PURPOSE If the interruption of macular fusion for an extended period of time is the key event that results in the development of monofixation syndrome, then the decreased macular input caused by dense cataracts may cause monofixation syndrome in adults. This study was designed to test this hypothesis. METHODS The study design was a retrospective chart review that identified patients with unilateral cataracts at two southern Louisiana medical centers. Patients were assigned to the dense cataract group if a unilateral cataract had been present for at least 3 months and led to a visual acuity of worse than 20/200. Patients in the control group had a unilateral cataract for more than 3 months and visual acuity better than 20/200 in the affected eye. Stereoacuity was assessed using the Titmus or Randot stereo test. A Worth 4-dot test viewed at a distance of 20 feet was used to assess the presence of a macular scotoma. The criteria for monofixation syndrome were met if stereoacuity was less than 60 seconds and the Worth 4-dot test demonstrated central macular scotoma at 20 feet. RESULTS The dense cataract group's association with monofixation syndrome was statistically significant when compared to the control group (P < .0001). CONCLUSIONS This study adds dense adult-onset cataracts to the list of causes of monofixation syndrome and reduced stereoacuity. A delay in treating dense lens opacities can result in good visual outcome but an inferior binocular visual outcome (poor stereoacuity). [J Pediatr Ophthalmol Strabismus. 2017;54(1):39-42.].