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Researchers investigate possible new uses of femtosecond technology
Laser-created microbubbles may help determine the biomechanical properties of ocular tissue.
Researchers at the University of Texas at Austin are developing a new approach to measuring the biomechanical properties of the eye using microbubbles created by a femtosecond laser.
In synthetic materials with properties similar to ocular tissue, Stanislav Emelianov, PhD, and colleagues have used sound waves bounced off laser-created microbubbles to determine the stiffness of the surrounding material. Dr. Emelianov told Ocular Surgery News in a telephone interview that variations in the bubbles’ vibrations could indicate the rigidity of corneal tissue, the crystalline lens and the vitreous humor when applied in vivo.
“Take a string on the guitar and just poke it and look at how it vibrates,” Dr. Emelianov said. “As it vibrates, it will produce specific sound to your ears. And if you listen to that sound, you can definitely tell which string is which. … We [can] use that sort of phenomena to interpret the elasticity of the tissue surrounding the bubble.”
Additionally, Dr. Emelianov and colleagues are applying their technique to investigate whether the microbubbles could be used to treat presbyopia. Specifically, they said they believe that by creating a series of pulsed-laser microbubbles in the outer rim of the crystalline lens, the changes in lens flexibility can be accurately measured, according to a press release from the university.
At this point, the researchers have tested the microbubbles in only synthetic tissue-mimicking materials; however, they intend to test them in extracted animal and cadaver eyes in the next few years. From there, Dr. Emelianov said he expects the technology to focus on corneal clinical applications first.
“The laser’s already used there, so that would be our definite first target because we can easily and quickly come into the clinic with that technology,” he said.
Testing stiff vs. soft tissue
Gelatin is the synthetic material that Dr. Emelianov and colleagues use in microbubble testing.
“We can make the gel very stiff to simulate corneal tissue, or we can make it very soft to simulate vitreous humor or crystalline lens tissue,” he said.
In stiffer cornea-like gel, the researchers first tested their technology using tiny glass spheres representing microbubbles.
“By irradiating [the spherical object] with ultrasound waves and monitoring the response of that object, we can predict what the elastic properties of the surrounding medium are,” Dr. Emelianov said.
The researchers then performed the same test with microbubbles, observing how the bubbles respond to ultrasound waves in terms of resonance and oscillation frequency.
A different elasticity test will be performed in softer tissue such as that of the vitreous humor or crystalline lens. Instead of observing the vibration response of the microbubbles, the researchers will evaluate the ultrasound wave’s ability to displace the bubble.
“There is no tool that can remotely measure viscoelastic properties of the vitreous humor in vivo,” Dr. Emelianov said. Knowing the biomechanical properties of the vitreous humor could help ophthalmologists in designing therapeutic strategies, understanding drug effects, and diagnosing and monitoring certain diseases, he said.
Microbubbles and LASIK
When created in corneal tissue, microbubbles could assist eye surgeons in gauging how much tissue to remove during LASIK, Dr. Emelianov said.
“From a material science perspective, as you take any piece of the tissue out, then you will by definition create what’s called residual stresses. … Tissues will start responding to those stresses,” he said.
By evaluating the stiffness of an individual’s cornea, ophthalmologists can cater the surgery to the individual patient. “We’re designing a patient-tailored, if you will, surgical procedure rather than just bluntly looking at the geometry. … Geometry is one factor, but the second and not least important factor is the mechanical properties of the cornea,” Dr. Emelianov said.
In current practice, vision is usually corrected to 20/20 immediately or soon after LASIK surgery. In some cases, however, the corneal tissue can slowly evolve so that the patient’s vision regresses over time, he said. If corneal stiffness is taken into account when the initial surgery is performed, vision will not be perfect immediately but will slowly improve to become 20/20 as stresses in the eye level out.
“More importantly, [vision] will never be changed with age anymore because all the residual stresses are vanished and the tissue has remodeled itself into perfect 20/20,” he said.
New technologies
With optical scientist Thomas Milner, Dr. Emelianov is developing new ultrasound transducers and optical probes to detect the vibrations of the microbubbles in the eye.
Additionally, the researchers are developing new ultrasound technology to measure the size of the bubbles. Dr. Emelianov said research progress depends on how quickly they can develop the necessary technologies for using the microbubbles in human eyes.
“Our next step would be to start working with extracted animal eyes and then maybe cadaver eyes, but that’s not going to be right away. … We have to design the specific instrument to go into the eye vs. what is done in phantom,” he said.
For more information:
- Stanislav Emelianov, PhD, can be reached at the Department of Biomedical Engineering, University of Texas at Austin, 1 University Station C0800, ENS Building, Room 636, Austin, TX 78712; 512-471-1733; fax: 512-471-0616; e-mail: emelian@mail.utexas.edu.
- Jessica Loughery is an OSN Staff Writer who covers all aspects of ophthalmology.