I know that neurons higher in visual pathways can learn their receptive fields after birth, but what about the connections between bipolar cells and Amacarine cells which form center/surround on/off receptive fields? Are they learnt or genetic coded?
This is a very interesting question!
I cannot give a definite answer, however. What I can provide is supportive, but indirect evidence for my personal view that peripheral sensory organs are genetically hardwired, and that the brain is the plastic center of the nervous system during development.
A 1985 review paper by Boothe et al. mentions that at that time, little information was available about the development of the receptive field properties of single neurons in primates, and that no studies were then available regarding the development of receptive fields of primate retinal ganglion cells. I could not find later works dealing with the development of center-surround structure.
What I did find was an interesting and relatively recent review by Maurer & Lewis (2001). They describe that the retinas of monkeys that were visually deprived by lid suture or dark-rearing had permanent deficits in visual acuity. However, the retina appeared normal, with no changes in the gross electrophysiological response (electroretinogram), the topography of photoreceptors, or the morphology of retinal ganglion cells.* These data strongly hint towards a genetically-based development of the retina, because visual deficits due to visual deprivation are mainly of a cortical nature, and hence plasticity is cortical and not retinal. However, the data only indirectly address your question and until electrophysiological studies are undertaken that specifically characterize center-surround fields in the visually-deprived retina, I cannot answer this question definitively. Unfortunately, much of the recent work has focused on cortical V1 and beyond after visual deprivation. Retinal re-structuring has been investigated mainly after photoreceptor degenerations.
*When visually deprived for more than 2 years retinal re-structuring was seen. This can, however, easily be explained by degenerative processes (at least, as far as I know, this was not mentioned in the paper).