Three-dimensional architecture of outer retinal tubulation in Bietti crystalline dystrophy.

PURPOSE: To characterize the three-dimensional morphology and cellular-level organization of outer retinal tubulation (ORT) in Bietti crystalline dystrophy (BCD) and to evaluate its structural relationship with the residual outer retina.

DESIGN

Observational case series.

SUBJECTS: Patients with BCD exhibiting ORT were included.

METHODS

ORT and contiguous ORT-associated regions were evaluated three-dimensionally using two complementary approaches: en face optical coherence tomography (OCT) images generated from the innermost ORT boundary to Bruch's membrane, and ellipsoid zone (EZ)-like band-to-Bruch's membrane thickness maps (hereafter referred to as EZ-to-Bruch's membrane thickness maps). Cellular-level ORT organization was further assessed using adaptive optics OCT (AO-OCT).

MAIN OUTCOME MEASURES: Three-dimensional ORT morphology, spatial relationship between ORT-associated structures and the EZ-like band, EZ-to-Bruch's membrane thickness distribution, and AO-OCT features of ORT wall organization were assessed.

RESULTS

Nineteen eyes from 19 patients were included. En face OCT images were analyzable in 15 eyes, and AO-OCT images were analyzable in 9 eyes. The EZ-like band could be traced to the hyperreflective ORT wall in all eyes assessed using en face OCT. En face OCT showed complex ORT-associated planar structures with branching and confluent configurations. EZ-to-Bruch's membrane thickness maps closely corresponded to the contours of these ORT-associated planar structures, suggesting that the maps reflected the overall geometry of the residual outer retina. Peripheral EZ-to-Bruch's membrane thickening was observed in most eyes, and quantitative thickness-distance analysis identified characteristic peripheral peak patterns in eyes with intermediate-sized ORT-associated regions, suggesting that these thickened regions may be associated with ORT formation. AO-OCT showed multiple hyperreflective dots arranged in rosette-like configurations around a central hyporeflective lumen, consistent with presumed photoreceptor nuclei within the ORT wall.

CONCLUSIONS

ORT in BCD showed complex three-dimensional planar configurations spatially associated with the residual outer retina. These findings suggest that the peripheral margin of the ORT-associated outer retina may represent a key site of structural reorganization and support the concept that ORT in BCD represents a manifestation of outer retinal structural reorganization in the setting of progressive degeneration.