The New Vision-Potential Retinal Regeneration

BY YEH SHIUAN LIN

Every time I pick up my cell phone or try to read something with the light off, I can almost hear my mom’s voice ringing through my head: “Don’t read in the dark!” “Don’t stare at your computer screen for too long, you’ll go blind!” In this day and age, ophthalmologists are echoing the same sentiments as they are presented with more and more cases of vision damage. The culprit? Our dependence on technology. Leaving the house without a cellphone, computer or tablet is practically blasphemy. Often, however, we fail to realize the true damage we cause ourselves by constantly staring at our electronic devices. Jeff Todd, chief operating officer of Prevent Blindness America, reported to WebMD that there has been an 89 percent increase in diabetic retinopathy rates and a 25 percent increase in macular degeneration rates over the last 12 years. Another 12-year study, published in 2009, reported that there has been a 17 percent increase in myopia (nearsightedness) diagnoses. According to a 2013 survey by Everyday Health, nearly 70 percent of US adults suffer from visual strain as a result of their increasing use of technology. Although many doctors warn their patients against prolonged use of electronic devices, the number of people with deteriorating eyesight still continues to increase. What are doctors to do when the very technology on which society is so reliant is actually a major cause of vision loss in its population? To answer a question with another question: What if one cell could instantly regenerate those losses? Researchers at the Schepens Eye Institute of the Harvard Medical School are investigating just that.

The eye is one of the most complex organs of the human body. Despite its very small size, it contains over 200 million moving parts. Of those 200 million parts, there are about 20 parts of the eye that are most vulnerable to disease: the retina, the macula, the lens and the optic nerve, to name a few. The leading causes of blindness and impaired vision are macular degeneration, diabetic retinopathy, cataracts and glaucoma. However, the diseases that currently affect young people the most are those associated with visual strain, such as macular degeneration.

The retina is a thin, light-sensitive piece of tissue in the back of the eye that plays a vital role in vision. Its main function is to receive the image of the outside world as seen through the cornea and lens. The central part of the retina is the macula; this is where the majority of images are projected, while the rest are projected onto the peripheral areas of the retina. The images are projected onto the retina and converted into electrical signals to be interpreted by the brain. Common diseases of the retina include retinal tears and retinal detachments — the latter being more severe because detachments if left completely untreated can lead to blindness. Since retinal tears and detachments are usually painless, they are difficult to detect. Common symptoms include floating specks and flashes in the field of vision. Retinal detachment occurs when the retina is pulled from its normal position. As a result, the retina is removed from its blood supply, effectively starving to death (ischemia). If treated promptly, the retina can be reattached via laser surgery or cryopexy. Laser surgery welds the retina back into place by means of precise, controlled burns (cauterization). Cryopexy reattaches the retina by freezing the area around the hole left by the retina, inducing scar tissue formation between the retina and its neighboring tissues. These procedures successfully treat over 90 percent of patients with retinal detachment. However, if the retina fully detaches, macula and all, the patient may suffer permanent vision loss. I know this will probably not deter you from answering your next text message or scrolling through Yik Yak; fortunately, a researcher at Harvard has made an interesting pilot discovery in the field of retinal detachment and macular degeneration.

Dr. Dong Feng Chen’s lab at the Harvard’s Schepens Eye Research Institute recently published a paper in The Investigative Ophthalmology and Visual Science journal discussing the transformation of non-neuronal cells to stem-like cells. This discovery gives hope to patients who suffer from retinal diseases such as macular degeneration and retinitis pigmentosa — even to patients who suffer permanent vision loss as a result of retinal detachment. Chen’s team chose to investigate Muller cells, which are the primary glial cells of the retina. Muller cells are multi-talented — they are able to recognize a variety of responses, transmit information from the retina to other parts of the eye, regulate neuronal activity of substances around the eye, and, like stem cells, produce undifferentiated cells within the eye. This gave the team the hope that this “super cell” — the Muller cell — will allow them to aid or even regenerate the tissue lost in retinal degeneration and detachments.

Chen’s team worked with glutamate and aminoadipate, both of which bind to the Muller cells. Both of these chemicals were injected subretinally into the mice. Since Muller cells differentiate into multiple cells, the team used fluorescent markers to track these cells in order to determine their fate after being injected with either glutamate or aminoadipate. Previous research showed that high concentrations of glutamate induce cell death, but this study hoped to find a possible benefit of injecting either glutamate or aminoadipate into the mice, theorizing that the influx of these molecules could shock the cell into cell cycle reentry.

The results of the study showed that, even though glutamate normally induces cell death, the injected glutamate stimulates Muller cells to reenter the cell cycle, allowing it to redifferentiate. Furthermore, the aminoadipate showed that the stimulated Muller cells migrated from the outer nuclear layer and differentiated into photoreceptor cells. This was the ultimate goal of Chen’s study. This discovery shows that the photoreceptors lost during retinal degeneration could be replenished by Muller cells. The most important takeaway of this study is that Muller cells can be induced to differentiate, migrate and become new retinal neurons, creating photoreceptors when stimulated by glutamate or aminoadipate.

With the breakthrough discovery of Muller cells, scientists can look towards applications in a clinical setting. Chen believes that if this is successful, a drug created from aminoadipate will have profound implications for patients with damaged retinas. This would be a scientific breakthrough free of physical intervention. This is extremely relevant to college students because many use laptops without taking breaks. As demonstrated by Shaban’s study, light emitted by modern technology degenerates the retina — over time, the damage from this prolonged exposure can accumulate to disastrous effect. Without a doubt, parents have a legitimate reason to scold their children for their heavy use of phones, tablets, laptops and all.

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