Diabetic retinopathy

Blurry Vision and Other Symptoms of Diabetes

Blurry vision is a common symptom of diabetes.  Other diabetic symptoms include excessive thirst, frequent urination, weight loss and fatigue.  Most of the symptoms are due to the lack of insulin which secondarily allows the sugar levels to sky rocket out of control.  This sets up sugar gradients that cause imbalances in water distribution in the body and in different organs.

One note, the blurry vision as a symptom of diabetes is not caused by the same mechanism as blurry vision from diabetic retinopathy.

“Osmolarity” – Water Follows Sugar

The fancy term for this concept is “osmolarity.”  One way to think of osmolarity is that sugar attracts water, or, water goes where the sugar goes.

Insulin Takes Sugar From the Blood and Delivers it to Your Cells

When we eat, food is broken down and absorbed into the bloodstream.  The sugars, the little energy units that serve as fuel for our cells, can not get into the cells without insulin.  Stated another way, insulin lowers blood sugar.

When the supply of insulin is insufficient, as in diabetes, sugar levels in the blood rise.  Remember the law of osmolarity, if the sugar stays in the blood, it draws water out and away from your cells and into the bloodstream.

Your body becomes dehydrated as the water is drawn into the blood stream.  This is a relative increase in the fluid volume of the blood, the kidneys then make more…urine.  The relative dehydration also explains the excessive thirst.

The frequent urination, and especially, frequent urination at night, are very common symptoms of diabetes.  Since the high sugar levels are constantly drawing water out from the cells, the body is constantly dehydrated causing extreme thirst.

Weight Loss

There are two reasons for the weight loss.  One cause is the loss of  water weight caused by the frequent urination.  This is similar to a wrestler trying to “make weight” by becoming dehydrated.  The second reason for weigh loss is the loss of body fat and muscle.

The body uses sugars, fat and then muscle, in that order, for energy sources.  If there is insufficient insulin, sugar can not be utilized as an energy source and the body then starts to burn fat and muscle, ergo, you lose weight.

Blurry Vision

This explanation is a bit more involved, but bare with me.

Sugar enters the natural lens in the eye.  Sugars are changed to “sorbitol” inside the lens.  Sorbitol can not exit the lens as easy as sugar, but sorbitol, too,  like sugar, attracts water.

The end result?  The lens takes on water and changes it’s focusing powers …causing blurry vision.  Again, this is distinct from the vision changes associated with diabetic retinopathy, a separate problem.

Correcting Blood Sugar

Taking insuling or oral medications causes the blood sugar to decrease.  The cells of your body can now retain water, the dehydration ceases and the excessive thirst and frequent urination disappear.

Sugar can now be metabolized by the cells, preserving fat and muscle, and the weight loss and energy returns.

As the sorbitol decreases in the lens, the relative water content decreases, and the  normal focusing power of the lens returns…vision improves!  This is why diabetics should only get examined for glasses when the sugar is at usual levels and controlled.

What Does This Mean?  There are two types of vision “loss” from diabetes.  The blurry vision as a symptom is temporary and reversible.  The second may develop long after the diagnosis if diabetes is made.  Vision loss, the principle “focus” of this blog, from diabetic retinopathy is less reversible and is a result of a disease rather than a symptom.

So, blurry vision may be a sign of high sugar.  If diabetic, you may develop the disease, diabetic retinopathy.

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Diabetic retinopathy Testing

Thirst, Frequency and Blurry Vision……Early Signs of Diabetes?

Excessive thirst, increased urinary frequency and blurry vision can all be early signs of undetected diabetes mellitus.

What you already know.  Diabetes mellitus is the body’s inability to decrease the sugar in the blood.  This “serum glucose” rises after every meal as our food is broken down into its basic components.  In the normal situation, a rise in blood sugar causes insulin to be secreted into the blood stream.  Insulin takes blood sugar out of the blood and delivers it to our tissues.  As a result, serum glucose levels are kept low and maintained at a steady state.  If  insufficient insulin or no insulin is produced, then the sugar remains in the blood stream and the sugar level rises.

High levels of sugar increase the “osmolarity” of the blood.  Osmolarity is a difficult term to understand, but it reflects the ability of a substance to attract water.  The higher the osmolarity of a liquid, the more water it will attract and retain.  In this case, as the serum glucose increases, it will literally draw water out of our tissues.  We feel thirsty because our tissues are actually dehydrated, hence the increased thirst.  The increased water in our blood then causes more urination.

What causes the blurry vision? Again, it is the high sugar and osmolarity, but with a slight twist.  The high sugar leaks into the eye and then gets absorbed by the natural lens.  The sugar, or glucose, is then changed to sorbitol, another form of sugar.  The sorbitol does not leave the lens very readily and is basically trapped.  Sorbitol, like glucose, also adds to osmolarity.  So, the sorbitol attracts water and causes the lens to swell.  This causes the vision to blur.  Even with correction of sugar, it may take weeks for the lens to return to its more normal state.

Usually, these are the first, early signs of diabetes.  The vision changes are usually not due to diabetic retinopathy at this time as this takes years to develop.

In the end, all three symptoms are based on the same mechanism.  Once the abnormality is identified and sugar returns to normal using either diet, oral agents or insulin, water redistributes normally, our tissues rehydrate and the eye returns to normal.  Vision, too, should return nicely.


Randall V. Wong, M.D.
Ophthalmologist, Retina Specialist

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glargine Insulin Does Not Cause More Diabetic Retinopathy

A five year prospective study reveals that insulin glargine is as safe as NPH insulin with regard to developing diabetic retinopathy. Patients placed on insulin glargine are no more likely to develop diabetic retinopathy than Type II diabetics on NPH insulin.

The study also found that the severity of the diabetic retinopathy was similar in the two groups.

Read the article.


Randall V. Wong, M.D.
Ophthalmologist, Retina Specialist

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