diabetic%20retinopathy
DIABETIC RETINOPATHY
Diabetic retinopathy is an abnormality of the microvasculature of the retina that occurs to almost all patients with chronic diabetes mellitus.
It is one of the leading cause of blindness worldwide and principal cause of impaired vision in patients aged 25-75 years of age.
The abnormality causes microaneurysms, retinal hemorrhages, lipid exudates, macular edema & neovascular vessel growth that may lead to blindness.

Classification

  • Treatment options for DR are based on the types & severity of DR

Types of Diabetic Retinopathy

  • Nonproliferative diabetic retinopathy (NPDR)
    • Earliest clinically apparent stage of DR
    • Characterized by abnormalities primarily in the posterior retina & macula consisting of:
      • Microvascular abnormalities (eg microaneurysms, occluded vessels & dilated/tortuous vessels)
      • Intraretinal hemorrhages
      • Nerve-fiber layer infarcts (cotton-wool spots)
      • Hard exudates
    • Visual loss is primarily caused by macular edema
    • As the disease progresses, gradual closure of the retinal vessels occur that eventually results to impaired perfusion & retinal ischemia manifested as:
      • Venous abnormalities (eg beading, loops)
      • Increasing retinal hemorrhages
      • IRMA
      • Increasing exudation
  • Proliferative diabetic retinopathy (PDR)
    • Onset of neovascularization of the inner surface of the retina that is induced by retinal ischemia
    • Neovascularization (NVD & NVE) causes preretinal & vitreous hemorrhage, subsequent fibrosis & traction retinal detachment
    • May develop from existing severe NPDR or w/o substantial NPDR

DR Disease Severity Level based on Findings upon Dilated Ophthalmoscopy1

  • No apparent retinopathy
    • No abnormalities observed
  • Mild NPDR
    • Have microaneurysms only
  • Moderate NPDR
    • Have more than just microaneurysms but less than severe NPDR
  • Severe NPDR have any of the following but w/ no signs of proliferative retinopathy:
    • >20 intraretinal hemorrhages in each of 4 quadrants
    • Definite venous beading in ≥ 2 quadrants
    • Prominent IRMA in ≥ 1 quadrant
  • Non-high risk PDR
    • Presents w/ neovascularization &/or vitreous/preretinal hemorrhage but does not meet the criteria for high risk PDR
  • High risk PDR
    • Have neovascularization w/in 1 disc diameter of the optic nerve head that are ≥ ¼-1/3 disc area &/or vitreous/preretinal hemorrhage associated w/ less extensive NVD or w/ NVE ≥ ½ disc area in size

Diabetic Macular Edema (DME)

  • Thickening located w/in 2 disc diameters of the center of the macula
  • Recommended to be evaluated through dilated examination using slit-lamp biomicroscopy, OCT, &/or stereoscopic fundus photography
  • Severity of DME can help determine the appropriate treatment modality to give the patient

DME Severity Scale based on Observation upon Dilated Ophthalmoscopy1

  • No macular edema if there is no retinal thickening or hard exudates in the posterior pole
  • Mild DME if the retinal thickening or hard exudates in the posterior pole is distant from the center of the macula
  • Moderate DME if the retinal thickening or hard exudates approaches the center of the macula but does not involve the center
  • Severe DME if the retinal thickening or hard exudates involves the center of the macula

Clinically Significant Macular Edema (CSME)

  • May occur at any stage of DR & defined to include any 1 of the following features:
    • Retinal thickening at or w/in 500 microns of the center of the macula (approximately ½ optic disc diameter)
    • Hard exudates at or w/in 500 microns of the center of the macula, if associated w/ thickening of the adjacent retina
    • Retinal thickening zone or zones of ≥ 1 disc area, any part of which is w/in 1 disc diameter of the center of the macula
  • Helps in differentiating different types of DR

1 Modified from: Wilkinson CP, Ferris FL III, Klen RE, et al. Proposed international clinical diabetic retinopathy and diabetic macular edema disease severity scales. Ophthalmology. 2003;110:1679-1680.

History

  • Chronic DM especially when it is uncontrolled
  • Non-compliance to antidiabetic medications
  • Poor glycemic control (HbA1c level)
  • Medical history (eg obesity, renal disease, hypertension)
  • Ocular history (eg ocular injections, trauma, surgery)

Ocular Exams

  • Visual acuity determines the extent of effect in the central vision
  • Slit-lamp biomicroscopy examines the posterior pole & midperipheral posterior pole, & assesses the presence & severity of DR
  • Intraocular pressure (IOP) determines the presence of glaucoma
  • Gonioscopy detects anterior chamber neovascularization if there is iris neovascularization or elevated IOP
  • Dilated fundoscopy including stereoscopic examination of the posterior pole
    • 0.5-1% Tropicamide &/or Phenylephrine use in pupil dilation is safe & markedly increases the sensitivity of DR screening

Ancillary Ophthalmological Exams

  • Fluorescein angiography
    • Evaluates the cause of unexplained decrease of visual acuity (eg macular capillary non-perfusion, capillary leakage that leads to macular edema) & guides in treating CSME
    • Used as a routine screening test in patients w/ no or minimal DR
    • Assess signs of likely macular ischemia
  • Color fundus photography
    • Documents the status of the retina if surgery is not performed, progression of the disease & response to treatment
  • Optical coherence tomography (OCT)
    • Quantify macular thickness, monitor resolution of macular edema & identify vitreo-macular traction in selected patients w/ DME
  • Ultrasonography
    • Detects retinal detachment in diabetic eyes w/ cataract or vitreous hemorrhage

Laboratory Tests

Ancillary Laboratory Exam

  • Fasting blood sugar (FBS) &/or oral glucose tolerance test (OGTT) assess the severity of DM
  • Glycosylated hemoglobin (HbA1c) assesses past glycemic control

Screening

  • Regular eye exam for DR should be done in all patients w/ diabetes mellitus (DM) w/ the following recommended schedule:
    • Adult w/ type 1 DM first eye exam at 3-5 yrs of onset then yrly follow-up
    • Adult w/ type 2 DM first eye exam at the time of diagnosis of DM then w/ yrly follow-up
    • Pregnant patients prior to conception or early in the 1st trimester should have eye screening for DR w/ follow-up every 3-12 mths for those w/ no retinopathy or mild to moderate NPDR & every 1-3 mths follow-up for those w/ severe NPDR or worse
    • Children w/ type 1 DM w/ 5-yr history first eye exam at 9 yrs old & those w/ 2 yrs history have it at 12 yrs old then yrly follow-up
    • Children w/ type 2 DM first eye exam at the time of diagnosis then yrly follow-up
  • Abnormal findings may require frequent follow-up exams

Level of urgency of referral criteria:

  • W/in 4 wks referral is advised if there are:
    • Unexplained drop in visual acuity
    • Hard exudates w/in 1 disc diameter of the fovea
    • Diabetic macular edema (DME)
    • Pre-proliferative or moderate NPDR
  • W/in 1 wk referral is advised if the following are present:
    • New vessels
    • Vitreous hemorrhage
    • Rubeosis iridis
  • Emergency referral w/in the day should be done when the following are found:
    • Sudden, severe visual loss or symptoms or
    • Signs suggesting retinal detachment
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