For demonstrating, by means of a model, the optical principles of the eye. The model eye consists fo a metal tank shaped roughly like a horizontal section of the eyeball. A window in one side of the tank is covered with a meniscus lens which serves as the cornea. The tank is filled with water which takes the place of the aqueous and vitreous humors. The interchangeable crystalline lens is mounted in a septum which marks the boundary between the humors. Two supports are provided for the insertion of additional lenses and a diaphragm. In front of the cornea are additional supports for spectacles lens. The retina is represented by a circular white area on a removable curved screen which may be located in various positions by means of a series of grooves in the wall of the tank. The blind spot is represented by a black spot on the retina. A set of seven lenses of different kinds, of the type used by opticians in ascertaining defects of the eye, and one diaphragm are supplied.