Being told you have one chronic condition can be a lot. Being told you might be experiencing another medical condition as a result of the first one can be downright frustrating. For a portion of people with diabetes, this scenario is all too familiar.
According to the National Eye Institute, diabetes—characterized by elevated blood sugar levels—is the leading cause of new blindness in the United States.
“The blood vessels in the eye are very small and can easily be damaged by a prolonged period of elevated blood sugar,” says Raghu C. Murthy, M.D., chief of pediatric retinal surgery at Cedars-Sinai Medical Center in Los Angeles. “If these blood vessels begin to corrode, they can leak into the vitreous as well as the retina.” The vitreous is that gel-like substance that sits behind your lens. Your retina is that layer of light-sensitive tissue at the back of your eyeball that’s responsible for converting images to electric signals, which get sent to your brain via the optic nerve.
When the blood vessels leak into the center of the retina—a.k.a. the macula—you can develop diabetic macular edema (DME), which affects up to 10% of people with diabetes. Edema means “swelling,” and DME specifically refers to swelling of the retina. “As fluid builds up within the macula, it can cause blurry or distorted vision and lead to several serious conditions such as a retinal detachment and blindness,” says Theodore Leng, M.D., retina specialist at Stanford Health Care in Stanford, CA. DME is a serious condition, but it can be treated.
Tests are never fun, but in order to diagnose DME, your doctor will have to run through a series of them to assess the state of your macula and determine the best course of treatment. “The macula's main role is to process information in our central vision,” says Michael Richardson, M.D., medical director of the Boston office of One Medical, a national primary-care practice. “When it’s impaired, like with DME, our central vision starts to deteriorate while our peripheral vision stays intact.”
If you’re worried about spending an entire day at the doctor’s office, don’t—despite the various tests you’ll need to go through to determine whether you have DME, you’ll be in and out in no time. “Patients will first receive the eye exam, which includes the visual acuity test, amsler grid and dilated eye exam,” Dr. Murthy says. “After this, OCT imaging and fluorescein angiography will be performed to provide further details on the patient's condition.” The eye exam takes about 15 minutes (not counting the typical waiting room, flip-through-magazines-and-scroll-through-Instagram time, of course). OCT imaging takes about two minutes, and fluorescein angiography takes about 10 minutes. To officially diaignose DME, your doctor will need to perform all of these, but thankfully, all that testing won’t eat up your whole day.
Here’s what to expect from each DME eye test:
Visual Acuity Test
If you’ve ever been to the eye doctor, you’ve probably taken a visual-acuity test. It’s the exam that uses a standardized chart of letters of varying sizes (called a Snellen chart). When you take a visual-acuity test, your doctor will ask you to sit or stand 20 feet (or 6 meters) from the chart and cover one eye while reading certain lines of letters out loud. This test helps your doctor figure out how well you can see through your central vision and whether your vision is getting worse.
“Visual acuity and the Amsler grid are subjective visual tests used to determine the extent of damage to a patient's vision,” Dr. Murthy says. “The Amsler grid is a grid composed of many identical squares with white lines and a black background. This test is used to determine if the patient is experiencing distorted vision and which regions of their visual field are affected. If you see the white lines within the grid as curved or wavy, this may be indicative of fluid within the macula.”
If you’ve ever had your eyes dilated, you know what’s in store: giant, Disney character-style pupils and some post-exam light sensitivity (so make sure to pack your sunnies). This painless test involves getting special drops put in your eyes that cause the muscles of your iris to contract—that’s what causes the pupils to enlarge. According to Dr. Murthy, the dilated-eye exam is the only way your eye doctor can get a good look at the peripheral part of your retina, which lets them see if there are other issues affecting it.
During the test, your doctor will perform what’s known as an “indirect ophthalmoscope,” which is a fancy way of saying they’ll shine a very bright light into your eye to examine the retina. This shouldn’t be too uncomfortable, but you may want to brace yourself for an intense light show.
Optical Coherence Tomography
“Several imaging studies like this one are also done to diagnose diabetic macular edema,” Dr. Murthy says. “Ocular coherence tomography (OCT) determines the amount of fluid or swelling in the macula by measuring retinal thickness.” The test uses a special light and a camera that gives detailed views of the retina’s cell layers. Using these tools, your doctor can determine the thickness of your retina, which can help them figure out whether the macula is swollen.
If your eye exam and OTC results have your doctor suspecting DME, you might have to get one more test called a fluorescein angiogram. This one isn’t too bad either, but be warned: It does involve getting a shot (in your arm, not your eye!). Your doctor will use a needle to inject you with a small amount of a yellow dye called fluorescein that reaches the blood vessels in the eye about 10-15 seconds after it’s injected into the arm. Once it reaches the eyes, it causes them to shine brightly, or fluoresce. “Fluorescein angiography is used to directly look at the health of the blood vessels in the eye,” Murthy says. “The injected dye illuminates the blood vessels in the eye and can show if any of the blood vessels are actively leaking within the macula.”