Differences in cysts characteristics and related influence on the anatomical response after dexamethasone implant in diabetic macular oedema

Purpose: To assess the clinical significance of suspended scattering particles in motion (SSPiM) and different cystic phenotypes in diabetic macular oedema (DME) treated with dexamethasone implant (DEX-i). Methods: A retrospective review of type 2 diabetic patients with DME treated with a DEX-i was conducted. Swept-source optical coherence tomography angiography (OCTA, PLEX Elite 9000) with a 3-mm volume cube was performed. Regions of interest were delineated with Fiji software (version 2.1.0/1.53.c) in the superficial vascular complex (SVC) and deep capillary plexus (DCP) at baseline, 2- and 4-months after DEX-i. SSPiM was defined as regions of variable reflectivity with a decorrelation signal. Without a detectable decorrelation signal, its counterpart was addressed as ‘corpuscular,’ while hyporeflective cysts were optical empty without hyperreflective material enclosed. Results: After treatment, the hyporeflective component demonstrated substantial reabsorption in the SVC (–95.4% at 2- and –84.4% at 4-months, p < 0.01 both) and DVC (–84.4%, 2-months), with a less critical decrease of the corpuscular component in the SVC (2-months: –41.9%, p = 0.001 and 4 months: –1.8%, p = 0.73), and not significant in the DVC. SSPiM did not significantly change in the SVC and DVC neither at 2- and 4-months (p > 0.05, all). Conclusions: After a single DEX-i, the clearance of different cystic phenotypes proceeds with resorption of hyporeflective, followed by corpuscular components. SSPiM demonstrated minimal response, indicating a severe BRB breakdown that may require repeated treatment to reach a satisfactory anatomical response.