Lawrence Sincich, PhD, is using an adaptive optics scanning laser ophthalmoscope to study the functional properties of cone photoreceptors in the living eye. With this instrument, it is possible to visualize and stimulate individual photoreceptors with different wavelengths of light and with very high precision. Optometry students Vasantha Kanukuntla and Paul Brown are being shown the operating principles of this retinal microscope, as they embark on their Master’s thesis work. Vasantha ’s project will examine the effect of microfocal differences on the efficiency of photon absorption in human subjects, while Paul’s measures how signals from photoreceptor pairs are summed using an electrophysiological approach in non-human primates.