Diabetic retinopathy, the leading cause of new cases of blindness in the United States, develops more rapidly in patients with Type 1 diabetes than in those with Type 2 diabetes. You’re likely to encounter diabetic retinopathy because about 50% of patients have some degree of the disease after they’ve had diabetes for 10 years. And after having diabetes for 15 years, about 80% of patients have diabetic retinopathy. However, your patient can have diabetic retinopathy and still have unimpaired vision.

Although the underlying cause of diabetic retinopathy isn’t fully understood, chronic hyperglycemia, blood platelet abnormalities, and blood vessel narrowing are thought to cause retinal capillary damage. The disease usually occurs in both eyes, but the severity may differ in each eye. Diabetic retinopathy is classified by stage as non proliferative, preproliferative, or proliferative.

You’ll see nonproliferative (or background) retinopathy more commonly than any other stage of the disease. In this stage, the retinal capillaries undergo several changes that impair their ability to transport essential oxygen and nutrients to the retina . This is what happens: The retinal capillary walls thicken, and capillary fluid leaks through them into the interstitial spaces, causing retinal edema. Eventually, this fluid forms thick yellow deposits, or hard exudates, which can be seen on ophthalmoscopic examination. Also, the retinal capillaries begin to become occluded, and microaneurysms form in the capillary walls. All of these changes cause the capillary walls to bleed easily, resulting in blot hemorrhages in the retina, which are visible on ophthalmoscopic examination.

If the micro aneurysms leak into or near the macular area of the retina, macular edema may result. This may cause blurred vision because the macula is the part of the retina that provides the most acute vision. Macular edema, which can occur at any stage of retinopathy, is the most common cause of decreased vision in nonproliferative retinopathy.

Preproliferative retinopathy involves further deterioration and obstruction of the retinal capillaries. Poor capillary perfusion may lead to retinal ischemia and infarction. More hemorrhages occur during this stage, but patients may have no symptoms.

Proliferative retinopathy, the most severe stage of diabetic retinopathy, involves the retina and vitreous cavity. As retinal capillaries become occluded, new blood vessels form to supply blood to the retina (a process called neovascularization). Over time, these new capillaries become fibrous and rupture easily, producing bleeding into the vitreous humor and contraction of the vitreous cavity wall. When blood enters the vitreous humor, light can’t reach the retina. Your patient may report seeing red or black spots or lines.

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The new fibrous tissue may stick to the cell layer surrounding the vitreous humor. Then the contraction of the fibrous tissue may pull on the vitreous cell layer and the retina, causing your patient to develop tractional retinal detachment. And if the macula is involved, she’ll have a complete vision loss.

Inside The Eye

This cross section shows you the internal structures of the eye. The sclera-the white, opaque outside coat of the eye-helps maintain the eye’s shape. The transparent cornea-the anterior, avascular portion of the sclerapermits light to enter the eye. The cornea lies over the pupil and the iris, the colored part of the eye. The aqueous humor, a clear liquid, fills the anterior chamber. The canal of Schlemm, a ring-shaped venous sinus located at the base of the cornea, drains the aqueous humor away from the anterior chamber and into the blood-stream. The avascular lens refracts and focuses images onto the retina.

The choroid, or middle coat, is made up of many arteries and veins. The retina, the innermost coat of the eyeball, is rich in neurons, including the rods and cones, which serve as visual receptors. The retina is connected to the optic nerve, which conducts visual information to the brain. The vitreous humor-a thick, gelatinous material-fills the space behind the lens. It maintains the shape of the eye­ball and placement of the retina.

Filed under: Chronic Complications