BACKGROUND: Accommodation-convergence spasm (spasm of the near reflex) is usually bilateral, resulting in increased myopia, convergence, and miosis. Unilateral spasm of accommodation has rarely been reported. PATIENTS: We investigated three females (age range 10-19 years) referred for investigations of retrobulbar optic neuritis (2 cases) and decompensated esophoria (1 case). RESULTS: They all presented unilateral spasm of accommodation with visual loss due to increased myopia (-3.5 to -11.75 diopters). Apart from that, results of neuro-ophthalmological examination were normal. CONCLUSIONS: Unilateral accommodation spasm is rare and can mimic retrobulbar optic neuritis and convergent strabismus. The three components of the accommodation-convergence spasm may not always be present simultaneously. Recognizing such an entity is important to prevent the patient from useless, costful and potentially harmful investigations.