LOS ANGELES, Aug 8 (Reuters) - Twin Guatemalan girls who spent the first year of life joined at the top of the head have opened their eyes and shown other promising movement nearly three days after being surgically separated, doctors said on Thursday.

Maria de Jesus Quiej-Alvarez and her twin Maria Teresa remain in critical condition with stable vital signs after a grueling 22-hour operation to divide them ended Tuesday morning at Mattel Children's Hospital at the University of California at Los Angeles.

Earlier on Thursday, UCLA said just one twin, Maria de Jesus, had briefly fluttered her eyes after being taken off drugs that prevented the twins from injuring their brains by coughing or moving in the very early stages of recovery.

"Both have opened their eyes and moved a little bit," Dr. Andy Madikians, the twins' attending intensive care physician, told reporters.

He said that Maria Teresa, who underwent a second procedure on Tuesday after suffering a blood clot on the brain, is responding less than Maria de Jesus, who looks around and can move her arms and legs, but that was to be expected.

"We are still very optimistic, cautiously of course. Things are moving the way we hoped," Madikians said.

In the days ahead, the the UCLA medical team will be looking for "more movement, more eye opening and more responsiveness," he said, adding that it is still too early to say when the girls will be removed from respirators.

The twins -- who have not yet seen each other -- were born in rural Guatemala with the tops of their heads fused and their faces tilted in opposite directions.

MOVEMENTS TO SHOW BRAIN FUNCTION

The twins' doctors, once the girls are no longer heavily sedated, will be looking for them to wake up, look around and move all parts of their bodies, said Dr. Edward Schlasko, director of pediatric surgery at Maimonides Medical Center in Brooklyn, not directly involved in the case.

"Everything that happens will show that another part of the brain is working properly," he said.

The major complication of the separation surgery centered on the fact that the girls shared some of the veins that drain blood from the brain.

Parents Leticia Alba and Wenceslao Quiej-Alvarez are from Belen, one of thousands of dirt-poor coastal hamlets along Guatemala's south coast where people eke out a living in the banana, sugar and coffee industries.

The twins' father, who makes a living packing bananas, on Wednesday thanked God for the successful outcome of the surgery. "I am feeling more happy knowing that everything is coming out well," he told reporters.

Lead neurosurgeon Dr Jorge Lazareff said he was "optimistic about the chances for a full recovery for both Maria Teresa and Maria de Jesus, and their ability to live full and normal lives."

The girls are affectionately known as "Las Maritas," or "Little Marias" and Guatemalans are following their progress closely.

Conjoined twins occur once in every 200,000 live births, but twins who are fused at the tops of their heads, known as craniopagus twins, make up only about 2 percent of those.

They usually die early because organs like the heart and kidneys of one twin are doing most of the work and once they start to fail both twins will die.

The nonprofit group Healing the Children arranged for the twins to be treated at UCLA, which puts the cost of their care at $1.5 million, not including the services of the doctors, nurses and other professionals who donated their time. Nampa-Reuters 0137 090802 WEB story ENDS (NAMPA 090140)