A map of retinal cells will help treat blindness

New research has uncovered more secrets about the retina of the eye. The information obtained can help in the development of treatments for the various causes of blindness and better methods of recognizing them.

Experts from the National Eye Institute (NEI) in the United States have described (https://www.pnas.org/doi/full/10.1073/pnas.2117553119) a previously poorly understood population of cells key to vision. These are cells of the retinal pigment epithelium (RPE). They form a layer that nourishes and supports light-sensitive receptor cells.

With the help of artificial intelligence, researchers have created an accurate map of these cells in the human eye.

“The results provide us with the first real framework needed to understand the different RPE populations and their susceptibility to retinal disease, and to develop treatments for them,” said NEI Director Dr. Michael F. Chiang.

“What we found will help us develop more precise cell and gene therapies for specific ocular degenerative diseases,” says fellow researcher Dr. Kapil Bharti.

As the researchers recalled, sight works in such a way that photoreceptors in the retina – cones and rods – respond to light and then send signals to subsequent cells arranged in a complex network. These, in turn, end up sending signals to the brain.

Just below the photoreceptors are these RPE cells, which form a single layer. Old age and disease can cause changes in these cells, which in turn lead to the degeneration of photoreceptors.

Depending on the degree and location of damage to RPE cells, the effects of the changes on sight can vary widely, from peripheral visual field disturbances to central vision loss, for example in macular degeneration (the main cause of blindness) .

To better understand these cells, the researchers first used artificial intelligence to analyze the shapes of RPE cells from different regions of the retina. The algorithms also checked the number of neighboring cells.

Previous studies have shown that the more densely packed RPE cells are, the better they perform.

Thus, the scientists analyzed nearly 50 million cells from deceased donors.

This analysis showed that there are up to 5 different populations of P1 to P5 labeled RPE cells in the human eye. They are arranged in concentric circles around what is called the fovea located in the center of the macula – the most light-sensitive part of the retina.

The central RPE appears to be more hexagonal in shape and denser than the periphery.

The exception is the P4 population close to the retinal margin, which resembles central cells.

This detail is important.

“The presence of the P4 subpopulation indicates cellular diversity at the periphery of the eye. This suggests that there may be functional differences between RPEs that we do not currently know about. Further research will be needed to help us understand the role of this subpopulation”, explains a researcher, Dr. Davide Ortolan.

In the next stages of the experiments so far, scientists have looked at RPE cells taken from deceased people with macular degeneration.

The disease was accompanied by a lack of cells in the center (P1), and the differences between the P2 and P5 populations were negligible.

Compared to cells in healthy individuals, the RPE accompanying the disease had a more elongated shape.

The researchers also compared cells from people with choroideremia with ocular vessel damage, late macular degeneration and retinal degeneration of unknown molecular causes.

This study also showed that different populations of RPE cells are damaged in different diseases.

“Overall, our results suggest that artificial intelligence can detect changes in RPE morphometry even before there is clearly visible degeneration,” says Dr. Ortolan.

Research based on this knowledge could therefore allow earlier diagnosis of possible disease in patients, which may mean more effective treatment.

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