Diabetes Mellitus

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Pathophysiology & Basics - Sweet Eye Trouble

  • Chronic hyperglycemia: central to ocular damage.
  • Key mechanisms:
    • Polyol pathway: glucose → sorbitol (aldose reductase) → osmotic stress (lens, nerves).
    • AGEs formation: damages vessel walls, thickens basement membranes.
    • PKC activation: ↑VEGF, ↑vascular permeability, promotes neovascularization.
    • Oxidative stress: contributes to cellular injury.
  • Ocular effects:
    • Refractive instability: due to lens hydration changes.
    • Cataract formation: sorbitol, oxidative damage.

⭐ Sorbitol accumulation in the lens, driven by aldose reductase activity, is key in diabetic cataract and transient refractive shifts.

Diabetic Retinopathy (DR) - Leaky Vessels Alert

  • Pathophysiology: Chronic hyperglycemia → pericyte loss, basement membrane thickening → capillary incompetence → retinal ischemia → ↑Vascular Endothelial Growth Factor (VEGF).
  • Key Stages & Features:
    • Non-Proliferative DR (NPDR):
      • Microaneurysms (earliest clinical sign)
      • Dot & blot hemorrhages
      • Hard exudates (intraretinal lipid deposits)
      • Cotton Wool Spots (CWS - nerve fiber layer infarcts)
      • Intraretinal Microvascular Abnormalities (IRMA)
      • Venous beading/looping
    • Proliferative DR (PDR):
      • Neovascularization (NVD: at disc; NVE: elsewhere)
      • Vitreous hemorrhage
      • Tractional retinal detachment
      • Rubeosis iridis (iris neovascularization)
  • Diabetic Macular Edema (DME): Commonest cause of ↓vision in diabetics. Can occur at any DR stage. Clinically Significant Macular Edema (CSME) is a key treatment indication.
  • Screening: Type 1 DM: within 5 yrs of Dx; Type 2 DM: at time of Dx. Annually thereafter, or more frequently if DR present.

Diabetic Retinopathy Severity Levels and Hallmarks

⭐ The presence of IRMA (Intraretinal Microvascular Abnormalities) is a key indicator of severe NPDR, signifying significant retinal ischemia and a high risk of progression to PDR within a year.

Macular Edema & Other Issues - Central Vision Crisis

  • Diabetic Macular Edema (DME): Major cause of vision loss in diabetics.
    • Patho: ↑VEGF → BRB breakdown → fluid in OPL/INL.
    • Types: Focal, Diffuse, Cystoid (CME).
    • Symptoms: Painless blurred central vision, metamorphopsia.
    • Diagnosis:
      • Slit-lamp (90D/78D): Macular thickening.
      • OCT: Gold standard; quantifies thickness, shows cysts. OCT showing diabetic macular edema with intraretinal cysts
      • FFA: Detects leakage (petaloid in CME).
    • Clinically Significant Macular Edema (CSME) criteria:

      ⭐ Retinal thickening within 500 µm of foveal center; OR Hard exudates within 500 µm of foveal center if associated with adjacent retinal thickening; OR Retinal thickening ≥1 DD (1500 µm) any part of which is within 1 DD of foveal center.

    • Treatment:
      • Anti-VEGF (Ranibizumab, Aflibercept) - 1st line.
      • Intravitreal steroids (Triamcinolone, Dex-implant).
      • Focal/Grid laser (non-center involving/adjunct).
  • Other Ocular Issues:
    • Cataract: Premature senile; Snowflake (Type 1 DM).
    • NVG (Neovascular Glaucoma): Rubeosis iridis → ↑IOP. Severe.
    • CN Palsies: III (pupil-sparing), IV, VI; transient.
    • Refractive Changes: Transient hyperglycemic myopia.

Screening & Management - Defend The Vision!

  • Screening Schedule:
    • Type 1 DM: Within 5 yrs of diagnosis (if onset age ≥10 yrs), then annually.
    • Type 2 DM: At diagnosis, then annually.
    • Pregnancy (pre-existing DM): Pre-conception, 1st trimester, then per trimester & postpartum.
  • Management Pillars:
    • Systemic: Strict glycemic control (HbA1c <7%), blood pressure control (<140/90 mmHg), lipid management.
    • Ocular Interventions:
      • Laser photocoagulation: Panretinal (PRP) for PDR; focal/grid for DME.
      • Anti-VEGF injections: For DME, PDR.
      • Vitrectomy: For non-clearing vitreous hemorrhage (VH), tractional retinal detachment (TRD).

⭐ Early detection and appropriate treatment can reduce the risk of severe vision loss from diabetic retinopathy by up to 95%.

High‑Yield Points - ⚡ Biggest Takeaways

  • Diabetic Retinopathy (DR): leading cause of new blindness in adults 20-74 years.
  • NPDR features: microaneurysms, retinal hemorrhages, hard exudates, cotton wool spots.
  • PDR features: neovascularization (NVD/NVE); high risk of vitreous hemorrhage & tractional RD.
  • Diabetic Macular Edema (DME): most common cause of visual impairment in diabetics; treat with anti-VEGF.
  • Pan-Retinal Photocoagulation (PRP) is mainstay for PDR; Anti-VEGF also used.
  • Other findings: True diabetic cataracts (snowflake, typically in young type 1 DM), rubeosis iridis (neovascular glaucoma).
  • Strict glycemic control is paramount to delay onset and progression of DR.

Practice Questions: Diabetes Mellitus

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A 45-year-old diabetic presents with sudden painless vision loss. Cotton wool spots and dot hemorrhages seen. HbA1c is 9.2. Most likely diagnosis?

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Flashcards: Diabetes Mellitus

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Hemoglobin SC and S-Thal disease have _____ severe ocular manifestations than HbSS

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Hemoglobin SC and S-Thal disease have _____ severe ocular manifestations than HbSS

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