Vision starts when light is absorbed in a photoreceptor and initiates a process called phototransduction. While the transduction of photons to electrical signals is well-characterized by a set of biochemical molecular events phototransduction is also accompanied by a change in light propagation through photoreceptors at minute spatiotemporal scales (nanometer/milliseconds). Outside of the eye, it is possible to achieve sufficient stability and signal-to-noise ratio (SNR) to record nm-scale changes related to functional activity from optical coherence tomography. However, within the living human eye, low SNR and retinal motion constitute major impediments to measure these nanometer scale changes. For this, I have been involved in the development of adaptive optics (AO), line-scan spectral domain OCT in the Department of Ophthalmology, University of Washington, Seattle under the supervision of Dr. Ramkumar Sabesan that overcomes the challenges of eye motion and SNR. We developed and validated this technology to objectively image the optical signature of light-induced functional activity in cones and rods in living humans at the cellular scale. We generally define such recording of light-induced optical signals from the retina, as an optoretinogram (ORG). This technology allows both structural and functional assessment of cone and rod photoreceptors and other retinal structure under normal and diseased conditions. For more details click here.

In biology most microscopy specimens, in particular living cells, are transparent. In cell imaging, it is hard to create an image of a cell which is transparent with a very small relative refractive index change with respect to the surrounding media. Various techniques like addition of staining and contrast agents and markers have been reported in the past for generating optical contrast. Many of the staining agents or markers are not applicable to live cell imaging as they are toxic. These transparent specimens have the capacity to alter the phase of the light passing through them and are called phase objects. To image these phase objects, I have been involved in the development of Digital holography Microscopy, data acquisition and interfacing and reconstruction algorithms at IIT Hyderabad under the supervison of Dr. Renu John. I have applied these techniques in the real-time imaging of transparent polydimethylsiloxane (PDMS) opto-microfluidic channel along with the of micro-electrodes patterned on glass substrate fluid flow, flow of live yeast cells through this channel, red blood cells and division of yeast cells. For more details click here.