The optic disc is a non-sensory spot in the retina where the axons of the ganglion cells carrying afferent light-induced impulses to the visual cortex of the brain converge to leave the eye.
It appears as a sharply defined light-colored round region, slightly to the nasal side of the center of the retina, and is also called the optic nerve head.
Swelling of this disc may occur due to a diverse range of etiologies, some inflammatory, others associated with vascular abnormalities, and still others due to increased intracranial pressure (ICP).
Papilledema is a term which literally means “swelling of the optic disc”, but whose meaning has narrowed since 1908, when it was coined.
The current meaning of the term is a swollen optic disc which is due solely to raised ICP.
Other causes of optic disc swelling include both pseudopapilledema (apparent swelling of the disc and true edema of the disc without elevation in the ICP.
Pseudopapillema may be due to optic disc drusen, or certain congenital conditions of the disc, as well as optic disc hypoplasia.
Non-papilledematous optic disc swelling may be due to infection, inflammation, or demyelination.
This differentiation is important both in terms of diagnosis of the true nature of the swelling, and the treatment which will be most beneficial in conserving visual acuity and field.
In terms of frequency, a swollen optic disc is due to either anterior ischemic optic neuropathy (AION) or optic neuritis in almost two-thirds of cases. True papilledema accounts for 14% of these cases.
Other causes include central retinal vein or artery occlusion, diabetic papillopathy, malignant hypertension, or toxic optic neuropathy.
Diagnosis of Papilledema/Optic Disc Swelling
Differentiation of papilledema from other causes of optic disc swelling is based on the history, clinical and ophthalmic examination, and various relevant tests.
The history should ask for systemic symptoms of various arteritic disorders, those which suggest high intracranial tension, and others which could indicate demyelinating or inflammatory disorders.
Ophthalmic examination will pick up many other helpful signs. It includes the following, among others:
- Visual acuity
- Swinging flashlight test for pupillary function
- Color vision
- Sensitivity to brightness
- Visual fields
- Dilatation of the pupils and examination of the whole fundus
A relative afferent pupillary defect is important in several conditions which affect the optic disc.
Unilateral swelling of the disc is rarely a sign of papilledema, which is usually present on both sides. However, some frontal tumors may induce nerve atrophy on one side with swelling of the disc in the other eye.
Signs which distinguish papilledema include:
- A swollen hyperemic disc
- Loss of margin demarcation
- Absence of spontaneous venous pulsations due to compression of the central retinal vein
- Exudates, hemorrhages, and cotton wool spots over the rest of the fundus are seen more characteristically in papilledema
A full neurologic examination should also be done.
Depending on the findings, urgent tests may be requested, such as:
- Gadolinium-enhanced MRI to rule out intracranial and orbital mass lesions
- Magnetic resonance venography for venous occlusion within the brain
- Lumbar puncture for the opening pressure if there is no mass lesion
- Cerebrospinal fluid examination for various intracranial pathologies
- Ultrasonography / optical coherence tomography (OCT), especially when distinguishing pseudopapilledema from papilledema
- Coagulation tests if risk factors for thrombotic disorders are present
Differentiation Between Papilledema and Other Causes of Optic Disc Swelling
- Signs and symptoms of increased intracranial pressure
- Few visual symptoms at first except for graying-out lasting a few seconds
- Usually bilateral and symmetric
- Hyperemic disc
- Veins are engorged
- Venous pulsations absent
- Peripapillary hemorrhages
- Uniformly swollen disc with ill-defined margins
- Cupping is present till an advanced stage
- The retinal nerve fiber layer is also raised
- Blood vessels on the disc are not visible
- Paton’s lines (radial retinal creases around the disc)
- Visual field defects in the form of enlargement of the blind spot or sometimes field constriction
- Color vision impaired
- Relative afferent pupillary defect
Optic Disc Swelling
In contrast to true papilledema, with AION or optic neuritis, there is a startling loss of visual acuity, but clear-cut field defects.
The presence of exudates, cotton wool spots, or hemorrhages is rare in most conditions associated with optic disc swelling other than papilledema and the non-arteritic form of AION.
The disc may be pale rather than engorged, and systemic symptoms are more pronounced in some conditions such as arteritic ION. Pain with eye movement is present in optic neuritis.
Every patient with optic disc swelling should be evaluated on an emergency basis to rule out rapidly progressive conditions which could rob the eyesight.
- Cupping is lost early
- Crowding of the disc
- No other disc or retinal features of papilledema
- Circumpapillary light reflex is present