In short
The leading cause of blindness in working-age adults, and its early stages cause no symptoms. What the grades mean, when your screening exam is due from the year of diagnosis, and what must not wait - a sudden shower of floaters, flashes, or a dark curtain across your sight is tonight, not next week.
Emergency if: Get eye care tonight, at an emergency eye department, for sudden loss of vision in one or both eyes, vision in one eye that has suddenly blurred or dimmed, a dark curtain or shadow moving across your vision, a sudden shower of floaters or a sudden increase in their number, repeated flashes of light, or a painful red eye with blurred vision. A curtain or a sudden storm of floaters can mean the retina has detached or has bled, and a detached retina has to be treated quickly to stop it permanently affecting sight. In an eye that already has proliferative diabetic retinopathy these are the expected complications, not unlikely ones. Do not wait for the scheduled appointment, and do not wait to see whether vision returns by morning.
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01
How does high sugar damage the retina, and why is it silent?
The damage is to plumbing, not to the lens. High blood sugar damages the small blood vessels of the retina, the light-sensing layer at the back of the eye. WHO describes raised blood glucose over time as leading to serious damage to many of the body's systems, especially the nerves and blood vessels, and says diabetes can cause permanent vision loss by damaging the blood vessels in the eyes. In the retina those vessels weaken and bulge, then leak fluid or bleed, then block off. Where they block, the retina is starved of oxygen and the eye responds by growing new, abnormal vessels that are fragile and leak or bleed easily.
It is silent because none of that has to touch the centre of your vision to be well advanced. The National Eye Institute states plainly that early stages of diabetic retinopathy usually do not have any symptoms, and some people notice changes that come and go. CDC says the same: you may not notice symptoms in the early stages. By the time reading becomes difficult, bleeding into the jelly of the eye or swelling at the centre of the retina has usually already happened. That single fact is the whole argument for a scheduled exam. CDC calls diabetic retinopathy the leading cause of blindness in working-age adults.
02
When is my first eye exam due, and how often after that?
It depends on which type of diabetes you have, and the clock starts at diagnosis, not at symptoms. For type 2 diabetes, clinical reviews set a fundus examination at the time of diagnosis and annually after that, because type 2 is often present for years before it is found and retinopathy can already be there on day one. For type 1 diabetes, the same reviews start yearly screening five years after onset. CDC describes the same two starting points - an eye exam straight away for newly diagnosed type 2, and a first exam within five years of diagnosis for type 1 - and its general advice to everyone living with diabetes is a comprehensive dilated eye exam at least once a year. Our separate stories on type 2 and type 1 diabetes cover what else is checked in the same annual review.
Two situations change the schedule. Pregnancy is one: the National Eye Institute advises anyone with diabetes who becomes pregnant to have a dilated exam as soon as possible and to ask whether more are needed during the pregnancy, because retinopathy can progress quickly in those months. The second is having any retinopathy already, which usually means more frequent screening rather than annual. Practice on interval differs by system: the NHS invites everyone with diabetes aged 12 or over for diabetic eye screening every one or two years, using photographs of the back of the eye, with more frequent screening once changes appear. A longer interval is something a screening programme assigns from your previous results; it is not an interval to adopt on your own. If you are unsure which schedule you are on, ask at your next diabetes review rather than assuming.
03
What do the grades mean, and what does each one lead to?
The grading ladder describes how much vessel damage the photograph shows, and it predicts what happens next. Non-proliferative diabetic retinopathy is the stage before new vessels grow. Very mild means microaneurysms only, the small outpouchings of weakened capillaries. Mild adds a few retinal haemorrhages and hard exudates, the yellow deposits of leaked fat and protein. Moderate means around twenty medium-to-large haemorrhages per quadrant in one to three quadrants, with cotton wool spots, which are small patches of retina starved of blood. The NHS uses plainer names for the same ladder: background retinopathy, where vision is not affected, then pre-proliferative retinopathy, where vision is at risk in the future.
Severe non-proliferative retinopathy is defined by the four-two-one rule: severe haemorrhages in all four quadrants, or venous beading in two or more quadrants, or moderate intraretinal microvascular abnormalities in one or more quadrants. Meeting one of those is severe; meeting two or more is very severe. This grade matters because it is the doorway to the next one. Proliferative diabetic retinopathy is when new abnormal vessels have grown, on the optic disc or elsewhere on the retina, and high-risk features include new vessels on the disc with vitreous haemorrhage. Those vessels are what bleed into the jelly of the eye and what pull the retina off with scar tissue.
04
Why does my vision blur when the grade sounds mild?
Because the grade describes the whole retina and your central vision depends on one small part of it. The macula is the area that does reading, faces and detail. When damaged vessels leak fluid into it, the macula thickens, and that is diabetic macular oedema. The National Eye Institute estimates that about 1 in 15 people with diabetes will develop it. It can be present with background changes elsewhere, which is why a report that sounds reassuring overall can sit alongside genuinely blurred central vision, and why maculopathy is graded separately from the retinopathy stage.
The formal definition is geographical rather than symptomatic: retinal thickening within 500 micrometres of the centre of the fovea, hard exudates within that distance with adjacent thickening, or an area of thickening one disc diameter or larger with any part of it within one disc diameter of the foveal centre. The practical distinction your ophthalmologist will make is whether the swelling involves the centre of the macula or not, because that decides the treatment. The NHS notes that diabetic maculopathy has no symptoms in its early stages and does not affect vision at first, which is the same argument for screening in a different place.
05
What treatments exist, and what is each one for?
Three things, aimed at three different problems. Injections of anti-VEGF medication into the eye are the first-line treatment for macular oedema that involves the centre of the macula; they work against the signal that makes vessels leak and grow, and the National Eye Institute describes them as able to slow diabetic retinopathy down. Laser comes in two forms. Focal or grid laser is the primary treatment for macular oedema that does not involve the centre. Panretinal photocoagulation, which treats the peripheral retina in many small burns, is the standard for high-risk proliferative retinopathy without macular oedema, and is combined with anti-VEGF when both are present.
Vitrectomy is surgery, and it is for what happens after. Its indications include a vitreous haemorrhage that is not clearing on its own, tractional retinal detachment where scar tissue has pulled the macula off, a combined tractional and tear-related detachment, and thick membranes pulling on the macula. Steroid implants in the eye are held back for macular oedema that has not responded to repeated anti-VEGF injections. None of these restore what has already been lost, which is the reason they are all described as treatments to protect remaining sight. Every dose and interval here is the one your ophthalmologist sets.
06
What actually slows it down?
Five things, and they are the same five your diabetes review already measures. Duration of diabetes is the factor nobody can change, and risk rises directly with it. The modifiable ones, in the order clinical reviews list them, are glycaemic control, blood pressure, lipids, kidney disease and weight: poor glycaemic control, uncontrolled hypertension, dyslipidaemia, nephropathy and obesity are all described as worsening progression. CDC adds smoking to high blood sugar, blood pressure and cholesterol as a risk factor that speeds it up, and the NHS lists managing blood glucose, blood pressure and cholesterol, not smoking, and attending every screening appointment as what reduces risk.
That makes retinopathy a whole-body reading rather than an eye problem. HbA1c is the number most directly tied to it, and our separate page on HbA1c explains what a given value represents; fasting and post-meal glucose describe the swings behind that average. Kidney involvement matters twice over, because nephropathy is itself listed as worsening retinopathy, which is why urine albumin-to-creatinine ratio, creatinine and eGFR belong in the same conversation as the eye report. LDL cholesterol and triglycerides carry the lipid half. None of this is a promise that good numbers prevent retinopathy, and some people develop it with reasonable control. It shifts the odds, and it is what is within reach.
07
Which symptoms mean do not wait for the next appointment?
Anything sudden. CDC's list of changes that mean calling your eye doctor is blurring, spots, flashes, blind spots, distortion, and difficulty reading or doing detail work. The NHS advises asking for an urgent appointment or getting help from its 111 service if you have diabetes and your eyesight suddenly gets worse or you get blurred vision. Dark floating spots or streaks that look like cobwebs are the National Eye Institute's description of bleeding into the jelly of the eye, and it advises getting treatment right away rather than watching them.
One pattern outranks the rest. A sudden shower of floaters or flashes of light, or a dark curtain or shadow moving across your vision, is how a detached retina presents, and the NHS says that needs to be treated quickly to stop it permanently affecting sight. In an eye with proliferative retinopathy, that curtain is the complication the whole grading ladder exists to prevent. Sudden loss of vision in one eye, and a painful red eye with blurred vision, belong in the same tonight category rather than in a clinic queue. Gradual worsening over months is still worth reporting, but it is a different conversation from these.
Diabetes and your eyes: what to do, and how fast
Routine — see a doctor
Book the screening exam you are due even though you can see perfectly well - a retinal photograph or dilated exam at diagnosis and yearly for type 2 diabetes, from five years after onset and yearly for type 1, and every one or two years under a national screening programme. Early retinopathy has no symptoms, so a normal reading experience is not evidence. Take the same appointment seriously if your last report said background or mild changes, since that grade is a reason for closer follow-up rather than reassurance. Eyesight that has worsened slowly over months, floaters you have had for a long time that have not changed, or difficulty seeing in low light should be checked by your doctor, diabetes team or an optician, and are worth mentioning even if screening was recently normal. Anything that arrived suddenly - a shower of floaters, flashes of light, a curtain or shadow - is not this row. It is the emergency row.
Same-day — call promptly
Changes that have come on over days or weeks, not minutes. Contact your eye doctor or diabetes team today if your vision has become blurred, if straight lines look bent or distorted, if there are new blind spots or patches missing from your vision, if reading or close work has gradually become harder, or if you have noticed new spots in your vision that came on slowly. Anything sudden belongs in the row below, tonight. Pregnancy is its own same-day reason: anyone with diabetes who becomes pregnant should have a dilated eye exam as soon as possible, because retinopathy can progress quickly during those months. If you have been told you have proliferative retinopathy or macular oedema and have missed injections or laser appointments, treat rebooking as urgent rather than routine.
Emergency — act now
Get eye care tonight, at an emergency eye department, for sudden loss of vision in one or both eyes, vision in one eye that has suddenly blurred or dimmed, a dark curtain or shadow moving across your vision, a sudden shower of floaters or a sudden increase in their number, repeated flashes of light, or a painful red eye with blurred vision. A curtain or a sudden storm of floaters can mean the retina has detached or has bled, and a detached retina has to be treated quickly to stop it permanently affecting sight. In an eye that already has proliferative diabetic retinopathy these are the expected complications, not unlikely ones. Do not wait for the scheduled appointment, and do not wait to see whether vision returns by morning.
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