Inflate a small balloon to approximately 4 inches in diameter. Cover the balloon with papier-mache. Mix 2 cups of glue with 1 cup of boiling water. Dip strips of newspaper into the mixture, and wrap around the balloon until the object is fully covered. Let dry.
Paint the papier-mache model white. Let dry. Poke the papier-mache to puncture the balloon.
Use a utility knife or box cutter to cut a 1-inch diameter round hole in the front of the eye. Wedge a spherical piece of white foam (also about 1-inch in diameter) inside the hole. This piece will serve as the sclera, once painted. Remove the piece.
Paint the iris and pupil on the foam. Paint a penny-size round iris blue, green, gray or yellow. Paint the pupil, which is about the size of a pencil eraser, black.
Cut a small piece of clear saran wrap to cover the foam. The saran wrap represents the cornea, the protective lens that covers the eye. Wedge the foam back inside the hole, with the iris and pupil facing outwards.
Use the utility knife to cut the eye model in half vertically to show interior. To do this, position the eye with the foam facing directly outwards on one side and cut the model in half from the top in the middle, so as not to cut the foam. Trace the rounded cut edge of one half on a piece of poster board. Cut out the circle.
Use permanent markers inside the circle to depict the inside of the eye. Color a quarter-inch black border around the circle to represent the chlorid.
Color a red circle the size of a quarter in the center to represent the macula. Inside this circle, color a dime-size circle to represent the fovea. Adjacent to the macula (the red circle), draw a dime-size egg shape to represent the optic disk. Use a red marker to draw the retinal blood vessels (2 to 3 inches in length) scattered throughout. Draw these vessels by making branches in different directions.
Fit the round poster board piece inside one half of the eye model. Replace the other half. Align the edges and use a piece of tape to reattach. Use the tape as a hinge to open and close the eye model.