Blind Spot: How Diabetes is Quietly Leading to Vision Loss

A middle-aged gentleman who was on treatment for diabetes mellitus came to the eye department with a peculiar sensation of a curtain falling before his eyes. An examination of the inner aspect of the eye called the fundoscopic examination revealed damage to the innermost layer of the eyeball, the retina. On further inquiry, he revealed that he had been diagnosed with diabetes about 20 years ago but was never advised to get an eye examination. He is permanently blind now. Had he visited the eye specialist a few years ago, his vision could have been salvaged.

Another lady with type 1 diabetes became pregnant. Just as in the previous scenario, a fundoscopic examination of the eye was never done in her. During the course of her pregnancy, she ended up losing her eyesight. An ophthalmological screening could have prevented her blindness, a complication that arose from her diabetes.

What happens to the eye in diabetes?

Let’s start from the beginning.

After a sumptuous meal, the glucose level in our blood shoots up. Glucose is the fuel that the cells in our body need to function. Here’s where insulin, a hormone released from an amazing organ in our body called the pancreas, comes in. What it does is regulate the glucose levels in our blood. It facilitates the storage of glucose in cells, especially liver and muscle cells, to be used at a later time when the body needs that excess energy.

Diabetes mellitus, commonly referred to as diabetes, is a longstanding disorder characterized by elevated blood glucose levels (hyperglycemia) resulting from defects in insulin production from the pancreas, insulin action at the level of muscle cells, or both.

Diabetes Mellitus is mainly of two types, although there are other not-so-common ones. For the sake of simplicity, we shall discuss the two most common types.

1. Type 1 Diabetes Mellitus – defect in insulin production

In this condition, our immune system mistakenly attacks and destroys the insulin-producing cells in the pancreas. No insulin is formed here, and the glucose level in the body rises unchecked. Genetic and environmental factors may be the cause of this disease. It begins in childhood or adolescence.

1. Type 2 Diabetes Mellitus – defect in insulin action

This is the most common type, and it develops in adults. The problem here is resistance to the action of insulin by receptors in our cells where glucose should have been stored. Over time, the pancreas may also lose its ability to produce enough insulin. Various factors contribute to the development of type 2 diabetes, including genetics, lifestyle, and obesity.

One of the major complications of diabetes is related to the eye and is called diabetic retinopathy. The retina is a layer that is present at the back of the eyeball. The images that we see are captured and focused on the retina from where It is sent as electric signals via the optic nerve to the brain. The brain processes these images to perceive a visual picture.

Diabetes causes damage to the retina. As the disease progresses, the damage becomes extensive and leads to blindness. This condition is called diabetic retinopathy and is the leading cause of blindness in working-age adults in the United States, and probably in the world.

How often does diabetic retinopathy occur?

Based on a study published in the Ophthalmology Journal by the American Academy of Ophthalmology, 22.27% of people diagnosed with diabetes were found to have diabetic retinopathy. In the Indian setting, a study published in 2022 estimates that 12.5% of people diagnosed with diabetes had diabetic retinopathy. Interestingly, this study also found that diabetic retinopathy was equally present in both urban and rural folk.

The prevalence varies with geographical location and increases with increasing duration of diabetes mellitus. North America, the Middle East, and North Africa have the highest prevalence of diabetic retinopathy globally.

When should one start to look for diabetic retinopathy?

Most doctors start on oral or injectable treatment for diabetes but forget to advise about routine eye evaluation as the patient has no complaints. Patients usually don’t have symptoms until later and hence remain unaware of the development of this disease in the early stages. This makes patients often ignore eye examinations as part of diabetes despite suggestions from their physicians. 

Screening for diabetic retinopathy helps us pick it up in its nascent stages when progression can be delayed before going into full-blown blindness. Once the disease sets in and sugars continue to remain uncontrolled, it progresses stealthily at a rapid rate. This feature of the disease again, warrants the need for a regular eye check-up.

A study done in Saudi Arabia among 386 diabetic patients found that 283 patients (73.3%) know that they must have an eye check-up regardless of their blood sugar level. However, the fact that blindness is a complication of diabetic retinopathy was known by only 65% of the diabetic patients in that study.

In adults with Type 2 diabetes mellitus, screening is recommended as soon as the diagnosis of diabetes is made. In children and adolescents with Type 1 diabetes mellitus, screening should be done within 5 years of diagnosis of the disease.

Type 2 diabetes may have gone undetected for a long time in newly diagnosed patients. Hence, they may have already acquired complications related to the disease at the time of diagnosis. This is the rationale behind screening as soon as possible. Type 1 diabetes has a more dramatic presentation at onset such that the disease rarely goes undetected. Therefore, it is alright to get screening done within 5 years of diagnosis.

Follow-up eye examinations are also necessary. A general rule of thumb is an annual eye examination. However, this is individualized based on the patient with more frequent follow-ups in those with advanced disease. One study showed that for patients with type 2 diabetes mellitus on insulin therapy and without diabetic retinopathy at baseline, the incidence of any stage of diabetic retinopathy at four years was a whopping 47 percent!

Does pregnancy increase the risk of diabetic retinopathy?

Pregnancy can cause two kinds of diabetes:

1. Gestational diabetes mellitus: This type of diabetes occurs post-conception. The patient never had diabetes prior to pregnancy.
2. Overt diabetes mellitus: This is the kind where the patient becomes pregnant while already diagnosed with diabetes.

In the case of gestational diabetes, the risk of complications including diabetic retinopathy is extremely rare. Hence, screening is not required.

Pregnant women with overt diabetes, on the other hand, need frequent screening for diabetic retinopathy. In these patients, pregnancy exacerbates underlying diabetic retinopathy resulting in rapid progression of disease. The first screening should be done before planning pregnancy. Post conception, follow-up screening should be done at least every trimester and more frequently if disease progression is seen.

How to prevent diabetic retinopathy?

Control of sugars is the best way to prevent the progression of the disease. For this, follow up with a family physician or an endocrinologist regularly. Other parameters that can help reduce the incidence of diabetic retinopathy are the control of blood pressure and cholesterol.

Maintaining BMI in the normal range (18.5-22.9 kg/m2), compliance with anti-diabetic medicines, a minimum of 30-45 minutes of physical activity of moderate intensity (such as brisk walking 5-6 km/hr) 5-6 days of the week., and cessation of smoking are additional factors that keep diabetic retinopathy at bay.

Impairment of vision can drastically affect occupation, daily chores, and quality of life. Diabetic retinopathy, although one of the major causes of blindness worldwide, is often underdiagnosed. 

The reason people are so ignorant of such an important cause of blindness is chronicity. People care less about something chronic that does not have sudden severe symptoms. When they don't have symptoms it gives a feeling of apparent good health. Only acute symptomatic complications raise the alarm for them. Take the case of warnings on cigarette packets. Who heeds it? However, most cigarette smokers quit after they face a respiratory problem. 

This is why it is important to create awareness among people about this condition. Because, if detected early, progression to permanent blindness can be arrested. So, if you know someone who is diagnosed with diabetes mellitus, make sure to tell them to get their eyes checked.

Edited by Christianez Ratna Kiruba.

Image by Janvi Bokoliya.