Researchers at the Indiana University Bloomington have used an optical coherence tomography (OCT) to study the nano-scale growth of cone cells in live human eye.
The researchers have reported their findings in Biomedical Optics Express, an open-access journal of the Optical Society.
The cone cells, which are unique light-sensing neurons situated in the retina close to the eyeball’s inner surface, help human to see colors. The outer part of these cells is the actual light-sensing part, which comprises a sequence of packed discs having a thickness of 30 nm. This part undergoes a nanoscale growth every day. Methods commonly used for imaging the live human retina are not capable of measuring these nano-scale changes.
According to the researchers, a light beam has to be split into two in order to perform an OCT analysis of the retina. One beam is used as a reference, while the other scatters off the retina. The light waves start in phase or synch with one another but they are not in phase thanks to the interactions between the scattering beam and the retina cells during the reunion of the two beams. This phase data can be used to accurately measure the position of a sample. However, since here the sample is a live human retina, these phase techniques have to be adapted to offset any motions that may be added to the data by the eyes of the subject.
In the novel method, the scientists recorded the phase variations between patterns deriving from the bottom and top of the outer segment of the cone cells in place the phase measurement of an individual interference pattern. Using this hidden phase data, the researchers measured the nano-scale changes down to 45 nm in cone cells of two test subjects with healthy eyes. The study demonstrates that the growth rate of the cone cells’ outer segments is 150 nm/h.