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Diabetic retinopathy is an eye condition that can affect the retina of people who have diabetes.

The retina is the light-sensitive tissue that lines the back of the eye, and it detects light that is then processed as an image by the brain. Chronically high blood sugar or large fluctuations in blood sugar can damage the blood vessels in the retina. This can result in bleeding in the retina or leakage of fluid.

Diabetic retinopathy can be divided into non-proliferative or proliferative diabetic retinopathy.

Non-proliferative diabetic retinopathy:  In the early stage of the disease, there is weakening of the blood vessels in the retina that causes out-pouching called microaneurysms. These microaneurysms can leak fluid into the retina. There can also be yellow deposits called hard exudates present in the retina from leaky vessels.

Diabetic macula edema is when the fluid leaks into the region of the retina called the macula. The macula is important for the sharp central vision needed for reading and driving. The accumulation of fluid in the macula causes blurry vision.

Proliferative diabetic retinopathy: As diabetic retinopathy progresses, new blood vessels grow on the surface of the retina. These blood vessels are fragile, which makes them likely to bleed into the vitreous, which is the clear gel that fills the middle of the eye. Bleeding inside the eye is seen as floaters or spots. Over time, scar tissue can then form on the surface of the retina and contract, leading to a retinal detachment. This is similar to wallpaper contracting and peeling away from the wall. If left untreated, retinal detachment can lead to loss of vision.

Symptoms of diabetic retinopathy:

• Asymptomatic: In the early stages of mild non-proliferative diabetic retinopathy, the person will usually have no visual complaints. Therefore, it is important for people with diabetes to have a comprehensive dilated exam by their eye doctor once a year.
• Floaters: This is usually from bleeding into the vitreous cavity from proliferative diabetic retinopathy.
• Blurred vision: This can be the result of fluid leaking into the retina, causing diabetic macular edema.

Risk factors for diabetic retinopathy:

• Blood sugar. Lower blood sugar will delay the onset and slow the progression of diabetic retinopathy. Chronically high blood sugar and the longer the duration of diabetes, the more likely chance of that person having diabetic retinopathy.
• Medical conditions. People with high blood pressure and high cholesterol are at greater risk for developing diabetic retinopathy.
• Ethnicity. Hispanics, African Americans, and Native Americans are at greater risk for developing diabetic retinopathy.
• Pregnancy. Women with diabetes could have an increased risk of developing diabetic retinopathy during pregnancy. If they already have diabetic retinopathy, it might worsen during pregnancy.

One of the most commonly asked questions in an eye exam comes right after the refraction, or glasses prescription check: “What is my vision?”

Almost invariably, people know the term “20/20”. In fact, it’s a measure of pride for many people. “My doctor says I have 20/20 vision.” Or, on the other side of that same coin, having vision that is less than 20/20, say 20/400, can be a cause of great concern and anxiety. In this discussion I will describe what these terms actually mean.

To lay the foundation, let’s discuss some common terms. Visual acuity (VA) is clarity or sharpness of vision. Vision can be measured both corrected (with glasses or contact lenses) and uncorrected (without glasses or contact lenses) during the course of an eye exam. The result of an eye exam boils down to two different but related sets of numbers: your VA and your actual glasses prescription.

The notation that doctors use to measure VA is based off of a 20-foot distance. This is where the first 20 in 20/20 comes from. In Europe, since they use the metric system, it is based on meters. The 20/20 equivalent is 6/6 because they use a 6-meter test distance. The second number is the smallest line of letters that a patient can read. In other words, 20/20 vision means that at a 20-foot test distance, the person can read the 20/20 line of letters.

The technical definition of 20/20 is full of scientific jargon - concepts such as minutes of arc, subtended angles, and optotype size. If you’d like to read more of the technical details there is a well-written article with illustrations by Dr. John Ellman, you can find here.  For the purposes of our discussion here I’ll try to explain it in less technical terms.

“Normal” vision is somewhat arbitrarily set as 20/20 (some people can see better than that). Let’s say you have two people: Person A with 20/20 vision and Person B with 20/40 vision. The smallest line of letters that person B can see at 20 feet is the 20/40 line.  Person A, with “normal” 20/20 vision, could stand 40 feet away from that same line and see it. There is somewhat of a linear relationship in that the 20/40 letters are twice the size of the 20/20 letters and someone with normal vision could see a 20/40 letter at twice the distance as the person with 20/40 vision.

So how does this translate to a glasses prescription?

Eye doctors can often estimate what your uncorrected VA will be based on your glasses prescription. This works mainly for near-sightedness. Essentially, every quarter step of increasing glasses prescription (i.e. -1.25 as compared to -1.50) means a person can see one less line on a VA chart.

A prescription of - 1.25 works out to roughly 20/50 vision, -1.50 to 20/60 and so on. Anybody with an anatomically sound eyeball, meaning the absence of any kind of disease process, should generally be correctable to 20/20 with glasses or contact lenses. It is important to note, however, that rarely a person’s best corrected VA may be less than 20/20 with no noticeable signs of disease.

Far-sightedness is more difficult to estimate because it is affected by a number of other factors, including one’s age and focusing ability. But that’s a topic for another article.

So there you have it! Hopefully this has shed some light on what these measurements that we take actually mean, and it has allowed you to understand your eye health a little bit better.