Results of a study indicate that embryonic stem cells can help improve vision in blind people. REUTERS

Human embryonic stem cells used to treat vision loss in 18 patients have been found to be safe three years after transplant while restoring sight in more than half the cases, says a study published in the Lancet.

Fear of rejection when used in transplants has been the biggest concern in using these cells that can develop into any cell type in the body.

It is because of this that immunoprivileged sites (that do not produce a strong immune response) such as the eye have become the first parts of the human body to benefit from this technology.

In the study, Human embryonic stem cells (hESCs) were differentiated into retinal pigment epithelium cells and transplanted into nine patients with Stargardt's macular dystrophy and nine patients with dry atrophic age-related macular degeneration, two leading causes of juvenile and adult blindness in the developed world.

The cells were well tolerated for up to 37 months after transplantation and any problems detected were ascribed to other reasons. Follow-up testing showed that 10 out of 18 treated eyes had substantial improvements.

"Our results suggest the safety and promise of hESCs to alter progressive vision loss in people with degenerative diseases and mark an exciting step towards using hESC-derived stem cells as a safe source of cells for the treatment of various medical disorders requiring tissue repair or replacement," said Professor Steven Schwartz from the Jules Stein Eye Institute, Los Angeles, USA, co-lead author of the study.

Since their discovery in the 90s, embryonic stem cells have been touted as the solution to many incurable diseases but remain dogged by ethical issues.

Most embryonic stem cells used for research are derived from embryos that develop from eggs that have been fertilised in vitro and donated for research purposes with informed consent of the donors.

Using an embryo to create the stem cells and then destroying it has kicked dust over the question of whether an embryo constitutes life.

With adult stem cells proving to be no less adept at turning into any cell type, besides remaining stable, opponents have questioned the need for embryonic stem cells.