Schlaegel lines: History, etiology, multimodal imaging, and differential diagnosis of curvilinear streaks in chorioretinal disorders

Schlaegel lines (SL) represent distinctive curvilinear patterns of chorioretinal atrophy that have emerged as a distinctive, yet non-pathognomonic, funduscopic sign across diverse ocular disorders. First described as related to presumed ocular histoplasmosis syndrome in the early 1980s in Histoplasma-endemic regions, these peripheral fundus lesions have since been documented across numerous other etiologies. The majority of SL arise in the context of inflammatory chorioretinal disorders, with idiopathic multifocal choroiditis and punctate inner choroiditis constituting the most frequent underlying causes. SL can also occur in a subset of inherited retinal diseases, where they may represent a secondary acquired sign of outer retinal damage. SL demonstrate a predilection for young to middle-aged myopic women. On fundus examination, SL appear as linear atrophic spots or streaks with variable pigmentation. Optical coherence tomography demonstrates retinal pigment epithelium-Bruch membrane-choriocapillaris complex disruption or, when SL are detected during the active inflammatory phase, hump-like hyperreflective RPE elevations. The differential diagnosis of SL requires recognition of the characteristic multimodal imaging patterns to distinguish them from mimicking conditions, such as Verhoeff lines and West Nile chorioretinitis. A comprehensive understanding of the diverse etiologies of SL is essential for accurate diagnosis and appropriate clinical management.