Archive for the ‘Optic nerve disorders’ Category

Optic Atrophy

Tuesday, August 19th, 2014

When is it optic atrophy?

The optic nerve comprises of 1.2 million myelinated axons. Once damaged, the axons do not regenerate (behaves more like a white matter tract than a true peripheral nerve). Thus optic atrophy is the common morphological endpoint of any optic neuropathy. Clinically, the neuro-retinal rim of the optic disc (the area excluding the cup) appears pale/yellow, with associated visual impairment. This is different to glaucoma, where the disease is characterized by an increased cup to disc ratio but the neuro-retinal rim remains pink. Optic atrophy is a clinical diagnosis and does not carry any implications on the underlying cause.

Causes of optic atrophy:

  • Compressive optic neuropathy (papilloedema, tumors, thyroid eye disease)
  • Ischaemic optic neuropathy (arteritic or non-arteritic, diabetes)
  • Optic neuritis (infectious or inflammatory)
  • Nutritional Deficiencies (vitamin B12 and folate deficiencies)
  • Toxic optic neuropathy (ethambutol toxicity, common in Hong Kong due to pulmonary tuberculosis being endemic in this locality)
  • Infiltrative diseases (leukemia, sarcoidosis)
  • Hereditary opic neuropathies (autosomal dominant, mitochondrial)
  • Iatrogenic – Radiation optic neuropathies (common in Hong Kong, due a high incidence of nasopharyngeal carcinoma, and the primary treatment being radiotherapy)
  • Traumatic
  • Glaucomatous optic neuropathy / glaucoma – optic atrophy in end-stage disease

Workup considerations of optic atrophy to dertermine the underlying cause:

  • Medical and family history
  • Visual acuity
  • Intraocular pressure
  • Pupillary reflexes
  • Colour vision
  • Visual field testing
  • Neuroimaging
  • Blood tests (vitamin B12, folate, VDRL, ANA)

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Papilloedema

Tuesday, August 19th, 2014

When is it true optic disc edema?

The optic nerve head consists of a bundle of densely packed axons from 1.2 million retinal ganglion cells and also encases the central retinal artery and vein. Thus, true optic disc swelling should have both mechanical and vascular signs present. The above photo (Figure 1) illustrates a typical appearance of optic disc swelling.

Mechanical signs of swelling:

  • Elevation of optic disc (best appreciated with stereoscopic view)
  • Blurring of optic disc margins
  • Filling-in of the optic cup
  • Oedemaof peri-papillary nerve fibre
  • Retinal and choroidal folds

Vascular signs of swelling:

  • Disc hyperaemia
  • Venous congestion
  • Flamed-shape haemorrhages near the disc (peri-papillary haemorrhages)
  • Exudates in the disc or peri-papillary area
  • Cotton wool spots near the disc (nerve fibre layer infarction)

Papilloedema is the most important differential diagnosis in the presence of bilateral optic disc swelling. Therefore urgent neuroimaging is indicated.

  • Defined as a bilateral, passive, non-inflammatory swelling of the optic disc secondary to raised intracranial pressure.
  • Symptoms: transient obscuration of vision with normal pupillary reflexes.
  • If permanent visual loss is present, or pupillary reflexes are abnormal; in the presence of optic disc edema, then other optic neuropathies should be considered, including: optic neuritis, ischaemic optic neuropathies and compression optic neuropathy.
  • Stages of papilloedema:
  1. Early papilloedema – disc hypaeremia, disc elevation, dilation of retinal veins, flamed shape haemorrhages around the disc margins
  2. Established papilloedema – Signs from early papilloedema + obscuation of all borders of the disc, optic cup appears filled
  3. Chronic papilloedema – optic cup is obliterated, hard exudates at optic disc
  4. Atrophic papilloedema – optic atrophy

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