Structural changes in individual retinal layers in diabetic macular edema tomoaki murakami* and nagahisa yoshimura
Answers
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.
Introduction
Diabetic macular edema (DME), a leading cause of visual impairment in individuals of working age, is mediated by multiple and complex mechanisms in its pathogenesis [1–4]. Pathophysiology, that is, vascular hyperpermeability and ischemia, is represented by clinical findings seen on fluorescein angiography (FA) images [5–8]. Basic research has elucidated the molecular mechanisms including vascular endothelial growth factor in DME and proliferative diabetic retinopathy (PDR) [9–18]. Using biomicroscopy, clinical ophthalmologists observe thickening of the sensory retina and vascular lesions in DME. However, it is difficult to objectively evaluate the neuroglial changes in the retina. In contrast, histologic studies have reported that cystoid spaces are present mainly in the inner nuclear layer (INL) and the outer plexiform layer (OPL) and contribute partly to macular thickening [19–21]. Electron microscopy showed that, in addition to the accumulation of the extracellular fluids, intracytoplasmic swelling of the Müller cells might be a pathophysiologic mechanism in DME.
Optical coherence tomography (OCT) provides retinal sectional images as in histology study (Figure 1) and is useful for qualitative and quantitative evaluation of pathological retinal changes [22]. The original instrument, time-domain OCT, has been replaced with spectral-domain OCT (SD-OCT), which has higher resolution and reduced speckle noise. Clinicians can appreciate the improved delineation of the fine pathological lesions and the clearer borders between the individual retinal layers