Day #214 Diplopia

The discussant went over an approach to diplopia:

• Neurological -- i.e. ischemia/vasculitis, demyelination, tumour (including leptomenegeal), infection (TB, syphilis, listeria, lyme), toxic/metabolic (alcohol/wernike's)
  
• NMJ - mysesthenia and other myesthenic syndromes
  
• Muscular/Structural - Graves, masses in the muscles, muscular impingement
  
• Opthomologic -- monocular diplopia -- think corneal or lens problem

The physical exam can be helpful in determining which cranial nerve is involved. This site is actually quite informative with regards to the innervation of the cranial nerves and the section on gaze is good to read. This site has some interactive eye movements examples.

Cranial Nerve III:

• Pupil spared/Involved
• Adducts the eye/Innervates Medial Rectus
• Typically "down and out" gaze on affected side with inability to adduct

Cranial Nerve IV:

• Inability to look down and in leading to diplopia while walking down stairs or reading newspaper
• Head characteristically tilted away from the lesion

Cranial Nerve VI:

• Inability to abduct the eye
• Eye deviated inwards
  

Intranuclear Opthalmoplegia:

• Typically normal gaze when looking straight ahead
• Inability to abduct the eye on the contralateral side of the lesion due to failure of co-ordination of gaze.