Embryology of the eye, retinal structure and phototransduction

At a glance

• The retina and optic nerve are outgrowths of the forebrain (diencephalon). The lens and corneal epithelium come from surface ectoderm. Neural crest mesenchyme forms the corneal stroma, sclera, choroid and iris stroma.
• The retina has a dual blood supply: the central retinal artery feeds the inner two-thirds; the choriocapillaris feeds the photoreceptors and the RPE.
• Phototransduction is a G protein cascade: photon, rhodopsin, transducin, PDE6, fall in cGMP, closure of cation channels, hyperpolarisation, less glutamate.