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By definition, papilledema is a
swollen optic nerve head (papilla) resulting from increased
intracranial pressure. As a rule, papilledema is bilateral and not
associated with significant visual field loss or loss of central vision unless
it continues untreated for weeks or months. The most common early visual field
finding in papilledema is enlargement of the
physiologic blind spots. Early in papilledema, there is
hyperemia of the disk. Subtle changes in the
nerve fibers and vessels can be detected on slit lamp examination.
Spontaneous venous pulsations are usually
obliterated when the intracranial pressure rises above 200 mm water. As the
papilledema worsens, the swelling then obscures the normal
disc margins and the
disc becomes elevated. Venous congestion
develops and peripapillary hemorrhages then
develop.
If the papilledema persists for months, the disc hyperemia slowly subsides,
leaving a pale disc that loses its central cup. |
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Knowledge of anatomy is important in understanding papilledema. The
subarachnoid space is continuous with the optic nerve sheath.
Thus, as the cerebrospinal fluid pressure increases, this same pressure is
transmitted to the optic nerve sheath. This increased pressure on the optic
nerve sheath then impedes axoplasmic flow, leading to the swelling of the nerve
head |
It is important to note that not every swollen, or edematous, optic nerve is papilledema.
The differential diagnosis of a swollen optic nerve is based on the "vital
signs" of neuro-ophthalmology: visual acuity, visual field and the presence or
absence of a relative
afferent pupillary defect (RAPD).
For example, anterior ischemic optic neuropathy (AION) presents as sudden
painless loss of vision in one eye associated with a swollen optic disc.
Prominent field and acuity loss are present from the beginning. Although involvement
of the other eye occurs in up to 40% of people over months or years, bilateral
simultaneous AION is extremely unusual unless caused by vasculitic conditions
(e.g., temporal arteritis). Anterior ischemic optic
neuropathy of the non-arteritic type (NAION) almost never occurs before the age
of 50 and is often associated with systemic risk factors for arteriosclerotic
disease (e.g. hypertension, diabetes mellitus, hyperlipidemia).
Optic neuritis most often presents as subacute loss of vision in one eye over
hours to days, commonly associated with mild to moderate pain on eye movement.
Like AION, but unlike papilledema, loss of vision and visual field are prominent
early signs of optic neuritis. Most cases of optic neuritis are associated with
demyelinating disease (i.e., multiple sclerosis) and more
often affect the retrobulbar optic
nerve. Therefore, retrobulbar optic neuritis is by definition not associated
with optic disc edema. However, anterior optic neuritis (aka, papillitis;
neuroretinitis) does occur in some cases of demyelinating disease, but is also
seen when the cause is infectious or infiltrating. |
