance of vision of one eye.
There is usually pain that worsens on movement of the eye.
There may have been previous attacks.
Examination The visual acuity may range from 6/6 to
perception of light. Despite a “normal” visual acuity, the patient
usually has an afferent pupillary defect and may notice that the
colour red looks faded when viewed with the affected eye (red
desaturation).
The field defect is usually a central field loss
(central scotoma).
It is extremely important to test the field of
the other eye, as a field defect in the “good” eye may suggest a
lesion of the optic chiasm or tract (for example, a pituitary
adenoma).
If the “inflammation” is anterior in the nerve, the
optic disc will be swollen. Accompanying symptoms of general
demyelinating disease such as pins and needles, weakness, and
incontinence suggest multiple sclerosis.
Management Most patients recover spontaneously, but they
may be left with diminished acuity and optic atrophy.
Treatment with systemic steroids does not alter the long term
visual prognosis but may hasten recovery. Systemic steroids may,
in selected patients, reduce the incidence of subsequent multiple sclerosis.
Referral to a neurologist is necessary.
Debate continues regarding the use of systemic steroids and
other disease modifying agents such as beta interferon.
If there is
doubt about the diagnosis, with atypical clinical features or
history, then the patient may need further investigation to
exclude a space occupying lesion.
Cardiovascular and cerebrovascular
disease
History Intermittent episodes of transient visual loss
(amaurosis fugax) and bilateral permanent visual field loss may
be caused by either cardiovascular or cerebrovascular disease.
The characteristic feature of a posterior visual pathway lesion is
a homonymous nature to the hemianopic or quadrantanopic
visual field defect, which respects the vertical midline.
The
patient may have a hemiparesis or hemisensory disturbance on
the same side as the visual field loss.
Patients sometimes
complain of “the beginning or end of a line of print
disappearing,” and some may complain of a decrease in acuity.
The visual pathways pass through a large area of the
cerebral hemispheres, and any vascular occlusion in these areas
will affect these pathways.
This is in contrast to vascular lesions
in the eye or optic nerve, which either affect the whole field of
one eye or if partial tend to respect the horizontal meridian in
that eye.
More posteriorly placed lesions in the brain tend to
spare the macular vision in the affected fields.
Examination The visual acuity should be preserved,
although patients may say half (either the left or right hand
side) of the Snellen chart is missing.
Management It is important to make the diagnosis and
exclude any underlying cause for the visual pathway damage.
The following conditions should be excluded:
● Hypertension
● Diabetes mellitus
● Abnormal serum lipid profile
● Hyperviscosity syndromes
● Cardiac arrhythmias
● Cardiac embolic disease
● Carotid artery disease
● Giant cell arteritis.
The visual field defects sometimes improve with time, and
patients should be taught to compensate for their field defect
with appropriate head and eye movements.
These techniques
can be taught in low vision assessment clinics.
Migraine
History Migraine may present initially with symptoms of visual
loss.
The features are well known and include:
● a family history of migraine
● attacks set off by certain stimuli for example, particular foods
● fortification spectra in both eyes these include zigzag lines and
multicoloured flashes of light
● associated headache and nausea although these symptoms may
not be present.
However, if patients present for the first time after 40 years
of age with migraine and associated neurological symptoms or
signs, consider the need for further investigation.
Examination The patient may have a bilateral field defect
but this usually resolves within a few hours.
Management Conventional treatment with analgesics and
antiemetics may be necessary. Long term prophylaxis may be
required if attacks occur often.
