The retina translates light into sight — and it is one of the first organs destroyed by chronic hyperglycaemia. This page explains the mechanism step by step, from pericyte loss and microaneurysms to neovascularisation and blindness, through Dr. Jason Fung's root-cause lens.
Diabetic retinopathy is the leading cause of blindness in working-age adults worldwide.[1] The retina — a paper-thin sheet of neurons lining the back of the eye — depends entirely on a dense network of tiny blood vessels. Chronic hyperglycemia attacks those vessels first, and the damage is silent until it is almost too late to reverse.
The Retina: Why It Is So Vulnerable
The retina is among the most metabolically active tissues in the body — per gram, it consumes more oxygen than almost any other organ. This demand is served by two vascular networks: the retinal capillaries (innermost layers) and the choroidal circulation (outer layers). The retinal capillaries are unusually delicate:
- They lack autoregulation — cannot constrict to buffer glucose spikes
- They are surrounded by pericytes, supporting cells that are exquisitely sensitive to glucose toxicity
- They maintain the blood–retinal barrier, analogous to the blood–brain barrier
When pericytes die — the first detectable lesion in diabetic eye disease — the capillary wall weakens and leaks.[3]
What the Eye Doctor Sees
The images below simulate what an ophthalmoscope (fundus camera) reveals. The optic disc appears as the bright oval; blood vessels branch outward; the macula (central vision) sits to the left. In the diabetic eye, several hallmark lesions appear:
Normal Retina
Diabetic Retinopathy
Normal Retina
- Clear vessels, uniform calibre
- Bright optic disc, intact macula
- No hemorrhages or deposits
Diabetic Retinopathy
- Red dots = microaneurysms
- Dark blots = hemorrhages
- Yellow spots = hard exudates (fat/protein leaks)
- White patches = cotton-wool spots (ischaemia)
- Fine red tangle near disc = new vessels (PDR)
The Molecular Cascade
Michael Brownlee's unifying mechanism[4] — excess glucose overloading mitochondria → electron leak → reactive oxygen species (ROS) — hits retinal pericytes especially hard, because they cannot downregulate glucose uptake when blood sugar rises.
ROS and AGEs damage the basement membrane shared by endothelial cells and pericytes. Without pericyte support:
- Tight junctions between endothelial cells break down
- Plasma proteins and lipids leak into the retina → hard exudates
- Fluid accumulates in the macula → macular oedema → blurred vision
- Capillaries form microaneurysms (pressure bulges) then close entirely
- Ischaemic retina releases VEGF — triggering neovascularisation
The cross-section diagram (left) shows healthy vs hyperglycaemic capillaries in the retina — note the microaneurysm bulge, the missing pericytes (✕), and the fluid pooling as macular oedema.
Four Stages of Diabetic Retinopathy
- Mild NPDR: Microaneurysms only — detectable by ophthalmoscopy but no symptoms. Fully reversible with glucose control.
- Moderate NPDR: Dot-and-blot hemorrhages, hard exudates, cotton-wool spots. Vision begins to be affected if the macula is involved.
- Severe NPDR: More than 20 hemorrhages in each quadrant, venous beading, retinal ischaemia. High risk of progression to PDR within a year.
- Proliferative DR (PDR): VEGF drives neovascularisation — fragile new vessels bleed into the vitreous. Traction retinal detachment and blindness become real risks.
Anti-VEGF injections (e.g. ranibizumab, bevacizumab) have transformed the treatment of PDR and macular oedema,[5] but they treat the consequence, not the cause.
Dr. Fung's Perspective — Treating the Root Cause
In The Diabetes Code,[6] Dr. Jason Fung frames diabetic retinopathy not as an inevitable complication of diabetes but as a downstream consequence of the same root cause he traces throughout the book: chronic hyperinsulinaemia driving chronic hyperglycaemia.
His logic is direct: every end-organ complication — retinopathy, nephropathy, neuropathy — shares the same upstream driver. The fatty liver overflows into a fatty pancreas (Roy Taylor's twin-cycle hypothesis[7]), β-cells fail, blood glucose rises uncontrolled, and years of vascular oxidative stress accumulate silently in the retina.
The corollary is hopeful: in patients who achieve genuine remission of Type 2 Diabetes — through very-low-calorie diet or extended fasting — early retinopathy lesions stabilise and, in some cases, regress. Microaneurysms can disappear when blood glucose is normalized before permanent structural scarring occurs.
"You cannot outrun a bad diet with eye injections. The only durable treatment for diabetic eye disease is fixing the blood sugar — and the only durable way to fix the blood sugar is to remove the cause." — paraphrasing Dr. Fung
References
- Cheung N, Mitchell P, Wong TY (2010). Diabetic retinopathy. The Lancet. https://pubmed.ncbi.nlm.nih.gov/20580421/
- Antonetti DA, Klein R, Gardner TW (2012). Diabetic retinopathy. New England Journal of Medicine. https://pubmed.ncbi.nlm.nih.gov/22455417/
- Eshaq RS, Aldalati AMZ, Alexander JS, Harris NR (2017). Diabetic retinopathy: Breaking the barrier. Pathophysiology. https://pubmed.ncbi.nlm.nih.gov/28757174/
- Brownlee M (2005). The Pathobiology of Diabetic Complications: A Unifying Mechanism. Diabetes. https://pubmed.ncbi.nlm.nih.gov/15919781/
- Stewart MW (2012). The expanding role of vascular endothelial growth factor inhibitors in ophthalmology. Mayo Clinic Proceedings. https://pubmed.ncbi.nlm.nih.gov/22469347/
- Fung J (2018). The Diabetes Code: Prevent and Reverse Type 2 Diabetes Naturally. Greystone Books. https://www.greystonebooks.com/products/the-diabetes-code
- Taylor R (2008). Pathogenesis of type 2 diabetes: tracing the reverse route from cure to cause. Diabetologia. https://pubmed.ncbi.nlm.nih.gov/18726069/