The ciliary body is the drawstring purse, in this analogy. The ciliary muscle within it is the drawstring. This change is necessary for near-focusing. The entire process of adjusting the focus to different distances is called accommodation . The outer segments of the rods and cones transduce the light and send the signal through the cell bodies of the ONL and out to their axons.
Horizontal cells are interneurons which aid in signal processing.
The bipolar cells in the INL process input from photoreceptors and horizontal cells, and transmit the signal to their axons. They travel all the way to the lateral geniculate nucleus. The fovea is directed towards whatever object you wish to study most closely - this sentence, at the moment. In the fovea there are almost exclusively cones, and they are at their highest density. In addition, at the fovea all of the other cell types squeeze out of the way to allow the most light to hit the cones.