A lot of people study the neural code of the retina. The output from retina are the retinal ganglion neurons (RGC). Their input-output relation and circuits are well modeled (but not fully understood).
Usual preparation is to put retina harvested from an animal on an electrode array and record their responses to movies. See references below:
- Baden, T., Berens, P., Franke, K., Román Rosón, M., Bethge, M., and Euler, T. (2016). The functional diversity of retinal ganglion cells in the mouse. Nature, 529(7586):345-350.
- Field, G. D., Gauthier, J. L., Sher, A., Greschner, M., Machado, T. A., Jepson, L. H., Shlens, J., Gunning, D. E., Mathieson, K., Dabrowski, W., Paninski, L., Litke, A. M., and Chichilnisky, E. J. (2010). Functional connectivity in the retina at the resolution of photoreceptors. Nature, 467(7316):673-677.
- Pillow, J. W., Paninski, L., Uzzell, V. J., Simoncelli, E. P., and Chichilnisky, E. J. (2005). Prediction and decoding of retinal ganglion cell responses with a probabilistic spiking model. Journal of Neuroscience, 25:11003-11013.