Diabetes and Visual Loss
Diabetes is the leading cause of blindness in Americans age 20-64. Diabetes causes visual loss through its damaging effects on the retina. Diabetes damages the retina by damaging the tiny microscopic blood vessels (capillaries) that supply the blood flow to the retina. The longer you have diabetes, and the higher your average blood sugar, the greater the chance that vision-threatening damage may occur. Over 90% of patients who are diabetic for 15 years will develop at least some retinopathy.
Although diabetes is a major cause of blindness, it is mostly preventable. No matter what level of diabetic retinopathy a person has, it is critical to maintain as normal of blood sugar, blood pressure and cholesterol levels as possible to prevent further disease progression. Even small dietary and exercise changes made early in the course of diabetes can result in great long-term "dividends" in preventing diabetic retinopathy. But even if retinopathy develops, early detection and treatment can often help patients maintain good to excellent vision.
Background Diabetic Retinopathy
The initial stage of diabetic damage to the retina is generally mild and is called background diabetic retinopathy. It has also been called non-proliferative retinopathy and the damage is limited to within the retina itself. Patients are often asymptomatic, but may have decreased or fluctuating vision. A dilated eye exam may reveal hard exudates, intraretinal hemorrhages, microaneurysms (MA), and other vascular abnormalities. Cotton wool spots, dot and blot hemorrhages, posterior subcapsular cataracts, and myopic shifts (from fluctuating blood sugar) are common. At the initial appearance of retinopathy, the need for more frequent eye examinations and better blood sugar control are emphasized because this can progress to more serious disease.
Clinically Significant Diabetic Macular Edema (CSDME)
The macula is the part of the retina that provides us with our sharp central visual acuity and is a major focus of vision-threatening damage due to diabetes. As diabetes creates damage in the capillaries of the macula, those blood vessels can begin to leak. This leakage into the retina causes the macula to swell, compromising its function and causing vision to decrease. This is called diabetic macular edema. This swelling can be slowly but relentlessly progressive, causing a slow but relentless blurring of vision. Sometimes the blurring is very mild but will typically grow progressively worse as time goes on.
Although diabetic macular edema does not usually result in complete blindness, it can potentially cause a severe loss of the central vision. Once diabetic macular edema has caused the vision to blur, the lost vision usually cannot be restored. This is why all diabetic patients should be monitored with periodic dilated examinations, with particular attention to the retina, to identify the development of macular edema before it results in significant visual blurring.
Laser Treatment for CSDME
The only proven effective treatment for diabetic macular edema is laser photocoagulation. Laser treatment is not recommended until the individual develops clinically significant diabetic macular edema (CSME or CSDME)." This means that the edema is becoming significant enough to either cause or threaten to cause visual blurring.
Laser treatment of diabetic macular edema is painless. It is unknown exactly how the laser works. It is felt that light laser spots help stimulate the retina to repair the vessel walls. If the leakage can be stopped by the laser treatment, the retinal swelling will often go away. More than one laser treatment may be necessary to stop the leakage, especially if the initial swelling is severe. If the leakage stops and the swelling resolves, the vision will often stabilize. Because the laser stimulates capillary repair, noticeable results often take 3-4 months.
Laser treatment does not cure the disease. Even after initially successful laser treatment, the underlying diabetic disease continues, more blood vessel damage can develop, and macular edema can recur in the future. If this occurs, laser treatment can usually be repeated. This typically is not considered until 3-4 months after the initial procedure.
Laser treatment can decrease but not eliminate the chances of developing visual loss due to diabetic macular edema. Some people will lose vision despite timely and appropriate laser treatment.
Possible Side Effects of Laser Treatment for CSDME
Occasionally, one may notice stationary, small spots in the vision of the treated eye following the laser treatment. These spots are usually off to one side from the center vision but occasionally may be close to central fixation. If one notices these spots, they will often fade and go away as time goes on. Occasionally, the spots will persist.
Rarely, patient movement during the laser treatment may result in a laser spot being placed in the center of the macula. This can potentially cause a decrease in central visual acuity. If the patient has difficulty maintaining steady fixation with the eye, so as to make laser treatment potentially hazardous, the eye may need to be anesthetized to allow the treatment to be performed safely.
The major cause of visual loss following laser treatment of diabetic macular edema is failure of the edema to respond to the laser treatment or progression of the disease despite laser treatment. Other forms of treatment, such as an intraocular injection of a steroid (kenalog), or surgery (vitrectomy), may be appropriate if the edema does not respond to laser.
Intravitreal Steroids (Kenalog) for CSDME
Although intravitreal triamcinolone acetate has not been proven to be effective in a large randomized trial, they have been a valuable addition to the treatment regimen for diabetic macular edema. Laser treatment is not always successful in stabilizing vision, especially when the edema is centrally located or very severe. In these cases, an injection directly into the vitreous cavity can give a long-acting medication (90 days on average) to help reduce the edema. This procedure is painless and takes approximately 15-20 minutes from start to finish. It may be repeated in severe cases and may be combined with laser for an optimal result. The two most common ocular side effects are cataract progression and glaucoma so patients are followed monthly for 3-4 months.
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