ABSTRACT The West Indian manatee ( Trichechus manatus manatus ), a sirenian species critically endangered throughout its range, possesses unique ocular adaptations to aquatic life, including reduced eyes, vascularized corneas and an anteriorly displaced lens. We aimed to document the first known case of congenital bilateral cataract associated with retinal dysplasia in a stranded manatee calf. We evaluated a manatee neonate calf, about 4 days old, kept in the Center for Rehabilitation of the National Center for Research and Conservation of Aquatic Mammals on Itamaracá Island, Pernambuco State, Brazil. Clinical signs included impaired postural behaviour, failure to avoid obstacles and inability to locate food independently. Ophthalmologic evaluation revealed absent menace response and glare reflex, supporting the hypothesis of visual impairment. Ultrasonographic imaging confirmed bilateral lens opacity and retinal folding consistent with retinal dysplasia, without signs of inflammation or persistent hyperplastic primary vitreous. Although congenital cataracts may regress in terrestrial mammals, follow‐up examination 2 years later indicated persistence and slight progression of lens opacity in this case. These findings expand current understanding of congenital ocular disorders in aquatic mammals and underscore the importance of early, thorough clinical assessments for rescued individuals. Furthermore, the presence of such conditions may complicate rehabilitation and release efforts, emphasizing the need for additional research into the aetiology, progression and conservation impact of congenital diseases in small, vulnerable populations of threatened species. Summary First documented case of congenital cataract and retinal dysplasia in an Antillean manatee. Visual impairment strongly correlated with reduced exploratory behaviour and is possible cause of stranding.