Subjectively quantified Maddox rod testing improves diagnostic yield over alternate cover testing alone in patients with diplopia

We aimed to assess the added diagnostic value of subjectively-quantified red Maddox rod testing in patients with diplopia or suspected strabismus. Over 9 months we compared measures of ocular alignment (inspection; alternate cover; Maddox rod) with final anatomic and etiologic diagnoses using clinical records in a cross-sectional study in an academic neuro-ophthalmology unit. Seventy-seven consecutive patients (98 visits) met study criteria. Mean age was 54 years (range 11–100 years). Most visits (73%) were for symptomatic diplopia and all three measures of alignment were generally available (92%). Maddox findings prompted additional diagnostic tests for 13 patients, leading to an important new diagnosis (systemic vasculitis; posterior fossa arachnoid cyst with mass effect; cavernous sinus mass) in three patients (4%). Maddox rod testing may add clinically relevant diagnostic information to that obtained by alternate cover testing alone. Its use might help prevent missed diagnoses in the evaluation of patients with diplopia or suspected strabismus.