Background. Accommodative spasm (AS) has been reported to be a rare cause of an acquired unilateral visual loss. We describe a unique case of acquired visual loss due to an apparent unilateral AS triggered by occlusion of the contralateral eye. Clinical examination and photorefraction techniques were performed during the acute phase of the disorder and in the follow-up evaluations. Case Report. An otherwise healthy 27-year-old woman presented with a 2-month decrease of vision in her left eye. Unaided visual acuity in the right eye was 20/20 and in the left eye was finger counting. Orthophoria existed at distance and near. The decrease in vision in the left eye was attributed to an apparent unilateral AS of 5 D, which occurred only when the right eye was occluded. Under the occluder, the right eye also manifested an AS. With the left eye occluded or with binocular viewing, the right eye and left eye accommodated normally. With a 5 D convex lens before the right eye, the visual acuity in the left eye was 20/20. Refractive error with cycloplegia revealed low hyperopia in each eye. Conclusion. AS can be the cause of acquired unilateral visual loss. To our knowledge, this is the first documented report of an apparent unilateral AS triggered by occlusion of the contralateral eye.