Diabetic Retinopathy

About 40 percent of people with diabetes will have at least mild retinopathy. Incidence increases with the disease's duration and when there is inconsistent control of blood glucose. Retinopathy is characterized by leakage of fluid or blood from vessels in the retina. It usually appears in stages:

1. mild background retinopathy, also known as non-proliferative diabetic retinopathy, which has few warning symptoms;
2. macular edema (fluid), which causes blurred vision and reduced sensitivity to color;
3. severe proliferative diabetic retinopathy, where leaking blood vessels, which already have caused visual damage, form scar tissue between the retina and the vitreous. This tissue may contract and, eventually, detach the retina. Once the retina is detached, reattaching it requires a lengthy surgical procedure (vitrectomy) involving the retina and vitreous bands. The surgery is not always successful, depending on the amount of scar tissue. Retinal detachment, therefore, may result in severe vision loss, or even blindness.

Retinopathy causes blurred or hazy vision, particularly if there are retinal hemorrhages or edema (swelling) of the macula.

Although the presence of retinopathy can be detected by looking into the eye, details are best identified by injecting a fluorescent dye into the bloodstream.

This allows the ophthalmologist to photograph and evaluate the retinal blood vessels, and to pinpoint areas that are leaking due to neovascularization (growth of fragile new blood vessels).

If such areas are found in the peripheral retina, laser treatment (panretinal photocoagulation) is recommended to seal off leaking vessels and destroy abnormal ones. If there is macular edema, scattered laser treatment in the macula may be recommended. In some cases, early treatment may restore vision, stabilize it or, at least, delay severe loss of sight.

Vitreous Hemorrhage

One of the complications of diabetic retinopathy is hemorrhage from fragile blood vessels leaking into the vitreous, the clear gel-like substance that fills the interior of the eye. If blood clouds the vitreous, light passing from the lens through the vitreous to the retina is blocked, and vision is markedly reduced. Blood can gradually clear up over several months, but if it does not, surgical removal of the vitreous, called vitrectomy, can be performed. Specialists in vitreo-retinal surgery can remove blood and scar tissue from the eye and replace the vitreous with a clear solution. This may result in useful, though reduced, vision.

Cataract

Diabetes increases the possibility of cataract, a clouding of the transparent lens of the eye. Cataract may cause hazy vision and glare sensitivity. If retinopathy has not damaged the retina, surgical removal of a cataract usually results in improved vision. If there is damage to the retina, the cataract may still be removed in order to improve the ophthalmologist's view of the retina. This makes it easier to evaluate the condition of the eye prior to laser treatment. When a person with diabetes has a cataract operation, standard surgical techniques are used.

Secondary Glaucoma

Fragile new blood vessels in the eye of someone with diabetes may form a new network directly on the iris, blocking the outflow of fluid from the eye. This condition, called secondary glaucoma, results in elevated pressure of the fluids within the eye, and can cause optic nerve atrophy and loss of the full visual field. Treatment involves the application of laser to the leaking areas. Standard glaucoma treatment with drops or diuretics may also be recommended to lower intraocular pressure.

Macular Damage

In chronic macular edema, faulty color vision may result and usually is irreversible. Even after the macula has been treated with laser, there may still be problems reading because of distortion. Low vision magnifying devices may be needed.

Changes in Refraction

High blood glucose levels that are characteristic of poorly controlled diabetes can also result in changes in refraction (the accurate focus of light rays on the retina). This is due to swelling of the lens, which causes myopia (near-sightedness). Before such transient refractive changes are corrected by standard prescription eyeglasses, improved control of blood glucose should be attempted. Glasses should be prescribed only after blood glucose has stabilized, or consecutive examinations reveal consistent refractions.