Diabetes causes visual loss through its damaging effects on the retina due to its damaging effect on the tiny microscopic blood vessels (capillaries) that supply blood flow to the retina.
The longer you have diabetes and the higher your average blood sugar reading, the greater the chance that vision-threatening damage may occur. Over 90% of patients who are diabetic for 15 years or more will develop at least some level of retinopathy.
All diabetic patients should be monitored with periodic dilated examinations, with particular attention to the retina, in order to identify the development of abnormal blood vessel growth and macular edema at the earliest possible stage before it results in significant visual blurring.
At the initial appearance of retinopathy, the need for more frequent eye examinations and better blood sugar control are emphasized as lack of treatment and awareness can progress to a more serious disease.
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.
There are different levels of diabetic retinopathy. These include:
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 (discharge within the eye)
- Intraretinal hemorrhages
- Microaneurysms (MA)
- Other vascular abnormalities
Cotton wool spots, dot and blot hemorrhages, cataracts, and shifting vision (from fluctuating blood sugar) are common.
The macula is the part of the retina that provides us with our sharp central visual acuity (visual clarity) and is a major focus of vision-threatening damage due to diabetes.
As diabetes creates damage in the capillaries of the macula, 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 slow but relentlessly progressive in blurring patient’s vision. Sometimes the blurring is mild but will typically grow progressively worse over time.
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 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 various 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.
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 vision.
Treatment options for diabetic retinopathy include:
- Laser Photocoagulation
- Intravitreal Steroids
- Cryopexy (Freezing)
- Avastin (for severe cases)
- Laser Photocoagulation
- For CSDME Treatment
- For PDR Treatment
- Intravitreal Steroids (Kenalog)
- Cryopexy (Freezing)
The only proven effective treatment for diabetic macular edema and proliferative diabetic retinopathy is laser photocoagulation. Laser treatment is not recommended until the individual develops clinically significant diabetic macular edema (CSME or CSDME) or the development abnormal blood vessels with vitreous hemorrhage. This means that the retinopathy is becoming significant enough to either cause or threaten to cause visual blurring.
- More than one laser treatment may be necessary to stop the leakage, especially if the initial swelling is severe.
- 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.
The laser treatment is painless and is believed to help stimulate the retina to repair vessel walls, which can cause retinal swelling to reduce or even go away and lead to stabilized vision.
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.
Possible Side Effects
- Stationary, small spots in the vision of the treated eye following the laser treatment. If one notices these spots, they will often fade and go away as time goes on.
- 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.
- A decrease in peripheral, near and night vision may occur.
- As long as abnormal blood vessels remain in the eye, hemorrhage can still occur and scar tissue may develop.
The major cause of visual loss following laser treatment of diabetic macular edema or proliferative diabetic retinopathy is failure of the retina 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 eye does not respond to laser.
This treatment is commonly used to treat macular edema alongside laser treatment. Although intravitreal triamcinolone acetate has not been proven to be effective in a large randomized trial, it is 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.
This treatment is commonly used to treat PDR alongside laser treatment.
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.
This treatment is commonly used to treat 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.