As a result, researchers say, fat excision should be a component of treatment for patients seeking to address this common complaint.
The study, published in the September issue of the peer-reviewed Journal of Plastic and Reconstructive Surgery, is the first to examine the anatomy of multiple subjects to determine what happens to the lower eyelid with age.
It is also the first to measure what happens to the face with age using high-resolution magnetic resonance imaging (MRI).
"A common treatment performed in the past and present is surgical excision of fat to treat a 'herniation of fat' - meaning that the amount of fat in the eye socket does not change but the cover that holds the fat in place, the orbital septum, is weakened or broken and fat slips out," said lead author Dr. Sean Darcy, a research associate in the division of plastic and reconstructive surgery at the David Geffen School of Medicine at UCLA and a plastic surgery resident at the University of California, Irvine.
"This orbital septum weakening or herniation-of-fat theory is what most plastic surgeons have been taught.
"However, our study showed there is actually an increase in fat with age, and it is more likely that the fat increase causes the baggy eyelids rather than a weakened ligament.
"There have been no studies to show that the orbital septum weakens," Darcy said.
The study looked at MRIs of 40 subjects (17 males and 23 females) between the ages of 12 and 80. The findings showed that the lower eyelid tissue increased with age and that the largest contributor to this size increase was fat increase.