■ BACKGROUND AND OBJECTIVE: Diabetic macular edema has several patterns on optical coherence tomography. This retrospective study aimed to assess which retinal layers show thickness changes in type 1 diffuse diabetic macular edema with preserved vision. ■ PATIENTS AND METHODS: Eleven eyes with diffuse diabetic macular edema on optical coherence tomography and eight control eyes with 20/20 best-corrected visual acuity were enrolled. Optical coherence tomography images were segmented using an algorithm of the authors' design (OCTRIMA): regional thickness data in the central area, pericentral rings, and peripheral rings were obtained for the retinal cellular layers. ■ RESULTS: The retinal nerve fiber layer showed no changes, the ganglion cell and inner plexiform composite layer and the ganglion cell complex were thicker only in the pericentral regions, and all other layers were thicker in all regions in diffuse diabetic macular edema. Macular thickness was normal in the peripheral region. ■ CONCLUSION: The results show that the outer retina in the foveal area is the most affected in diffuse diabetic macular edema.
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