The clouded lens of a cataract in a human eye. Wikimedia

Stem cells have been successfully used in a technique to grow new eye lens in human babies suffering from cataract. They have also been used to generate various tissues of the eye, including the lens, cornea, and conjunctiva and restore vision.

In the first case, the precursors of the lens cells found in the eye were tweaked to regenerate the lens after the damaged one was removed. In the second, adult pluripotent stem cells were grown in the lab and developed into various eye tissues.

After testing on animals and a small human clinical trial, researchers at University of California, San Diego School of Medicine and Shiley Eye Institute, with colleagues in China, relied upon the regenerative potential of endogenous stem cells, those in place already.

In the human eye, lens epithelial stem cells or LECs generate replacement lens cells throughout a person's life with decline in production with age. In cataract surgeries much of the LECs is removed with the lens and the few remaining ones are unable to generate any vision.

But the team saw the potential of the LECs in animal models and left a large chunk behind with the lens capsule in a method that left the capsule intact while stimulating the LECs to grow and form a new lens with vision.

Fewer surgical complications than in the current standard-of-care cases were noticed and all 12 of the pediatric cataract patients developed vision with regenerated lenses.

The findings are published in the March 9 online issue of Nature.

Cataracts are caused when the proteins in the lens clump up to block vision. Treatment usually consists of removing the damaged lens and replacing it with a plastic lens.

Congenital cataracts that occurs at birth or shortly thereafter is not treated except after a certain age and usually the patients require corrective eyewear after cataract surgery.

But while LECs have regenerated the lens in the babies, the method is limited in adults who have fewer stem cells in the eye.

Vision restored in blind rabbits 
That is where the work of Japanese and British scientists could help. The researchers from Osaka and Cardiff universities have been able to grow in lab many of the tissue types found in the eye by using pluripotent stem cells. These are ordinary cells that can be taken from any place like the skin and pushed into becoming stem cells.

They have been able to show that the corneal epithelial cells can be cultivated and transplanted onto the eyes of blind rabbits to surgically repair the front of the eye. The cells grew into corneas.
The work is expected to pave the way for human clinical trials of anterior eye transplantation to restore lost or damaged vision. The study is published in Nature.

The study's co-author, Prof Andrew Quantock, said: "This research shows that various types of human stem cells are able to take on the characteristics of the cornea, lens and retina.
"Importantly, it demonstrates that one cell type - the corneal epithelium - could be further grown in the lab and then transplanted on to a rabbit's eye where it was functional, achieving recovered vision."

Stem cells are the body's growth and maintenance units that differentiate in the growing embryo into the various cell types that go on to build organs. At later stages, they are used by the body to replace damaged tissues. These stem cells are found in most tissue types as well as in the embryo.