Phases

1. Vasoconstrictive Phase: Due to elevated luminal pressures, autoregulatory mechanisms cause the retinal arteriole narrowing and vasospasm to reduce flow
2. Sclerotic Phase: Persistent increase in BP causes intima thickening → worsening arteriolar narrowing
3. Exudative Phase: Severely increased BP → disruption of BBB and leakage of blood and plasma into vessel wall → retinal haemorrhage, hard exudate formation, retinal ischaemia
   1. Retinal haemorrhages develop when necrotic vessels bleed into either the nerve fibre/superficial retinal layer (flame-shaped haemorrhage) or inner retina (dot blot haemorrhage)
   2. Ischaemia to the nerve fibre layer occurs secondary to fibrinous necrosis and luminal narrowing (cotton wool spots)
   3. Exudates occur later in course of disease surrounding areas of haemorrhage as a result of lipid accumulation

Grades

Grade 1

• Thickening of arterioles causing silver wiring appearance of the retinal vessels

Grade 2

• Focal arteriolar spasms and constriction of veins at arterial crossings (AV nipping)
• Some narrowing of retinal vessels

Grade 3

• Haemorrhages (flame shaped)
• Cotton wool exudates (ischemia)
• Hard waxy exudates (lipid deposits)

Grade 4

• Papilledema (swelling of the optic nerve head and macula scar)