Optometry case study – Microvascular CN VI palsy

A curious case of double trouble

by Jennifer Du, Specsavers


86 year old female presented for a routine check
Reason for visit: routine eye examination, no other problems reported.
General health: unremarkable
Medication: Magnesium tablets
POH: bilateral IOL 2 years previously
FOH: none

Pupils: PERRLA
Motility – full and smooth
Refraction: R -0.25/-0.75 x 105 L: plano / -0.25 x 5
Add: +2.25 n5

Ocular examination – nothing abnormal detected



  • New bifocals prescribed. Px returned for follow up 2 /52 later c/o headaches with her new bifocals
  • No dispensing error noted
  • No changes in her refraction
  • During the exam, the patient said she was intermittently seeing double while reading the letter chart
  • Subsequently noted 10PD esophoria that was breaking down into esotropia
  • 6 Prism BO in the right eye was found at the end of the test

Differential diagnosis

  • Thyroid eye disease
  • Myasthenia gravis – normally vertical diplopia noted.
  • Symptoms worsen at end of day, ptosis noted
  • Orbital inflammation – Usually presents with pain, proptosis
  • No trauma reported
  • VI nerve palsy – most likely diagnosis

Provisional diagnosis

  • Microvascular CN VI palsy – causes intermittent horizontal diplopia with no other symptoms

Optometrist management

  • Px referred urgently to ophthalmology to investigate sudden onset diplopia

Ophthalmology management

Ophthalmologist’s findings:

  • 6PD esotropia with bilateral LR weakness
  • Further questioning revealed that the px’s GP had asked the patient to stop taking cholesterol meds owing to musculoskeletal side effects 6 months previous


  • Microvascular CN VI palsy


  • Reviewed by optometrist 6/52 later
  • Diplopia had resolved spontaneously

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