Optometry case study – Microvascular CN VI palsy

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

Examination
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

Management

• 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

Diagnosis

• Microvascular CN VI palsy

Follow-up

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