Retinal Vascular & Hemoglobin Pathology

Primary Hypertension (Pathogenesis)

• Mechanisms leading to development remain unknown

• Interplay of genetics & environment

  • Reduced renal sodium excretion

  • Increased vascular resistance

  • Genetic factors

    • SMC growth

    • Sodium excretion

  • Environmental factors

Hypertensive Retinopathy (Early Findings)

• Narrowing of arteriolar vessels

• Vasospasms

• Increased vascular tone

Chronic Hypertension (HR)

• Intima thickening

• Hyaline degeneration

• Vessel wall pacification

• Microaneurysms

• Cotton Wool Spots

• Hard Exudates

• 
  

Hypertensive Chorioretinopathy

• Acute elevations in BP

• Fibrinoid necrosis of choroidal arterioles

  • Non-perfusion in chorizo capillaries

  • Focal ischemic damage to RPE

  • Macular edema

  • Retinal detachment

Retinal Artery Occlusion

• Systemic emboli causing obstruction of central retinal artery

  • Central retinal artery occlusion (CRAO)

  • Branch retinal artery occlusion (BRAO)

  • Cilioretinal artery occlusion (CLRAO)

• Blockage to retina vascular supply

  • Emboli

  • Atherosclerosis

  • Inflammation

  • Trauma

  • Hypercoagulation

Retinal Emboli

• Found in 24-40% of eyes with CRAO

• Most common cause of nonarteritic CRAO & BRAO

RBC (Erythrocytes)

• Made in bone marrow

• Globular molecule made up of 4 subunits

• Carry hemoglobin (Hb)

  • HbAA contains two pairs of polypeptides (a & B chains)

• Lose nucleus before entering circulation

• Expressed as hematocrit or % of blood

• 7.5 um in diameter, 2 um thick

• Biconcave shape

  • Large SA:V ratio

  • Form stacks: rouleaux

  • Bend & flex

Sickle Cell Disease (SCD)

• Group of inherited RBC disorders

• Inherited abnormal Hb genes

• Characterized by:

  • Intravascular hemolysis

  • Defective oxygen transport

• RBCs have crescent or “sickle” shape

SCD (Pathogenesis)

• Single nucleotide mutation in HBB gene

  • Adenine → thymine substitution

  • Create valine AA

• Upon deoxygenation, the hydrophobic valine in HbSS causes molecules to polymerize, leading to stiffness

• Autosomal recessive mode of inheritance

  • Homozygous: HbSS

  • Heterozygous variants: HbSC, HbSB - thalassemia disease

Signs & Symptoms (SCD)

• Newborns: symptoms appear at 5-6 months

• Yellowing of skin & sclera

• Fatigue from anemia

• Painful swelling of hands & feet

Diagnosis & Treatment (SCD)

• Diagnosis: blood test screenings

• Treatment:

  • Medicine: Hydroxyurea to reduce pain

  • Blood transfusions

  • Bone marrow transplant

  • Gene therapy

Sickle Cell Retinopathy (NP)

• Salmon Patch Hemmorrhages

  • Vessel wall rupture (blow outs)

• Iridescent Spots

  • Hemosiderin (iron-storage complex)

  • Macrophage debris

• Black Sunbursts

  • Localized choroidal ischemic damage to overlying RPE

Sickle Cell Retinopathy (P)

• Stage I: peripheral arterial occlusions

• Stage II: peripheral arterioles out anastomoses

• Stage III: neovascular & fibrous proliferations

• Stage IV: vitreous hemorrhage

• Stage V: retinal detachment

SCD

• Characterized by RBC damage & defective O2 transport

• Autosomal recessive mode of inheritance

  • HbSS (homozygous)

  • HbSC & HbSB (heterozygous)

• Can develop irregular ocular manifestations anteriorly & posteriorly

• NP SCD & P SCD classification dependent on sea fan formations