Gold beads help image eye movements

Imaging methods such as MRI cannot capture movements of much of the eye’s orbit — the cone-shaped bony cavity that protects the eye. Because the movements of the eye’s muscles and connective tissue are unknown, scientists do not fully understand how the brain moves the eyes.

Joel M. Miller and colleagues from Smith-Kettlewell Eye Research Institute in San Francisco implanted tiny gold beads (see figure) in the orbit of an anesthetized monkey to see if the beads could reliably tag orbital tissue and provide quality images of tissue movement over extended periods.

As reported in the May issue of the Journal of Vision, the researchers created gold beads about 0.1 mm in diameter and inserted them into hypodermic needles. About 40 beads were then injected into tissue surrounding the monkey’s eye (procedures were approved by the USDA-authorized Animal Care and Use Committee). After the animal recovered, the researchers viewed the gold bead implants using a dental x-ray system from Gendex Dental Systems of Des Plaines, Ill., and a 26 x 34-mm digital sensor with 39-μm square pixels from Sirona Dental Systems LLC of Charlotte, N.C.

As the trained monkey gazed at lighted targets (because eye motion would cause smeared images), the researchers distinguished clear bead images against shadows of the orbital bones. They used images from several points of view to reconstruct the 3-D locations of the beads, which were followed across different gazes.

Miller’s team also collected data after six months and found that 76 percent of the implanted beads remained stable. Those that did drift moved only a few hundred microns. The researchers believe their results indicate that the beads may be useful for further study of fast movements, such as those of eye muscles and connective tissue, and of slow movements, such as those associated with growth.