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Our most recent book has answers to the 200 most common questions that readers have asked us over the 19 years since this site began. Get it here: Your Diabetes Questions Answered
Retinopathy: Diabetic Blindness
Retinopathy means "sick retina" and it is among the most terrifying of the classic diabetic complications. What happens in retinopathy is that, with continual exposure to high blood sugars, tiny blood vessels start to grow in a disordered and out of control fashion in the retina--the part of the eye where nerves transmit light images to the brain.
Unlike healthy vessels, these diabetic blood vessels have weak walls, and eventually they burst, releasing blood into the eye. Not only that, but if they are left untreated, these overgrown vessels eventually destroy the retina's ability to transmit images to the brain, resulting in permanent blindness.
There are various terms doctors use to refer to retinopathy. One is "proliferative retinopathy" referring to the way that the tiny blood vessels proliferate. Another is "macular edema" referring to swelling in the part of the retina that gives us central vision. Actos (pioglitizone) and Avandia (rosiglitazone) have been found to cause an increase in macular edema which is a major reason they are probably the last drug anyone with diabetes should be taking.
Doctors currently treat retinopathy by using lasers to zap shut bleeding or swollen blood vessels in the eye. This helps retain vision, though it cannot restore vision that has been lost. Over time if blood sugars continue to be high--200 mg/dl (11 mmol/l) or more-- vision will deteriorate despite with this treatment.
Injections of Avastin (bevacizumab) have also been found to improve retinopathy in a small but significant number of those who used it and to retard its progression in more. Details HERE.
The only way to reliably reverse retinopathy (which does not involve sticking needles in your eyeballs) is to get blood sugars down to truly normal levels--not the levels flagged as "good for diabetics."
That is because recent research has found retinopathic changes happening in the eyes of 1 out of ever 12 people diagnosed with prediabetes, so just getting your blood sugars to the mediocre levels most doctors suggest for people with diabetes (well within the prediabetic range) is not enough.
DPPT Data and Pre-Diabetic Retinopathy
You can read more about the evidence that links retinopathy with prediabetic blood sugar levels here: Research Connecting Blood Sugar Level with Organ Damage
You can learn how to bring your blood sugar down to a safe level here: How to Lower Your Blood Sugar.
Getting Better Control Occasionally Will Temporarily Worsen Retinopathy
If you have been running very high blood sugars for a long time, lowering your blood sugars may initially make retinopathy worse, not better. But this does not mean it isn't worth doing. Over time, many studies including the landmark DCCT study have found that those people who experienced worsened retinopathy after lowering their blood sugars ended up with better vision years later than those who did not lower their blood sugar.The damage is done by things that occur while you have the very high high blood sugars and chemicals that develop in your eye in response to these high sugars, it is not caused by correcting them.
This worsening, which is fairly rare, almost always happens to people who are using insulin to lower blood sugar, not diet.
There is no evidence that lowering blood sugars more slowly avoids this kind of worsening.
Here's an excellent review that discusses the published research on this subject:
Diabetic Retinopathy Donald S. Fong, MD, et al. Diabetes Care 27:2540-2553, 2004
From that article:
Patients who developed early worsening as a result of the intensive treatment were similar to or had more favorable outcomes than those in the conventional group who did not have early worsening. Analysis did not suggest reduction of early worsening with more gradual reduction of glycemia.
One thing is certain, as troublesome as temporary worsening might be, if you don't lower your blood sugar, the end results for your vision will much, much worse.
Blurry Vision is NOT a Sign of Retinopathy
On diagnosis many people with Type 2 diabetes report that they have long had problems with blurry vision that comes and goes. When they lower their blood sugar, many will suddenly find that their glasses seem to have stopped working, too.
This kind of visual problem is not caused by retinopathy. It happens because changing blood sugar concentrations change the concentration of sugar in your lens and in the fluids of your eye and this changes your vision, just as if you had changed an eyeglass prescription. This sensitivity to high blood sugars is especially noticeable when you are old enough to need bifocals.
There are no warning symptoms of the kind of retinopathy that causes blindness until you start experiencing eye bleeds, though an ophthalmologist can see early signs of abnormal blood vessel growth in your retina long before the vessels rupture. This is why if you are diagnosed with diabetes you should see an ophthalmologist, not an optometrist, every year for a full dilated eye exam.
If you experience vision changes with blood sugar changes, be sure to measure your blood sugar before you get the optometrist to prescribe lenses for you and make sure your blood sugar is in your target range so that your glasses will continue to work well.
Many people have found it a good idea NOT to get new glasses right after a diabetes diagnosis. Wait until you've lowered their blood sugars to the normal range because glasses prescribed when blood sugars are high are running high will no longer correct vision properly when you have lowered your blood sugar.
Your Retinas Tell You how the Rest of Your Blood Vessels Are Faring.
The retina is the only place where your blood vessels are visible, and their health tells you a lot about the health of the rest of your hidden cardiovascular system. It has also been found that the presence and severity of retinopahty can give insight into your your chances of developing Alzheimers too.
When you see an ophthalmologist (and you should see one, rather than an optometrist, if possible) don't just take his assurances that your eyes are "fine." Insist on getting an answer to the question, "Do you see any signs of early retinopathy." If you do, ask to have retinal photos taken to document the extent of it, as this will make it possible going forward to learn how well your efforts are working at stopping or reversing the damage.
https://newsroom.uw.edu/news/eye-conditions-provide-new-lens-screening-alzheimer’s