Diabetic retinopathy

Diabetic retinopathy is retinopathy (damage to the retina) caused by complications of diabetes mellitus, which can eventually lead to blindness. It is an ocular manifestation of systemic disease which affects up to 80% of all patients who have had diabetes for 10 years or more^[1]. Despite these intimidating statistics, research indicates that at least 90% of these new cases could be reduced if there was proper and vigilant treatment and monitoring of the eyes.

Normal vision. Courtesy NIH National Eye Institute

The same view with diabetic retinopathy.

Signs and symptoms

Diabetic retinopathy often has no early warning signs. Even macular edema, which may cause vision loss more rapidly, may not have any warning signs for some time. In general, however, a person with macular edema is likely to have blurred vision, making it hard to do things like read or drive. In some cases, the vision will get better or worse during the day.

As new blood vessels form at the back of the eye as a part of proliferative diabetic retinopathy (PDR), they can bleed (hemorrhage) and blur vision. The first time this happens, it may not be very severe. In most cases, it will leave just a few specks of blood, or spots, floating in a person's visual field, though the spots often go away after a few hours.

These spots are often followed within a few days or weeks by a much greater leakage of blood, which blurs vision. In extreme cases, a person will only be able to tell light from dark in that eye. It may take the blood anywhere from a few days to months or even years to clear from the inside of the eye, and in some cases the blood will not clear. These types of large hemorrhages tend to happen more than once, often during sleep.

On fundoscopic exam, a doctor will see cotton-wool spots, flame hemorrhages, and dot-blot hemorrhages.

Pathogenesis

Diabetic retinopathy is the result of microvascular retinal changes. Hyperglycemia-induced pericyte death and thickening of the basement membrane lead to incompetence of the vascular walls. These damages change the formation of the blood-retinal barrier and also make the retinal blood vessels become more permeable.^[2]

Small blood vessels – such as those in the eye – are especially vulnerable to poor blood sugar (blood glucose) control. An overaccumulation of glucose and/or fructose damages the tiny blood vessels in the retina. During the initial stage, called nonproliferative diabetic retinopathy (NPDR), most people do not notice any change in their vision.

Some people develop a condition called macular edema. It occurs when the damaged blood vessels leak fluid and lipids onto the macula, the part of the retina that lets us see detail. The fluid makes the macula swell, which blurs vision.

As the disease progresses, severe nonproliferative diabetic retinopathy enters an advanced, or proliferative, stage. The lack of oxygen in the retina causes fragile, new, blood vessels to grow along the retina and in the clear, gel-like vitreous humour that fills the inside of the eye. Without timely treatment, these new blood vessels can bleed, cloud vision, and destroy the retina. Fibrovascular proliferation can also cause tractional retinal detachment. The new blood vessels can also grow into the angle of the anterior chamber of the eye and cause neovascular glaucoma. Nonproliferative diabetic retinopathy shows up as cotton wool spots, or microvascular abnormalities or as superficial retinal hemorrhages. Even so, the advanced proliferative diabetic retinopathy (PDR) can remain asymptomatic for a very long time, and so should be monitored closely with regular checkups.

Risk factors

All people with diabetes mellitus are at risk – those with Type I diabetes (juvenile onset) and those with Type II diabetes (adult onset). The longer a person has diabetes, the higher the risk of developing some ocular problem. Between 40 to 45 percent of Americans diagnosed with diabetes have some stage of diabetic retinopathy. ^[3] After 20 years of diabetes, nearly all patients with type 1 diabetes and >60% of patients with type 2 diabetes have some degree of retinopathy.^[4]

Prior studies had also assumed a clear glycemic threshold between people at high and low risk of diabetic retinopathy.^{[5] [6]} However, it has been shown that the widely accepted WHO and American Diabetes Association diagnostic cutoff for diabetes of a fasting plasma glucose ≥ 7.0 mmol/l (126 mg/dl) does not accurately identify diabetic retinopathy among patients.^[7] The cohort study included a multi-ethnic, cross-sectional adult population sample in the US, as well as two cross-sectional adult populations in Australia. For the US-based component of the study, the sensitivity was 34.7% and specificity was 86.6%. For patients at similar risk to those in this study (15.8% had diabetic retinopathy), this leads to a positive predictive value of 32.7% and negative predictive value of 87.6%.

Published rates vary between trials, the proposed explanation being differences in study methods and reporting of prevalence rather than incidence values.^[8]

During pregnancy, diabetic retinopathy may also be a problem for women with diabetes. It is recommended that all pregnant women with diabetes have dilated eye examinations each trimester to protect their vision.

Diagnosis

Diabetic retinopathy is detected during an eye examination that includes:

• Visual acuity test: This test uses an eye chart to measure how well a person sees at various distances (i.e., visual acuity).
• Pupil dilation: The eye care professional places drops into the eye to widen the pupil. This allows him or her to see more of the retina and look for signs of diabetic retinopathy. After the examination, close-up vision may remain blurred for several hours.
• Ophthalmoscopy: This is an examination of the retina in which the eye care professional: (1) looks through a device with a special magnifying lens that provides a narrow view of the retina, or (2) wearing a headset with a bright light, looks through a special magnifying glass and gains a wide view of the retina. Note that hand-held ophthalmoscopy is insufficient to rule out significant and treatable diabetic retinopathy.
• Optical coherence tomography (OCT): This is an optical imaging modality based upon interference, and analogous to ultrasound. It produces cross-sectional images of the retina (B-scans) which can be used to measure the thickness of the retina and to resolve its major layers, allowing the observation of swelling and or leakage.
• Digital Retinal Screening Programs: Systematic programs for the early detection of eye disease including diabetic retinopathy are becoming more common, such as in the UK, where all people with diabetes mellitus are offered retinal screening at least annually. This involves digital image capture and transmission of the images to a digital reading center for evaluation and treatment referral. See Vanderbilt Ophthalmic Imaging Center [1] and the English National Screening Programme for Diabetic Retinopathy [2]
• Slit Lamp Biomicroscopy Retinal Screening Programs: Systematic programs for the early detection of diabetic retinopathy using slit-lamp biomicroscopy. These exist either as a standalone scheme or as part of the Digital program (above) where the digital photograph was considered to lack enough clarity for detection and/or diagnosis of any retinal abnormality.

Of the 18 million to 20 million diabetics in the United States, only about half receive annual eye examinations for retinopathy risk. In an effort to increase diabetic patient’s compliance for regular eye exams, Digital Healthcare, a Wake Forest, NC company specializing in retinal risk assessment, has announced the introduction of Retasure, a new retinal imaging risk assessment solution that connects primary care physicians with ophthalmic specialists to perform retinal imaging.

Retasure allows primary care physicians to capture digital images of diabetic patients’ retinas in a non-invasive procedure that takes just a few minutes. The images are then transmitted over a secure, HIPAA compliant network to a board certified ophthalmologist at an accredited reading center for examination. Results are returned to the primary care physician within 72 hours.

Retasure has been available throughout Europe, and more than one million people have benefited from the system annually.

The eye care professional will look at the retina for early signs of the disease, such as: (1) leaking blood vessels, (2) retinal swelling, such as macular edema, (3) pale, fatty deposits on the retina (exudates) – signs of leaking blood vessels, (4) damaged nerve tissue (neuropathy), and (5) any changes in the blood vessels.

Should the doctor suspect macular edema, he or she may perform a test called fluorescein angiography. In this test, a special dye is injected into the arm. Pictures are then taken as the dye passes through the blood vessels in the retina. This test allows the doctor to find the leaking blood vessels.

Management

There are three major treatments for diabetic retinopathy, which are very effective in reducing vision loss from this disease. In fact, even people with advanced retinopathy have a 90 percent chance of keeping their vision when they get treatment before the retina is severely damaged. These three treatments are laser surgery, injection of triamcinolone into the eye and vitrectomy.

It is important to note that although these treatments are very successful, they do not cure diabetic retinopathy. Caution should be exercised in treatment with laser surgery since it causes a loss of retinal tissue. It is often more prudent to inject triamcinolone. In some patients it results in a marked increase of vision, especially if there is an edema of the macula.

Avoiding tobacco use and correction of associated hypertension are important therapeutic measures in the management of diabetic retinopathy. ^[9]

The best way of addressing diabetic retinopathy is to monitor it vigilantly.

Laser photocoagulation

Laser photocoagulation can be used in two scenarios for the treatment of diabetic retinopathy.

Panretinal photocoagulation

Panretinal photocoagulation, or PRP (also called scatter laser treatment), is used to treat proliferative diabetic retinopathy (PDR).The goal is to create 1,000 - 2,000 burns in the retina with the hope of reducing the retina's oxygen demand, and hence the possibility of ischemia. In treating advanced diabetic retinopathy, the burns are used to destroy the abnormal blood vessels that form in the retina. This has been shown to reduce the risk of severe vision loss for eyes at risk by 50%. ^[10]

Before the laser, the ophthalmologist dilates the pupil and applies anesthetic drops to numb the eye. In some cases, the doctor also may numb the area behind the eye to prevent any discomfort. The patient sits facing the laser machine while the doctor holds a special lens to the eye. The physician can use a single spot laser or a pattern scan laser for two dimensional patterns such as squares, rings and arcs. During the procedure, the patient may see flashes of light. These flashes may eventually create an uncomfortable stinging sensation for the patient. After the laser treatment, patients should be advised not to drive for a few hours while the pupils are still dilated. Vision may remain a little blurry for the rest of the day, though there should not be much pain in the eye.

The treatment shrinks the abnormal blood vessels. Patients may lose some of their peripheral vision after this surgery, but the procedure saves the rest of the patient's sight. Laser surgery may also slightly reduce colour and night vision.

A person with proliferative retinopathy will always be at risk for new bleeding as well as glaucoma, a complication from the new blood vessels. This means that multiple treatments may be required to protect vision.

Intravitreal Triamcinolone acetonide

Triamcinolone is a long acting steroid preparation. When injected in the vitreous cavity, it results in a decrease in the macular edema (thickening of the retina at the macula) caused due to diabetic maculopathy, along with an increase in the visual acuity. The effect of triamcinolone is transient, lasting up to three months, and necessitating repeated injections for maintaining the beneficial effect. Complications of intravitreal injection of triamcinolone include cataract, steroid induced glaucoma and endophthalmitis.

Vitrectomy

Instead of laser surgery, some people need an eye operation called a vitrectomy to restore vision. A vitrectomy is performed when there is a lot of blood in the vitreous. It involves removing the cloudy vitreous and replacing it with a saline solution made up of salt and water. Because the vitreous is mostly water, there should be no change between the saline solution and the normal vitreous.

Studies show that people who have a vitrectomy soon after a large hemorrhage are more likely to protect their vision than someone who waits to have the operation. Early vitrectomy is especially effective in people with insulin-dependent diabetes, who may be at greater risk of blindness from a hemorrhage into the eye.

Vitrectomy is often done under local anesthesia. The doctor makes a tiny incision in the sclera, or white of the eye. Next, a small instrument is placed into the eye to remove the vitreous and insert the saline solution into the eye.

Patients may be able to return home soon after the vitrectomy, or may be asked to stay in the hospital overnight. After the operation, the eye will be red and sensitive, and patients usually need to wear an eyepatch for a few days or weeks to protect the eye. Medicated eye drops are also prescribed to protect against infection.

Other treatments

Though not yet commercially available, c-peptide has shown promising results in treatment of diabetic complications incidental to vascular degeneration. Once thought to be a useless byproduct of insulin production, it helps to ameliorate and reverse many symptoms of diabetes^[11].

References

• The original text of this document was taken from the public domain resource document "Facts About Diabetic Retinopathy", at http://www.nei.nih.gov/health/diabetic/retinopathy.asp See the copyright statement at http://www.nei.nih.gov/order/index.htm, which says "Our publications are not copyrighted and may be reproduced without permission. However, we do ask that credit be given to the National Eye Institute, National Institutes of Health."

External links

• Diabetic Retinopathy Resource Guide from the National Eye Institute (NEI).
• National Diabetes Information Clearinghouse
• Educational website on Diabetic Retinopathy
• English National Screening Programme for Diabetic Retinopathy