There are some excellent interactive guides to the human eye available online. I have used them in class but also as the basis of a flipped learning activity which I then followed up with an eyeball dissection and this highly effective model eye demonstration.
This resource from Lenstore takes you on a journey right through the centre of the eye from the cornea to the optic nerve. Pop-up labels provide a brief outline of each part of the eye but these can be expanded to find out more.
Contact lens manufacturers Acuvue provide another interactive model as well as video tutorials and diagrams explaining the causes of nearsightedness and farsightedness and the ways in which they can be corrected.
VisionDirect also offer an interactive model with more simple explanations, more suited for Key Stage 3 learners. There is also a worksheet to accompany it.