By Paul Spinrad

In myopia, images focus in front of the eye’s retina and require corrective lenses. But in high myopia, weakness in the sclera causes ongoing growth and lengthening of the eyeball throughout life and can lead to vision-threatening complications like retinal detachment and macular degeneration.
ILLUSTRATION BY CHRISTINE GRALAPP

It is one of the world’s leading causes of blindness. High axial myopia, or extreme nearsightedness, stems from progressive thinning and weakening of the sclera, the eye’s white outer wall, causing the eyeball to elongate even under normal intraocular pressures.

James Su, a graduate student researcher co-advised by Kevin Healy, professor of materials science and engineering and bioengineering, and Christine Wildsoet, professor of vision science and optometry, is investigating a promising new treatment for the condition based on a synthetic biomaterial known as hydrogel.

“The area hasn’t seen much research because the condition is not very prevalent in the United States,” Su explains. “It’s a much bigger problem in Asia, where myopia is at least three times more common than it is here. About 10 percent of myopic people in Asia have a refractive error measuring –6 diopters or worse, which is considered high myopia.”

Simple myopia—also known as nearsightedness—is a refractive error resulting from a mismatch between the eye’s optical power and its length that causes images to focus in front of rather than on the eye’s retina. The causes of myopia are a matter of considerable controversy, but some research has implicated environmental factors like close work (tasks that require holding things up close, like reading or sewing), exposure to daylight and even stress. The result is blurry vision, which can be improved with corrective lenses.

But in high myopia, the weakened sclera, in combination with intraocular pressure (normal pressure exerted by fluids inside the eyeball), causes the eyeball to progressively elongate, like a balloon when squeezed around its middle. This pulls on the eye’s retina—the nerve layer in the back of the eye that transmits images to the brain—and can lead to blinding complications such as retinal detachment and macular degeneration as well as cataracts and glaucoma. Sufferers rely on thick glasses, contact lenses or refractive surgeries like LASIK; but even the latter is only a temporary fix for eyes that continue to elongate.

In Professor Kevin Healy’s Stanley Hall lab, (from left) graduate student James Su, vision scientist Christine Wildsoet and Healy observe the changing properties of hydrogel.
PHOTO BY PEG SKORPINKSI

“People who wear contact lenses or get LASIK might think that their problem has gone away,” Su says, “but these just correct the eye’s refractive error. That is only the symptom, not the underlying cause of their condition.”

To correct the problem, the eye’s wall must be strengthened against its internal pressure to slow or prevent further elongation. One experimental treatment involves suturing strips of sclera around the back of the eyeball to reinforce the eye’s own sclera and push it forward. The scleral bands are typically constructed from donated eyes, which are scarce; an experimental synthetic alternative made from Teflon® carries the risk of cutting into the eyeball. Either way, sewing on the bands is a delicate and risky operation.

In search of a simpler and less invasive treatment, Su is working with a functionalized biomimetic hydrogel, an advanced biodegradable material that takes the form of an injectable liquid at cool temperatures but becomes a soft, rubber-like solid at body temperature.

The surgical procedure, currently undergoing experimental testing, involves injecting the hydrogel at the back of the eyeball, under Tenon’s capsule (a thin sheath that overlies the sclera and surrounds the posterior half of the eyeball). The gel conforms to the shape of the eye wall and, as it warms up, stiffens, adding strength to the back side of the eyeball. Because the material never penetrates the eye to reach such delicate structures as the retina and lens, the procedure is potentially quite safe. One hydrogel injection would not last a lifetime; patients would require ongoing injections once or twice a year that would be performed as an outpatient procedure.

When the injectable hydrogel (left) reaches a temperature above 34 degrees Celsius, it undergoes a phase transformation, becoming stiffer and opaque (right).
PHOTO BY PEG SKORPINKSI

Su hopes to patent and commercialize the treatment within several years and then launch operations in Asia. With venture backing, he thinks FDA approval could be expedited because the biocompatability of hydrogel injections has already been established. In the future, Su says, hydrogel could be formulated to contain and release therapeutic agents to enhance treatment; one drug known to inhibit progression of myopia is already under consideration. The procedure could also be used as a preventive measure for children likely to progress to high myopia.

“Vision care is moving in the direction of prevention,” Su says. “This can reduce lifetime vision care costs and has broader economic implications; of course, it’s also better for the patient.” Healy is working with some of his other students on a hydrogel containing biomaterials such as growth factors that could be injected into the heart to rebuild damaged cardiac tissue.

Su’s project, under the name Ophtherix, was named one of six finalists out of a field of 58 in last year’s Venture Lab Competition, a College of Engineering program that provides funding, on-campus workspace and networking opportunities for researchers with brilliant ideas.