Differential Diagnosis   
Common Signs in Optic Disc  
  • optic disc swelling
  • unilateral disc swelling and optic atrophy
  • optic atrophy
(Abnormal optic discs are commonly encountered in the clinical examination. Diagnosis is usually straightforward provided you consider the 3 Cs each time: Colour, Contour and Cup. Do not forget to look for associated signs if you come across conditions like optic disc pit (looks at the macula for pigmentary changes suggestive of previous central serous retinopathy) or optic disc drusen (angioid streaks and retinitis pigmentosa.)

Optic disc swelling

1. Pseudo-papilloedema
      (In the presence of blurred optic disc, always remember to consider the possibility of pseudo-papilloedema.)

2. True disc swelling
      (Always look at both eyes as the presence of bilateral swellings suggest an intracranial process, whereas an unilateral swelling suggests a lesion either in the optic nerve or in the orbit. The most common cases seen in the examination is benign intracranial hypertension. )

Unilateral disc swelling

Bilateral disc swelling
    (This usually suggests the presence of papilloedema ie. raised intracranial pressure. However, unilateral papilloedema can occur and this can be caused by the presence of unilateral optic atrophy or unilateral congenital fenestration of the optic nerve.)  

Unilateral optic atrophy and disc swelling
(These signs are uncommon but have been known to appear in the examination. Although they classically appear in the Foster-Kennedy's syndrome, they are more common in patients with giant cell arteritis affecting the discs at different time)

Optic atrophy
(This is another common clinical case. It may be presented as a straightforward fundus examination with direct ophthalmoscope / indirect ophthalmoscope with lens, or as pupillary examination in which the patient has a relative afferent pupillary defect. In either way, you may be expected to determine the cause of the optic atrophy (such as advanced glaucoma, retinitis pigmentosa, central retinal artery occlusion etc.) or be able to give a good differential diagnosis.
Before making a diagnosis of optic atrophy remember that certain existing ocular conditions may give a false appearance of pale disc for example in aphakia or in patient with a unilteral pseudophakia.
The following differential diagnosis is based on the aetiology)