For the first time, an experimental treatment made from human embryonic stem cells has shown evidence of helping someone, partly restoring sight to two people suffering from slowly progressing forms of blindness.

Although the purpose of the experiment was to test the safety of stem cells injected into the eye, both patients “had measurable improvement in their vision that persisted through the duration of the study,” said Robert Lanza, chief scientific officer at Advanced Cell Technology, the Massachusetts biotech company that sponsored the experiment.

The operations in July on two Southern California women yielded practical results. One of them no longer needs a large magnifying glass to read. The other has begun to go shopping on her own.

Reported online in the Lancet on Monday, the project used the cells under highly favorable conditions not likely to exist with many diseases.

The cells were transplanted into the eye, an organ in which the chance of immune rejection is low. The complex, 10-layer architecture of the retina was intact, so the cells were not asked to perform a heroic act of reconstruction. The researchers were able to monitor progress – and watch for complications – in real time by looking into the eyes.

Lanza cautioned that the findings are preliminary, the improvements could disappear and complications could emerge. Nevertheless, he thinks the two cases will provide useful lessons for the field.

“Hopefully, this is just the beginning of many exciting new stem cell therapies that will move from bench to bedside in the next few years,” he said.

Embryonic stem cells are able to develop into virtually any type of tissue in the body, but to obtain them, embryos are manipulated and sometimes destroyed. Many researchers hope the cells – or other “pluripotent” cells derived from less controversial sources – will offer cures for heart disease, cancer, Alzheimer’s dementia, spinal cord injury and other ailments.

Until now, the strategy had shown promise only in laboratory studies and animal tests. After many delays, the Food and Drug Administration last year approved two experiments in people. The blindness trial is the first to publish evidence that the approach might be working.

“We have to be careful not to turn this into: ‘Everybody needs stem cells right now,’ ” said Steven D. Schwartz, a UCLA ophthalmologist who is leading the experiment. “But what it does say is that in the short term, this has been surprisingly positive.”

The report was not greeted with enthusiasm everywhere.

“We object to the idea that you would sacrifice some members of the human race, even at the earliest stage of development, for the potential treatment of other members of the human race,” said David Prentice, a cell biologist at the Family Research Council.

He said other strategies, such as one that uses skin cells that have been “induced” to become stem cells, are more promising and ethical.