Retina is the thin layer of cells at the back of the eyeball where light is converted into neural signals sent to the brain while choroid is the vascular layer of the eye lying between the retina and the sclera. Choroid is bluish in colour and contains many blood vessels. Its anterior part is thick and forms ciliary body which gives rise to iris. Iris is the visible portion of the eye and the portion surrounded by iris is called pupil. It does not contain photosensitive cell and therefore no image is formed on choroids. Retina is the innermost layer of eyeball. It consists of three sub layers which are - ganglion cells, bipolar cells and photo-receptor cell. Inverted image is formed on retina.