Oculomotor abnormalities in Friedreich's ataxia

Area of Science:

• Neuro-ophthalmology
• Clinical Electrophysiology

Background:

• Friedreich's ataxia is a rare inherited neurodegenerative disorder.
• Ocular motor deficits are common in Friedreich's ataxia but optic nerve involvement is rare.

Purpose of the Study:

• To investigate ocular motor function in patients with Friedreich's ataxia.
• To correlate ocular motor deficits with disease severity.

Main Methods:

• Clinical neuro-ophthalmological examination.
• Electro-oculography (EOG) including vestibulo-ocular reflex (VOR) and optokinetic nystagmus (OKN) testing.

Main Results:

• No optic nerve dysfunction was observed.
• Ocular motor deficits included square wave jerks, jerky pursuit, gaze paretic nystagmus, rebound nystagmus, and saccadic hypermetria.
• Reduced vestibulo-ocular reflex function and impaired optokinetic nystagmus slow-phase velocity were noted.

Conclusions:

• Ocular motor abnormalities in Friedreich's ataxia are common and relate to disease severity.
• Findings suggest involvement of the cerebellar flocculus and vermis or their brainstem connections.
• No abnormalities were found in unaffected family members.