Time spent outdoors may improve vision

Some Hopkins students might have grown up with long afternoons spent doing homework in their rooms instead of playing outside. Sure, that hard work has played an important role in bringing students here today, but those who must wear glasses or contacts to see the blackboard at the front of the lecture hall might be interested to hear that nearsightedness has recently been linked to the amount of time spend indoors as children.

In a study conducted at the Northwestern University Feinberg School of Medicine, a team of researchers led by Assistant Professor of Ophthalmology Greg Schwartz discovered a cell in the retina whose dysfunctions can lead to myopia.

Myopia, a condition more commonly known as nearsightedness, is caused by overgrowth of the eye. When the eye grows to be too long, light that comes into the eye through the pupil and lens is focused in front of the retina instead of directly on it. Because of this, images from far away are blurry to an individual with myopia.

Myopia is very common. More than 30 million people in the United States, or one third of the population between the ages of 12 and 54, are affected by myopia. Worldwide, over a billion people are known to have the condition.

Unfortunately, myopia incidents are only on the rise. In the 30 years between 1970 and 2000, nearsightedness increased by 66 percent in the U.S. Between 2000 and 2010, the number of myopia cases across the nation increased by four million, as reported by the National Eye Institute (NEI). The NEI also projects that by 2050, there will be more than 10 million more cases of myopia than today.

What Schwartz and his research team found can offer one explanation for this upward trend.

From prior studies, scientists know that the retina contains a signal that regulates eye growth during childhood, a stage in development that is essential in determining a person’s vision in adulthood. The eye needs to stop growing at exactly the right moment to ensure that the images collected by the eye can be properly focused on the retina. However, it was unknown which cell was responsible for the vital role of regulating eye growth.

The newly discovered retinal cell, which Schwartz named “ON Delayed,” is potentially the missing link. It is highly sensitive to light and sends signals to a neural circuit that dictates and controls the process of eye growth.

Adam Mani, a postdoctoral fellow in ophthalmology at Feinberg and co-author of the study, used microscopic glass electrodes to observe electrical signals from the retina of mice in response to patterns of light on a digital projector.

With this technique, researchers found that the ON Delayed ganglion cell’s unique light sensitivity becomes overstimulated by the indoor light spectrum, which has high levels of red/green contrast. This contrast creates artificial contrast images on the retina, confusing the ON Delayed cell to become hyper-activated and causing over-growth of the eye and myopia.

These results pose one factor that could play a role in the drastic increase in myopia throughout the years.

With the rise of technology and indoor entertainment since the late 20th Century, children are spending much more time indoors, where they are exposed to artificial light with high levels of contrast. It is unsurprising that people today are more likely to suffer from myopia as compared to their counterparts decades before.

This study is part of Schwartz’s mission to reverse-engineer the retina, identify all retinal cell types and analyze their neurological connections to the brain. He also hopes to understand their genetic component, promising research that could lead to the future use of gene therapy to treat blindness and other eye conditions.