How Does Diabetes Affect the Eye?
Underlying all bodily harm from diabetes is the fact that elevated blood sugar causes blood vessel damage. Fine blood vessels in critical organs such as the eyeball are particularly vulnerable. Over time, these vessels become leaky, bleed, and unable to transmit blood and oxygen to the tissues they serve.
In the retina, tiny vessels are critical to supporting the robust metabolism that is required to create vision. As the walls of these vessels become less water-tight (think of an old, leaky hose), fluid can escape and accumulate within in the layers of the retina. This leads to swelling and distortion of the retinal layers in the center of the vision, a condition called diabetic macular edema (DME). Diabetic macular edema is the leading cause of vision loss in diabetics.
As years of poor blood sugar control take their toll, the retinal blood vessels lose the ability to provide adequate oxygen to the eye. In this ‘oxygen-starved’ state, the eye begins releasing chemical signals to stimulate new blood vessel growth. The most important of these signals is called vascular endothelial growth factor (VEGF).
In response to elevated VEGF, the retina begins to grow new blood vessels, also known as neovascularization. The presence of neovascularization marks the most advanced stage of diabetic eye disease, called proliferative diabetic retinopathy. Unfortunately, these new vessels grow in an uncoordinated fashion, pulling and disrupting the retina’s delicate structure. The vessels also bleed spontaneously, causing rapid onset of dark floaters and loss of vision. Eventually, the new blood vessels pull and detach the retina, leading to severe and permanent vision loss.
What Are the Symptoms of Diabetes in the Eye?
The most common initial symptom of diabetic retinopathy is painless blurry vision in one or both eyes. Be careful to test one eye at a time because sometimes the stronger eye will cover for the weaker one. Occasionally, a diabetic may experience the sudden onset of floaters, which represents bleeding in the jelly that fills the eye. Rarely, elevated pressure and pain may occur in advanced cases.
Diabetic changes in the eye can be asymptomatic for a long time. Asymptomatic does not mean all is well, however. Too many patients wait until after they get symptoms to see an eye doctor. By that time, some of their vision may be permanently lost regardless of treatment.
I have diabetes. Should I see an ophthalmologist?
The American Academy of Ophthalmology recommends that adult diabetics should receive a dilated examination by an eye doctor every year. These examinations will be looking for signs of blood vessel damage, growth of new blood vessels, or swelling of the retina that threatens vision. Many of these changes can be asymptomatic initially but lead to bigger problems if they are not identified early.