the eye contains 800 photoreceptor sensory units called ommatidia, these contain 22 cells, 8 of which are photosensitive and have been called R cells, currently 8 types have been described that are listed from 1 to 8 with the letter R, during the development of the ommatidia is expressed by the B088 proteins and through a reaction with the RTKs ligand of R8 induction occurs to the formation of the R7 precursor
