Fill in the Blanks Unit 3. Human interaction and health II. The sense of sight.Online version We are going to review what have we learnt about the sight, its elements and its functions. by Daniel de la Cruz Manjón Pozas 1 iris Light expands amount centre front contracts pupil ? The is at the of the eyeball . enters the eye through the , a small hole in the of the iris . The pupil and depending on the of light it receives . 2 focus iris shape lens ? Behind the , there is a flexible . The lens changes to the image . 3 retina receptor optic stimulus eyeball signals brain ? The , at the back of the , contains the cells . They capture the and send along the nerve to the .