Structural changes in individual retinal layers in diabetic macular edema

Abstract

Optical coherence tomography (OCT) has enabled objective measurement of the total retinal thickness in diabetic macular edema (DME). The central retinal thickness is correlated modestly with visual impairment and changes paradoxically after treatments compared to the visual acuity. This suggests the clinical relevance of the central retinal thickness in DME and the presence of other factors that affect visual disturbance. Recent advances in spectral-domain (SD) OCT have provided better delineation of the structural changes and fine lesions in the individual retinal layers. Cystoid spaces in the inner nuclear layer and outer plexiform layer are related to quantitative and qualitative parameters in fluorescein angiography. OCT often shows vitreoretinal interface abnormalities in eyes with sponge-like retinal swelling. Serous retinal detachment is sometimes accompanied by hyperreflective foci in the subretinal fluid, which exacerbates the pathogenesis at the interface of the photoreceptors and retinal pigment epithelium. Photoreceptor damage at the fovea is thought to be represented by disruption of the external limiting membrane or the junction between the inner and outer segment lines and is correlated with visual impairment. Hyperreflective foci in the outer retinal layers on SD-OCT images, another marker of visual disturbance, are associated with foveal photoreceptor damage.

Figure 1

(a) Retinal sections of the physiologic macula dissecting along the green line on fundus photography using SD-OCT. (b) The magnified image at the fovea shows three lines over the retinal pigment epithelium (RPE), that is, the external limiting membrane (ELM), the junction between inner and outer segments (IS/OS), and the cone outer segment tips (COST). (c) A magnified parafoveal image shows the individual retinal layers. NFL: nerve fiber layer; GCL: ganglion cell layer; IPL: inner plexiform layer; INL: inner nuclear layer; OPL: outer plexiform layer; ONL: outer nuclear layer.

Figure 2

Quantification of the total retinal thickness using OCT. The retinal thickness can be measured semiautomatically (b) or manually using calipers (a). (c) A two-dimensional map of the retinal thickness can be constructed from the automatically measured retinal thickness. (d) The average thickness in each subfield of Early Treatment Diabetic Retinopathy Study grid is shown. (e) The average thickness in the central subfield is correlated modestly with the logarithm of the minimum angle of resolution VA in center-involved DME.

Figure 3

Characteristics of cystoid spaces in DME. ((a), (b)) Early-phase FA shows an enlarged foveal avascular zone and surrounding microaneurysms (arrowheads). (c) A late-phase image shows fluorescein pooling at the fovea. (d) Cystoid spaces (arrows) are accompanied by microaneurysms (arrowhead). (e) A late-phase FA image shows petalloid- (e) or honeycomb-pattern (f) fluorescein pooling, which is considered to correspond to cystoid spaces in OPL (arrow) or INL (arrowhead), respectively, on OCT image. Foveal cystoid spaces (arrowheads) have higher OCT reflectivity and its heterogeneity (g) or lower and homogeneous reflectivity (h).

Figure 4

Several patterns of vitreomacular interface abnormalities in DME. (a) A posterior hyaloid membrane is sometimes depicted on OCT images (arrows). (b) ERM often is accompanied by sponge-like retinal swelling (arrows). (c) A perifoveal vitreous separation sometimes induces vertical traction, as in idiopathic macular holes (arrows). (d) Some eyes have separation of a posterior vitreous membrane (arrows).

Figure 5

A representative case with hyperreflective foci (arrowheads) in subretinal fluids. The preoperative decimal VA is 0.6. (b) DME is improving after focal/grid photocoagulation, although hyperreflective foci have accumulated at the fovea (arrowheads). The postoperative VA is 0.09. (c) OCT sometimes shows that cystoid spaces in the OPL rupture to subretinal fluids (arrow), which might modulate the pathogenesis in SRD.

Figure 6

Pathological changes in the photoreceptor layers in DME. (a) Both the ELM and IS/OS lines are continuous. (b) The ELM line seems almost continuous, whereas the IS/OS line is discontinuous on the left (arrow). (c) The ELM line is disrupted, and the IS/OS line is absent at the fovea, accompanied by hyperreflective foci in the outer retinal layers (arrowheads).