A new study describes a pioneering new cataract treatment - tested in animals and in a small trial with human patients - where, after the cloudy lens is removed, the eye grows a new lens from its own stem cells.
The researchers - including teams from the University of California-San Diego (UCSD), Sun Yat-sen University in Guangzhou and Sichuan University, both in China - describe their new regenerative medicine approach in a paper published in the journal Nature.
The treatment was tested in 12 babies born with cataracts. It resulted in significantly fewer surgical complications than current treatments, say the researchers. Sight was improved in all 12 patients.
One of the study leaders, Kang Zhang, a professor of ophthalmology and chief of Ophthalmic Genetics at UCSD, says:
"We believe that our new approach will result in a paradigm shift in cataract surgery and may offer patients a safer and better treatment option in the future."
Being born with a lens that is cloudy or shortly becomes so is rare, but it is a significant cause of blindness in children. Estimates suggest it affects around 3 out of 10,000 children, although this rate varies throughout the world.
The clouded lens stops light getting to the retina, resulting in significant loss of vision. Current treatments can be difficult and result in complications in very young patients. Most children need to wear glasses after cataract surgery.
Method uses stem cells in the eyes to grow new lens
In the new study, the team used the ability of stem cells to grow new tissue. They did not use the more common approach - where stem cells are taken out of the patient, grown in the lab and then put back in the patient. This method can introduce disease and raise the risk of immune rejection.
Instead, the team coaxed stem cells in the patients' eyes to regrow the lenses. So-called endogenous stem cells are stem cells that are naturally already in place, ready to regenerate new tissue in the case of injury or some other problem.
In the case of the human eye, the endogenous stem cells - known as lens epithelial stem cells (LECs) - generate replacement lens cells throughout a person's life, although production wanes with age.
Current approaches to cataract surgery remove LECs along with the faulty lens - any few that are left can generate some lens cells, but the growth is random and disorganized in infants, resulting in no useful vision, note the researchers.
The approach the researchers describe in their paper has two important differences to conventional cataract surgery: it leaves the lens capsule intact, and it stimulates LECs to form a new lens. The lens capsule is a thin membrane that helps give the lens its required shape to function.
The regenerative power of the body
The researchers first tested the method in rabbits and macaques and showed it allowed LECs that stayed in the eye to regenerate functional lenses.
The researchers then ran a small human trial in patients under the age of 2. Twelve infants were treated with the new approach, while 25 other babies received the standard cataract procedure.
The patients treated with the new approach had fewer complications and healed faster than the group treated with the standard approach. After 3 months, all the operated eyes had regrown a new lens curved on both sides (biconvex).
The children who received standard surgery had a higher rate of post-surgery inflammation, developed high pressure in the eye and increased lens clouding, note the researchers.
Prof. Zhang says the ultimate goal of stem cell research is to treat patients using their own stem cells. He concludes:
"The success of this work represents a new approach in how new human tissue or organ can be regenerated and human disease can be treated, and may have a broad impact on regenerative therapies by harnessing the regenerative power of our own body."
He and his colleagues plan to extend their findings to treat the sort of cataracts that develop in older people. One of the challenges they will face is how to make stem cells more productive, because they become less active with age.
Age-related cataracts is the leading cause of blindness around the world. In the US, over 20 million people are living with the condition, and over 4 million cataracts are removed every year in operations that replace the clouded lens with a plastic one. However, while new technology has much improved cataract replacement surgery, many patients still need to wear glasses for driving or reading.