Professor Jack Werner on 'Visualising the Initiation of Sight'

Read below about the research conducted by our Visiting Fellow Professor Jack Werner on developing imaging techniques to capture the living human retina. Jack talks about his research conducted during his time at Pembroke as part of his Leverhulme Visiting Professorship, supported by the Leverhulme Trust. 

One of the goals of my time in Pembroke, funded by the Leverhulme Trust, is to facilitate high resolution 3D imaging of the living human retina at a cellular scale. Such imaging was previously only possible in postmortem histology. 

To achieve this resolution in the living eye involves adaptive optics (AO) and optical coherence tomography (OCT). Adaptive optics is a mature technology that originated in astronomy to capture images of celestial bodies by correcting optical aberrations caused by turbulence in the atmosphere. The Department of Engineering Science in Oxford is a world center for this technology under Martin Booth, whilst Hannah Smithson’s laboratory in Experimental Psychology routinely uses AO for correcting temporally varying aberrations in the human eye to image the human photoreceptor mosaic. These are the cells that initiate vision. Additional methods are required, however, to capture images of cells in all three dimensions. 

For this, it is possible to harness optical coherence tomography, a technique that is analogous to ultrasound, but uses light which has shorter wavelengths and permits much higher resolution. At each cell layer, light is reflected back and compared to a reference light via interference. The interference of the reference light amplifies light from the eye to permit high sensitivity despite only one photon in a billion reflected back from the retina. 

The high lateral resolution of AO combined with the high axial resolution of OCT will permit structures in the retina to be imaged in detail in three dimensions. Additionally, by incorporating phase analysis of the interfered OCT signal the change in axial distances of retinal structures can be measured with precision on the order nanometers (0.000001 mm). Once AO-OCT is fully developed it will be possible to see changes in the thickness of individual retinal neural cells when light is absorbed by the photoreceptors, the first event in seeing. This advancement opens up a whole new approach in human neuroscience.