1-10 RVD - DR

Question 1

Diabetes diagnose how?

Answer 1

HbA1c (Gylcated haemoglobin test)
- 41-49mmol/mol = pre
- >49 mmol/mol = diabetes

Question 2

Diabetes underlying pathophysiology
- Which BVs affected?
- Hyperglycaemia has what cellular effects?
- That affects BVs how?
- Leads to…

Answer 2

Since BVs affected, it affects retina since it’s filled w/ small BVs.
Mechanisms unclear. Proposed that…
- Chronic hyperglycemia alters gene expression
- Glycosylation of proteins alters function
- Chronic hyperglycemia causes oxidative stress –> ROS formation

Hyperglycemia causes…
Capillary wall changes:
- BM thickening
- Selective pericyte loss (apoptosis)
- Endothelial damage + loss
Haematological:
- RBC deformation
- Platelet aggregation (due to deformed RBC)
- Less O2 transport (since everything’s clumped/viscous)
All result in non-perfusion of retinal capillaries.

Microvascular leakage. Inner BRB integrity compromised so leaks hard exudate and fluid components.

Leads to capillary dropout due to progressive retinal ischaemia and hypoxia.
- Forms abnormal ateriovenous shunts to bypass occulusions
- Neovascularisation due to angiogenic factors like VEGF released from ischaemic cells.

Question 3

Describe background features of DR

Answer 3

Microaneurysms:
- Earliest detectable DR lesions
- Due to outpouching of capillary wall due to weak wall due to pericyte loss
- At INL
- Appear as isolated, round red dots (variable size)
- May leak and lead to intraretinal haemorrhage, hard exudate, or oedema, or thrombosed.

Intraretinal haemorrhages:
Ruptured/leaking microaneurysm/retinal capillary
- Dot/blot heamorrhages
– Venous end of capillaries
– within INL and OPL
– Dark red, sharply outlined dot-blot configuration
- Flame heamorrhages
– Arise from larger superficial pre-capillary arterioles
– Diffuse, flame-shaped, often follows RNFL bundle configuration.

Hard exudates + Intraretinal oedema
- BRB breakdown causes fluid leak
- Hard exudates = Lipoprotein + lipid-filled macrophages
– Deposited at junction of normal and oedematous retina post chronic localized retinal oedema.
– Waxy, yellow lesions. Distinct margins. Typically surround leaking microvascular lesions in ring pattern (circinate exudate) or star-shaped (macula star)

Question 4

Describe diabetic maculopathy
- Image how?

Answer 4

When macula is involved in diabetic pathology either by
- Ischaemia (DMI)
- Oedema + hard exudates (DMO/DME)
DMI = Gradual atrophy of retinal capillary at macula from long-term hypoxia/non-perfusion
- Results in enlarged/irregular foveal avascular zone (FAZ)
DMO = Retinal microaneurysms fluid leak + dilated capillary segments near fovea

DMI = Fluorescein angiography. Dark middle zone is avascular and this zone is large.
DMO = OCT. Shows macular oedema raising macula. Fluorescein can show hyperfluorescence at late stage when dye pools up at oedema area.

Question 5

Describe non-proliferative DR

Answer 5

Venous changes:
Resulting from severe retinal hypoxia
- Dilatation
- Beading (irregular constrictions + dilatations along path)
- Loop (obvious loop deviation from normal linear path)
- Reduplication (2 or more reuniting parallel branches)

IRMAs:
Intraretinal Microvascular Abnormalities (name is neutral since not sure if de novo or if they’re AV shunts)
- Abnormal intraretinal shunts going from arterioles to venules (bypass capillaries)
- At areas of poor retinal perfusion, appear as branching/dilatation of capillaries.
- Fine red lines resembling focal areas of flat new retinal vessels.

Cotton Wool Spots
- Focal infarcts of RNFL causing axoplasmic flow interruption causing material to build up.
- Yellowish, fluffy cloud-like superficial lesions obscuring underlying BVs
- May regress as fibres die as dead zone increases where transported materials can’t get to.

Question 6

Describe proliferative DR

Answer 6

Neovascularisation:
Any neovasc = PDR
- Collateral circulation responding to local non-perfusion and ischaemia
- Start as endothelial proliferations and pass through any space that happens to exist between the retina and vitreous. Some places of retina have more of these gaps so these places more common.
- NVD (Neovascularisation at Disc) if within 1 disc diameter.
- NVE if elsewhere
- Angiogenic factors can reach iris (Rubeosis Iridis)

Pre-retinal Haemorrhages:
Since new vessels made are fragile, often leak/rupture spontaneously
- Pre-retinal = sub-hyaloid space or under ILM. Blood appears oddly contained as that’s where PVD has occurred.
- Vitreous = Bleed into vitreous body. Appears more diffuse.

Fibrous Membranes:
New vessels are accompanied by fibrotic tissue.
- Membranes can be opaque and if obscure macula, can impaire vision
- Contraction causes tractional RD.