Long-Term Follow-Up of Diabetic Retinopathy in Patients with Retinitis Pigmentosa: A Case Series of Nine Patients

The human eye relies on a delicate balance of energy and blood flow to function. At the back of the eye, a layer of light-sensitive cells called photoreceptors captures images and sends them to the brain. These cells require a steady supply of oxygen, which is delivered by a network of tiny blood vessels. When a person has diabetes, high blood sugar can damage these vessels, causing them to leak or grow abnormally. This condition, known as diabetic retinopathy, is a leading cause of vision loss. In a separate but related process, a group of inherited diseases called retinitis pigmentosa causes the light-sensitive cells to slowly die off. As these cells disappear, the eye consumes less oxygen. Scientists have long wondered what happens when both conditions strike the same person. Does the loss of light-sensitive cells, which reduces the eye's hunger for oxygen, protect the blood vessels from the damage usually caused by diabetes? Or do the two diseases combine to destroy vision even faster?

To answer this, researchers at Beijing Tongren Hospital followed nine patients who lived with both type 2 diabetes and retinitis pigmentosa for as long as sixteen years. They did not just look at a single moment in time; they watched these patients over many years to see how their eyes changed. The group included two men and seven women, ranging in age from twenty-seven to eighty-two. The team tracked their vision, examined the back of their eyes with cameras and special lights, and recorded any treatments they received. Their goal was to map the long-term journey of these rare patients and understand how the two diseases interacted over a lifetime.

The results revealed a complex and often difficult picture. In three of the patients, the diabetes did cause the blood vessels to grow abnormally, a severe stage known as proliferative diabetic retinopathy. These patients required surgery to remove scar tissue or laser treatment to seal leaking vessels. While these procedures successfully stopped the immediate bleeding and stabilized the eye's structure, the patients' vision did not stay fixed. Even after the surgery, their sight slowly continued to fade over the following years. This decline was not caused by the diabetes returning, but by the underlying retinitis pigmentosa, which continued to destroy the light-sensitive cells regardless of the blood vessel health. In fact, the vision loss in these patients was often more severe than what is typically seen in people with retinitis pigmentosa alone, suggesting that having both conditions might accelerate the overall damage.

However, the story was different for the other six patients. In these individuals, the diabetes did not cause the typical damage to the blood vessels at all. This group fell into two distinct patterns. Some patients had developed diabetes early in their lives, while their retinitis pigmentosa was still in its early stages. In these cases, the disease progressed to the point where blood vessel damage appeared, though it was often less severe than expected. The other group consisted of patients who had lived with advanced retinitis pigmentosa for decades before they developed diabetes. By the time their blood sugar levels became high, their light-sensitive cells had already died off in large numbers. Because these cells were gone, the eye no longer demanded much oxygen, and the blood vessels remained healthy despite the diabetes. This finding supports the idea that the state of the light-sensitive cells at the moment diabetes begins determines whether the blood vessels will be damaged.

One patient in the study offered a particularly unique glimpse into the nature of these diseases. This woman had diabetes for only two months when she was found to have retinitis pigmentosa in just one eye, while her other eye remained perfectly healthy. Genetic testing showed she carried changes in three different genes linked to the disease. This rare case of a single affected eye suggests that the mutation might have occurred only in the cells of that specific eye during early development, rather than being present throughout her entire body. It also highlighted that severe vision loss can occur from retinitis pigmentosa alone, even before diabetes has had time to cause any harm.

The long-term follow-up of these nine patients shows that while doctors can successfully treat the blood vessel problems caused by diabetes, they cannot stop the slow, progressive loss of vision caused by the degeneration of the light-sensitive cells. When both diseases are present, the outcome depends heavily on the timing. If diabetes arrives while the eye still has many healthy cells, the blood vessels may still suffer damage. If the eye has already lost most of its cells to the inherited disease, the blood vessels may remain safe from diabetes. Ultimately, the study suggests that the interaction between these two conditions is not a simple battle, but a shifting relationship where the history of the eye dictates the future of the disease.