#075 A Drama Deep in the Eye

Lecturer OKAMOTO Fumiki, Faculty of Medicine

Human eyeballs may be smaller than ping-pong balls, but they are organs with a complex structure and functions. The vitreous body fills the middle of the eyeball. It is composed almost entirely of water and protects the function of the eyeball, but also causes various eye diseases. For this reason, vitrectomy, or surgical removal of the vitreous body, is frequently performed as an ophthalmic treatment. Dr. Okamoto was the first in the world to develop an artificial vitreous body to replace a removed vitreous body.

The retina, which is located in the very back of the eyeball, is an important tissue that catches light signals collected by the lens and sends them to the optic nerve. Problems in the retina can even lead to loss of eyesight. A gel-like substance called the vitreous body that fills the middle of the eyeball presses the retina against the inside of the eyeball. It is composed almost entirely of water and causes a variety of retinal diseases when its shape changes due to causes such as external shock, age, or inflammation. The vitreous body must be surgically removed to treat such retinal diseases. Dr. Okamoto is an ophthalmologist who performs hundreds of vitreous surgeries a year.

Vitreous surgeries used to have a lot of complications and were very challenging to perform, but technology has advanced an astonishing amount in the past decade or so. Removed vitreous bodies do not regenerate, but the eyeball is soon refilled with a replacement fluid. Right after removal of the vitreous body, the eyeball is injected with a supplemental substance to keep the retina firmly pressed against the back of the eyeball. Silicon oil or gas is normally used for this purpose. However, these are not very biocompatible, and in rare cases, can even injure the retina again. They also cause a large inconvenience for patients, who have to rest in a prone position for several days after surgery to ensure that the injected oil or gas does not shift. That is why researchers worked to develop an artificial vitreous body for many years.

Dr. Okamoto and his colleague Dr. Sujin Hoshi had always been searching for a material that could replace the vitreous body. Then, they came across a research paper published in the journal Science. Gels typically absorb water and steadily begin to expand (swell). However, the paper that Dr. Okamoto read described a unique high molecular weight gel with properties that defied conventional thinking. He promptly reached out to the author of the paper, Associate Professor Takamasa Sakai of the University of Tokyo, and started a research collaboration.

Gels resemble living tissues in certain ways and are used in products such as contact lenses and bandages, but had almost never been used inside of the body before due to problems with swelling. However, the gel that Dr. Okamoto and his team developed swells very little, degrades naturally over time, and ultimately turns into water. Human vitreous bodies also liquify and turn into water with age, so this was just the material they were looking for. After about 3 years of endlessly repeated cycles of molecule design, synthesis, and experimentation, the team finally completed the optimal gel. When they tested the gel in vitrectomies on rabbits, they found that the rabbits did not need to rest after the surgery and did not experience any side effects for over a year.

The work was highly acclaimed because the team went beyond just proposing a new material for the world's first artificial vitreous body and was one step away from clinical application of the material. Their paper was accepted to the journal Nature Biomedical Engineering, and was even featured in the Hot Topics sections of Nature and Nature Materials. It is said that many researchers studying gels as materials attempt to synthesize them without a specific application in mind, and doctors do not have the means to meet their own needs for medical materials. This research collaboration was exciting and gratifying for both researchers and doctors. The team will continue clinical studies on applications in humans and research to make them a reality.

"Team medicine", or collaboration between multiple hospital departments and specialized staff, has recently become a trend in medicine. This kind of collaborative approach improves the quality of care, but there still has to be a division of labor. Dr. Okamoto chose to become an ophthalmologist because he was fascinated by the idea of being personally responsible for all aspects of a patient's care, including testing and diagnosis, surgery and other treatments, and postoperative care. However, he also needs to consult with other departments because symptoms of systemic diseases such as diabetes and connective tissue disease can appear in the eyes. Though it may seem that an ophthalmologist only deals with the eyes, the job in fact demands a wide range of medical knowledge. This discipline is considered mundane in the medical field, and there are few TV shows or movies starring ophthalmologists. However, ophthalmologists outside Japan appear to be highly respected. This is because eyes are still a very important organ, even if eye problems are rarely life-threatening.

A vitrectomy is performed by inserting a thin tool about the width of a hair into the eyeball and carefully cutting out the retina and vitreous body under observation with a microscope. Doing 10 or more of these 30 to 60-minute operations a day is tough on the shoulders and back, but even older doctors can do it because it is performed under a microscope. Another advantage of being an ophthalmologist is that you can keep actively practicing for many years without your skills deteriorating. As Dr. Okamoto works on the front lines, the material he developed will be used in large numbers of people. This is the ultimate reward for a clinician.

Treating patients while also conducting research leaves little free time, but the meaningful work keeps Dr. Okamoto motivated.

Article by Science Communicator at the Office of Public Relations