Eyes are delicate. Diabetes can do major damage to them, causing poor vision and even blindness. Fortunately you can prevent this complication, and if it does develop, there are now good treatments.
How does the eye work, and how does diabetes interfere? Light comes in through the pupil, the black circle in the middle of the front of the eye. Light passes through the “lens” which directs it to the retina, a thin layer of tissue containing nerve cells that actually do the seeing. Those cells transmit signals down the optic nerve to the brain, which figures out what we are looking at.
Most of the retinal nerves are called “rods.” They see only black and white and sense movement. More detailed vision, such as reading, driving, and making out colors and shapes, is done by cells called “cones.” Cones are mostly located in the macula, an area in the retina’s center about the size of this capital O. Only the macula sees detail. That’s why you have to be looking directly at something to see it well.
-- Keep an eye on your vision! Learn about preventive steps and treatments for diabetic retinopathy from retinal specialist Dr. Charles Wykoff. >>
In diabetes, high blood sugar levels damage the tiny blood vessels, called capillaries, that feed the nerves in the retina. This damage is called diabetic retinopathy (pronounced ret-in-OP-a-thee) or DR for short. DR develops in stages and can cause visual loss, including blindness.
Last week I interviewed Dr. G. Robert Hampton, a leading ophthalmologist and retina surgeon. Dr. Hampton explained that DR damages eyes in several ways. Poor blood supply can cause nerve cells to stop working well. This may or may not cause noticeable symptoms.
Later, fluids, fats, and protein can leak from blood vessels into the retina. Dr. Hampton compares this leakage to “a blister on the retina.” The extra fluid in the eye disturbs light from getting through to the nerves that do the seeing. It also blocks circulation, putting more strain on the nerve cells. This is called “diabetic macular edema” or DME. Edema (pronounced ed-EE-ma) means swelling.
When the eye senses these blood vessel problems, the body tries to grow new blood vessels. The problem is that these new vessels are weak and fragile. They may be in places they don’t belong. They leak more easily and bleed more heavily than the older ones. This is called “proliferative retinopathy.”
At this stage vision loss usually becomes more severe. There may be cloudiness, black spots, or complete visual loss. The bleeding may form scar tissue that pulls on the macula or detaches the retina, leading to blindness, according to Dr. A Paul Chous on the website of the National Federation of the Blind.
According to Dr. Hampton, about 60% of people with Type 1 and 84% of people with Type 2 have DR 10 years after diagnosis. The numbers keep going up from there. DR is the leading cause of new cases of blindness in adults.
Along with the retina, diabetes affects the lens and the optic nerve. People with diabetes are more likely than others to get cataracts, a clouding of the lens. In glaucoma, an increase in fluid pressure inside the eye leads to optic nerve damage. A person with diabetes is nearly twice as likely to get glaucoma as other adults.
These complications mostly come from blood vessel damage caused by high glucose, so good control of diabetes is the best prevention. Dr. Hampton says keeping A1C below 7.0 goes a long way toward preventing DR. For people who already have DR, he sometimes tries to get their A1C below 6.5.
Older people with diabetes are also subject to age-related macular degeneration, or AMD. The effects of AMD are similar to DR, but the causes and pathways are a bit different. You can have both together.
Preventing and managing eye complications
There are several ways you can protect your eyes from DR and other complications:
• Maintain the best glucose control you can.
• Have regular dilated eye exams, where your pupil is opened wide and the examiner can see the state of your retina. According to Dr. Hampton, people with Type 1 should be tested within five years of diagnosis, then yearly. With Type 2, you should be tested at the time of diagnosis and yearly after that, depending on results. Signs of DR should be referred to a specialist.
• Keep your blood pressure as low as you can, preferably below 130/80 or so.
• Keep your LDL (“bad”) cholesterol as low and your HDL (“good”) as high as you can.
• Don’t smoke! Make stopping nicotine your top priority.
• To prevent AMD, eat a lot of leafy greens, nuts, and fish oil, and wear sunglasses. These ideas may not necessarily help DR, but you could have both going on.
• Recent studies show the supplements alpha-lipoic acid and benfotiamine improve eye function in DR. Other supplements may as well.
Until a few years ago, the only effective treatment for DR and DME was laser therapy. It is still widely used. Lasers can cauterize leaky blood vessels. They can also treat proliferative retinopathy by stopping new vessels from growing.
Some laser treatments cover the whole eye except the macula, to stop new vessel growth. Other treatments hit specific spots in the macula where vessels can be seen leaking, and dry them up. Lasers can clean up fats and proteins left behind by leakage, which can clear up spots of cloudy vision.
Lasers are good, but new drugs appear to be more effective for DR and DME. The most widely used are Lucentis (ranibizumab), Avastin (bevacizumab), and Eylea (aflibercept). The first two are made by Genentech. Eylea is made by a company called Regeneron. These drugs work by blocking a protein called VEGF (vascular endothelial growth factor). They stop unwanted new vessel growth and promote leaked fluid to reabsorb.
These drugs are genetically engineered “monoclonal antibodies .” They were originally approved for AMD only a few years ago. They just became available for treatment of DME and proliferative DR after 2012. They are given by direct injection into the eye using a needle like the ones used for insulin injections. The eye is numbed before the injection, and the discomfort is not severe. Dr. Hampton says he “has never had a patient who couldn’t get used to it.”
For DME, injections are usually given once a month to start. If the patient responds well, they can be slowed down and sometimes stopped completely. Sometimes laser treatments are used to clean up problem areas after the swelling has been stopped with drugs. People with good glucose control are more likely to get off injections.
The drugs are expensive, about $1,000 to $2,000 a dose for Lucentis and Eylea. Good insurance will usually cover it. Some people have copays as high as $500 a dose, though. Genentech and Regeneron have assistance programs to help with costs. Avastin, a cancer medicine not approved by the FDA for use in the eye, is far cheaper, about $60 a dose, because it is diluted from much larger doses used to treat several types of cancer. It is repackaged in compounding pharmacies, which may add an additional risk of contamination.
All three drugs appear to work about equally well. The takeaway message is to optimize your glucose and blood pressure levels, consider supplements, get your dilated eye exams regularly, and don’t be afraid of these high-tech treatments. They are an amazing blessing for people who need them.