Outer retinal tubulation associated with photoreceptor degeneration.

Outer retinal tubulation (ORT) is a distinct structural manifestation of chronic photoreceptor degeneration, observed across a broad spectrum of retinal diseases. Initially described histologically as rosette-like formations, ORT has gained clinical relevance with the advent of high-resolution imaging modalities such as spectral-domain optical coherence tomography (SD-OCT) and adaptive optics scanning laser ophthalmoscopy (AO-SLO), which enable in vivo visualization of its tubular architecture. ORT arises from sustained photoreceptor and retinal pigment epithelium (RPE) injury, leading to the reorganization of surviving cones ensheathed by gliotic Müller cell processes. This review integrates historical, histological, and imaging data to elucidate ORT's cellular composition, formation mechanisms, and disease-specific patterns. We introduce a novel etiological classification of ORT, categorized as degenerative, fibrotic, or edematous ORT according to predominant pathogenic drivers, to facilitate cross-disease comparison and prognostic stratification. Clinically, ORT serves as a non-exudative biomarker of chronic retinal injury, aiding differential diagnosis and informing treatment strategies. In age-related macular degeneration, ORT is associated with subretinal fibrosis and poor visual outcomes; in geographic atrophy, it may signal slower lesion progression. In inherited retinal dystrophies, ORT reflects genotype-specific vulnerabilities and residual photoreceptor survival, with implications for therapeutic targeting. As imaging technologies advance, ORT offers promise as a structural marker of disease chronicity, photoreceptor resilience, and Müller cell plasticity, enhancing diagnostic precision and supporting its role as a meaningful endpoint in clinical trials.