Structural effects of intraretinal cysts on outer retinal layers in eyes with diabetic macular edema

Diabetic macular edema (DME) is the main cause of visual loss in individuals with diabetic retinopathy (DR). This study aims to investigate the effects of central macular intraretinal cysts on the underlying outer retinal layer (ORL) in patients with diabetic macular edema (DME).

In this retrospective and cross-sectional study, diabetic patients with or without DR were categorized into three groups: without DME (group 1), with DME but without any cyst featuring a plateau in the lower region (group 2), and patients with cyst featuring an inferior cyst plateau (group 3), defined as a flat conformation at its posterior aspect. Variables such as central macular intraretinal cyst height, inferior cyst plateau, and ORL thickness were measured, and ellipsoid zone (EZ) disruption was assessed via Spectral-domain optical coherence tomography (SD-OCT) and compared between groups. Correlations between OCT-measured variables and best-corrected visual acuity (BCVA) were investigated.

A total of 164 eyes were included: 48 in group 1, 47 in group 2 and 69 in group 3. Compared with Groups 1 and 2, Group 3 presented a greater intraretinal cyst height (p < 0.001), a thinner mean ORL beneath the cysts (p < 0.0001) and more frequent EZ disruption (p < 0.0001), which was associated with lower BCVA values. Cyst height, cyst plateau and ORL thickness were significantly correlated with BCVA (p < 0.0001). EZ disruption was associated with the cyst height, the cyst plateau and the underlying ORL thickness. Correlations were observed between cyst height and ORL thickness (r = - 0.32, p < 0.001), between cyst height and cyst plateau (r = 0.60, p < 0.001), and between cyst plateau and ORL thickness (r = - 0.56, p < 0.001). Every increase of 10 μm in plateau width and in cyst height results in reductions of 0.16 μm and 0.29 μm in ORL thickness, respectively, independent of the other parameters. The optimal cutoff point for cyst height that best discriminates plateau formation was determined to be 130.5 μm, with a sensitivity of 89.9% and specificity of 83%.

In patients with DME, large central intraretinal cysts may assume a flat configuration in their lower region, termed a plateau, and are associated with photoreceptor damage due to compression, which can result in visual impairment. These findings can be understood based on modified Hertz's mechanical contact theory.