A Clearer View

A new microscopy technique developed by University of Maryland researchers could make the popular LASIK vision-correction surgery more accurate—and even nearly eliminate the need for any cutting of the eye.

The findings by Giuliano Scarcelli, an assistant professor in the Fischell Department of Bioengineering, and members of his Optics Biotech Laboratory, were published this week in Physical Review Letters.

In the 20 years since the Food and Drug Administration first approved LASIK surgery, more than 10 million Americans have had the procedure, which can free patients from wearing glasses or contact lenses—if it works as planned.

While LASIK has a very high success rate, virtually every procedure involves an element of guesswork, because doctors have no way to precisely measure the refractive properties of the eye. Instead, they rely heavily on approximations that correlate with the patient’s vision acuity—how close to 20/20 he or she can see without corrective lenses.

Scarcelli’s new microscopy technique could allow doctors to perform LASIK using precise measurements of how the eye focuses light. 

“This could represent a tremendous first for LASIK and other refractive procedures,” Scarcelli said. “Light is focused by the eye’s cornea because of its shape and what is known as its refractive index. But until now, we could only measure its shape. Thus, today’s refractive procedures rely solely on observed changes to the cornea, and they are not always accurate.”

The cornea—the outermost layer of the eye—functions like a window that controls and focuses light that enters the eye. When light strikes the cornea, it is bent—or refracted. The lens then fine-tunes the light’s path to produce a sharp image on the retina, which converts the light into electrical impulses that are interpreted by the brain as images. Common vision problems, such as nearsightedness or farsightedness, are caused by the eye’s inability to bring an image into sharp focus on the retina.

To fix this, LASIK surgeons use lasers to alter the shape of the cornea and change its focal point. But, they do this without any ability to precisely measure how much the path of light is bent when it enters the cornea. 

To measure the path light takes, one needs to measure a quantity known as the refractive index; it represents the ratio of the velocity of light in a vacuum to its velocity in a particular material.

By mapping the distribution and variations of the local refractive index within the eye, doctors would know the precise degree of corneal refraction. Equipped with this information, they could better tailor the LASIK procedure so that instead of simply having better vision, patients could expect to walk away with perfect vision—or vision that tops 20/20.

Even more, doctors might no longer need to cut into the cornea.

“Non-ablative technologies are already being developed to change the refractive index of the cornea, locally, using a laser,” Scarcelli said. “Providing local refractive index measurements will be critical for their success.”

In addition to Scarcelli, bioengineering Ph.D. student Antonio Fiore, the paper’s first author, and Carlo Bevilacqua, a visiting student from the University of Bari Aldo Moro in Italy, contributed to the paper.