Diabetes Mellitus

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.

⭐ 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.
    • 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.