Effect of Phenytoin on the Ganglion Cell Layer in Patients With Optic Neuritis

a Phase II Double Blind, Randomized, Placebo Controlled Trial of Effect of Phenytoin on the Ganglion Cell Inner Plexiform Layer (GCIPL) Thickness and Visual Field in Patients With a First Episode of Acute Optic Neuritis

Optic neuritis typically occurs in young (mean age, 32 years), female (77%) patients, and it presents as subacute monocular visual loss that develops over several days.

As yet, treatment with intravenous corticosteroid for optic neuritis had no long-term beneficial effect on vision.

There are a number of factors that contribute to nerve fibre damage including increased level of sodium, so blocking sodium entry could help to protect them against damage.

The main objective of the study is determine whether phenytoin (which blocks sodium entry) can protect nerve fibre and improve final visual function after optic neuritis.

Inclusion Criteria:

• isolated, unilateral, first acute optic neuritis (confirmed by neuroophthalmologist)
• willing to receive a steroidal regimen
• no pathologic finding in first oct
• no pathology and history of optic neuritis in contralateral eye
• <14 days since onset visual loss

Exclusion Criteria:

• Contraindication or known allergy to Phenytoin
• Use of a calcium channel or sodium channel blocker in the past 2 months
• Corticosteroid use in the past 2 months
• Pregnancy
• Significant cardiac, renal or liver abnormalities
• Prior clinical episode of optic neuritis in either eye
• Bilateral acute optic neuritis
• Known ocular or neurological conditions or abnormalities other than refractive error that impair visual function
• Refractive error of greater than +5 or -5 diopters
• Any condition that may interfere with performance of Optical Coherence Tomography (OCT): corneal, lens or fundoscopic abnormality, a co-morbid ocular condition not related to optic neuritis as detected on the OCT reading