APRIL 16, 2009--"Corneal defect is the second most common cause of blindness in the world," said Min Yao, MD, PhD, of the Wellman Center for Photomedicine at Massachusetts General Hospital and Harvard Medical School (Boston, MA). Remedying this condition is routinely accomplished by the delicate procedure of amniotic membrane transplantation (AMT). But the conventional, invasive use of sutures to secure the graft easily damages critical tissue—and can even cause graft rejection. Now a laser-activated, noninvasive technology, photochemical tissue bonding(PTB), promises an alternative with significantly less damage potential and faster healing. The approach uses an FDA-approved dye that absorbs laser light and reacts with proteins chemically (not thermally) to create a tight seal to the corneal surface.
A randomized test of both the laser-based and suture techniques in 24 rabbits showed that the PTB method achieved comparable AMT success, and produced dramatically less inflammation and neovascularization (that is, generation of new blood vessels in eye tissue, which can interfere with vision). The photodynamic method also produced significantly less scar-tissue formation in the corneas. These results indicate faster healing and better retention of eye function.
Dr. Yao spoke with BioOptics World during the 29th Annual Conference of the American Society for Laser Medicine and Surgery (ASLMS), where she and her colleagues presented their research results. A plastic surgeon for 15 years in China before coming to the U.S., Dr. Yao used to treat many patients with corneal damage due to burn, trauma and industrial accidents. She told BioOptics World that "suturing for the cornea doesn't work well."
She explained that the photochemical tissue bonding approach uses the FDA-approved dye called Rose Bengal "to stain the amniotic membrane that is placed on the damaged cornea. Rose Bengal solution absorbs Nd:YAG light irradiation (532 nm) and reacts with proteins to seal the amniotic membrane surface to another tissue surface--the ocular surface." She went on to say that, "this noninvasive technique took about three minutes and caused much less inflammation or infection and much less neovascularization (i.e., development of new blood vessels in eye tissue) compared to suture treatment. With this approach, successful bonding occurred via photochemical reactions rather than by heating the tissue, plus faster and better wound healing was documented."
For testing purposes, the researchers created a corneal defect in the left eye of 24 live rabbits. The eyes were randomized into two repair groups: AMT using sutures; and AMT using PTB via Rose Bengal and Nd:YAG laser irradiation. The researchers examined the eyes for re-epithelialization (bonding success) for up to 28 days after surgery: All corneal repairs were harvested to evaluate wound healing based on inflammation, neovascularization and scar formation on post-operative days 1, 3, 14 and 28.
Results indicated that:
+ Corneal re-epithelialization did not differ significantly between the suture and PTB groups
+ Dramatically less inflammation was measured in the PTB group compared to the suture group
+ Dramatically less neovascularization was measured in the PTB group compared to the suture group
+ Much less scar formation of corneas was determined in the PTB group compared to the suture group
"Based on our initial results, superior wound healing and improved outcomes were indicated with the laser bonds for amniotic membrane transplantation and possibly other tissue grafts on the cornea," Yao said. She told BioOptics World that the next phase of testing will involve 48-60 rabbits. Photochemical tissue bonding is a "very new" process, she said, but noted that it is a "very promising technique that has the potential to revolutionize corneal transplantation and merits further study in clinical trials."
For more on Dr. Yao and her work, see her page on the Wellman Center site.