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Ocular System

Diabetic macular edema (DME)

Retinal thickening caused by the accumulation of intraretinal fluid, primarily in the inner and outer plexiform layers as a result of hyperpermeability of the retinal vasculature.

  • M/C cause of vision loss among diabetics

Clinically-significant macular edema (CSME):

Early Treatment of Diabetic Retinopathy Study (ETDRS) definition, consisting of any of the following
  1. Retinal thickening at or within 500 µ or 1/3 the disc diameter of the fovea.
  2. Hard exudates at or within 500 µ of the fovea, with adjacent retinal thickening.
  3. Retinal thickening greater than one disc diameter (1500 µ) in size that is within one disc diameter from the fovea.
Schematic view of clinically significant macular edema. | Gundogan, F. C., Yolcu, U., Akay, F., Ilhan, A., Ozge, G., & Uzun, S. (2016). Diabetic Macular Edema. Pakistan journal of medical sciences, 32(2), 505–510. https://doi.org/10.12669/pjms.322.8496

Aetiology

Systemic risk factors:

  • Age, male gender
  • Systolic blood pressure
  • Hyperlipidemia
  • Proteinuria
  • Insulin use
  • Diuretic use
  • Duration of diabetes
  • Higher glycosylated hemoglobin
  • Pan-retinal photocoagulation (PRP)

Local factors:

Angiogenic factors
  • Vascular endothelial growth factor (VEGF)
  • Protein kinase C (PKC)
  • Prostaglandins
  • Growth hormone
  • Anatomy of the posterior hyaloid face

Clinical features

DME present with a range of visual symptoms depending on the degree to which the fovea is involved and the chronicity of the edema.

  • Metamorphopsia
  • Fluctuation of vision from day-to-day or even over the course of a day

Diagnosis

DME is diagnosed stereoscopically.

Fundus examination:

A macular lipid star is a common fundus sign in diabetic macular edema and indicates that the center of the macula is a preferential site for accumulation of extracellular fluid | Browning, D. J., Stewart, M. W., & Lee, C. (2018). Diabetic macular edema: Evidence-based management. Indian journal of ophthalmology, 66(12), 1736–1750. https://doi.org/10.4103/ijo.IJO_1240_18

Fluorescein angiography (FA)

Optical coherence tomography (OCT):

Diagnostic test of choice
Fundus fluorescein angiography (FFA) (2a) and optical coherence tomography (2b) images of diabetic macular edema. Fluorescein leakage (2a) and cystoid spaces (2b) are seen in FFA and OCT, respectively. | Gundogan, F. C., Yolcu, U., Akay, F., Ilhan, A., Ozge, G., & Uzun, S. (2016). Diabetic Macular Edema. Pakistan journal of medical sciences, 32(2), 505–510. https://doi.org/10.12669/pjms.322.8496

Differential diagnosis:

  • Hypertension
  • Retinal vein occlusion (RVO)
  • Ruptured microaneurysm
  • Radiation
  • Irvine-Gass syndrome
  • Subfoveal choroidal neovascularisation

Management

Laser photocoagulation:

Mainstay treatment for clinically-significant macular edema (CSME)
  • Focal laser photocoagulation
  • Scatter laser photocoagulation

Anti–VEGF agents:

  • Ranibizumab
  • Bevacizumab
  • Aflibercept “VEGF trap”

Intravitreal corticosteroids:

Benefits of glucocorticoids depend on their anti-inflammatory and anti-VEGF effects
  • Triamcinolone acetonide (TA)

Pars plana vitrectomy (PPV):

Removes traction forces and proinflammatory substances and increases the oxygenation of inner retinal layers; indicated in refractory cases
Schematic summarization of the mechanisms of action of the various treatments for diabetic macular edema. The color-filled blocks represent different treatment modalities for diabetic macular edema | Browning, D. J., Stewart, M. W., & Lee, C. (2018). Diabetic macular edema: Evidence-based management. Indian journal of ophthalmology, 66(12), 1736–1750. https://doi.org/10.4103/ijo.IJO_1240_18

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