Confocal microscopy yields higher-resolution images

August 15, 2008

Confocal microscopy can be used for refractive surgery to address concerns regarding wound healing and the interface, especially when assessing different techniques. The technology also can be used to assess problems after LASIK regarding dry eye.

Key Points

Images obtained with the first generation of the technology allow visualization of the deposits in the LASIK flap interface and corneal nerves in the anterior stroma a few months after refractive surgery. The resolution that the new-generation imaging system now provides is in marked contrast to that of the previous generation, Dr. Baudouin said.

"Confocal microscopy can be used for refractive surgery to address concerns regarding wound healing and the interface, especially when assessing different techniques," he said. "It also can be used to assess problems after LASIK regarding dry eye."

"We are also able to see nicely activated keratocytes on the anterior stroma just beneath the flap and the interface with the microparticles," he said. "In some cases, an interface that is clinically relevant can be examined. Interestingly, when comparing the interface following flap creation using a mechanical microkeratome and after [using a femtosecond laser], confocal microscopy shows that the microparticles in the interface are not the result of metallic deposits."

Dr. Baudouin also said that in the periphery of the cornea, it is interesting to compare a femtosecond laser procedure with a mechanical microkeratome procedure in an area with epithelial cells. After a procedure in which a mechanical microkeratome was used to create a flap, less well-defined limits were found compared with the femtosecond laser procedure.

He also reported a case with epithelial interface with deposits within the limits of the flap and a fibrotic reaction in the stroma 1 month after LASIK.

Dry eye after LASIK

Dry eye is a common problem after refractive surgery and results from the cutting of the corneal nerves. Confocal microscopy allows the surgeon to monitor the regrowth of the corneal nerves a few months after LASIK. Examination allows visualization of the abnormal nerve head and has led to a hypothesis that abnormal regrowth of the nerve head may contribute to dry eye after uncomplicated refractive surgery. Confocal microscopy provides images of abnormally enlarged nerves and fast tear film break-up time, indicating abnormal regrowth as long as 6 months after LASIK. Disruption of the sensory loop of the nerve can cause abnormal incomplete blinking without contact of the upper and lower eyelids.

In a case of dry eye, Dr. Baudouin said that infiltration of numerous inflammatory cells into the corneal epithelium indicate that several mechanisms can cause dry eye.

"A disease with biologic involvement at different levels can cause a vicious cycle," he said. "There are numerous ways to enter the vicious cycle of dry eye, including an uncomplicated, well-performed LASIK procedure that can stimulate a disease process."

The future of confocal microscopy technology, according to Dr. Baudouin, is greatly improved resolution over the currently available 1-μm resolution, and refinements of the technology will show intracellular elements with fragmentation of the nuclei. The future also will allow recognition of inflammation and all cell processes at the biologic and histologic level, he said.

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