Optic disk swelling
Papilledema is the swelling of the optic nerve as it enters the back of the eye due to raised intracranial pressure. Fluid surrounding the brain is constantly produced and reabsorbed, maintaining just enough intracranial pressure to help protect the brain if there is blunt head trauma.
Not all optic disc swelling is papilloedema. Careful history and examination are needed to distinguish papilloedema from other causes of optic disc swelling such as central retinal artery or vein occlusion, congenital abnormalities and optic neuritis.
The optic disc is the round spot on the retina formed by the passage of the axons of the retinal ganglion cells, which transfer signals from the photoreceptors of the eye to the optic nerve, allowing us to see.
Optic disk swelling may result from intraocular disease, orbital and optic nerve lesions, severe hypertensive retinochoroidopathy, or raised intracranial pressure, the last necessitating urgent imaging to exclude an intracranial mass or cerebral venous sinus occlusion. Intraocular causes include central retinal vein occlusion, posterior uveitis, and posterior scleritis.
Optic nerve lesions causing disk swelling include anterior ischemic optic neuropathy; optic neuritis; optic nerve sheath meningioma; and infiltration by sarcoidosis, leukemia, or lymphoma. Any orbital lesion causing nerve compression may produce disk swelling.
Papilledema (optic disk swelling due to raised intracranial pressure) is usually bilateral and most commonly produces enlargement of the blind spot without loss of acuity. Chronic papilledema, as in idiopathic intracranial hypertension and cerebral venous sinus occlusion, or severe acute papilledema may be associated with visual field loss and occasionally with profound loss of acuity.
All patients with chronic papilledema must be monitored carefully especially their visual fields and cerebrospinal fluid shunt or optic nerve sheath fenestration should be considered in those with progressive visual failure not controlled by medical therapy (weight loss where appropriate and usually acetazolamide). In idiopathic intracranial hypertension, transverse venous sinus stenting is also an option.
Optic disk drusen and congenitally crowded optic disks, which are associated with farsightedness, cause optic disk elevation that may be mistaken for swelling (pseudopapilledema). Exposed optic disk drusen may be obvious clinically or can be demonstrated by their autofluorescence. Buried drusen are best detected by orbital ultrasound or CT scanning. Other family members may be similarly affected.
Swelling of the optic disc presents with symptoms based on the underlying causative condition. In the majority, therefore, patients complain of a sudden diminution of visual acuity and visual field. Visual field defects in NA-AION are mostly inferonasal in location. Altitudinal field defects, affecting only half of the vertical field of vision, are more common in optic neuritis, but scotomas of different types or an enlargement of the blind spot are also often present.
Pain on eye movement is seen more frequently in optic neuritis, but is typically absent in ischemic neuropathy. In compressive forms of optic neuropathy, various intracranial tumors should be ruled out. A relative afferent pupillary defect is characteristic, but pain is usually absent.
If papilloedema is suspected (ie optic disc arising from raised ICP), there is an urgent need to rule out an intracranial mass.
Optic disc swelling that is not thought to be papilloedema should be referred according to the severity of the symptoms.
All patients with apparent optic nerve swelling should have an ophthalmological assessment and, unless an alternative diagnosis is clear, it is prudent to assume that the swollen disc is papilloedema until proven otherwise. Ultimately, the underlying cause needs to be addressed.