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