Diabetic Retinopathy
Diabetes Mellitus
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.
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.
Proliferative Diabetic Retinopathy
As the damage to the capillaries becomes worse, the retina does not get adequate blood flow. Because it is not getting enough blood flow, the eye stimulates the growth of new blood vessels in an attempt to increase the blood flow to the retina. Vascular endothelial growth factor (VEGF) is believed to play a prominent role in this process. The new blood vessels that grow are abnormal, however, and do not supply additional blood flow to the retina. The blood vessels grow from the surface of the retina rather than within the retina. The blood vessels can result in the development of multiple vision-threatening problems within the eye.
These blood vessels are abnormally leaky and have a great tendency to bleed (hemorrhage) within the eye. It is possible for a person with diabetes to have extensive blood vessel damage and extensive growth of abnormal new blood vessels in the eye before they notice any change in vision. Hemorrhage from the abnormal blood vessels can occur at any time, and can be mild or severe. If the hemorrhage is severe, the vision can be severely affected.
The growth of abnormal blood vessels is also associated with the development of fibrous or scar tissue on the retina. This fibrous or scar tissue can pull on the retina and create distortion of the retina or even retinal detachment which can severely affect the vision. The natural history of proliferative diabetic retinopathy is that the abnormal blood vessels and scar tissue will grow progressively worse and may eventually completely blind the eye.
All diabetic patients should be monitored with periodic dilated eye examinations, with particular attention to the retina, to identify the development of any evidence of abnormal blood vessel growth at the earliest possible stage.
Laser Treatment for PDR
The primary treatment for abnormal blood vessel growth in proliferative diabetic retinopathy is laser photocoagulation. Laser treatment is recommended either when the individual has developed abnormal blood vessel growth with a vitreous hemorrhage, or in some individuals who develop extensive abnormal blood vessel growth. The laser is applied in a “panretinal pattern” throughout the periphery of the retina. Because of the amount of treatment required, we often anesthetize the eye with an injection, or in some cases, the patient can be put under general anesthesia.
The purpose of laser treatment is to try to get the abnormal vessels to shrink or regress. Anywhere from 1000 to 1500 laser “spots” are applied to the retinal periphery. We generally combine this with cryopexy treatment in a single session. In some individuals, additional laser treatments may be necessary to attempt to control the proliferative diabetic retinopathy.
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 abnormal blood vessel growth can recur in the future. If this occurs, laser treatment can usually be repeated, or vitrectomy surgery can be performed. Laser treatment can decrease but not eliminate the chances of developing visual loss due to proliferative diabetic retinopathy.
Some people will lose vision despite timely and appropriate laser treatment. In people who develop severe hemorrhage or retinal detachment due to the blood vessel growth, laser treatment alone may not be effective, and vitrectomy surgery may be necessary to save vision.
Possible Side Effects of Laser Treatment
Diabetic macular edema can occasionally develop or grow worse soon following panretinal laser treatment. This can cause the central vision to blur. In many patients this will resolve with observation, but some will require an injection of steroid to decrease the edema.
Some people will notice a decrease in their peripheral vision, their night vision, or their dark adaptation following laser treatment.
Some people may notice trouble focusing with their near vision following laser treatment, and occasionally, the pupil may remain partially dilated following laser treatment.
As long as any abnormal blood vessels remain in the eye, hemorrhage can still occur.
As the laser treatment is causing the abnormal blood vessels to go away, occasionally the associated scar tissue can grow worse and still place traction on the retina or even cause retinal detachment.
The major cause of visual loss following laser treatment of proliferative diabetic retinopathy is failure of the retinopathy to respond to the laser treatment adequately or progression of the disease despite laser treatment.
The above side effects do not occur in all individuals, and many individuals notice none of the above side effects. Once you have developed proliferative diabetic retinopathy, your chances of losing vision are much greater without treatment than with treatment.
Cryopexy (Freezing) for PDR
Cryopexy is another way to cause peripheral retinal destruction to decrease the production of VEGF and other growth factors responsible for PDR. It is applied to the sclera (white part of eye) to the peripheral retina where it is difficult to treat with laser. We often combine this treatment with laser PRP to have a better total effect, as this can treat more peripherally without the need for perfect visualization.
Avastin for Severe PDR
Avastin is an anti-cancer drug which binds to and inactivates VEGF. Because this is found in elevated levels in patients with proliferative diabetic retinopathy, it is occasionally used in the treatment of PDR. Since this is an off-label use of the drug and is not consistently covered by insurance, only some patients will elect this treatment. For now, it is probably best given in additional to standard therapy or when standard therapy fails.
Conclusions
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.
