Rewriting Life

Molecular Sunglasses for Macular Degeneration

Dampening a light-sensing reaction in the eye might slow a common cause of blindness.

Molecules designed to slow the production of toxic byproducts in the eye by making it less sensitive to light are now being tested in patients with macular degeneration, the leading cause of blindness in people age 50 and older. If successful, the compounds would provide a much needed therapy for the disease, which affects more than 15 million people in the United States.

Eye shade: Scientists hope that new compounds that make the eye less sensitive to light will slow the buildup of yellow spots–called drusen–seen here in the center of this retinal image from a patient with macular degeneration.

In macular degeneration, cells in the center of the eye, called the macula, deteriorate. A handful of new treatments for the more severe form of the disease, known as wet AMD, have been approved in recent years. But no treatments are yet available for the dry form, which accounts for about 90 percent of cases. Some dry cases ultimately progress to the wet form, which accounts for a large part of AMD-related blindness. “If you can treat dry AMD, you can kill two birds with one stone,” both reducing early symptoms and preventing progression to the wet form, says Paul Sieving, director of the National Eye Institute, in Bethesda, MD.

While scientists are still trying to understand the causes of AMD–age is the biggest risk factor, with genetics and lifestyle factors also playing a role–a growing pool of evidence suggests that the build up of specific compounds in the eye can hasten the cellular damage that underlies the disease. These compounds accumulate in the photoreceptors–cells in the retina that detect light–during normal eye function as the light-sensitive pigments in these cells change conformation in response to photons.

One form of the photopigment, a derivative of vitamin A, is highly reactive and leaks into nearby tissue called the retinal pigment epithelium. “Over time we think these compounds are a burden for the retinal pigment epithelium, which is essential for the healthy function of the photoreceptors,” says Janet Sparrow, director of the Retinal Cell Biology Laboratory at Columbia University, in New York. “In age-related macular degeneration, particularly the dry form, these cells die, and the photoreceptors follow.”

Failing vision: Photoreceptor cells (the tube-shaped cells) generate a toxin byproduct (yellow spots) during normal eye function that can damage cells in the retina, leading to macular degeneration.

While this reaction is vital for sight, researchers believe that slowing the cycle in the subset of photoreceptors responsible for night vision, known as rods, could slow damage without having a large impact on daytime vision. (Preliminary results suggest it can affect dark-adaptation–when our eyes adjust to low-light conditions.) “During the daytime, the rods are spinning like crazy, wasting vitamin A for no good use,” says Ryo Kubota, an ophthalmologist and founder of Acucela, a Seattle-based startup that is developing treatments for macular degeneration. “It’s like a CCD camera pointed at the sun.”

One compound developed by Acucela that is in clinical trials inhibits the enzyme that converts the photopigment in photoreceptors from one form to another. This process happens only in the eye, allowing the drug to be administered systemically without affecting other tissue, says Kubota. The company has finished initial safety testing in humans and plans to begin a clinical trial assessing the compound’s effectiveness in patients with late-stage dry macular degeneration in a few weeks. Kubota also aims to test the compound in diabetic retinopathy and Stargardt disease, a rare, genetically inherited form of macular degeneration.

A second drug that acts by a slightly different mechanism is being evaluated for macular degeneration by Sirion Therapeutics, a Florida-based pharmaceutical company. The compound is a synthetic vitamin A derivative that is thought to reduce toxin buildup by binding to one of the proteins involved in the reaction. According to preliminary results from tests of the drug in patients with late-stage dry macular degeneration, it can slow the scarring that is characteristic of the disease by 45 percent. However, scientists won’t know if the results are statistically significant until completion of the study next year. Because no treatments have been approved for dry AMD, the U.S. Food and Drug Administration has fast-tracked the drug, speeding the review process.

Tech Obsessive?
Become an Insider to get the story behind the story — and before anyone else.

Subscribe today

Uh oh–you've read all of your free articles for this month.

Insider Premium
$179.95/yr US PRICE

More from Rewriting Life

Reprogramming our bodies to make us healthier.

Want more award-winning journalism? Subscribe and become an Insider.
  • Insider Premium {! insider.prices.premium !}*

    {! insider.display.menuOptionsLabel !}

    Our award winning magazine, unlimited access to our story archive, special discounts to MIT Technology Review Events, and exclusive content.

    See details+

    What's Included

    Bimonthly home delivery and unlimited 24/7 access to MIT Technology Review’s website.

    The Download. Our daily newsletter of what's important in technology and innovation.

    Access to the Magazine archive. Over 24,000 articles going back to 1899 at your fingertips.

    Special Discounts to select partner offerings

    Discount to MIT Technology Review events

    Ad-free web experience

    First Look. Exclusive early access to stories.

    Insider Conversations. Listen in as our editors talk to innovators from around the world.

  • Insider Plus {! insider.prices.plus !}* Best Value

    {! insider.display.menuOptionsLabel !}

    Everything included in Insider Basic, plus ad-free web experience, select discounts to partner offerings and MIT Technology Review events

    See details+

    What's Included

    Bimonthly home delivery and unlimited 24/7 access to MIT Technology Review’s website.

    The Download. Our daily newsletter of what's important in technology and innovation.

    Access to the Magazine archive. Over 24,000 articles going back to 1899 at your fingertips.

    Special Discounts to select partner offerings

    Discount to MIT Technology Review events

    Ad-free web experience

  • Insider Basic {! insider.prices.basic !}*

    {! insider.display.menuOptionsLabel !}

    Six issues of our award winning magazine and daily delivery of The Download, our newsletter of what’s important in technology and innovation.

    See details+

    What's Included

    Bimonthly home delivery and unlimited 24/7 access to MIT Technology Review’s website.

    The Download. Our daily newsletter of what's important in technology and innovation.

/
You've read all of your free articles this month. This is your last free article this month. You've read of free articles this month. or  for unlimited online access.