Contrast enhanced MRI in acute optic neuritis- length of enhancement a visual prognosis indicator?

Abstract

To study the baseline length of optic nerve enhancement on contrast enhanced MRI in patients with acute optic neuritis and its correlation to visual acuity, color vision, visual field and contrast sensitivity.The prospective cohort study was conducted on 30 patients attending Ophthalmology clinics with complaint of sudden painful loss of vision and clinical examination findings suggestive of acute optic neuritis. All patients underwent contrast enhanced MRI (1.5 Tesla) at presentation and then treated with intravenous and oral steroids with monthly follow up for 3 months. Visual acuity using Snellen’s chart (in LogMAR), Color vision using Ishihara chart and contrast sensitivity by means of Pellie Robson chart were evaluated. The visual field was analyzed by Humphrey’s Field Analyser, using a full threshold 30-2 programme.On contrast-enhanced MRI, all affected optic nerves showed enhancement. The length of portions enhanced for each affected optic nerve was measured. The optic nerves were divided into two categories of length ≤ 17mm and >17mm. At baseline, visual acuity worsened with an increasing length of optic nerve enhancement, color vision and visual field was better in subjects with enhancement <17mm while they do not correlate with the final visual outcome. On the contrary, Contrast sensitivity was found to be improved in subjects with <17mmm of enhancement on the last follow up.Contrast- enhanced MRI plays a critical role as an adjunct to diagnosing acute optic neuritis especially in patients with retrobulbar neuritis. Initial length of enhancement does not correlate with the final visual outcome.