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Throwing light on the retina

Novel optical contrast agents for eye microsurgery

Munich, 05/20/2011

The precision and versatility of microsurgical methods have markedly improved in recent years. This is particularly true for surgery on the tissues at the back of the eye, where such interventions can result in striking improvements in vision. However, the new techniques also present considerable challenges to the eye surgeon, who must be able to localize delicate and highly vulnerable structures with confidence. Optical contrast agents help to provide a clearer view of the area of interest, and compounds with improved properties could make the surgeon’s task that much easier. Like the contrast agents used by radiologists, optical contrast agents enhance the visually perceptible contrasts between the various tissues, thus making it possible to recognize and distinguish subtle differences in their structures.

“There have been several previous attempts to find better contrast agents, but they met with little success," says Professor Heinz Langhals of the Department of Chemistry at LMU. In collaboration with Professor Anselm Kampik and Professor Christos Haritoglou of the Ophthalmic Clinic at LMU Munich University Hospital, he has now been able to develop new optical contrast agents, which have the potential to broaden the therapeutic applicability of microsurgical techniques in eye surgery.

In the new study the researchers first chose a type of fluorescent dye – a so-called chromophore – with a particular kind of structure, and chemically modified it to make its fluorescent properties compatible with the optical sensitivity of the eye and the lighting conditions used during eye operations. They then coupled the modified chromophore to a molecule that specifically binds to the target tissue. "The new optical contrast agent not only allows one to visualize the target tissue with very good contrast, the high fluorescence yield means that it can be used successfully at high dilution," explains Langhals.

Unlike older optical contrast agents such as indocyanine green (ICG), which has been reported to be toxic, the newly developed dyes have no untoward effects on patients. Moreover, they are degraded relatively rapidly following the operation, so that vision is not compromised for so long during the post-operative phase. The new compound will soon be ready for routine use in patients, and promises to open up new opportunities for eye surgery, which should in turn lead to effective treatments for otherwise intractable diseases of the retina.


"Cyanine dyes as optical contrast agents for ophthalmological surgery"
H. Langhals, A. Varja, P. Laubichler, M. Kernt, K. Eibl, C. Haritoglou, J.
Med. Chem. 2011
DOI: 10.1021/jm2001986.

Professor Dr. Heinz Langhals
Department of Chemistry
Phone: 089 2180 77699

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